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Gillen, ZM, Shoemaker, ME, McKay, BD, Bohannon, NA, Gibson, SM, and Cramer, JT. Influences of the stretch-shortening cycle and arm swing on vertical jump performance in children and adolescents. J Strength Cond Res 36(5): 1245–1256, 2022—This study compared the influences of the stretch-shortening cycle and arm swing on vertical jump performance during static jumps (SJs), counter-movement jumps (CMJs), and CMJs with arm swing (CMJAs) in young male and female athletes. Twenty-one boys (age = 12.1 ± 1.1 years) and 21 girls (age = 12.1 ± 1.1 years) performed SJs, CMJs, and CMJAs on force plates that sampled at 1 kHz. Measurements included peak force, rate of force development, peak power (PP), eccentric impulse (ECC), concentric impulse (CON), estimated jump height (JH), and changes in PP and JH across vertical jumps. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and thigh muscle cross-sectional area. Analyses of variance were used to analyze growth measurements across sex, as well as vertical jump outcome measures. Pearson product moment correlation coefficients were used to determine the relationships between changes in PP and JH across vertical jumps and growth measurements. There were differences in PP and JH such that SJ < CMJ < CMJA (p < 0.001), and ECC such that SJ < CMJA < CMJ (p ≤ 0.048). Changes in PP were greater from the SJ to CMJ than CMJ to CMJA (p ≤ 0.001). The change in PP from the SJ to CMJ exhibited moderate-to-high relationships with growth measurements for boys and girls (r = 0.543–0.803). Because young children may not have the skeletal musculature or strength necessary to absorb and reapply large eccentric preloading forces, future studies should consider using the CMJA, rather than the CMJ, to maximize vertical jump performance and minimize ECC. Coaches and practitioners can expect approximately 27–33% greater PP and 15–17% greater estimated JH when an arm swing is included during the CMJ. [ABSTRACT FROM AUTHOR]

Jenkins, NDM, Miramonti, AA, Hill, EC, Smith, CM, Cochrane-Snyman, KC, Housh, TJ, and Cramer, JT. Mechanomyographic amplitude is sensitive to load-dependent neuromuscular adaptations in response to resistance training. J Strength Cond Res 35(11): 3265–3269, 2021—We examined the sensitivity of the mechanomyographic amplitude (MMGRMS) and frequency (MMGMPF) vs. torque relationships to load-dependent neuromuscular adaptations in response to 6 weeks of higher- vs. lower-load resistance training. Twenty-five men (age = 22.8 ± 4.6 years) were randomly assigned to either a high- (n = 13) or low-load (n = 12) training group and completed 6 weeks of leg extension resistance training at 80 or 30% 1RM. Before and after 3 and 6 weeks of training, mechanomyography signals were recorded during isometric contractions at target torques equal to 10–100% of the subjects' baseline maximal strength to quantify MMGRMS and MMGMPF vs. torque relationships. MMGRMS decreased from Baseline to weeks 3 and 6 in the high-load, but not low-load group, and was dependent on the muscle and intensity of contraction examined. Consequently, MMGRMS was generally lower in the high- than low-load group at weeks 3 and 6, and these differences were most apparent in the vastus lateralis (VL) and rectus femoris muscles at higher contraction intensities. MMGMPF was greater in the high- than low-load training group independent of time or muscle. The MMGRMS vs. torque relationship was sensitive to load-dependent, muscle-specific neuromuscular adaptations and suggest reductions in neuromuscular activation to produce the same absolute submaximal torques after training with high, but not low loads. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the effects of high-intensity interval training (HIIT) with or without β-alanine (BA) supplementation on the electromyographic fatigue threshold (EMGFT) and efficiency of electrical activity (EEA) in young women. Forty-four women (mean ± SD; age [yrs]: 21.7 ± 3.7; height [cm]: 166.3 ± 6.4; body mass [kg]: 66.1 ± 10.3) were randomly assigned to one of 3 treatment groups. The supplement groups performed HIIT on the cycle ergometer 3 times-wk-1 for 6 weeks. Electromyographic fatigue threshold and EEA were assessed at baseline (PRE), after 3 weeks of training (MID), and after 6 weeks of HIIT (POST). Two 2-way mixed factorial analyses of variance (time [PRE vs. MID vs. POST] x treatment (BA vs. PL vs. CON)] were used to analyze EMGFT and EEA with a predetermined level of significance a of 0.05. For EMGFT, there was no interaction (p = 0.26) and no main effect for time (p = 0.28) nor treatment (p = 0.86); thus, there were no changes in EMGFT regardless of training or supplementation status. For EEA, there was no interaction (p = 0.70) nor treatment (p = 0.79); however, there was a main effect for time (p < 0.01). Our findings indicated that neither training nor supplementation was effective in improving EMGFT in women. Efficiency of electrical activity was altered, potentially because of a learning effect. Coaches and practitioners may not use these tests to monitor training status; however, they may find EEA as a useful tool to track cycling efficiency. [ABSTRACT FROM AUTHOR]

