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MacLennan, RJ, Mota, JA, Thompson, BJ, and Stock, MS. Effects of strength and conditioning on maximal isometric strength, motor unit behavior, and concentric isokinetic peak torque in middle-school boys. J Strength Cond Res XX(X): 000-000, 2020-It has long been theorized that improvements in muscle strength in young athletes are mediated by motor unit adaptations. The ability to decompose surface electromyographic signals obtained during isometric contractions now allow for such research questions to be answered. We examined changes in isometric and concentric isokinetic strength, as well as vastus lateralis motor unit behavior, after 16 weeks of strength training and conditioning in middle-school aged boys. Nine boys (mean ± SD age = 12 ± 1 years) participated in training. Five boys (age = 13 ± 1 years) served as control subjects. The training subjects performed 90 minutes of high-intensity, multi-joint exercise twice per week. Assessments of unilateral maximal voluntary isometric contraction (MVIC) force of the knee extensors, concentric peak torque at velocities of 60, 180, and 300°·s-1, and vastus lateralis motor unit data during 50 and 80% MVIC tests were performed. Strength training and conditioning did not improve MVIC force. Greater training-induced strength increases were observed at faster isokinetic velocities, with a large effect size at 300°·s-1 (d = 0.813). The slopes and y-intercepts of the mean firing rate vs. recruitment threshold relationship and the action potential amplitude vs. recruitment threshold relationship were unaffected by training. Sixteen weeks of middle-school strength and conditioning did not enhance maximal isometric strength or vastus lateralis motor unit control, but improvements were observed during rapid isokinetic muscle actions. Given the lack of training (multi-joint) vs. testing (single-joint) specificity, we propose that motor unit adaptations in youth are task specific.

This narrative review provides an overview of the current knowledge of B-mode ultrasound-derived echo intensity (EI) as an indicator of skeletal muscle quality. PubMed and Google Scholar were used to search the literature. Advanced search functions were used to find original studies with the terms ‘echo intensity’ and/or ‘muscle quality’ in the title and/or abstract. Publications that conceptually described muscle quality but did not include measurement of EI were not a focus of the review. Importantly, the foundational premise of EI remains unclear. While it is likely that EI reflects intramuscular adiposity, data suggesting that these measurements are influenced by fibrous tissue is limited to diseased muscle and animal models. EI appears to show particular promise in studying muscular aging. Studies have consistently reported an association between EI and muscle function, though not all chronic interventions have demonstrated improvements. Based on the existing literature, it is unclear if EI can be used as a marker of muscle glycogen following exercise and nutritional interventions, or if EI is influenced by hydration status. Inconsistent methodological approaches used across laboratories have made comparing EI studies challenging. Image depth, rest duration, participant positioning, probe tilt, and the decision to correct for subcutaneous adipose tissue thickness are all critical considerations when interpreting the literature and planning studies. While some areas show conflicting evidence, EI shows promise as a novel tool for studying muscle quality. Collaborative efforts focused on methodology are necessary to enhance the consistency and quality of the EI literature.

The psychomotor vigilance task (PVT) is a commonly used test that effectively assesses neurobehavioral alertness. The originally developed PVT is 10 minutes in duration, which presents practical and logistical issues, particularly when administered to large samples or on a repetitive basis. More recently the PVT has been used in both 3- and 5-minute formats. While both of these durations have been shown to be field sensitive to identify impairments from sleep- and fatigue-related interventions, the 5-minute version has been suggested to be more valid than the 3-minute. However, while these have shown field-validity in a number of working populations, there is a paucity of data reporting the test-retest reliability statistics of the 5-minute PVT, particularly in working-aged females. The purpose of the study was to examine the test-retest reliability of a comprehensive set of PVT variables for the 5-minute PVT in a population of working-aged females (20-63 years).Participants reported to the laboratory on two separate days and performed a 5-minute PVT on each occasion. Outcome measures included the mean reaction time (MRT), fastest and slowest 10% of reaction times (F10RT% and S10RT%, respectively), standard deviation of reaction times (SDRT) as well as error-based metrics including major and minor lapses, anticipations, and false starts. In addition, total errors (ERR) were computed as a composite of all types of errors. Reliability statistics were reported as intraclass correlation coefficients (ICCs), standard error of measurement (SEM, SEM%), and minimal difference to be considered real (MD, MD%). Systematic error was also evaluated between sessions.Overall high reliability was shown for the MRT (ICC = 0.79, SEM% = 4.14%) and F10RT% (ICC = 0.83, SEM% = 4.43%) variables, with moderate relative reliability (based on ICCs) for the false starts, ERR, and sleepiness scale (ICC = 0.50 - 0.70) variables but these all exhibited poor absolute reliability (based on SEM% values of 32.60 - 168.69%). Poor relative reliability was found for the SDRT and S10RT% variables (ICCs0.50) but the S10RT% variable had good absolute reliability (SEM% = 7.12%). The minor and major lapses and anticipations variables had too few of event occurrences for a confident determination of the reliability.The finding that the MRT variable displayed systematic error (P = 0.01) indicating that a learning curve may have been present, but the F10RT% did not show systematic error, suggests the F10RT% may be the most reliable PVT variable in a 5-minute duration test. These findings provide researchers and practitioners with reliability statistics that may help in determining which variable(s) to use, and which to avoid when specifically conducting 5-minute PVT assessments, particularly in a population of working-aged females. These results suggest that the 5-minute PVT can be used in place of the 10-minute version, if used appropriately.

