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Purpose: Unilateral strength training may attenuate the decline in muscle strength and size in homologous, contralateral muscles. This study aimed to determine whether the cross-education of strength could specifically attenuate the effects of detraining immediately after a short (prehabilitation-type) period of strength training. Methods: Twenty-six strength-trained participants were assigned to either four weeks of unilateral strength training of the stronger arm (UNI) or detraining (Detrain). Motor evoked potential (MEP) and cortical silent period (cSP) responses, muscle cross-sectional area (CSAFlexor; peripheral quantitative computed tomography) and maximal strength, rate of force development (RFD) and muscle activation (EMG) were examined in both elbow flexors before and after the intervention period. Results: In UNI, one-repetition maximum (1-RM) strength improved in both the trained (∆ = 2.0 ± 0.9 kg) and non-trained (∆ = 0.8 ± 0.9 kg) arms despite cessation of training of the weaker arm, whereas 1-RM strength was unchanged in Detrain. Maximal voluntary isometric contraction, isokinetic peak torque, and RFD did not change in either group. No neural changes were detected in UNI, but cSP increased in Detrain (∆ = 0.010 ± 0.015 s). CSAFlexor increased in the trained arm (∆ = 51 ± 43 mm2) but decreased in the non-trained arm (∆ = -53 ± 50 mm2) in UNI. CSAFlexor decreased in both arms in Detrain and at a similar rate to the non-trained arm in UNI. Conclusion: UNI attenuated the effects of detraining in the weaker arm as shown by the improvement in 1-RM strength. However, the cross-education of strength did not attenuate the decline in muscle size in the contralateral arm. [ABSTRACT FROM AUTHOR]

One key focus in the literature is the need to better understand how males and females perform neuromuscular control, which requires consideration of muscle morphology, as it may change neural drive during force production. Although previous studies focused on muscles around the knee and ankle, it is crucial to explore the behavior of other muscles, such as the hip abductors, since many lower limb conditions more common in females have been associated with alterations in hip muscles. Are electromyography (EMG) variables (amplitude and low- and high frequency bands) of hip abductors during submaximal isometric tasks different between males and females? How is muscle size associated with EMG responses during these tasks? Thirty-six participants (males, n = 18; females, n = 18) had muscle and subcutaneous thickness of gluteus medius (GMed) and tensor fascia latae (TFL) measured. They then performed an estimated one-repetition maximum (1RM) test in a side-lying hip abduction exercise, followed by two 10-s submaximal tasks: (i) side-lying hip abduction with 50 % 1RM and (ii) with 20 % 1RM. GMed and TFL EMG amplitude and frequency bands (low and high frequency components) were analyzed. Females had higher GMed EMG amplitude, lower low-frequency, and higher high-frequency components than males in both tasks (p = 0.001–0.040). No differences were observed in TFL EMG variables. Greater GMed thickness was associated with lower amplitudes in the 50 % 1RM task (r = − 0.35; p = 0.03), while greater TFL thickness was associated with lower low-frequency [20 % 1RM: r = − 0.70; p = 0.002; 50 %-1RM: r = − 0.65; p = 0.005] and higher high-frequency components [20 % 1RM: r = 0.74; p = 0.001; 50 %-1RM: r = 0.76; p < 0.001] only in females. Males and females employ different neuromuscular control strategies, which vary among the synergists for hip abduction. • The differences in neuromuscular control between males and females are still under debate. • Neural drive during movement may be influenced by muscle morphology. • Females showed significant differences in activation compared to males only in the gluteus medius. • The thickness of the gluteus medius is associated with its amplitude of activation. • The thickness of the tensor fascia latae is associated with frequency components only in females. [ABSTRACT FROM AUTHOR]

Emerging evidence indicates a complex interplay between skeletal muscle and cognitive function. Despite the known differences between muscle quantity and quality, which can be measured via computed tomography (CT), the precise nature of their associations with cognitive performance remain underexplored. To investigate the links between muscle size and density and cognitive impairment (CI) in the older adults with hip fractures, we conducted a post hoc, cross-sectional analysis within a prospective cohort study on 679 patients with hip fractures over 65. Mini-Mental State Examination (MMSE) and routine hip CT imaging were utilized to assess cognition function and muscle characteristics in older adults with hip fractures. The CT scans provided data on cross-sectional area and attenuation for the gluteus maximus (G.MaxM) and the combined gluteus medius and minimus (G.Med/MinM). Participants were categorized into CI and non-CI groups based on education levels and MMSE scores. Multivariate logistic regressions, propensity score (PS) methods, and subgroup analysis were employed to analyze associations and validate findings. This study included 123 participants (81.6 ± 6.8 years, 74% female) with CI and 556 participants (78.5 ± 7.7 years, 72% female) without. Compared to the non-CI group, muscle parameters, especially density, were significantly lower in the CI group. Specifically, G.Med/Min muscle density, but not size was robustly associated with CI (odds ratio (OR) = 0.77, 95% confidence interval = 0.62–0.96, P  = 0.02), independent of other medical situations. Sensitivity analysis corroborated that G.Med/Min muscle density was consistently lower in the CI group than the non-CI group, as evidenced in the PS matched (P  = 0.024) and weighted cohort (P  = 0.033). Enhanced muscle parameters, particularly muscle density in the G.Med/MinM muscle, correlate with a lower risk of CI. Muscle density demonstrates a stronger association with cognitive performance than muscle size, highlighting its potential as a key focus in future cognitive health research. [ABSTRACT FROM AUTHOR]

While resistance training promotes muscle hypertrophy and strength, accessibility of equipment is a barrier. This study evaluated a wearable VAriable Resistance Suit (VARS) as a novel and alternative method to achieve muscle strength improvement. It was hypothesized that by providing adjustable, bi-directional and speed dependent resistance, VARS can target specific muscles to improve muscle strength via an accessible and portable device. Twelve untrained healthy male adults (22.08 ± 4.1 years old) participated in an 8-week long resistance training using VARS to strengthen four muscles (biceps brachii, triceps brachii, biceps femoris, rectus femoris) of their non-dominant arm and leg using VARS. The results showed significant improvements in the muscle strength measured by isokinetic dynamometer – 49.9±9.6% increase in isokinetic force and 30.6±7.6% increase in isometric force. Muscle size and body composition were also assessed using ultrasound imaging and bioelectrical impedance analysis, which did not show significant changes. The study demonstrates the efficacy and feasibility of VARS as a resistance training tool to achieve muscle strength improvement and its potential extension to clinical populations.

We tested a hypothesis that individuals with low maximal voluntary isometric contraction relative to muscle cross-sectional area (MVC/mCSA) would have greater strength gain compared to those with high MVC/mCSA in an early stage from beginning of isometric training to volitional failure. Male adults (n = 24; 22.4 ± 2.5 years, 174.1 ± 6.5 cm, 75.8 ± 14.1 kg) conducted a 3-week isometric training to volitional failure (60-80% MVC, 2-3 times/week, 3 sets/session) in elbow joint flexion with 90° flexion of each arm. Based on the relationship between MVC and mCSA before the intervention, we assigned 16 arms to the higher group (HIGH), 14 to the lower group (LOW) and 18 to the mean group (MEAN). Before the intervention and at the beginning of every week, we measured MVC (myometer) and muscle thickness of anterior upper arm (ultrasound). The mCSA was derived from muscle thickness. The 3-week isometric training to volitional failure increased MVC in all groups, but the relative change in MVC through the intervention was higher in LOW than in HIGH and MEAN groups. The current findings of this study support the abovementioned hypothesis.