The purpose of the present report was to provide test- and position-specific normative reference values for combine test results based on a large, nationally representative sample of high school-aged American football players in their freshman, sophomore, and junior classes. Cross-sectional anthropometric and performance data were obtained from 12 different high school American football recruiting combines between March 7, 2015, and January 9, 2016, across the United States. Subjects included a sample (n = 7,478) of high school-aged American football athletes in their junior (n = 3,779), sophomore (n = 2,514), and freshman (n = 1,185) classes. The database included combine date, school state, position, class, height, body mass (BM), 40-yard dash, pro-agility, 3-cone, vertical jump, broad jump, and power push-up. Each player self-classified their American football positions as defensive back, defensive end, defensive linemen, linebacker, offensive linemen, quarterback, running back, tight end (TE), or wide receiver. Test- and position-specific normative values were generated by aggregating data from freshman, sophomore, and junior classes. Mean differences were found among classes for all positions and all measurements (p ≤ 0.05), except for TE BM (p > 0.05). Greater differences for all variables were observed from freshman to sophomore classes than from sophomore to junior classes. These normative reference values may provide realistic comparisons and evaluations in performance for young American football players, parents, and coaches with collegiate football aspirations. High school strength and conditioning professionals should use these norms to set attainable goals and reward accomplishments for young football players. [ABSTRACT FROM AUTHOR]

The primary purpose of this study was to evaluate test-retest reliability of the static (SP) and countermovement (CMP) power push-up test in young male athletes. The secondary purpose was to compare the reliability of vertical ground reaction forces versus torque measurements during the power push-up tests. Twenty boys (age = 11.60 ± 1.15 years) performed SPs and CMPs on force plates with the knees as the fulcrum on 2 laboratory visits separated by 2-7 days. Performance measurements included peak force (PF), peak rate of force development (pRFD), peak torque (PT), peak rate of torque development (pRTD), peak power (PP), average power (AP), eccentric impulse (ECC), and concentric impulse (CON) for both power push-up techniques. Age, maturity offset, height, body mass, fat-free mass, and estimated arm cross sectional area were obtained as measurements of growth. Intraclass correlation coefficients (ICC), SEM, coefficients of variation, and minimum detectable changes (MDC) were reported. Only PF (ICC = 0.87-0.88, SEM = 59-84 N) and PT (ICC = 0.89-0.90, SEM = 60-88 N•m) showed acceptable reliability. Neither pRFD, pRTD, PP, AP, ECC, or CON were reliable outcomes. There were no meaningful differences between force-time and torque-time curve measurements. The SP showed slightly lower CVs (33-34%) than the CMP (CVs = 39-40%). Coaches and practitioners would need to see 58-71% increases in upper-body strength measurements evaluated via power push-up on force plates to be 95% confident that the improvements exceeded the measurement variability. [ABSTRACT FROM AUTHOR]