Crane, JS, Thompson, BJ, Harrell, DC, Bressel, E, and Heath, EM. Comparison of high versus low eccentric-based resistance training frequencies on short-term muscle function adaptations. J Strength Cond Res XX(X): 000-000, 2020-Eccentric resistance training is beneficial for improving a number of performance and health metrics. However, the recommendations on eccentric training frequency have not been established. This study investigates the effects of volume-matched resistance training frequency comparing 1 vs. 3 training days per week of isokinetic multiple-joint eccentric training on strength and lower-body function adaptations during a 4-week training period. Thirty subjects were assigned to either 3 days per week (high-frequency [HF]) or 1 day per week (low-frequency [LF]) training conditions for 4 weeks. An eccentric dynamometer was used for the training and testing. Eccentric strength and vertical jump (VJ) measures were taken at Pre, Mid (2 weeks), and Post (4 weeks) intervention. Soreness (visual analog scale [VAS]) and rate of perceived exertion (RPE) were taken throughout the training period. There was no group × trial interaction for eccentric strength (p = 0.06) or VJ (p = 0.87). For eccentric strength, all trials were significantly different (p < 0.001) from each other. For VJ, there was a main effect for trial such that VJ increased from Pre to Post (p < 0.001) and Mid to Post (p < 0.01). High frequency reported lower RPE (p < 0.01) and soreness (p = 0.04) compared with LF. Both HF and LF protocols elicited large (36.8 and 27.4% strength increases, respectively) and rapid neuromuscular adaptations for improved strength. Eccentric-based workload may be dispersed across a given period to allow for reduced soreness and perceived exertion levels without compromising neuromuscular adaptations. Some eccentric training transfer to functional (VJ) task may also be observed, independent of training frequency.

Gait speed is now recognized as an important clinical tool in the older adult population. However, fast gait speed appears to better reflect lower-extremity muscle performance and declines more rapidly in advanced age than comfortable gait speed. We examined the ability of leg lean mass and absolute and rapid strength characteristics to predict fast gait speed in younger versus older adults. Twenty-four younger (12 men, 12 women; age = 22 ± 3 years) and 22 older (11 men, 11 women; age = 72 ± 6 years) adults participated in the study. Fast gait speed was assessed at 10- and 400-m distances. Leg lean mass was quantified with dual X-ray absorptiometry. Isometric squat peak torque and the rate of torque development at 200 ms (RTD200) were tested with a 120° knee joint angle. Statistical analyses included independent samples t tests, partial correlations, and stepwise regression. Large differences between age groups were observed for peak torque, RTD200, and gait speed (P ≤ 0.006, d ≥ 0.79), whereas the difference in leg lean mass was small (P = 0.246, d = 0.35). In older adults only, the partial correlation for 400-m speed versus RTD200 was significant (r = 0.463, P = 0.040). Stepwise regression revealed that peak torque was a significant predictor of 10-m (R2 = 0.257, P = 0.016) and 400-m (R2 = 0.239, P = 0.021) gait speed in older adults. As adults age, lower-extremity, multi-joint muscle strength becomes increasingly important in regulating fast gait speed, whereas lean mass is not predictive.

Early adaptations in eccentric training show several advantages over those in concentric training. The purpose of this study was to quantify the effects of 4 weeks of multiple-joint eccentric versus traditional leg press (TLP) training on muscle strength, rate of torque development (RTD), and jump and sprint performance adaptations. Twenty-six resistance-trained adults performed either an eccentric or a TLP resistance-training program twice per week for 4 weeks. Single-joint isometric maximal and rapid strength (peak torque and RTD, respectively) and isokinetic strength of the knee extensors and flexors, multiple-joint eccentric strength, leg press strength (1-repetition maximum), 40-m sprint, and vertical and long jump were measured before, at the midpoint, and after a 4-week training period. Four weeks of isokinetic multiple-joint eccentric training elicited greater test-specific strength gains (effect size (ES) = 1.06) compared with TLP training (ES = 0.11). The eccentric group also yielded moderate improvements in the middle-late phase RTD (RTD100–200; ES = 0.51 and 0.54 for the knee flexors and extensors, respectively), whereas the TLP group showed small-moderate improvements (ES = 0.37). The majority of the single-joint strength variables showed negligible improvements. Performance tests showed no (broad jump) to small (vertical jump; sprint for the leg press) improvements. Multiple-joint eccentric training induced significant improvements in lower body strength in a short amount of time in a recreationally trained population. These accelerated adaptations along with the lower energy requirements of eccentric exercise, may be useful for clinicians or practitioners when prescribing training programs for those who are injured, sedentary, or elderly as a means to elicit time- and metabolically efficient muscle function improvements.

BACKGROUND Declines in muscle morphology and function are commonly reported as a consequence of aging. However, few studies have investigated the influence of age on a comprehensive set of muscle function-related measures (i.e., reactive strength, power, etc.) that focuses on a dynamic performance task such as the vertical jump across the adult life span. This study aimed to examine the effects of age on muscle morphology characteristics (muscle cross-sectional area [CSA] and echo intensity [EI]) and vertical jump height, power, and reactive strength index (RSI) in females. METHODS Twenty-six young (22±2 years), 30 middle-aged (36±5 years), and 23 older (71±5 years) females participated in this study. Muscle CSA and EI were determined from ultrasound scans of the vastus lateralis. Countermovement jumps were used to assess jump height, RSI, movement time, and peak power (Pmax). RESULTS Muscle CSA, jump height, and Pmax were higher for the young compared to the old and middle-aged (P≤0.027) and for the middle-aged compared to the old (P