Purpose: To date no studies have compared resistance training loading strategies combined with dietary intervention for fat loss. Methods: Thus, we performed a randomised crossover design comparing four weeks of heavier-(HL; ~80% 1RM) and lighter-load (LL; ~60% 1RM) resistance training, combined with calorie restriction and dietary guidance, including resistance trained participants (n=130; males=49, females=81). Both conditions performed low-volume, (single set of 9 exercises, 2x/week) effort matched (to momentary failure), but non-work-matched protocols. Testing was completed pre- and post-each intervention. Fat mass (kg) was the primary outcome, and a smallest effect size of interest (SESOI) was established at 3.3% loss of baseline bodyweight. Body fat percentage, lean mass, and strength (7-10RM) for chest press, leg press, and pull-down exercises were also measured. An 8-week washout period of traditional training with normal calorie interspersed each intervention. Results: Both interventions showed small statistically equivalent (within the SESOI) reductions in fat mass (HL: -0.67 kg [95%CI -0.91 to 0.42]; LL: -0.55 kg [95%CI -0.80 to -0.31]) which were also equivalent between conditions (HL - LL: -0.113 kg [95%CI -0.437 kg to 0.212 kg]). Changes in body fat percentage and lean mass were also minimal. Strength increases were small, similar between conditions, and within a previously determined SESOI for the population included (10.1%). Conclusions: Fat loss reductions are not impacted by resistance training load; both HL and LL produce similar, yet small, changes to body composition over a 4-week intervention. However, the maintenance of both lean mass and strength highlights the value of resistance training during dietary intervention. [ABSTRACT FROM AUTHOR]

This article discusses a study on thigh muscles in freestyle wrestlers, examining the relationship between muscle size, testosterone levels, and strength. The study found that wrestlers with a thigh circumference of 55-59 cm had greater muscle strength compared to those with a circumference of 60-65 cm. The article highlights the importance of muscle size and testosterone in improving strength for wrestlers. It also mentions the impact of factors like muscle fibers, nerve activation, muscle contraction speed, and testosterone levels on strength. The study concludes that muscle size alone does not determine strength and suggests further research on other variables like electrical signals, cholesterol ratio, skin fat, and muscle length. Physical training is considered the most effective way to improve strength and testosterone levels. [Extracted from the article]

Purpose: To compare the effects of different resistance training volumes on muscle performance and hypertrophy in trained men. Methods: Thirty-seven volunteers performed resistance training for 24 weeks, divided into groups that performed 5 (G5), 10 (G10), 15 (G15), and 20 (G20) sets per muscle group per week. Ten-repetition maximum (10RM) tests were performed for the bench press, lat pulldown, 45° leg press, and stiff-legged deadlift. Muscle thickness was measured using ultrasound at biceps brachii, triceps brachii, pectoralis major, quadriceps femoris, and gluteus maximus. All measurements were performed at the beginning (pre), 12 (mid), and 24 weeks (post) of training. Results: All groups showed significant increases in all 10RM tests and muscle thickness measures after 12 and 24 weeks when compared with pre (P <.05). There were no significant differences in any 10RM test or changes between G5 and G10 after 12 and 24 weeks. G5 and G10 showed significantly greater increases for 10RM than G15 and G20 for most exercises at 12 and 24 weeks. There was no group by time interaction for any muscle thickness measure. Conclusions: The results bring evidence of an inverted "U-shaped" curve for the dose–response curve for muscle strength. Although the same trend was noted for muscle hypertrophy, the results did not reach significance. Five to 10 sets per week might be sufficient for bringing about optimal gains in muscle size and strength in trained men over a 24-week period. [ABSTRACT FROM AUTHOR]

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Background: The effectiveness of strength training with free-weight vs. machine equipment is heavily debated. Thus, the purpose of this meta-analysis was to summarize the data on the effect of free-weight versus machine-based strength training on maximal strength, jump height and hypertrophy. Methods: The review was conducted in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, and the systematic search of literature was conducted up to January 1st, 2023. Studies that directly compared free-weight vs. machine-based strength training for a minimum of 6 weeks in adults (18–60 yrs.) were included. Results: Thirteen studies (outcomes: maximal strength [n = 12], jump performance [n = 5], muscle hypertrophy [n = 5]) with a total sample of 1016 participants (789 men, 219 women) were included. Strength in free-weight tests increased significantly more with free-weight training than with machines (SMD: -0.210, CI: -0.391, -0.029, p = 0.023), while strength in machine-based tests tended to increase more with machine training than with free-weights (SMD: 0.291, CI: -0.017, 0.600, p = 0.064). However, no differences were found between modalities in direct comparison (free-weight strength vs. machine strength) for dynamic strength (SMD: 0.084, CI: -0.106, 0.273, p = 0.387), isometric strength (SMD: -0.079, CI: -0.432, 0.273, p = 0.660), countermovement jump (SMD: -0.209, CI: -0.597, 0.179, p = 0.290) and hypertrophy (SMD: -0.055, CI: -0.397, 0.287, p = 0.751). Conclusion: No differences were detected in the direct comparison of strength, jump performance and muscle hypertrophy. Current body of evidence indicates that strength changes are specific to the training modality, and the choice between free-weights and machines are down to individual preferences and goals. Key point: If your goal is to maximize strength adaptations, the choice between free-weight and machines should be based on individual preference. The principle of specificity applies, which states that you should choose the exercise you want to be stronger in. This is important for athletes who are tested in specific exercises. For muscle hypertrophy one should consider individual preference when choosing between modalities. We speculate that the combination could result in more complete hypertrophy. [ABSTRACT FROM AUTHOR]

Summary: Background: Muscle mass influences performance and health in horses. It is important to be able to easily evaluate muscle mass in horses. Objectives: To develop an equine muscle condition score (MCS) to be used by veterinarians, horse owners, trainers and other people involved in horse management and training. Study design: Observational, cross‐sectional study. Methods: Twenty‐five Thoroughbred horses at different training levels were included. Initial assessment included body condition score, height and bodyweight. Seven muscles (m. splenius, m. brachiocephalicus, m. multifidus, m. longissimus dorsi, m. gluteus medius, m. semitendinosus and m. tensor fascia latae) were imaged using ultrasonography and measured. Repeatability of ultrasonographic measurements was tested in advance by measuring each muscle 10 times in two horses. Muscle sizes were compared between two groups; trained and untrained to determine difference in muscle mass. Horses were subsequently ranked according to measured muscle mass, and palpable and visual differences between horses at different ranks were identified. A 5‐point MCS was developed. The MCS was tested by an independent, blinded operator in all 25 horses. Results: Ultrasonographic measurement of all muscles had a coefficient of variation under 5%. All muscle sizes were significantly correlated to each other except for m. brachiocephalicus, which was not correlated to m. semitendinosus and m. multifidus. All muscles were significantly larger in trained horses than in untrained horses except for m. brachiocephalicus and m. splenius. After testing, minor adjustments were made to optimise usability of the score. Main limitations: The study population consisted of very similar horses. Further studies are needed to test the reliability of the MCS in horses of different breeds, disciplines, body condition scores and health. Conclusion: This study resulted in an equine MCS that could identify differences in muscle mass between horses. The resulting MCS was similar to other muscle assessment systems developed independently from our study, thus strengthening the findings. [ABSTRACT FROM AUTHOR]

This article aims to provide an overview of the effects of ibuprofen ingestion on muscle hypertrophy and determine factors that may moderate its effect. Currently, only 2 studies reported that ibuprofen has a differential effect from placebo on muscle hypertrophy. One study reported that 1,200 mg of ibuprofen augments muscle hypertrophy in older adults. Another study found that the same dose of ibuprofen attenuated muscle hypertrophy in young adults. These contrasting findings are likely explained by the differences in inflammatory levels between the age groups. Older adults generally have higher levels of inflammation, which is why an anti-inflammatory medication might have contributed to muscle hypertrophy. Studies that used lower doses of ibuprofen, such as 400 mg, did not report a negative or positive effect of ibuprofen use. More importantly, the modulating effects of ibuprofen on muscle hypertrophy should be currently considered preliminary because they have not yet been replicated. Meta-analytical data also did not find a significant difference between the effects of placebo and ibuprofen on muscle hypertrophy in middle-aged and older adults. In summary, ibuprofen use may modulate the effects of resistance training on muscle hypertrophy, but more research on the topic is needed before making any conclusive recommendations. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine if muscle growth mediates increases in a strength task which was not directly trained. One hundred fifty‐one participants were randomized into control, one‐repetition maximum training (1RM‐TRAIN), or traditional training (TRAD‐TRAIN). Training groups performed isotonic elbow flexion 3x/week for 6 weeks. Anterior muscle thickness at 50%, 60% and 70% upper arm length, and maximal isokinetic torque at 60°/sec were assessed pre‐ and post‐training. Change‐score mediation models (adjusted for sex, pre‐muscle thickness, and pre‐strength) were constructed for each muscle thickness site. The effects of each training group were evaluated relative to the control. Data is presented as coefficient (95% CI). There were no significant relative direct effects on nonspecific strength for either training group outside of the 60% model (1.7 [0.13, 3.27] Nm). The relative effect of 1RM‐TRAIN on muscle thickness was greater in 60% (0.09 [0.01, 0.17] cm) and 70% (0.09 [0.00, 0.17] cm) models; while TRAD‐TRAIN was greater in all three: (50% = 0.24 [0.15, 0.32]; 60% = 0.24 [0.16, 0.33]; 70% = 0.22 [0.14, 0.31] cm). The effect of muscle thickness on nonspecific strength was only significant for the 60% (−3.06 [−5.7, −0.35] Nm) model. The relative indirect effect on nonspecific strength was not significant for the 1RM‐TRAIN or TRAD‐TRAIN. Similar to previous findings on specific strength, we did not find evidence for a mediating effect of muscle growth on training induced increases in nonspecific strength. The importance of muscle growth for changes in nonspecifically trained strength may need to be reconsidered. [ABSTRACT FROM AUTHOR]

The primary aim of this investigation was to assess the interrelations among the ratios of hamstring-to-quadriceps muscle size and strength, as well as the associations with hamstring and quadriceps muscle size, tibia length, and muscle strength. A total of 47 recreationally active male participants voluntarily took part in the study, with an average age of 21.06±1.52 years, height of 179.47±6.21 cm, body weight of 77.18±10.51 kg, and a body mass index of 23.96±2.97. The knee flexion and extension strength were assessed at a velocity of 60º/s. Additionally, using ultrasonography, the thickness of the total quadriceps muscle, (vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris), and the thickness of the total hamstring muscle (biceps femoris short and long head, semitendinosus, and semimembranosus) were measured at 50% of muscle length. The data were presented as mean and standard deviation, and Pearson product-moment correlation and related samples t-test were utilized for data analysis. The results of the study revealed no significant correlation between the size and strength of the hamstring and quadriceps muscles (r=0.166, p>0.05; r=0.279, p>0.05) and between the H: Q size ratio and H: Q strength ratio (r=0.129, p>0.05). The research findings indicate that the muscle thickness of the knee extensor and flexor muscle groups is not related to the isokinetic force produced in the corresponding muscles, and that muscle thickness is insufficient in determining isokinetic force.