This study examined the acute effects of passive stretching on electromechanical delay (EMD), peak twitch force (PTF), rate of force development (RFD), and peak-to-peak M-wave (PPM) for the soleus muscle during evoked isometric plantar flexion muscle actions. Fourteen men (mean age ± SD = 21.2 ± 2.4 years; body mass = 80.0 ± 14.9 kg; height = 176.9 ± 7.2 cm) and 20 women (20.9 ± 2.5 years; 61.3 ± 8.9 kg; 165.3 ± 7.5 cm) volunteered for the study. Five single-square, supramaximal transcutaneous electrical stimuli (each separated by 5 s) were delivered to the tibial nerve before and after passive stretching. A time × gender interaction was observed for EMD, and the post hoc dependent-samples t tests indicated that EMD increased 4% for the women (p = .023), but not for the men (p = .191). There were no other stretching-related changes for PTF, RFD, or p-p M-wave for either the men or women (p > .05). These findings tentatively suggested that mechanical factors related to the stiffness of the muscle-tendon unit may contribute to the explanation for why stretching caused an acute increase in the EMD during evoked twitches in the women, but not in the men. [ABSTRACT FROM AUTHOR]

Objectives To determine the test-retest reliability and minimum detectable change scores for seven common clinical measurements of muscle strength and physical function in a multiethnic sample of sarcopenic, malnourished men and women. Design Each participant visited the laboratory seven times over 25 to 26 weeks. Reliability was assessed for each measurement from Familiarization 1 to Familiarization 2 (R1), Familiarization 2 to baseline testing (R2), Familiarization 3 to 12-week testing (R3), and Familiarization 4 to 24-week testing (R4). Setting Data were collected during a clinical trial at 23 sites in the United States, Belgium, Italy, Mexico, Poland, Spain, Switzerland, and the United Kingdom. Participants Sarcopenic, malnourished, older adults (N = 257; n = 98 men aged 76.8 ± 6.3, n = 159 women aged 75.9 ± 6.6). Measurements During each visit, participants completed the Short Physical Performance Battery ( SPBB) and isometric handgrip and isokinetic leg extensor and flexor strength testing at a slow (1.05 rad/s) and fast (3.15 rad/s) velocity. Results Handgrip strength, gait speed, SPPB score, and isokinetic leg extension and flexion peak torque ( PT) had intraclass correlation coefficients ( ICCs) that were significantly greater than 0 (all ≥0.59) at R1, R2, R3, and R4, although most of these variables demonstrated systematic increases at R1, and several exhibited systematic variability beyond the baseline testing session. Conclusion The ICCs and standard errors of the measurement ( SEMs) generally improved with familiarization, which emphasizes the need for at least one familiarization trial for these measurements in sarcopenic, malnourished older adults. A three tier-approach to interpreting the clinical importance of statistically significant results that includes null hypothesis testing, examination and interpretation of the effect magnitude, and comparison of individual changes with the SEM and minimum detectable change of the measurements used is recommended. [ABSTRACT FROM AUTHOR]

BACKGROUND: Previous investigations have examined the torque and neuromuscular responses to maximal concentric and isometric muscle actions. The literature, however, has paid less attention to the effects of performing maximal eccentric muscle actions. Furthermore, the available information in this regard is contradictory. OBJECTIVE: The purpose of the present investigation was to examine eccentric, isokinetic peak moment (PMe), electromyographic (EMG) amplitude (AMP), EMG mean power frequency (MPF), mechanomyographic (MMG) AMP, and MMG MPF patterns of responses to repeated, maximal, eccentric muscle actions at 60, 120, and 180°/s. METHODS: Twelve resistance-trained men visited the laboratory on three occasions (separated by ≥ 72 h) and performed 30 repeated, maximal, eccentric muscle actions of the dominant leg extensors on an isokinetic dynamometer at randomly ordered velocities of 60, 120, and 180°/s. RESULTS: There were no changes (p > 0.05) across the 30 repeated, eccentric muscle actions for PMe, MMG AMP, and EMG MPF for any of the velocities. There were, however, increases in EMG AMP and decreases in MMG MPF for each velocity. CONCLUSIONS: The decrease in MMG MPF, which reflects the global firing rate of the activated motor units, in conjunction with the lack of change in MMG AMP, which reflects motor unit recruitment, suggested that the increase in EMG AMP was due to motor unit synchronization. [ABSTRACT FROM AUTHOR]

