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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 Recent evidence suggests that nutritional interventions may improve muscle outcomes in malnutrition and sarcopenia. Objectives We evaluated the effects of 2 high-quality oral nutritional supplements (ONS) differing in amount and type of key nutrients in older adult men and women. Design A multicenter, randomized, double-blinded, controlled clinical trial. Participants Malnourished and sarcopenic men and women, 65 years and older (n = 330). Intervention A 24-week intervention period with 2 energy-rich (330 kcal) ONS treatment groups: Control ONS (C ONS , 14 g protein; 147 IU vitamin D 3 ) versus Experimental ONS (E ONS , 20 g protein; 499 IU vitamin D 3 ; 1.5 g CaHMB) taken twice daily. Both ONS also contained other vitamins, minerals, and nutrients in varying amounts. Measurements Isokinetic peak torque (PT, Nm) leg strength, grip strength (kg), and gait speed (m·s −1 ) were assessed at baseline and 12 and 24 weeks. Left and right leg muscle mass (LMM, kg) were assessed by dual-energy x-ray absorptiometry (DXA). Muscle quality (MQ) was leg strength expressed relative to the tested LMM (Nm·kg −1 ). Subgroup analyses were performed: severe sarcopenia (low skeletal mass index, low grip strength [<30 kg men; <20 kg women], low gait speed [<0.8 m·s −1 ]) and mild-moderate sarcopenia (low skeletal mass index, normal gait speed, or normal grip strength). Results Both ONS groups (E ONS and C ONS ) improved PT, MQ, grip strength, and gait speed from baseline with no treatment differences. Those with severe sarcopenia (44%) exhibited lower baseline PT and MQ, with no differences in strength improvements between treatments. However, participants with mild-moderate sarcopenia exhibited higher baseline PT and MQ, with differences in strength improvements at 12 weeks (E ONS > C ONS , P = .032) in those with normal grip strength. There were no treatment differences based on sarcopenic severity for either grip strength or gait speed. Conclusion ONS improved strength outcomes in malnourished older adults with sarcopenia. In those with mild-moderate sarcopenia, but not severe sarcopenia, consumption of the E ONS improved leg muscle strength and quality compared with the standard C ONS . [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 discusses research on the effect of periodized squat training on body composition and strength. The 6-week training program examined squat strength in young men who had some recreational weight training experience. The application of whole-body low-frequency vibration (WBLFV) and its effect on dynamic strength are discussed.

The article presents the results of a study which investigated whether whole-body vibration would affect jumping performance. An overview of related previous research is provided, along with details of the experimental protocol, which involved low-frequency vibrations at various amplitudes and countermovement jump tests.

Abstract: This study investigated neuromuscular fatigue following low-intensity resistance exercise with vascular restriction (VR) and without vascular restriction (control, CON). Fourteen males participated in two experimental trials (VR and CON) each separated by 48h. Each participant performed two isometric maximum voluntary contractions (MVCs) before and after five sets of 20 dynamic constant external resistance leg extension exercises (DCER-EX) at 20% of one-repetition maximum (1-RM). The participants were asked to lift (1.5s) and lower (1.5s) the load at a constant velocity. Surface electromyography (EMG) was recorded from the vastus lateralis during MVC and DCER-EX. Twitch interpolation was used to assess the percent of maximal voluntary activation (%VA) during the MVC. During performing five sets of 20 DCER-EX, the increases (p <0.05) in EMG amplitude and decreases (p <0.05) in EMG mean power frequency were similar for both VR and CON. However, there were significant differences between VR and CON for MVC force, %VA, and potentiated twitch force and significant interactions for EMG amplitude. VR decreased MVC force, %VA, potentiated twitch force, and EMG amplitude more than CON. Our findings suggest that the VR-induced fatigue may have been due to a combination of peripheral (decreases in potentiated twitch) and central (decreases in %VA and EMG amplitude) fatigue. [Copyright &y& Elsevier]

The article presents the results of a study which investigated the effects of whole-body low-frequency vibration (WBLFV) on isometric force/time characteristics during squat training. It was found that there were benefits to adding WBLFV to resistance training, and adding vibration between sets may be an alternative to adding vibration during training.

The article presents the results of a study which investigated the effect of periodized squat training with a Smith machine and whole-body vibration (WBV) on jumping ability. The experimental protocol included tests of jumping ability and six weeks of periodization training, both with and without WBV. It was found that jumping ability benefited from the addition of WBV to a periodized squat exercise program.

The article looks at the effects of a six-week squat training program on the jumping ability of males between the ages of 20 and 30. The author compares the effects of the program with and without the use of whole-body low-frequency vibration. Results indicate that resistance training experience and baseline squat strength are important factors of the program.