This study aimed to investigate the relationship between maximal muscle strength and neuromuscular activation, muscle size, and quality of quadriceps (QF) and hamstring muscles (HM). The study included 24 young men and women. The neuromuscular activation parameter was recorded using a single‐channel surface electromyography (EMG) with the root mean square (RMS) during maximal isometric knee extension and flexion from four muscles: rectus femoris and vastus lateralis for QF; biceps femoris and semitendinosus for HM. In addition, the peak torque was measured during the same session. B‐mode ultrasonographic transverse images were obtained from the anterior, lateral, and posterior thighs. Furthermore, we calculated the muscle thickness (MT) and echo intensity (EI) of the four muscles as indicators of muscle size and quality. The averaged MT, EI, and absolute RMS of QF were calculated by averaging the values of the rectus femoris and vastus lateralis, and that of HM was calculated by averaging the values of the biceps femoris and semitendinosus. The knee extension peak torque was correlated with EI (r = −0.61, P < 0.01) and RMS (r = 0.53, P < 0.01) in the QF. In contrast, the knee flexion peak torque was correlated with RMS (r = 0.53, P < 0.05) but not with MT and EI in HM. In addition, EI and RMS in QF, and RMS in HM were selected as the major determinants of muscle strength in the stepwise regression analysis. These results suggest that muscle strength is moderately associated with different factors related to the thigh muscles in young individuals. [ABSTRACT FROM AUTHOR]

Although muscle weakness and/or imbalance of the rotator cuff are thought to contribute to the development of shoulder instability, the association between muscular dysfunction and shoulder instability is not completely understood. The purpose of this study was to evaluate rotator cuff and deltoid muscle cross-sectional areas in different types of shoulder instability (anterior, posterior, and multidirectional instability [MDI]) and to determine the associations between muscular imbalance and shoulder instability direction. Preoperative magnetic resonance images of patients with shoulder instability who subsequently underwent arthroscopic glenohumeral labral repair or capsular plication were evaluated. Shoulder instability was classified into 3 categories by direction: (1) anterior, (2) posterior, and (3) MDI. The rotator cuff (supraspinatus, subscapularis, and infraspinatus + teres minor) and deltoid (anterior and posterior portions, and total) muscle areas were measured on T1 sagittal and axial slices, respectively. The ratios of the subscapularis to infraspinatus + teres minor area and the anterior deltoid to posterior deltoid area were calculated to quantify the transverse force couple imbalance. A total of 189 patients were included, where each group consisted of 63 patients. The infraspinatus + teres minor muscle area was smaller than the subscapularis muscle area in the anterior instability group (P =.007). The subscapularis muscle area was smaller than the infraspinatus + teres minor muscle area in the posterior instability and MDI groups (P ≤.003). The anterior deltoid muscle area was smaller than the posterior deltoid muscle area in all groups (P ≤.001). The subscapularis–to–infraspinatus + teres minor area ratio in the anterior instability group (1.18 ± 0.40) was higher than that in the posterior instability and MDI groups (0.79 ± 0.31 and 0.93 ± 0.33, respectively; P <.001). There was no difference in the anterior deltoid–to–posterior deltoid area ratio among the 3 groups. Patients with anterior instability have smaller muscle area of the posterior rotator cuff as compared with the anterior rotator cuff. In contrast, patients with posterior instability and MDI have smaller muscle area of the anterior rotator cuff as compared with the posterior rotator cuff. Thus, the direction of shoulder instability is associated with rotator cuff muscle area. [ABSTRACT FROM AUTHOR]

Abstract Background Patients with a first hip fracture are at high risk of fracturing their other hip. Despite this, preventive therapy is often not given. Because little is known about specific risk factors of a second hip fracture, we investigated the association with areal bone mineral density (aBMD), muscle size, and density. We also investigated whether muscle parameters predict the risk of a contralateral fracture independently of aBMD. Methods Three groups were included, one without hip fracture (a subcohort of the China Action on Spine and Hip Status study), one with a first, and one with a second hip fracture. Subjects with fractures were recruited from the longitudinal Chinese Second Hip Fracture Evaluation (CSHFE). Computed tomography scans of CSHFE patients, which were obtained immediately following their first fracture, were used to measure cross‐sectional area and density of the gluteus maximus (G.MaxM) and gluteus medius and minimus (G.Med/MinM) muscles. Computed tomography X‐ray absorptiometry was used to measure aBMD of the contralateral femur. Median follow‐up time to second fracture was 4.5 years. Cox proportional hazards models were used to compute hazard ratios (HR) of second hip fracture risk in subjects with a first hip fracture. Multivariate logistic regressions were used to compare odds ratios (OR) for the risk of a first and second hip fracture. Results Three hundred and one participants (68.4 ± 6.1 years, 64% female) without and 302 participants (74.6 ± 9.9 years, 71% female) with a first hip fracture were included in the analysis. Among the latter, 45 (79.2 ± 7.1 years) sustained a second hip fracture. ORs for first hip fracture were significant for aBMD and muscle size and density. ORs for a second fracture were smaller by a factor of 3 to 4 and no longer significant for femoral neck (FN) aBMD. HRs for predicting second hip fracture confirmed the results. G.Med/MinM density (HR, 1.68; CI, 1.20–2.35) and intertrochanter aBMD (HR, 1.62; CI, 1.13–2.31) were the most significant. FN aBMD was not significant. G.Med/MinM density remained significant for predicting second hip fracture after adjustment for FN (HR, 1.66; Cl, 1.18–2.30) or total hip aBMD (HR, 1.50; 95% Cl, 1.04–2.15). Conclusions Density of the G.Med/MinM muscle is an aBMD independent predictor of the risk of second hip fracture. Intertrochanteric aBMD is a better predictor of second hip fracture than FN and total hip aBMD. These results may trigger a paradigm shift in the assessment of second hip fracture risk and prevention strategies.

Purpose: We aimed to perform a systematic review and meta-analysis of the effects of training to muscle failure or non-failure on muscular strength and hypertrophy. Methods: Meta-analyses of effect sizes (ESs) explored the effects of training to failure vs. non-failure on strength and hypertrophy. Subgroup meta-analyses explored potential moderating effects of variables such as training status (trained vs. untrained), training volume (volume equated vs. volume non-equated), body region (upper vs. lower), exercise selection (multi- vs. single-joint exercises (only for strength)), and study design (independent vs. dependent groups). Results: Fifteen studies were included in the review. All studies included young adults as participants. Meta-analysis indicated no significant difference between the training conditions for muscular strength (ES = –0.09, 95% confidence interval (95%CI): –0.22 to 0.05) and for hypertrophy (ES = 0.22, 95%CI: –0.11 to 0.55). Subgroup analyses that stratified the studies according to body region, exercise selection, or study design showed no significant differences between training conditions. In studies that did not equate training volume between the groups, the analysis showed significant favoring of non-failure training on strength gains (ES = –0.32, 95%CI: –0.57 to –0.07). In the subgroup analysis for resistance-trained individuals, the analysis showed a significant effect of training to failure for muscle hypertrophy (ES = 0.15, 95%CI: 0.03–0.26). Conclusion: Training to muscle failure does not seem to be required for gains in strength and muscle size. However, training in this manner does not seem to have detrimental effects on these adaptations, either. More studies should be conducted among older adults and highly trained individuals to improve the generalizability of these findings.