Akehi, K, Palmer, TB, Conchola, EC, Thompson, BJ, Kasl, A, Bice, M, and Unruh, S. Changes in knee extension and flexion maximal and rapid torque characteristics during a collegiate women's soccer season. J Strength Cond Res 36(5): 1389-1395, 2022-The purpose of this study was to assess the changes in maximal and rapid torque capacities of the knee extensor and flexor muscles over the course of a competitive season in NCAA Division II women's soccer players. Eighteen female soccer athletes performed 2 maximal voluntary isometric contractions (MVICs) of the knee extensor and flexor muscles before, during, and at the end of the competitive season. Peak torque (PT) and rate of torque development (RTD) at 50 (RTD50), 200 (RTD200), and 100-200 (RTD100-200) milliseconds were extracted from each MVIC for both legs. The rapid (RTD50) to maximal force ratio (RTD:PT), hamstring-to-quadriceps (H:Q) strength ratio, and bilateral strength differences were also calculated. Results indicated that PT, RTD50, and RTD200 decreased 11-21% from the preseason to the midseason for the knee extensors (p0.02) and RTD50 increased approximately 11% from the midseason to the end of season for the knee flexors (p0.01). Rate of torque development-to-PT ratios for the knee extensors and flexors increased 12-25% at the end of the season (p0.05). Also, H:Q strength ratios using PT, RTD50, and RTD200 increased 12.5-24% after the season started (p = 0.001-0.04). There were no bilateral strength differences (dominant vs. non-dominant limbs) across the season (p0.05). These findings suggest that participation in a soccer season can change maximal and rapid torque production of the knee extensors and flexors. Coaches and clinicians should consider incorporating a season-long strength training and maintenance plan for soccer players with the aim to improve athletic performance and minimize the risk of musculoskeletal injuries to the lower extremities.

Many diseases, disabilities, and mental health conditions associated with aging can be delayed or prevented through regular exercise. Several barriers to exercise, many of which are exacerbated in rural communities, prevent mid-life and older adults from accessing its benefits. However, recently, a racquet sport named pickleball has become popular among older adults, and it appears to overcome some of these barriers. We conducted a feasibility study to evaluate the impact of a six-week pickleball intervention on measures of muscle function, cognitive function, perceived pain, and cardio-metabolic risk, as well as several psychosocial factors contributing to adherence in sedentary rural participants. Participants improved their vertical jump, cognitive performance, and reported a decrease in self-reported pain, suggesting improved physical and cognitive health across the sample. Participants also reported high levels of satisfaction and demonstrated good adherence over the duration of the study. Perhaps of greatest value was the overwhelmingly positive response from participants to the intervention and follow-up interviews reporting a desire to continue pickleball play beyond the study period. Overall, pickleball appears to be a promising intervention to, (1) elicit functional- and cognitive-related improvements, and (2) motivate mid-life and older adults to adhere to exercise sufficiently long to benefit their health.

High-intensity strength and conditioning programs aimed at improving youth performance are becoming increasingly prevalent. The purpose of this study was to investigate the effects of a 16-week after-school strength and conditioning program on performance and body composition in middle-school-aged boys. Subjects in the training group (n = 16, mean age = 11.8 years) performed 90 minutes of supervised plyometric and resistance training twice weekly for 16 weeks. A group of control subjects (n = 9, age = 12.1 years) maintained their current activity levels. Sprint speed, 5-10-5 proagility, jump height, isometric peak torque of the leg extensors and flexors, and dual energy x-ray absorptiometry-derived body composition were examined during pretesting and posttesting. Data were analyzed by performing independent samples t-tests on the absolute change scores between groups. The primary findings were that the training intervention elicited significant improvements in 20-m sprint times (p = 0.03; mean change for training group = -0.17 seconds) and body-fat percentage (p = 0.03; 2.5% absolute improvement), the latter of which was a function of reduced fat mass (p = 0.06; -0.84 kg). Between-group differences were not noted for agility, jump height, lean mass, or strength measures; however, effect sizes generally showed greater improvements for the training group. In contrast to findings in longitudinal studies performed in collegiate athletes, sprint speed may be particularly adaptable during adolescence. In addition to potentially improving sport performance, high-intensity plyometric and resistance training programs offer the added benefit of improved body composition. These programs appear less effective for agility and jump performance and do not elicit substantial improvements in muscle mass above maturation.

The potential dissociation between muscle strength and size has led to interest in the ability to assess muscle quality across the lifespan. OBJECTIVES We examined the association between echo intensity and specific tension in middle-school boys. APPROACH Twenty-five boys participated in this study. Sixteen (mean ± SD age = 12 ± 1 years) engaged in a 16-week after-school strength and conditioning program. Nine boys (12 ± 1 years) served as controls. The program involved two 90 min sessions per week of lower-body speed, power, and resistance training. Before and after the intervention, ultrasound imaging was used to quantify vastus lateralis and rectus femoris echo intensity. MAIN RESULTS Specific tension was calculated as voluntary isometric peak torque divided by dual energy x-ray absorptiometry-derived thigh lean mass (Nm kg-1). The pretest echo intensity and specific tension data were not significantly correlated (r = 0.040, p = 0.850). Training resulted in a small mean increase in specific tension (change = 1.93 Nm kg-1; d = 0.42). The echo intensity values were not affected by training or maturation (training change = -1.13 arbitrary units (A.U.); control = 0.00 A.U.). Both variables showed no interaction and no group or time main effects. The echo intensity and specific tension change scores were not correlated for all subjects (r = -0.080, p = 0.705) or groups (training r = -0.095, p = 0.727; control r = -0.004, p = 0.992). SIGNIFICANCE In middle-school boys, a relationship between echo intensity and the ratio of muscle strength relative to lean mass does not exist.

Reactive agility tests have become popular in sport for talent identification; however, the ability of these tests to evaluate physical function and falls risk in clinical populations warrants future study. To examine the reliability and construct validity of a novel functional reactive agility test (FRAT) across the lifespan. Forty-three young (24 ± 2 years), 32 middle-aged (50 ± 2 years), and 19 old (66 ± 4 years) men performed a FRAT that included a rapid lateral movement (1.5 m) in response to a randomly delayed visual stimulus. Test–retest reliability and minimum difference (MD) scores were determined from a subset of participants. There was no systematic error (P > 0.087) between testing days, and the intraclass correlation coefficients, standard error of measurement (% of the mean), and MD values for decision time, movement time, and total time ranged from 0.876 to 0.949, 4.16–9.24%, and 0.128–0.138 s, respectively. The young men had faster decision times (P = 0.027) when compared to the older men and faster total times when compared to the middle-aged and older men (P