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The article cites a study which investigates if the critical heart rate (CHR) model for cycle ergometry could be applied to treadmill running and examines the times to exhaustion and the VO2 responses during constant HR runs at the CHR. The study findings indicated that the CHR model for cycle ergometry was applicable to treadmill running and represented a sustainable intensity but cannot be used to demarcate exercise intensity domains.

The article presents a study which aims to determine the relative contributions of isokinetic forearm flexion (FLX) and extension (EXT) peak torque (PT), and fat-free mass (FFM) to the prediction of estimated propulsive force (EPF) in young male swimmers. These swimmers were measured for FLX and EXT PT. The results suggest that age-related increases in HT and FFM as well as training for increases in FLX and EXT strength may improve propulsive force and swimming performance.

OBJECTIVE: This study examined the effects of %sex gender on peak torque (PT), average power (AP), and the time (AMP) and frequency (MPF) domain parameters of the electromyographic (EMG) and mechanomyographic (MMG) signals following very short-term resistance training (VST) of the forearm flexors. Based on the results of previous studies it was hypothesized that three training sessions would increase PT, EMG MPF, and MMG MPF of the forearm flexors at 60 and 180°/s in men only, without changes to AP, EMG AMP, or MMG AMP for either men or women. METHODS: Nine men and nine women completed two pretests, three training sessions, and a posttest that included concentric isokinetic muscle actions of the forearm flexors at 60 and 180°/s. The AMP and MPF of the EMG and MMG signals were recorded from the biceps brachii. RESULTS: The results indicate increases in PT, AP, and MMG AMP at 60 and 180°/s for the men only, but no changes in EMG AMP, EMG MPF, or MMG MPF for either the men or women. CONCLUSION: There were gender differences in the PT and AP responses to VST of the forearm flexors that were not associated with increased agonist muscle activation. These findings have implications for the development of gender-specific VST programs for the forearm flexors in clinical settings. [ABSTRACT FROM AUTHOR]

The article presents information on the impact of resistance training and protein supplementation on human body. Topics discussed include acute improvements in muscle protein synthesis (MPS) by resistance training and protein consumption, chronic adaptations of protein supplementation and resistance training, and negative effects of protein supplementation on kidneys.

The article cites a research study on the test-retest reliability of the interpolated twitch technique during submaximal and maximal isometric muscle actions. The study subjects were 14 men and eight women who completed 4 maximal voluntary contractions (MVCs) and nine randomly ordered submaximal isometric planter flexions from 10 to 100 percent of the MVC.

BACKGROUND: The rate of torque development (RTD) and the rate of velocity development (RVD) have previously been described as related; however, a direct comparison has not been performed. OBJECTIVE: The purposes of this study were to compare voluntary and evoked RVD and RTD during the same maximal isokinetic leg extensions muscle actions and to indirectly explore the influence of motor unit discharge frequency on these variables.METHODS: Sixteen men completed three maximal voluntary and three maximal evoked isokinetic leg extension muscle actions at 60°·s^{-1}. Peak RVD, general RVD, peak RTD, and electromechanical delay (EMD) were calculated from the voluntary and evoked muscle actions. Voluntary and evoked RTD and RVD were also calculated for each 10 ms epoch up to 200 ms of the muscle actions. RESULTS: There was no interaction between voluntary and evoked RVD across time (p=0.12), but there was an interaction for RTD (p<0.01). However, peak RTD occurred prior to the isokinetic load range. Peak RTD (p<0.001), peak RVD (p< 0.01), general RVD (p< 0.01), isokinetic load range (p<0.001), EMD (p<0.001), and PT (p<0.001) were greater for voluntary than evoked muscle actions, which was expected due to the influence of voluntary motor unit firing rates. CONCLUSIONS: Overall, these results suggested that the calculation of RTD during the acceleration phase of an isokinetic muscle action may not be valid due to the unknown load and increasing velocity. Furthermore, the RVD may be influenced by motor unit firing rate, but to a lesser extent than RTD. [ABSTRACT FROM AUTHOR]