Abstract This study aimed to investigate the relationship between maximal muscle strength and neuromuscular activation, muscle size, and quality of quadriceps (QF) and hamstring muscles (HM). The study included 24 young men and women. The neuromuscular activation parameter was recorded using a single‐channel surface electromyography (EMG) with the root mean square (RMS) during maximal isometric knee extension and flexion from four muscles: rectus femoris and vastus lateralis for QF; biceps femoris and semitendinosus for HM. In addition, the peak torque was measured during the same session. B‐mode ultrasonographic transverse images were obtained from the anterior, lateral, and posterior thighs. Furthermore, we calculated the muscle thickness (MT) and echo intensity (EI) of the four muscles as indicators of muscle size and quality. The averaged MT, EI, and absolute RMS of QF were calculated by averaging the values of the rectus femoris and vastus lateralis, and that of HM was calculated by averaging the values of the biceps femoris and semitendinosus. The knee extension peak torque was correlated with EI (r = −0.61, P

We compared the magnitude of strength and muscle mass changes in response to resistance training (RT) between stronger older women and their weaker counterparts. Older women (n = 207) were grouped into tertiles according to their baseline muscular strength index. The upper and lower tertiles participants were categorized as stronger (STR, n = 69) and weaker (WKR, n = 69), respectively. Both groups engaged in a 12-week whole-body RT program. Outcomes included one-repetition maximum (1RM) tests in the three lifts and assessment of segmental lean soft tissue (LST) and skeletal muscle mass (SMM). The 1RM increase was similar between groups for the chest press [between-groups effect size of the differences (ESdiff) and 95% confidence interval (95%CI) = 0.10 (95%CI: −0.52, 0.31), P = 0.617] and preacher curl [ESdiff = 0.08 (95%CI: −0.48, 0.32), P = 0.681]. Changes were greater in WKR than STR for 1RM leg extension [ESdiff = −0.45 (95%CI: −0.86, −0.04), P = 0.030]. The increases of segmental LST and SMM were similar between-groups (ESdiff contains zero, P ≥ 0.434). We conclude that stronger and weaker older women benefit similarly for muscle mass and upper-limb strength gains. Notably, weaker older women may experience greater lower-limbs strength gains. [ABSTRACT FROM AUTHOR]

Background and purpose: Weight loss and muscle mass loss are common in patients with chronic obstructive pulmonary disease (COPD). Muscle density and fat infiltration based on CT images may be more sensitive than muscle mass by DXA in the assessment of sarcopenia for COPD patients. However, the age-related changes of cross-sectional trunk muscle compositions based on lung CT scans are still unknown. Thus, we aimed to investigate over time the change in muscle density, size, and fat deposition of L1-level trunk muscles in patients with COPD. Materials and methods: 129 male COPD patients with a second chest CT scan (from 2013-2019 to 2014-2020) were enrolled. The CT images at first and second CT scans are analyzed by OsiriX software. Trunk muscles at the level of the 1st lumbar vertebrae were selected for analysis. Attenuation of lumbar vertebrae 1 was also measured from chest CT images. The pulmonary function values were calculated based on forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC). Results: The mean age of the 129 patients with COPD was 69.7 years. The durations of COPD of this cohort were from 8-17 years. The mean area and density of L1 trunk muscles were 85.5 cm² and 36.4 HU. At baseline, muscle area and density and vertebral density were negatively associated with age (p<0.0001), while the intermuscular fat area and the fat infiltration ratio were not significantly associated with age (p>0.05). The per-year loss of trunk muscle area was 2.83 cm2 (p<0.0001) which accounts for 3.3% decrease per year, and the per-year decrease of trunk muscle density was 2.41 HU (p<0.0001) which accounts for 6.6% decrease per year. The per-year increase of intermuscular fat in trunk muscles was 0.57 cm² (p=0.006) which accounts for 11.1% increase per year. The bone density loss was 5.63 HU/per year (p<0.0001). Conclusion: Men with COPD had accelerated muscle loss as well as increased fat infiltration. Compared to muscle quantity loss the decline in muscle quality is much larger indicating the importance of relevant interventions focusing on improving muscle quality. [ABSTRACT FROM AUTHOR]

Background: One key focus in the literature is the need to better understand how males and females perform neuromuscular control, which requires consideration of muscle morphology, as it may change neural drive during force production. Although previous studies focused on muscles around the knee and ankle, it is crucial to explore the behavior of other muscles, such as the hip abductors, since many lower limb conditions more common in females have been associated with alterations in hip muscles., Research Questions: Are electromyography (EMG) variables (amplitude and low- and high frequency bands) of hip abductors during submaximal isometric tasks different between males and females? How is muscle size associated with EMG responses during these tasks?, Methods: Thirty-six participants (males, n = 18; females, n = 18) had muscle and subcutaneous thickness of gluteus medius (GMed) and tensor fascia latae (TFL) measured. They then performed an estimated one-repetition maximum (1RM) test in a side-lying hip abduction exercise, followed by two 10-s submaximal tasks: (i) side-lying hip abduction with 50 % 1RM and (ii) with 20 % 1RM. GMed and TFL EMG amplitude and frequency bands (low and high frequency components) were analyzed., Results: Females had higher GMed EMG amplitude, lower low-frequency, and higher high-frequency components than males in both tasks (p = 0.001-0.040). No differences were observed in TFL EMG variables. Greater GMed thickness was associated with lower amplitudes in the 50 % 1RM task (r = - 0.35; p = 0.03), while greater TFL thickness was associated with lower low-frequency [20 % 1RM: r = - 0.70; p = 0.002; 50 %-1RM: r = - 0.65; p = 0.005] and higher high-frequency components [20 % 1RM: r = 0.74; p = 0.001; 50 %-1RM: r = 0.76; p < 0.001] only in females., Significance: Males and females employ different neuromuscular control strategies, which vary among the synergists for hip abduction., Competing Interests: Declaration of Competing Interest We the undersigned declare that this manuscript is original, has not been published before and is not currently being considered for publication elsewhere. We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property. We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He/she is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author and which has been configured to accept email from the GAIT AND POSTURE., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Rugby is a popular sport requiring high-intensity and maximal speed actions. Numerous studies have demonstrated that physical performance variables, such as strength, sprinting, and jumping, are different between the forwards and backs. However, there is little information about muscle morphological characteristics specific for each rugby playing position. This study aimed to clarify the morphological characteristics of the thigh muscles in forwards and backs. Ultrasound images were obtained from the proximal, middle, and distal regions of the thigh. Then, the anatomical cross-sectional areas of particular muscles in the hamstrings and quadriceps femoris were calculated for seven forwards, seven backs, and ten non-athletes. The anatomical cross-sectional areas were normalised by the two-third power of lean body mass, and the normalised values of the three regions were averaged as that of the individual muscle. In the hamstrings, the normalised anatomical cross-sectional areas of the biceps femoris long head were significantly greater in forwards than in non-athletes, whereas those of the semitendinosus were significantly greater in backs than in non-athletes. Furthermore, in the quadriceps femoris, the normalised anatomical cross-sectional areas of the rectus femoris and vastus intermedius were significantly greater in forwards than in backs and non-athletes. These results suggest that forwards have great muscularity of the biceps femoris long head and vastus intermedius which can generate large force, whereas backs possess great muscularity of the semitendinosus which can generate high contraction velocity. These findings allow coaches to design more effective training programs according to particular rugby playing positions. [ABSTRACT FROM AUTHOR]

Purpose: The hamstrings (HS) muscle group plays a fundamental role in maintaining knee stability, thus contributing to the prevention and rehabilitation of lower limb musculoskeletal injuries. However, little is known about HS structural and functional adaptations after periods of prolonged inactivity. Our purpose was to investigate the HS morphological and contractile properties changes during 10 d of bed rest (BR). Methods: Ten young healthy males underwent a 10-d BR. HS cross-sectional area (CSA) (at 30%, 50%, and 70% of femur length) and biceps femoris long head (BFlh) architecture were assessed by ultrasound imaging after 0 d (BR0), 2 d (BR2), 4 d (BR4), 6 d (BR6), and 10 d (BR10) of BR, whereas BFlh contractile properties (radial twitch displacement [Dm] and contraction time [Tc]) were evaluated at the same time points by tensiomyography. HS muscle volume was assessed by magnetic resonance imaging at BR0 and BR10. Results: A reduction in muscle volume was observed in BFlh (P = 0.002; Δ = −3.53%), biceps femoris short head (P = 0.002; Δ = −3.54%), semitendinosus (P = 0.002; Δ = −2.63%), semimembranosus (P = 0.002; Δ = −2.01%), and HS pooled together (P < 0.001; Δ = −2.78%). Early changes in CSA were detected at 30% femur length already at BR6 for BFlh (P = 0.009; Δ = −2.66%) and biceps femoris short head (P = 0.049; Δ = −1.96%). We also found a reduction in fascicle length at BR6 (P = 0.035; Δ = −2.44%) and BR10 (P < 0.001; Δ = −2.84%). Dm and Tc increased at BR2 (P = 0.010; Δ = 30.0%) and B10 (P = 0.019; Δ = 19.7%), respectively. Conclusions: Despite being a nonpostural muscle group, HS exhibited a moderate reduction in muscle dimensions in response to a short unloading period. Small changes in BFlh fascicle length were also observed, accompanied by alterations in BFLh contractile properties. These HS modifications should not be ignored from a clinical perspective. [ABSTRACT FROM AUTHOR]