Palmer, TB, Thiele, RM, and Thompson, BJ. Age-related differences in maximal and rapid torque characteristics of the hip extensors and dynamic postural balance in healthy, young and old females. J Strength Cond Res 31(2): 480-488, 2017-The purpose of this study was to examine age-related differences in maximal and rapid torque characteristics of the hip extensor muscles and dynamic postural balance in healthy, young and older females. Eleven younger (age, 26 ± 8 years) and 11 older (age, 67 ± 8 years) females performed 2 isometric maximal voluntary contractions (MVCs) of the hip extensor muscles. Absolute and relative peak torque (PT) and rate of torque development (RTD) at early (0-50 ms) and late (0-200 ms) phases of muscle contraction were examined during each MVC. Dynamic postural balance was assessed using a commercially designed balance testing device, which provides a measurement of dynamic stability based on the overall stability index (OSI). Results indicated that absolute PT and early (RTD50) and late (RTD200) RTD variables were lower (p = 0.009-0.050), and postural OSI was higher (p = 0.011) in the old compared with the younger females; however, no differences were observed for relative PT or RTD variables (p = 0.113-0.895). A significant relationship was also observed in the older (r = -0.601; p = 0.050) but not the younger (r = -0.132; p = 0.698) females between RTD50 and OSI. The lower absolute PT and RTD and higher OSI values for the old females may contribute to the increased functional limitations often observed in older adults. The significant relationship observed in the older females between OSI and RTD50 perhaps suggests that these age-related declines in explosive strength may be an important characteristic relevant to dynamic balance scores, especially in older populations.

The reactive capacity of the muscle-tendon complex is commonly assessed using the reactive strength index (RSI). Conventionally, the RSI is a ratio of rebound jump height to ground contact time in depth jumping. Several assumptions regarding the linear mechanics acting through the whole-body center of gravity may threaten the internal validity of computation and interpretation of RSI scores. First, it is common for rebound jump height to be predicted from rebound jump flight time. This assumes that the angular positioning of body segments is equivalent at the time instances of rebound jump take-off and landing. Prior literature supports a mixed-methods approach for computing the RSI that is void of this assumption. The mixed-methods approach gives a more valid estimation of rebound jump height. In this approach, rebound jump height is estimated from rebound jump take-off velocity of the whole-body center of mass. This is accomplished by subtracting an estimate of impact velocity, acquired using videography, from change in whole-body center of mass velocity estimated from integrated vertical ground reaction force data. Second, it is often assumed that vertical displacement of the whole-body center of mass during the drop phase of the depth jump is predicted perfectly from the height of the platform used to perform the drop. This assumption may affect the internal validity of comparing RSI scores across individuals and within individuals performing depth jumps from varied heights. The purpose of the present study was to investigate the internal validity of RSI scores computed using the conventional approach and impact velocity variability, which may affect the interpretation of RSI scores. Seventy physically active young adults performed depth jumps from drop heights of 0.51, 0.66, and 0.81 m. RSI was computed using the conventional approach and a mixed-methods approach featuring the use of 2-dimensional videography, body segment parameters, and force platform dynamometry. The two computational methods were compared using linear regression performed on data from each drop height. In addition, a 2 (computational method) by 3 (drop height) Analysis of Variance (ANOVA) was performed to evaluate for main effects and interactions in RSI data. Multiple one sample t-tests were performed to compare estimated and theoretical impact velocities. The ANOVA revealed no main effect or interactions between computational approaches (p = 0.467&ndash, 0.938). Linear regression revealed moderately strong associations between RSI scores computed using the conventional and mixed-methods approaches (R2 = 0.685&ndash, 0.741). Moreover, linear regressions revealed that the conventional approach tends to overestimate the mixed methods approach for RSI scores below 1.0 and underestimate the mixed methods approach for RSI scores above 1.0. Lastly, estimated impact velocities were observed to be as much as 13% lower versus theoretical (p &lt, 0.001). Researchers with access to motion capture and force platform technology may consider using a mixed-methods approach for computing the RSI, which likely maximizes the internal validity of scores. In addition, results suggest for practitioners to practice caution when comparing conventional RSI scores across individuals.

Introduction We examined correlations among echo intensity and muscle thickness versus measures of athleticism and isometric strength in healthy children. Methods B-mode ultrasonography was used to examine the vastus lateralis (VL) and rectus femoris (RF) in 28 boys (mean age = 12 years). Tests of athleticism included jump height and peak velocity, sprint speed, and agility. Peak torque and the rate of torque development (RTD) at 100 and 200 ms from torque onset were assessed. Results Several significant correlations existed after controlling for age and mass. RF thickness showed the strongest correlations with the dependent variables. Both RTD time intervals, but not peak torque, correlated with VL thickness. Peak torque was greatly influenced by age and mass. Echo intensity and muscle thickness correlated highly with agility performance. Conclusions VL and RF echo intensity and muscle thickness may help predict athleticism, and to a lesser extent, RTD, in boys. Muscle Nerve 55: 685-692, 2017.

Objective This study aimed to examine the effects of accumulating nursing work on maximal and rapid strength characteristics in female nurses and compare these effects in day versus night shift workers. Background Nurses exhibit among the highest nonfatal injury rates of all occupations, which may be a consequence of long, cumulative work shift schedules. Fatigue may accumulate across multiple shifts and lead to performance impairments, which in turn may be linked to injury risks. Method Thirty-seven nurses and aides performed isometric strength-based performance testing of three muscle groups, including the knee extensors, knee flexors, and wrist flexors (hand grip), as well as countermovement jumps, at baseline and following exposure to three 12-hour work shifts in a four-day period. Variables included peak torque (PT) and rate of torque development (RTD) from isometric strength testing and jump height and power output. Results The rigorous work period resulted in significant decreases (−7.2% to −19.2%) in a large majority (8/9) of the isometric strength-based measurements. No differences were noted for the day versus night shift workers except for the RTD at 200 millisecond variable, for which the night shift had greater work-induced decreases than the day shift workers. No changes were observed for jump height or power output. Conclusions A compressed nursing work schedule resulted in decreases in strength-based performance abilities, being indicative of performance fatigue. Application Compressed work schedules involving long shifts lead to functional declines in nurse performance capacities that may pose risks for both the nurse and patient quality of care. Fatigue management plans are needed to monitor and regulate increased levels of fatigue.