The article reports on research which was conducted to investigate the effect a carbohydrate, protein and ribose-containing repletion drink during eight weeks of endurance training had on aerobic capacity, endurance performance and body composition. Researchers evaluated the drink with 32 men. They found that while the drink did not augment body weight, aerobic capacity or time to exhaustion it did improve body composition.

The article reports on research conducted to examine the relationship between the critical velocity (CV) test and maximal oxygen consumption (VO2max) and develop a regression equation to predict VO2max based on the CV test in 35 female collegiate rowers. They found that the positive relationship between CV, anaerobic rowing capacity and VO2max suggests that the CV test may be a practical alternative to measuring the maximal oxygen uptake in the absence of a metabolic cart.

The purpose of this study was to determine the effects of four weeks of interval training with concurrent creatine supplementation on cardiorespiratory fitness and endurance performance (maximal oxygen consumption (o2PEAK), time-to-exhaustion (o2PEAKTTE), ventilatory threshold (VT), and total work done (TWD)) in college-aged men. Forty-three recreationally active college-aged men (Age: 23.5 ± 4.8 yrs; o2PEAK: 43.9 ± 9.9 ml·kg·min-1) volunteered to participate in this double-blind, placebo-controlled study. Participants were randomly assigned to one of three groups: creatine (Cr-5g Cr plus 15g flavored dextrose; n = 16), placebo (PL-20g flavored dextrose; n = 17), or control (n = 10) groups. Each supplement group ingested the assigned supplement twice daily on training days only (10g/day, 5 days/week). Prior to and following supplementation, each participant performed a continuous maximal oxygen consumption test (o2PEAK) on a cycle ergometer (Corival Lode, Gronigen, the Netherlands), which was further used to establish o2PEAKTTE (seconds) and VT (l·min-1). Participants were further assessed for TWD (kJ), calculated from the total time (T; seconds) completed at a workload corresponding to 110% of their maximal power output (watt, W) determined from the maximal oxygen consumption test [TWD (kJ)= (T × W)/1000]. Following initial testing, a two week familiarization period of training and supplementing occurred. Baseline values were then measured and all participants in the Cr and PL groups engaged in four weeks of high-intensity interval training (HIIT) training on a cycle ergometer. Each training session consisted of 5 bouts of a 2:1 minute cycling work to rest ratio, introduced in an undulating progression starting at 80% o2PEAK power output and reaching 120%. Separate two-way ANOVAs (group [Cr vs. PL vs. CON] × time [Baseline- vs. Post-]) were used to identify any group by time interactions. A significant time × treatment interaction occurred for o2PEAK (p < 0.001) and o2PEAKTTE (p < 0.001). Post hoc analyses indicated no significant differences between groups. Both groups increased in o2PEAK (Cr: 7.5%; Pl: 9.6%) and o2PEAKTTE (Cr: 6.2%; PL: 7.4%) following four weeks of HIIT. A significant time × treatment interaction occurred for VT (p = 0.040). Post hoc analyses indicated improvements in only the Cr (p = 0.001; 16.4% increase) group over time. No changes were observed in TWD in any group over time. Both o2PEAK and o2PEAKTTE improved following four weeks of HIIT. Cr supplementation seemed to only have an effect on VT, since improvements were observed in the Cr group while there were no changes in the PL group. TWD did not change following HIIT or Cr supplementation. HIIT seems to be an effective and time-efficient way to improve maximal endurance performance. The addition of Cr seemed to improve VT, but did not increase TWD. Therefore, 10g of Cr per day for 5 days per week does not seem to further augment maximal oxygen consumption, greater than HIIT alone; however, Cr supplementation may improve submaximal exercise performance. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to examine the effects of intermittent isometric fatigue on maximal voluntary contraction (MVC) strength, percent voluntary activation (%VA), peak twitch force (PTF), peak rate of force development (PRFD), half relaxation time (HRT). and maximal compound action potential (M-wave) amplitude of the soleus and medial gastrocnemius muscles before and after creatine (Cr) loading. Methods: Using a double-blinded, placebo-controlled, randomized design, 12 women were assigned to a Cr (n = 6; mean age ± SD = 23.3 ± 3.0 yr) or placebo (PL; n = 6; mean age ± SD = 21.3 ± 1.6 yr) group. Participants supplemented four times daily for 5 d with 5 g of Cr+ 10 g of fructose or 10 g of fructose. At baseline and after testing, an isometric MVC and the twitch interpolation procedure were used before and after a 4-min isometric fatigue protocol of the plantarflexor muscles, which consisted of six intermittent duty cycles per minute (7-s contraction, 3-s relaxation) at 70% MVC. Results: There were no interactions between the Cr and PL groups (P > 0.05) for any dependent variable. The fatigue protocol reduced voluntary strength (-17.8%, P < 0.001) and %VA (-3.7%, P = 0.005). Baseline PTF (P < 0.005) and PRFD (P < 0.001) values were less than those of all respective time points, but PTF value decreased from 3 min to 4 min and after testing (P < 0.005). HRT increased from baseline to minutes 1 and 2 and then returned to baseline at minutes 3 and 4 and after testing. The M-wave did not change (/" > 0.05). Conclusions: Five days of Cr loading did not influence isometric force, %VA, evoked twitch properties, or the central and peripheral aspects of fatigue measured in this study. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to examine the acute effects of dynamic stretching on concentric leg extensor and flexor peak torque, eccentric leg flexor peak torque, and the conventional and functional hamstring-quadriceps (H:Q) ratios. Methods: Twenty-one women (mean ± SD age = 20.6 ± 2.0 yr, body mass = 64.5 ± 9.3 kg, height = 164.7 ± 6.5 cm) performed maximal voluntary isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60°•s-1 and 180°•s-1 before and after a bout of dynamic hamstring and quadriceps stretching as well as a control condition. Results: Leg flexion peak torque decreased under both control (mean ± SE for 60°•s-1 = 75.8 ± 4.0 to 72.4 ± 3.7 N•m, 180°•s-1 = 62.1 ± 3.2 to 59.1 ± 3.1 N•m) and stretching (60°•s-1 = 73.1 ± 3.9 to 65.8 ± 3.3 N•m, 180°•s-1 = 61.2 ± 3.3 to 54.7 ± 2.6 N•m) conditions, whereas eccentric hamstring peak torque decreased only after the stretching (60°•s = 87.3 ± 5.1 to 73.3 ± 3.6 N•m, 180°•s-1 = 89.2 ± 4.4 to 77.0 ± 3.4 N•m) intervention (P ≤ 0.05). Stretching also caused a decrease in conventional H:Q (60°•s-1 = 0.58 ± 0.02 to 0.54 ± 0.02, 180°•s-1 = 0.67 ± 0.02 to 0.61 ± 0.03) and functional H:Q ratios (60°•s-1 = 0.69 ± 0.03 to 0.60 ± 0.03, 180°•s-1 = 1.00 ± 0.06 to 0.60 ± 0.03) (P ≤ 0.05). Conclusions: Because dynamic stretching reduced concentric and eccentric hamstring strength as well as the conventional and functional H:Q ratios, fitness and allied-health professionals may need to be cautious when recommending dynamic rather than static stretching to maintain muscle force. [ABSTRACT FROM AUTHOR]