Background: Muscle atrophy and increased intramuscular fat (IMF) content in individuals with obesity have been associated with increased cardiovascular disease risk but unknown in normal-weight individuals. We aimed to investigate the relationships between the vascular structure and function and body and thigh compositions among normal-weight men aged 50-79 years. Methods: A total of 45 normal-weight middle-aged and older men were included herein and subsequently measured for mean carotid intima-media thickness (IMT) in near and far walls, central systolic blood pressure, augmentation index at a heart rate of 75 bpm (AIx@75), mid-thigh muscle cross-sectional area (CSA) and IMF contents using magnetic resonance imaging, and body fat percentage via electrical impedance analysis. Results: No difference in body or muscle composition was observed among the age groups. Near wall IMT was significantly positively correlated with IMF content among those in their 70s but not among those in their 50s and 60s. On the other hand, AIx@75 was strongly inversely correlated with muscle CSA per body weight, and positively correlated with body fat percentage among those in their 60s. Conclusions: The findings presented herein suggested that muscle atrophy and increased body fat percentage could affect age-specific changes in vascular structure and function among normal-weight men in their 60s. [ABSTRACT FROM AUTHOR]

Objective: In this review, we critically evaluate studies directly comparing the effects of plyometric vs. resistance training on skeletal muscle hypertrophy. Methods: We conducted electronic searches of PubMed/MEDLINE, Scopus, SPORTDiscus, and Web of Science to find studies that explored the effects of plyometric vs. resistance training on muscle hypertrophy. Results: Eight relevant studies were included in the review. Six studies compared the effects of plyometric vs. resistance training on muscle hypertrophy, while 2 studies explored the effects of combining plyometric and resistance training vs. isolated resistance training on acute anabolic signaling or muscle hypertrophy. Based on the results of these studies, we conclude that plyometric and resistance training may produce similar effects on whole muscle hypertrophy for the muscle groups of the lower extremities. Therefore, it seems that plyometric training has a greater potential for inducing increases in muscle size than previously thought. Despite the findings observed at the whole muscle level, the evidence for the effects of plyometric training on hypertrophy on the muscle fiber level is currently limited for drawing inferences. Compared to isolated resistance training, combining plyometric and resistance exercise does not seem to produce additive effects on anabolic signaling or muscle growth; however, this area requires future study. The limitations of the current body of evidence are that the findings are specific to (a) musculature of the lower extremities, (b) short-term training interventions that lasted up to 12 weeks, and (c) previously untrained or recreationally active participants. Conclusion: This review highlights that plyometric and resistance training interventions may produce similar effects on whole muscle hypertrophy, at least for the muscle groups of the lower extremities, in untrained and recreationally trained individuals, and over short-term (i.e., ≤12 weeks) intervention periods.

Supplemental Digital Content is Available in the Text. Kassiano, W, Nunes, JP, Costa, B, Ribeiro, AS, Schoenfeld, BJ, and Cyrino, ES. Does varying resistance exercises promote superior muscle hypertrophy and strength gains? A systematic review. J Strength Cond Res 36(6): 1753–1762, 2022—Fitness professionals routinely employ a variety of resistance training exercises in program design as a strategy to enhance muscular adaptations. However, it remains uncertain whether such an approach offers advantages over a fixed-exercise selection. The objective of this review was to review the effects of exercise variation on muscle hypertrophy and strength. A search of the literature was conducted using PubMed/MEDLINE, Scopus, and Web of Science databases. Eight studies were identified as meeting inclusion criteria. The combined total sample of the studies was N = 241, comprising all young men. The methodological quality of included studies was considered "good" and "excellent" based on the Physiotherapy Evidence Database Scale. The available studies indicate that varying exercise selection can influence muscle hypertrophy and strength gains. Some degree of systematic variation seems to enhance regional hypertrophic adaptations and maximize dynamic strength, whereas excessive, random variation may compromise muscular gains. We conclude that exercise variation should be approached systematically with a focus on applied anatomical and biomechanical constructs; on the contrary, employing different exercises that provide a redundant stimulus, as well as excessive rotation of different exercises (i.e., high frequency of change), may actually hinder muscular adaptations. [ABSTRACT FROM AUTHOR]

Introduction: The use of ultrasound images for analyzing muscle quality and size is continuing to grow in the literature. However, many of these manuscripts fail to properly describe their measurement techniques and steps involved in analyzing ultrasound images. Aim of this study: To evaluate the intra- and inter-rater reliability of the steps involved when analyzing ultrasound images to measure cross-sectional area and echo intensity. Material and methods: Twenty ultrasound images of the rectus femoris and vastus lateralis images were blinded and replicated, and then analyzed by experienced raters. The raters then were asked to analyze the images using open-source software for scaling measurements, subcutaneous fat thickness, cross-sectional area, and echo intensity. Matched image values for each measurement where compared for intra- and inter-rater reliability. Results: Intra-rater reliability ranged from fair (ICC3,1 = 0.32) to high (0.98), with echo intensity values being the least reliable (>0.55), and scaling and depth measurements being the most reliable (

Skeletal muscle stiffness is altered after spinal cord injury (SCI). Assessing muscle stiffness is essential for rehabilitation and pharmaceutical interventions design after SCI. The study used magnetic resonance elastography to assess the changes in stiffness after chronic SCI compared to matched able-bodied controls and determine its association with muscle size, spasticity, and peak torque in persons with SCI. Previous studies examined the association between muscle stiffness and spasticity, however, we are unaware of other studies that examined the effects of muscle composition on stiffness after SCI. Ten participants (one female) with chronic SCI and eight (one female) matched able-bodied controls participated in this cross-sectional study. Magnetic resonance elastography was utilized to monitor stiffness derived from shear waves propagation. Modified Ashworth scale was used to evaluate spasticity scores in a blinded fashion. Peak isometric and isokinetic torques were measured using a biodex dynamometer. Stiffness values were non-significantly lower (12.5%; P = 0.3) in the SCI group compared to able-bodied controls. Moreover, stiffness was positively related to vastus lateralis whole muscle cross-sectional area (CSA) (r2 = 0.64, P < 0.005) and vastus lateralis absolute muscle CSA after accounting for intramuscular fat (r2 = 0.78, P < 0.0007). Stiffness was also positively correlated to both isometric (r2= 0.55-0.57, P < 0.05) and isokinetic peak (r2= 0.46-0.48, P < 0.05) torques. Our results suggest that larger clinical trial is warranted to confirm the preliminary findings that muscle stiffness is altered after SCI compared to healthy controls. Stiffness appeared to be influenced by infiltration of intramuscular fat and modestly by the spasticity of the paralyzed muscles. The preliminary data indicated that the relationship between muscle stiffness and peak torque is not altered with changing the frequency of pulses or angular velocities. All study procedures were approved by the Institutional Review Board at the Hunter Holmes McGuire VA Medical Center, USA (IRB #: 02314) on May 3, 2017.

• In this meta-analysis, there was no significant difference between resistance training to failure vs. non-failure on strength and hypertrophy. • There was no significant difference between training conditions in subgroup analyses that stratified the studies according to body-region, exercise selection, or study design. • When considering studies that did not equate training volume between the groups, the analysis showed significant favoring of non-failure training on strength gains. Additionally, in the subgroup analysis for resistance-trained individuals, the analysis showed a significant effect of training to failure for muscle hypertrophy. We aimed to perform a systematic review and meta-analysis of the effects of training to muscle failure or non-failure on muscular strength and hypertrophy. Meta-analyses of effect sizes (ESs) explored the effects of training to failure vs. non-failure on strength and hypertrophy. Subgroup meta-analyses explored potential moderating effects of variables such as training status (trained vs. untrained), training volume (volume equated vs. volume non-equated), body region (upper vs. lower), exercise selection (multi- vs. single-joint exercises (only for strength)), and study design (independent vs. dependent groups). Fifteen studies were included in the review. All studies included young adults as participants. Meta-analysis indicated no significant difference between the training conditions for muscular strength (ES = –0.09, 95% confidence interval (95%CI): –0.22 to 0.05) and for hypertrophy (ES = 0.22, 95%CI: –0.11 to 0.55). Subgroup analyses that stratified the studies according to body region, exercise selection, or study design showed no significant differences between training conditions. In studies that did not equate training volume between the groups, the analysis showed significant favoring of non-failure training on strength gains (ES = –0.32, 95%CI: –0.57 to –0.07). In the subgroup analysis for resistance-trained individuals, the analysis showed a significant effect of training to failure for muscle hypertrophy (ES = 0.15, 95%CI: 0.03–0.26). Training to muscle failure does not seem to be required for gains in strength and muscle size. However, training in this manner does not seem to have detrimental effects on these adaptations, either. More studies should be conducted among older adults and highly trained individuals to improve the generalizability of these findings. [Display omitted] [ABSTRACT FROM AUTHOR]