Introduction We examined the effects of aging on passive stiffness, size, quality, and strength characteristics of the posterior hip and thigh muscles. Methods Fifteen young (25 ± 3 years) and 15 old (72 ± 5 years) men participated in this study. Echo intensity (EI) and cross-sectional area (CSA) were determined from ultrasound scans of the hamstrings. Straight-leg raises were used to assess passive stiffness, which was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle–torque curve. Peak torque (PT) and rate of torque development (RTD) were assessed through maximal voluntary contractions. Results Phase 2 slope and EI were higher (P ≤ 0.024), and CSA, PT, and RTD were lower (P ≤ 0.011) in the old compared with the young men; however, no difference (P = 0.145) was observed for phase 1 slope. Conclusions Decreases in muscle quality, as indicated by increases in EI, may contribute to the greater passive stiffness observed in older adults. Muscle Nerve 55: 305–315, 2017

Aim Cognitive dysfunction is associated with slower gait speed in older women, but whether cognitive function affects gait performance earlier in life has yet to be investigated. Thus, the objective of this study was to test the hypothesis that cognitive function will discriminate gait performance in healthy younger women. Methods Fast-pace and dual-task gait speed were measured in 30 young to middle-aged (30–45 y) and 26 older (61–80 y) women without mild cognitive impairment. Visuoperceptual ability, working memory, executive function, and learning ability were assessed using neuropsychological tests. Within each age group, women were divided by the median into lower and higher cognitive function groups to compare gait performance. Results Younger women with higher visuoperceptual ability had faster fast-pace (2.25 ± 0.30 vs. 1.98 ± 0.18 m/s, p ≤ 0.01) and dual-task gait speed (2.02 ± 0.27 vs. 1.69 ± 0.25 m/s, p ≤ 0.01) than women with lower visuoperceptual ability. The difference in dual-task gait speed remained significant (p = 0.02) after adjusting for age, years of education, and other covariates. Dividing younger women based on other cognitive domains showed no difference in gait performance. In contrast, working memory and executive function discriminated dual-task gait speed (p Conclusion To our knowledge, this is the first study to show that poorer cognitive function even at a relatively young age can negatively impact mobility. Different cognitive functions discriminated gait performance based on age, highlighting a possible influence of aging in the relationship between cognitive function and mobility in women.

BACKGROUND Physical demands may vary between white collar and blue collar occupations when evaluating specific physiological differences such as one's weight, body mass index and body fat percentage. OBJECTIVE To explore nutritional, anthropometric, and physical-activity differences between young and middle-aged WC and BC workers. METHODS Ninety-one male participants aged 19-64 that were either WC and/or BC workers completed a 3-day food recall, modified Baecke Questionnaire, and had their height, weight, body mass index and body fat percentage measured. Participants were classified as: young-white-collar, young-blue-collar, middle-white-collar or middle-blue-collar workers. RESULTS No nutritional differences within ages or between occupations were reported. Body mass index and body fat percentage were lower for young vs. middle-aged workers. Lastly, physical-activity at work was higher for young and middle-aged Blue collar workers, while White collar workers participated in more physical activity outside of work. CONCLUSIONS The present findings suggest that the observed increases in body fat percentage and body mass index with age, are independent of occupation.

Objectives The time delay between the onset of a muscle's electrical activity and force is believed to have important functional implications, and has been shown to decrease following resistance training in males. The purpose of this investigation was to examine changes in the voluntary electromechanical delay (EMD) for the leg extensors and flexors following a short-term resistance training intervention in females. Design Pretest/posttest control group experiment. Methods Twenty-two previously untrained females (mean ± SD age = 21 ± 2 years; mass = 65.4 ± 13.3 kg) were randomly assigned to training (n = 10) and control (n = 12) groups. The training group performed barbell back squats and deadlifts twice per week for four weeks. EMD for the vastus lateralis (extensors) and biceps femoris (flexors) was examined during maximal voluntary contractions at pre- and posttesting. Data were examined using analyses of covariance (ANCOVAs) with the pretest and posttest scores serving as the covariate and dependent variable, respectively, and by evaluating the number of participants that exceeded the minimal difference statistic. Results For the leg extensors, the adjusted EMD posttest mean for the training group was significantly lower than that for the control group (74.3 vs. 91.8 ms; p = 0.015; ή2 = 0.275), and five training participants displayed decreases that exceeded the minimal difference. The ANCOVA for the leg flexors was not significant (adjusted means = 98.0 vs. 90.0 ms; p = 0.487; ή2 = .026). Conclusions Four weeks of multi-joint resistance training resulted in decreased EMD for the leg extensors, but not the flexors.

Background: Maximal and rapid strength characteristics of the knee extensor and flexor muscles play an important role in fall prevention and walking-related performances; however, few studies have investigated the ability of these variables to identify chair-rise performances in very old adults. Purpose: To examine the effectiveness of maximal and rapid isometric strength characteristics of the knee extensors and flexors to differentiate between very old adults who are able (higher functioning) versus unable (lower functioning) to independently rise from a chair. Methods: Nine higher functioning (age, 87 ± 6 years) and 6 lower functioning (age, 89 ± 6 years) very old adults performed 2 isometric maximal voluntary contractions of the knee extensors and flexors. Peak moment and absolute and relative rate of moment development (RMD) at the early (0-50 ms) and late (0-200 ms) phases of muscle contraction were examined during each maximal voluntary contraction. Results: Absolute and relative RMD values at 0 to 50 ms were greater (P = .02 and .03, respectively) in the higher functioning than in the lower functioning individuals for both the knee extensors and flexors. However, no group-related differences (P = .39-.58) were observed in either muscle group for peak moment or absolute and relative RMD at 0 to 200 ms. Conclusions: Early rapid moment production of the knee extensors and flexors may be an effective measure for discriminating between very old adults of different chair-rise performance abilities. Physical therapists and other practitioners may use these findings to help with the identification and early detection of older adults who are at a high risk for functional decline.