This study aimed to evaluate maximum toe flexor strength, foot arch height, intrinsic toe flexor muscle size and foot arch stiffness among individuals with different body sizes, and to compare these variables between sitting and standing positions. Maximum toe flexor strength in sitting and standing, and intrinsic foot muscle thicknesses (flexor hallucis brevis: FHB, flexor digitorum brevis: FDB, abductor hallucis: AH and quadratus plantae: QP), were measured using a toe grip dynamometer and a B-mode ultrasound in healthy young men. FHB was thicker than AH, FDB and QP, AH was thicker than FDB and QP, and no significant difference was found between FDB and QP. Toe flexor strength was correlated with FHB and AH, and foot arch height was correlated with FHB. Toe flexor strength was greater in standing than in sitting. Stepwise multiple regression analysis identified FHB and AH as determinants of toe flexor strength in standing, and the relative muscle strength values per body weight in standing were determined by QP, foot arch index and foot arch stiffness. Overweight individuals had a decreased rate of increase in relative toe flexor strength compared to normal individuals. These results suggest that a large muscle thickness of intrinsic foot muscle a key contributor to toe flexor strength. Moreover, toe flexor muscle in upright standing could have the potential to generate force independently of intrinsic foot muscle size, but obese individuals who chronically put weight on their feet might impair the force amplification mechanism in upright standing., Competing Interests: Declaration of Competing Interest In the name of the authors of the manuscript, I declare that we do not have any financial and personal relationships with other people or organisations that could inappropriately influence (bias) their work. We have no conflicts of interest include employment, consultancies, stock ownership, honoraria, paid expert testimony, patent applications/registrations, and grants or other funding., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Aim: To relate quantitative magnetic resonance imaging (MRI) of ankle plantar flexor muscles to clinical functional tests in adults with cerebral palsy (CP) and neurologically intact (NI) adults. Methods: Eleven adults with CP (aged 41 ± 12, GMFCS level I-II) and 11 NI adults (aged 35 ± 10) participated in this case-control study. We used MRI to assess muscle volume and composition of the triceps surae muscles. We quantified muscle function as maximal voluntary plantarflexion (MVC) torque and countermovement jump (CMJ) height. Results: Compared to NI adults, the MRI intramuscular fat fraction estimate was significantly higher and MRI muscle volume and functional abilities (MVC and CMJ) significantly lower in adults with CP. In NI adults, but not adults with CP, MRI muscle volume correlated significantly with MVC and CMJ. In adults with CP, the estimate of intramuscular fat levels correlated significantly with jump height in a CMJ. Discussion: This study shows reduced muscle volume and altered muscle composition in adults with CP. Muscle composition appears to provide a better marker than muscle volume of reduced muscle function and impaired performance in this population. Measurements of muscle composition could be used in the assessment of neuromuscular impairments and in the determination of rehabilitation protocols in individuals with neurological disorders. [ABSTRACT FROM AUTHOR]

While concurrent training is regularly used in older populations, the inverse relationship between fibre size and oxidative capacity suggests that endurance training in resistance-trained individuals may result in some loss of resistance training-induced gains in muscle mass, which may be more pronounced in older people. We investigated the impact of superimposed endurance training in younger (28.5 ± 4.8 years; n = 8) and older (67.5 ± 5.5 years; n = 7) highly resistance-trained men. Participants underwent a 10-week endurance cycling training programme consisting of five 6-min intervals at 75% max heart rate (HRmax) separated by 4-min intervals at 90% HRmax. The anatomical cross-sectional area (ACSA) of the thigh muscles, as determined with MRI, was 24% smaller in older compared to younger participants (p < 0.001). Although maximal oxygen consumption (VO2max) was also lower in the older group (p < 0.001), VO2max per kg body mass did not differ significantly between younger and older participants. Histological analyses of biopsies of the m. vastus lateralis showed that endurance training induced an increase in succinate dehydrogenase activity in both younger and older participants (p ≤ 0.043), and an increase in the number of capillaries around type I fibres (p = 0.017). The superimposed endurance training did not induce a significant decrease in thigh ACSA, fibre cross-sectional area, or knee extensor maximum voluntary isometric force. These observations indicate that adding endurance training to resistance training can lead to positive endurance-related adaptations without negative consequences for muscle size and strength in older and younger resistance-trained people. [ABSTRACT FROM AUTHOR]

Cabre, HE, Greenwalt, CE, Gould, LM, Hirsch, KR, Blue, MNM, and Smith-Ryan, AE. Exploring the "Athlete's Paradox": Division I cross-country runners demonstrate similar muscle characteristics to recreationally trained young adults. J Strength Cond Res 35(11): 3213–3217, 2021—Endurance training can influence body composition and muscle characteristics. Endurance athletes have demonstrated elevated intramuscular fat (IMF), yet individuals with greater body fat also demonstrate elevated IMF. The purpose of this study was to examine differences in muscle characteristics (echo intensity [EI] and muscle cross-sectional area [mCSA]) and body composition between Division I collegiate athletes and college-age adults matched for percent fat (%fat). Thirty cross-country athletes (XC) and 30 normal-weight (NW) recreationally active college students (male athletes: n = 30; female athletes: n = 30; mean ± SD : age: 19.2 ± 1.1 years; body mass: 61.7 ± 8.7 kg; %fat: 18.0 ± 5.2%) underwent a panoramic ultrasound scan of the vastus lateralis to evaluate EI and mCSA. A full-body dual-energy x-ray absorptiometry scan was used to assess fat mass (FM), lean mass (LM), and %fat. Independent t -tests were used to evaluate mCSA, EI, and body composition. Significance level was set at ≤ 0.05. There were no significant differences between the XC and NW cohorts in mCSA (mean difference [MD; XC − NW], −1.30 ± −0.40 cm3; p = 0.340) or EI (MD: 3.97 ± 2.66 a.u.; p = 0.478). Body composition was not different between the groups: FM (MD: −0.14 ± −0.54 kg; p = 0.848), LM (−3.07 ± 1.25 kg; p = 0.268), or bone mineral content (−0.21 ± 0.03 kg; p = 0.120). There were also no significant differences for any outcome variables when stratified by male athletes (p = 0.097–0.468) or female athletes (p = 0.055–0.700). These results suggest that XC athletes may have similar muscle characteristics to NW individuals when matched for %fat. Understanding and tracking muscle characteristics in XC athletes may be important for performance, injury prevention, and the transition to retirement. [ABSTRACT FROM AUTHOR]

Aim: To relate quantitative magnetic resonance imaging (MRI) of ankle plantar flexor muscles to clinical functional tests in adults with cerebral palsy (CP) and neurologically intact (NI) adults.Methods: Eleven adults with CP (aged 41 ± 12, GMFCS level I-II) and 11 NI adults (aged 35 ± 10) participated in this case-control study. We used MRI to assess muscle volume and composition of the triceps surae muscles. We quantified muscle function as maximal voluntary plantarflexion (MVC) torque and countermovement jump (CMJ) height.Results: Compared to NI adults, the MRI intramuscular fat fraction estimate was significantly higher and MRI muscle volume and functional abilities (MVC and CMJ) significantly lower in adults with CP. In NI adults, but not adults with CP, MRI muscle volume correlated significantly with MVC and CMJ. In adults with CP, the estimate of intramuscular fat levels correlated significantly with jump height in a CMJ.Discussion: This study shows reduced muscle volume and altered muscle composition in adults with CP. Muscle composition appears to provide a better marker than muscle volume of reduced muscle function and impaired performance in this population. Measurements of muscle composition could be used in the assessment of neuromuscular impairments and in the determination of rehabilitation protocols in individuals with neurological disorders.

Hypertrophy can be operationally defined as an increase in the axial cross-sectional area of a muscle fiber or whole muscle, and is due to increases in the size of pre-existing muscle fibers. Hypertrophy is a desired outcome in many sports. For some athletes, muscular bulk and, conceivably, the accompanying increase in strength/power, are desirable attributes for optimal performance. Moreover, bodybuilders and other physique athletes are judged in part on their muscular size, with placings predicated on the overall magnitude of lean mass. In some cases, even relatively small improvements in hypertrophy might be the difference between winning and losing in competition for these athletes. This position stand of leading experts in the field synthesizes the current body of research to provide guidelines for maximizing skeletal muscle hypertrophy in an athletic population. The recommendations represent a consensus of a consortium of experts in the field, based on the best available current evidence. Specific sections of the paper are devoted to elucidating the constructs of hypertrophy, reconciliation of acute vs long-term evidence, and the relationship between strength and hypertrophy to provide context to our recommendations.

Muscle weakness is a common clinical symptom in children with spastic cerebral palsy (SCP). It is caused by impaired neural ability and altered intrinsic capacity of the muscles. To define the contribution of decreased muscle size to muscle weakness, two cohorts were recruited in this cross-sectional investigation: 53 children with SCP [median age, 8.2 (IQR, 4.1) years, 19/34 uni/bilateral] and 31 children with a typical development (TD) [median age, 9.7 (IQR, 2.9) years]. Muscle volume (MV) and muscle belly length for m. rectus femoris, semitendinosus, gastrocnemius medialis, and tibialis anterior were defined from three-dimensional freehand ultrasound acquisitions. A fixed dynamometer was used to assess maximal voluntary isometric contractions for knee extension, knee flexion, plantar flexion, and dorsiflexion from which maximal joint torque (MJT) was calculated. Selective motor control (SMC) was assessed on a 5-point scale for the children with SCP. First, the anthropometrics, strength, and muscle size parameters were compared between the cohorts. Significant differences for all muscle size and strength parameters were found (p ≤ 0.003), except for joint torque per MV for the plantar flexors. Secondly, the associations of anthropometrics, muscle size, gross motor function classification system (GMFCS) level, and SMC with MJT were investigated using univariate and stepwise multiple linear regressions. The associations of MJT with growth-related parameters like age, weight, and height appeared strongest in the TD cohort, whereas for the SCP cohort, these associations were accompanied by associations with SMC and GMFCS. The stepwise regression models resulted in ranges of explained variance in MJT from 29.3 to 66.3% in the TD cohort and from 16.8 to 60.1% in the SCP cohort. Finally, the MJT deficit observed in the SCP cohort was further investigated using the TD regression equations to estimate norm MJT based on height and potential MJT based on MV. From the total MJT deficit, 22.6–57.3% could be explained by deficits in MV. This investigation confirmed the disproportional decrease in muscle size and muscle strength around the knee and ankle joint in children with SCP, but also highlighted the large variability in the contribution of muscle size to muscle weakness.

• Based on the results of the studies included in our review, it seems that plyometric and resistance training may produce similar effects on whole muscle hypertrophy for the muscle groups of the lower extremities, in untrained and recreationally trained individuals, and over short-term (i.e., ≤12 weeks) intervention periods. • The evidence for the effects of plyometric training on hypertrophy on the muscle fiber level is currently limited for drawing inferences. • Combining plyometric and resistance exercise does not seem to produce additive effects on anabolic signaling or muscle growth, even though this area requires future study. In this review, we critically evaluate studies directly comparing the effects of plyometric vs. resistance training on skeletal muscle hypertrophy. We conducted electronic searches of PubMed/MEDLINE, Scopus, SPORTDiscus, and Web of Science to find studies that explored the effects of plyometric vs. resistance training on muscle hypertrophy. Eight relevant studies were included in the review. Six studies compared the effects of plyometric vs. resistance training on muscle hypertrophy, while 2 studies explored the effects of combining plyometric and resistance training vs. isolated resistance training on acute anabolic signaling or muscle hypertrophy. Based on the results of these studies, we conclude that plyometric and resistance training may produce similar effects on whole muscle hypertrophy for the muscle groups of the lower extremities. Therefore, it seems that plyometric training has a greater potential for inducing increases in muscle size than previously thought. Despite the findings observed at the whole muscle level, the evidence for the effects of plyometric training on hypertrophy on the muscle fiber level is currently limited for drawing inferences. Compared to isolated resistance training, combining plyometric and resistance exercise does not seem to produce additive effects on anabolic signaling or muscle growth; however, this area requires future study. The limitations of the current body of evidence are that the findings are specific to (a) musculature of the lower extremities, (b) short-term training interventions that lasted up to 12 weeks, and (c) previously untrained or recreationally active participants. This review highlights that plyometric and resistance training interventions may produce similar effects on whole muscle hypertrophy, at least for the muscle groups of the lower extremities, in untrained and recreationally trained individuals, and over short-term (i.e., ≤12 weeks) intervention periods. [Display omitted] [ABSTRACT FROM AUTHOR]

Muscle weakness is a common clinical symptom in children with spastic cerebral palsy (SCP). It is caused by impaired neural ability and altered intrinsic capacity of the muscles. To define the contribution of decreased muscle size to muscle weakness, two cohorts were recruited in this cross-sectional investigation: 53 children with SCP [median age, 8.2 (IQR, 4.1) years, 19/34 uni/bilateral] and 31 children with a typical development (TD) [median age, 9.7 (IQR, 2.9) years]. Muscle volume (MV) and muscle belly length for m. rectus femoris, semitendinosus, gastrocnemius medialis, and tibialis anterior were defined from three-dimensional freehand ultrasound acquisitions. A fixed dynamometer was used to assess maximal voluntary isometric contractions for knee extension, knee flexion, plantar flexion, and dorsiflexion from which maximal joint torque (MJT) was calculated. Selective motor control (SMC) was assessed on a 5-point scale for the children with SCP. First, the anthropometrics, strength, and muscle size parameters were compared between the cohorts. Significant differences for all muscle size and strength parameters were found (p ≤ 0.003), except for joint torque per MV for the plantar flexors. Secondly, the associations of anthropometrics, muscle size, gross motor function classification system (GMFCS) level, and SMC with MJT were investigated using univariate and stepwise multiple linear regressions. The associations of MJT with growth-related parameters like age, weight, and height appeared strongest in the TD cohort, whereas for the SCP cohort, these associations were accompanied by associations with SMC and GMFCS. The stepwise regression models resulted in ranges of explained variance in MJT from 29.3 to 66.3% in the TD cohort and from 16.8 to 60.1% in the SCP cohort. Finally, the MJT deficit observed in the SCP cohort was further investigated using the TD regression equations to estimate norm MJT based on height and potential MJT based on MV. From the total MJT deficit, 22.6–57.3% could be explained by deficits in MV. This investigation confirmed the disproportional decrease in muscle size and muscle strength around the knee and ankle joint in children with SCP, but also highlighted the large variability in the contribution of muscle size to muscle weakness. [ABSTRACT FROM AUTHOR]

Aim: Previous work in non‐resistance‐trained individuals has found that an increase in muscle size has no additive effect on changes in strength. However, it is thought that muscle growth is of increased importance for resistance‐trained individuals. Purpose: Experiment 1: To examine changes in muscle thickness (MT) and one repetition maximum (1RM) strength following 8 weeks of bi‐weekly 1RM practice or traditional training. Experiment 2: To determine whether increasing muscle size increases strength potential when followed by 4 weeks of 1RM training. Methods: Participants performed biceps curls for 8 weeks (Experiment 1). One arm performed 4 sets of as many repetitions as possible with approximately 70% of 1RM (TRAD), and the other arm performed a single 1RM. For experiment 2, both arms trained for muscle size and strength. Results: Experiment 1 (n = 25): for MT, the posterior probabilities favoured the hypothesis that MT changed more in the TRAD condition [mean difference: 50% site 0.15 (−0.09, 0.21) cm; 60% site 0.14 (0.06, 0.23) cm; 70% site 0.17 (0.10, 0.23) cm]. For 1RM strength, each condition changed equivalently. Experiment 2 (n = 18): for MT, the posterior probabilities favoured the hypothesis that MT changed similarly between conditions following a 4‐week strength phase. For changes in 1RM strength, the evidence favoured neither hypothesis (i.e. null vs. alternative). Of note, the mean difference between conditions was small [0.72 (4.3) kg]. Conclusions: 1RM training produces similar increases in strength as traditional training. Experiment 2 suggests that increases in muscle mass may not increase the 'potential' for strength gain. [ABSTRACT FROM AUTHOR]