OBJECTIVE: The aim of this study was to determine the impact of a demanding work schedule involving long, cumulative work shifts on response time and balance-related performance outcomes and to evaluate the prevalence of musculoskeletal disorders between day and night shift working nurses. METHODS: A questionnaire was used to identify the prevalence of past (12-month) and current (7-day) musculoskeletal disorders. Nurses worked three 12-hour work shifts in a 4-day period. Reaction time and balance tests were conducted before and after the work period. RESULTS: The work period induced impairments for reaction time, errors on reaction time tasks, and balance performance, independent of shift type. Musculoskeletal symptom prevalence was high in workers of both work shifts. CONCLUSIONS: Compressed work shifts caused performance-based fatigue in nurses. Reaction time and balance tests may be sensitive fatigue identification markers in nurses. Language: en

Fatigue-related impairments in the nursing workforce contribute to a multitude of health, safety, and economic consequences at the individual, organizational and societal levels. Long and compressed work schedules are commonly worked in the healthcare industry, but more research is needed to understand the cumulative effects of multiple work shifts on physiology-based performance outcomes in nurses. The purpose of this study was to compare the effects of a single nursing work shift versus three compressed (one every 24 hours) 12 hour shifts on performance-based fatigue in nurses and aides. Twenty-six fulltime hospital working nurses and aides (age = 36.1 ± 13.3 years) reported to the lab for testing before, immediately after working a single 12 hour shift, and after working three 12 hour shifts in a 72 hour period. Outcome measures included vigilance-based reaction time, lapses of attention, and muscle function assessments (lower and upper body muscle strength, explosive strength and vertical jump performance). All variables except hand grip strength showed a significant decline following the three work shifts. The psychomotor vigilance reaction time and lapses of attention variables also generally showed a significant decline from the end of shift one to the end of shift three, indicting an accumulation of fatigue in these metrics with increasing number of shifts worked. Muscle function variables responded early in the duty cycle, showing a significant decline after a single work shift, but did no further decline by the end of the third shift. These findings use objective measures to substantiate that fatigue impairments occur from working a single 12 hour shift, and in several instances, increase further with more successive work shifts. Caution should be employed by personnel and administrators with work schedules involving multiple compressed 12 hour shifts. Fatigue management strategies may be used to improve risks and consequences from fatigue-related mishaps, and this study reports several variables that appear sensitive to identifying and tracking fatigue in this population.

The purposes of this study were to examine the age-related differences in absolute and normalized torque-time parameters in five distinct groups across the adult lifespan, and the relationship between rapid strength and limb acceleration capacities across the lifespan. One-hundred and thirty-six healthy men were categorized as young athletes (n = 27; age = 20.7 yrs), young controls (n = 32; 21.9 yrs), middle young (n = 32; 49.8 yrs), middle old (n = 15; 58.9 yrs), and old (n = 30; 71.3 yrs) cohorts. Participants performed maximal voluntary contractions (MVCs) of the leg extensors under isometric and isokinetic (240 deg.·s−1) conditions. Outcome measures included peak torque (PT), absolute and MVC normalized (norm) rate of torque development (RTD) at 50 and 200 ms, RTD50/PT ratio, and rate of velocity development (RVD). The PT and absolute RTD at 200 ms declined from young to old age (P

The purpose of the present study was to examine the relationships between neuromuscular function and functional balance performance in firefighters. Fifty career firefighters (35.1 ± 7.5 yr) performed isometric leg extension and flexion muscle actions to examine peak torque (PT), and absolute (aTQ) and normalized (nTQ; %PT) rapid torque variables at 50, 100, 150, and 200 ms. A performance index (PI) was determined from the functional balance assessment completion time. Partial correlations were used to examine the relationship between the PI and the maximal and rapid TQ variables for each muscle and the composite value, while controlling for demographic data related to the PI. Multiple regression analyses examined the relative contributions of the maximal and rapid aTQ variables, and demographic data on the PI. After controlling for age and %BF, the majority of the later aTQ and nTQ variables (100–200 ms) and PT were associated with the PI (r = −0.501–−0.315). Age, %BF, and aTQ100 explained 42–50% of the variance in the PI. Lower rapid strength, increased age, and poorer body composition were related to worse performance during the functional balance assessment. Strategies to improve rapid strength and %BF, especially in aging firefighters may impact dynamic balance abilities in firefighters.

Isometric force- or torque-time parameters are commonly reported in the research literature. The processing methods of the electronic dynamometer-derived signal may influence the outcome measures. This study determined the influence of filtering and sample rate (SR) on isometric torque-time parameters and provides specific signal processing recommendations for future studies. Twenty-three subjects performed 49 isometric maximum voluntary contractions (MVCs) of the knee extensors on an isokinetic dynamometer. Outcome measures included peak torque (PT), and rate of torque development at peak (RTDPEAK), 50 (RTD50) and 200 (RTD200) ms for seven filter conditions including low-pass filter cutoffs at 5, 10, 20, 50, 100 and 150 Hz and a notch filter at 100 and 200 Hz. Comparisons were also made across four SR conditions at 100, 500, 1000 and 2000 Hz. The RTDPEAK variable was markedly changed (−5.4 to −37.9%) for all filter frequencies compared to the 150 Hz condition and the RTD50 variable was altered for all frequencies between 50 and 5 Hz. No differences were found for RTD200. For SR, compared to the 2000 Hz condition, differences were revealed for the 100 Hz condition for the RTDPEAK and RTD50 variables. The filtering or SR did not alter PT across any of the conditions. The filter and SR applied to the signal was capable of distorting the MVC signal and skewing the torque–time parameters, specifically for the early and maximum RTD variables of the MVC curve (RTD50 and RTDPEAK). For traditional isokinetic dynamometers, a low-pass filter cutoff of 150 Hz and a SR of at least 1000 Hz is recommended when assessing early isometric force- or torque-time MVC parameters.

We examined the means, medians, and variability for motor-unit interpulse intervals (IPIs) during voluntary, high force contractions. Eight men (mean age = 22 years) attempted to perform isometric contractions at 90% of their maximal voluntary contraction force while bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and vastus medialis muscles. Surface EMG signal decomposition was used to determine the recruitment thresholds and IPIs of motor units that demonstrated accuracy levels ≥ 96.0%. Motor units with high recruitment thresholds demonstrated longer mean IPIs, but the coefficients of variation were similar across all recruitment thresholds. Polynomial regression analyses indicated that for both muscles, the relationship between the means and standard deviations of the IPIs was linear. The majority of IPI histograms were positively skewed. Although low-threshold motor units were associated with shorter IPIs, the variability among motor units with differing recruitment thresholds was comparable.

A previous study has demonstrated the ability to roughly estimate the percentage of fast-twitch muscle fibers for the vastus lateralis through the analysis of peak torque values during fatiguing isokinetic testing. We examined whether use of the hamstrings influenced peak torque and electromyographic (EMG) responses for the quadriceps during fatiguing isokinetic muscle actions. On 2 separate occasions, 21 men (mean age = 23 years) performed 50 repeated, maximal concentric isokinetic muscle actions of the left leg extensors at a velocity of 180°·s. For 1 trial, the subjects maximally flexed the knee joint after each full extension to bring the dynamometer's lever arm back to the starting position. For the other trial, the subjects relaxed after each maximal extension and an investigator assisted in returning the lever arm. Surface EMG signals were detected from the vastus lateralis and biceps femoris throughout testing. Dependent variables that assessed the decline in peak torque and EMG mean frequency for the vastus lateralis were examined using dependent samples t-tests, effect size statistics, and the number of subjects who exceeded the minimal difference needed to be considered real. Our results showed small mean differences between the trials (Cohen's d ≤0.136). For the estimated percentage of fast-twitch fibers, none of the subjects showed a difference between trials that we considered meaningful. The mean estimated percentages of fast-twitch fibers were 61.6 and 60.1. Collectively, use of the hamstrings during fatiguing isokinetic testing of the quadriceps had little influence on peak torque and EMG.

The aims of this study were to 1) examine the influence of age and occupation on maximal and rapid strength of the lower-extremity muscles and 2) examine the relationship between maximal and rapid strength and physical workload (work index (WI)) in the blue-collar (BC) cohort. Peak torque (PT) and peak rate of torque development (peakRTD) of the leg extensors (LE), leg flexors (LF), and plantar flexors (PF) were assessed in 47 young (age = 24.1 ± 2.4 years) and 41 middle-aged (52.4 ± 5.2 years) white-collar (WC) and BC men. Middle-aged workers exhibited lower PT for all muscles, and peakRTD for the LF and PF muscles. A positive relationship (r = 0.59; P < 0.01) was observed between WI and peakRTD for the PF in the young BC workers, however, this relationship was negative (r = −0.45; P = 0.053) for the LF of the middle-aged BC workers. Lowering physical work demands and/or incorporating effective health-related practices for employees may be appealing strategies to enhance aging workers' productivity and longevity in the workforce.

Context Passive straight-legged–raise (SLR) assessments have been performed with the ankle fixed in dorsiflexion (DF), plantar-flexion (PF), or neutral (NTRL) position. However, it is unclear whether ankle position contributes to differences in the passive resistance measured during an SLR assessment. Objective To examine the influence of ankle position during an SLR on the passive torque, range of motion (ROM), and hamstrings electromyographic (EMG) responses to passive stretch of the posterior hip and thigh muscles. Design Crossover study. Setting Research laboratory. Patients or Other Participants A total of 13 healthy volunteers (5 men: age = 24 ± 3 years, height = 178 ± 6 cm, mass = 85 ± 10 kg; 8 women: age = 21 ± 1 years, height = 163 ± 8 cm, mass = 60 ± 6 kg). Intervention(s) Participants performed 6 randomly ordered passive SLR assessments involving 2 assessments at each condition, which included the ankle positioned in DF, PF, and NTRL. All SLRs were performed using an isokinetic dynamometer programmed in passive mode to move the limb toward the head at 5°/s. Main Outcome Measure(s) During each SLR, maximal ROM was determined as the point of discomfort but not pain, as indicated by the participant. Passive torque and EMG amplitude were determined at 4 common joint angles (θ) separated by 5° during the final common 15° of ROM for each participant. Results Passive torque was greater for the DF condition than the NTRL (P = .008) and PF (P = .03) conditions at θ3 and greater for the DF than NTRL condition (P = .02) at θ4. Maximal ROM was lower for the DF condition than the NTRL (P = .003) and PF (P < .001) conditions. However, we found no differences among conditions for EMG amplitude (P = .86). Conclusions These findings suggest that performing SLRs with the ankle positioned in DF may elicit greater passive torque and lower ROM than SLRs with the ankle positioned in PF or NTRL. The greater passive torque and lower ROM induced by the DF condition possibly were due to increased tension in the neural structures of the proximal thigh.

The purpose of this study was to examine the reliability of ultrasound (US) measures of cross-sectional area (CSA), muscle thickness (MT) and echo intensity (EI) of the hamstrings, with comparisons between males and females. In 20 healthy participants (10 males, 10 females), CSA, MT and EI were measured from panoramic US scans of the hamstrings on 2 separate days. The intra-class correlation coefficients and standard errors of measurement as a percentage of the mean for CSA, MT and EI ranged from 0.715 to 0.984 and from 3.145 to 12.541% in the males and from 0.724 to 0.977 and from 4.571 to 17.890% in the females, respectively. The males had greater CSAs and MTs and lower EIs than the females (p = 0.002-0.049), and significant relationships were observed between CSA and MT (r = 0.714-0.938, p ≤ 0.001-0.023). From an overall reliability standpoint, these findings suggest that panoramic US may be a reliable technique for examining muscle size and quality of the hamstrings in both males and females.