Surgical repair of the Achilles tendon can lead to prolonged calf atrophy and functional limitations, even with early weightbearing. The use of neuromuscular electrical stimulation (NMES) has been studied in muscle rehabilitation programs following anterior cruciate ligament repair. Accelerated recovery and pain reduction were noted. The aim of the present study was to evaluate the use of electrical stimulation on maintaining calf muscle cross-sectional area volume and improving patient reported outcome measures following Achilles tendon surgery. Randomized controlled clinical trial. Forty patients were enrolled. All patients had undergone repair of the Achilles tendon. A 4 lead NMES device was applied at time of surgery with both patient and surgeon blinded to activity of the device. All patients followed a standardized postoperative protocol. Group 1 consisted of 20 patients who received protocol specific NMES. Group 2 was the "sham device" control group, receiving subtherapeutic electrical stimulation. Preoperative and postoperative calf circumference (2, 6, 12 weeks) and magnetic resonance imaging (MRI) scans (2, 6 weeks) were conducted. Patient-reported functional outcome scores were measured. Of the 40 patients, 23 (57.5%) were male and 17 (42.5%) were female. The mean age was 48.9 years (11.1 standard deviation [SD]) with a mean body mass index of 32.2 kg/m2 (5.7 SD). Calf measurements for Group 1 (39.3 cm and 39.7 cm) were slightly higher compared Group 2 (38.4 cm and 39.2 cm) at 6 and 12 weeks postoperative. Functional scores were similar between Groups 1 and 2 at final follow-up. Foot/Ankle Computer Adaptive Test scores were 55.1 (6.9 SD) versus 58.4(8.6 SD), and American Orthopaedic Foot and Ankle Society Ankle-Hindfoot scores were 82.3 (8.2 SD) and 83.9 (9.3 SD), respectively. The visual analog scale at 12-week visit for Groups 1 and 2 was 8.4 (9.3 SD) and 8.4 (9.1 SD), respectively. This prospective randomized controlled trial was undertaken to quantify and validate the effect and ability of NMES to minimize calf atrophy after acute or chronic repair. No statistically significant difference was found between active NMES and sham control group. There was a trend showing some maintenance of calf volume per MRI study. [ABSTRACT FROM AUTHOR]

The aim of this review was to summarize the evidence from longitudinal studies assessing the effects induced by resistance training (RT) performed to failure (RTF) vs. not to failure (RTNF) on muscle strength, hypertrophy, and power output in adults. Three electronic databases were searched using terms related to RTF and RTNF. Studies were eligible if they met the following criteria: randomized and nonrandomized studies comparing the effects of RTF vs. RTNF on muscle hypertrophy, maximal strength, and muscle power in adults, and RT intervention >6 weeks. Results were presented as standardized mean differences (SMDs) between treatments with 95% confidence intervals, and calculations were performed using random effects models. Significance was accepted when p < 0.05. Thirteen studies were included in this review. No difference was found between RTF and RTNF on maximal strength in overall analysis (SMD: -0.08; p = 0.642), but greater strength increase was observed in RTNF considering nonequalized volumes (SMD: -0.34; p = 0.048). Resistance training performed to failure showed a greater increase in muscle hypertrophy than RTNF (SMD: 0.75; p = 0.005), whereas no difference was observed considering equalized RT volumes. No difference was found between RTF and RTNF on muscle power considering overall analysis (SMD: -0.20; p = 0.239), whereas greater improvement was observed in RTNF considering nonequalized RT volumes (SMD: -0.61; p = 0.025). Resistance training not to failure may induce comparable or even greater improvements in maximal dynamic strength and power output, whereas no difference between RTF vs. RTNF is observed on muscle hypertrophy, considering equalized RT volumes. [ABSTRACT FROM AUTHOR]

Objective: Recumbent rest elicits a decrease in muscle size of the lower extremity, but the extent of decrease may be related to differences in muscle quality. This could have implications for ultrasound-derived measures of muscle size, particularly in individuals with a large proportion of intramuscular contractile elements. The research objective was to determine whether decreases in muscle size following recumbent rest are related to ultrasound-derived corrected echo intensity in resistance-trained males. Methods: Cross-sectional area (CSA), echo intensity (EI), subcutaneous fat thickness (SFT), and EI corrected for SFT (EICor) of the vastus lateralis (VL) were measured via ultrasonography in 30 resistance-trained males. Measures were obtained immediately following recumbency (T0) and 15 minutes after recumbency (T15). The association between EICor and percentage change in CSA (%ΔCSA) from T0 to T15 was examined. Comparisons of morphological characteristics were examined between a subset of participants with the lowest (LO; n = 10; <33rd percentile) and highest (HI; n = 10; >66th percentile) EICor. Results: EICor was not correlated with %ΔCSA (P =.151), and the decrease in CSA from T0 to T15 did not differ between the LO and HI groups. Conclusions: Muscle quality (EICor) is not related to the decrease in CSA of the VL following recumbent rest among resistance-trained, young males. The time frame of muscle CSA acquisition should not differ based solely on differences in muscle quality. [ABSTRACT FROM AUTHOR]

This study examined whether the association between hamstring (H) and quadriceps (Q) strength with size depends on the region and the muscle used to examined cross-sectional area (CSA). Maximum isometric contraction knee extension and flexion torque was obtained from 20 young participants while Q and H CSA was recorded using extended field of view ultrasonography at four sections along the thigh. Stepwise linear regression models using the maximum CSA of individual muscles showed a significant association of quadriceps (R2 = 0.793) and hamstring (R2 = 0.275) CSA with MVC torque (p < 0.05). The association was lower when maximum or section-specific muscle group CSAs were used as indices of size. The H:Q CSA ratio showed a significant association (R2 = 0.275, p < 0.05) and a moderate correlation (r = 0.48) with H:Q torque ratio. These results indicated that the association between muscle CSA and strength differs between the knee extensors and flexors. Amongst the various indices of muscle size, the combination of maximum CSA values of each muscle displayed the greatest relationship between strength and CSA. The H:Q CSA ratio can explain a significant but small part of the H:Q isometric strength ratio. [ABSTRACT FROM AUTHOR]

Considering that the squat exercise requires flexion and extension of the knee and hip joints, a resistance training program based on squat exercises should efficiently increase the flexion and extension strength of both the knee and hip. To our knowledge, however, no study has simultaneously investigated the effects of squat training on both flexion and extension strength in both the knee and hip. Low-intensity squat exercises at slow speeds can be expected to effectively and safely improve knee and hip flexion and extension strength in a wide range of individuals. This study aimed to clarify whether knee and hip flexion and extension strength improved after an 8-week low-intensity squat training program at slow speed. Twenty-four untrained young men were randomly assigned to a training or control group. Participants in the training group performed 40% one-repetition maximum parallel squats at slow speed (4 s for concentric/eccentric actions), 3 days per week for 8 weeks. Before and after the intervention, isometric peak torque of the knee and hip flexors and extensors during maximal voluntary contraction (MVC) was determined. For the knee flexors and extensors, muscle volume was also measured. There were significant training-induced increases in peak torque (P < 0.05). The training effects on knee and hip extension torque (effect size = 0.36–0.38) were higher than those on knee and hip flexion torque (effect size = 0.09–0.13). The squat training used here increased both knee and hip flexion and extension strength, but the training effects on the flexion strength were less than those on the extension strength. Regarding the knee extensors, a significant training-related increase in muscle volume was found (P < 0.05) without neuromuscular adaptations. In addition, there were significant correlations between the training-induced increases in muscle volume and peak torque of KE. These results suggest that muscle hypertrophy may be responsible for increased muscle strength of the knee extensors after an 8-week low-intensity squat training program at slow speed.

Abstract Background Muscular dystrophy (MD) is characterized by progressive muscle wasting and weakness, yet few comparisons to non‐MD controls (CTRL) of muscle strength and size in this adult population exist. Physical activity (PA) is promoted to maintain health and muscle strength within MD; however, PA reporting in adults with MD is limited to recall data, and its impact on muscle strength is seldom explored. Methods This study included 76 participants: 16 non‐MD (CTRL, mean age 35.4), 15 Duchenne MD (DMD, mean age 24.2), 18 Becker's MD (BMD, mean age 42.4), 13 limb‐girdle MD (LGMD, mean age 43.1), and 14 facioscapulohumeral MD (mean age 47.7). Body fat (%) and lean body mass (LBM) were measured using bioelectrical‐impedance. Gastrocnemius medialis (GM) anatomical cross‐sectional area (ACSA) was determined using B‐mode ultrasound. Isometric maximal voluntary contraction (MVC) was assessed during plantar flexion (PFMVC) and knee extension (KEMVC). PA was measured for seven continuous days using triaxial accelerometry and was expressed as daily average minutes being physically active (TPAmins) or average daily percentage of waking hours being sedentary (sedentary behaviour). Additionally, 10 m walk time was assessed. Results Muscular dystrophy groups had 34–46% higher body fat (%) than CTRL. DMD showed differences in LBM with 21–28% less LBM than all other groups. PFMVC and KEMVC were 36–75% and 24–92% lower, respectively, in MD groups than CTRL. GM ACSA was 47% and 39% larger in BMD and LGMD, respectively, compared with CTRL. PFMVC was associated with GM ACSA in DMD (P = 0.026, R = 0.429) and CTRL (P = 0.015, R = 0.553). MD groups were 14–38% more sedentary than CTRL groups, while DMD were more sedentary than BMD (14%), LGMD (8%), and facioscapulohumeral MD (14%). Sedentary behaviour was associated with LBM in DMD participants (P = 0.021, R = −0.446). TPAmins was associated with KEMVC (P = 0.020, R = 0.540) in BMD participants, while TPAmins was also the best predictor of 10 m walk time (P