Recently, an equation that allows investigators to correct echo intensity for subcutaneous fat was developed. We evaluated correlations between uncorrected and corrected echo intensity versus measures of lower-extremity function. Twenty-three older adults (11 men, 12 women; mean age = 72 y) participated. B-Mode ultrasonography was used to quantify rectus femoris echo intensity and subcutaneous fat thickness. Knee extensor isometric peak torque and rate of torque development at 200 ms (RTD200) were determined (joint angle = 90°). Fast gait speed was evaluated at 10- and 400-m distances. Partial correlations between normalized peak torque, RTD200 and 10- and 400-m gait speed versus uncorrected echo intensity were weak and insignificant. Correction for subcutaneous fat strengthened the correlations (peak torque r = −0.500, RTD200 r = −0.425, 10-m r = −0.409, 400-m r = −0.410). Correcting echo intensity values for subcutaneous fat strengthened the associations with lower-extremity muscle function in older adults.

This study aimed to provide a comprehensive strength-based physiological profile of women’s NCAA Division I basketball and gymnastic athletes; and to make sport-specific comparisons for various strength characteristics of the knee flexor and extensor muscles. A focus on antagonist muscle balance (hamstrings-to-quadriceps ratios, H:Q) was used to elucidate vulnerabilities in these at-risk female athletes. Fourteen NCAA Division I women’s basketball and 13 gymnastics athletes performed strength testing of the knee extensors and flexors. Outcome measures included absolute and relative (body mass normalised) peak torque (PT), rate of torque development at 50, 100, 200 ms (RTD50 etc.) and H:Q ratios of all variables. The basketball athletes had greater absolute strength for all variables except for isokinetic PT at 240°s−1 and isometric RTD50 for the knee extensors. Gymnasts showed ~20% weaker body mass relative concentric PT for the knee flexors at 60 and 120°·s−1, and decreased conventional H:Q ratio...

This study investigated the impact of age, knee joint angle, and strength testing modality on lower body maximal and rapid strength production and assessed the transferability of these characteristics to mobility-related function. Twenty young (age=21.9 yrs) and eighteen elderly (71.1 yrs) adults performed single-joint and multiple-joint isometric maximal voluntary contractions at three knee angles. Outcome measures included peak torque (PT), rate of torque development (RTD), jump height, power, 10 and 400 m walk, and timed chair stand. Older adults exhibited greater reductions in RTD for the multiple-joint (45%) than for the single-joint mode (18%). The 10 m walk was best predicted by multiple-joint RTD at 90°, the 400 m walk by jump height, and the chair stand by single-joint PT at 20°. Single-joint strength tests may underestimate age-related rapid strength impairments, likely due to requirements to exert muscular force in excess of one’s body mass in an upright position.

The current understanding of age-related declines in muscle strength capacities is largely based upon strength testing at joint angles of optimal performance, but many activities of daily living involve force generation at muscle lengths/angles outside of optimal force. This study investigated the influence of age, joint angle, and muscle group (knee extensors and flexors) on maximal and rapid strength characteristics. Young (n = 21; age = 22.1 years) and older (23; 72.6 years) adults performed maximal voluntary contractions for the knee extensors and flexors at 20°, 60°, and 90° joint angles. Peak torque (PT) and rate of torque development (RTD) were calculated. An age, angle, and muscle interaction was found for PT, revealing differences for the knee flexors at all three joint angles for the older adults, whereas the young adults were similar between the 20° and 60° angles. The later RTD variable showed an age and muscle group interaction, whereas no interactions were found for early RTD. The angle of strength testing for maximal strength (PT) of the knee flexors showed dissimilar changes in strength characteristics for young versus older adults across joint angles. For later RTD variables, the testing angle was a more prominent factor for the knee extensors, but less so for the flexors.

The purpose of this study was to determine if passive muscle-tendon properties of the posterior muscles of the hip and thigh and lower-body muscle power could discriminate between athletic status in division I female soccer athletes and nonathlete controls. Ten athletes (mean ± SE, age = 18.70 ± 0.34 years; mass = 64.61 ± 2.16 kg; height = 165.99 ± 1.46 cm; thigh muscle cross-sectional area = 94.08 ± 2.58 cm) and 11 nonathletes (mean ± SE, age = 19.64 ± 0.51 years; mass = 62.81 ± 2.60 kg; height = 162.44 ± 2.20 cm; thigh muscle cross-sectional area = 86.33 ± 2.81 cm) performed 2 instrumented straight-leg raise (iSLR) assessments using an isokinetic dynamometer programmed in passive mode to move the foot toward the head at 5°·s. During each iSLR, passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curve, and maximum range of motion (ROM) was determined as the point of discomfort but not pain, as indicated by the participant. Lower-body power characteristics were assessed through a countermovement vertical jump (CMJ) test. The results indicated that phase 1 and 2 slopes, CMJ height, and peak power (Pmax) were significantly higher (p = 0.004-0.036) for the athletes compared with the nonathletes; however, maximum ROM was not different (p = 0.601) between groups. Significant relationships were also observed between phase 1 and 2 slopes, and CMJ height and Pmax (r = 0.483-0.827; p ≤ 0.001-0.027). These findings suggest that in addition to traditional power characteristics, passive stiffness may also be a sensitive and effective measure for discriminating athletes from nonathletes. Coaches and practitioners may use these findings when designing training programs aimed at increasing musculotendinous stiffness of the posterior hip and thigh muscles and to help identify athletes with high overall athletic potential.