The article discusses a study to examine the acute effects of static versus dynamic stretching on peak torque and electromyographic and mechanomyographic amplitude of the biceps femoris (BF) muscle during isometric maximal voluntary contractions of the leg flexors at four different knee joint angles. The results suggested that the decreases in strength after static stretching may be the result of mechanical rather than neural mechanisms for the BF muscle.

Abstract: The purposes of this study were to examine the mechanomyographic (MMG) and electromyographic (EMG) time and frequency domain responses of the vastus lateralis (VL) and rectus femoris (RF) muscles during isometric ramp contractions and compare the time–frequency of the MMG and EMG signals generated by the short-time Fourier transform (STFT) and continuous wavelet transform (CWT). Nineteen healthy subjects (mean±SD age=24±4 years) performed two isometric maximal voluntary contractions (MVCs) before and after completing 2–3, 6-s isometric ramp contractions from 5% to 100% MVC with the right leg extensors. MMG and surface EMG signals were recorded from the VL and RF muscles. Time domains were represented as root mean squared amplitude values, and time–frequency representations were generated using the STFT and CWT. Polynomial regression analyses indicated cubic increases in MMG amplitude, MMG frequency, and EMG frequency, whereas EMG amplitude increased quadratically. From 5% to 24–28% MVC, MMG amplitude remained stable while MMG frequency increased. From 24–28% to 76–78% MVC, MMG amplitude increased rapidly while MMG frequency plateaued. From 76–78% to 100% MVC, MMG amplitude plateaued (VL) or decreased (RF) while MMG frequency increased. EMG amplitude increased while EMG frequency changed only marginally across the force spectrum with no clear deflection points. Overall, these findings suggested that MMG may offer more unique information regarding the interactions between motor unit recruitment and firing rate that control muscle force production during ramp contractions than traditional surface EMG. In addition, although the STFT frequency patterns were more pronounced than the CWT, both algorithms produced similar time–frequency representations for tracking changes in MMG or EMG frequency. [Copyright &y& Elsevier]

Previous studies have demonstrated increases in peak torque (PT) and decreases in acceleration time (ACC) after only 2 days of resistance training, and other studies have reported improvements in isokinetic performance after 5 days of creatine supplementation. Consequently, there may be a combined benefit of creatine supplementation and short-term resistance training for eliciting rapid increases in muscle strength, which may be important for short-term rehabilitation and return-to-play for previously injured athletes. The purpose of this study, therefore, was to examine the effects of 3 days of isokinetic resistance training combined with 8 days of creatine monohydrate supplementation on PT, mean power output (MP), ACC, surface electromyography (EMG), and mechanomyography (MMG) of the vastus lateralis muscle during maximal concentric isokinetic leg extension muscle actions. Twenty-five men (mean age ± SD = 21 ± 3 years, stature = 177 ± 6 cm, and body mass = 80 ± 12 kg) volunteered to participate in this 9-day, double-blind, placebo-controlled study and were randomly assigned to either the creatine (CRE; n = 13) or placebo (PLA; n = 12) group. The CRE group ingested the treatment drink (280 kcal; 68 g carbohydrate; 10.5 g creatine), whereas the PLA group received an isocaloric placebo (70 g carbohydrate). Two servings per day (morning and afternoon) were administered in the laboratory on days 1-6, with only 1 serving on days 7-8. Before (pre; day 1) and after (post; day 9) the resistance training, maximal voluntary concentric isokinetic leg extensions at 30, 150, and 270°·s-1 were performed on a calibrated Biodex System 3 dynamometer. Three sets of 10 repetitions at 150°·s-1 were performed on days 3, 5, and 7. Peak torque increased (p = 0.005; η2 = 0.296), whereas ACC decreased (p > 0.001; η2 = 0.620), from pretraining to post-training for both the CRE and PLA groups at each velocity (30, 150, and 270°·s-1). Peak torque increased by 13% and 6%, whereas ACC decreased by 42% and 34% for the CRE and PLA groups, respectively, but these differences were not statistically significant (p > 0.05). There were no changes in MP, EMG, or MMG amplitude; however, EMG median frequency (MDF) increased, and MMG MDF increased at 30°·s-1, from pretraining to post- training for both the CRE and PLA groups. These results indicated that 3 days of isokinetic resistance training was sufficient to elicit small, but significant, improvements in peak strength (PT) and ACC for both the CRE and PLA groups. Although the greater relative improvements in PT and ACC for the CRE group were not statistically significant, these findings may be useful for rehabilitation or strength and conditioning professionals who may need to rapidly increase the strength of a patient or athlete within 9 days. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to examine the inter-individual variability for the patterns of responses for mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus isometric torque in lower-strength (LS) and higher-strength (HS) individuals. Twelve participants (mean±S.D. age=25+4 years) performed two isometric maximal voluntary contractions (MVCs) before and after completing nine submaximal step muscle actions (15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% MVC) of the right leg extensors. MMG signals were recorded from the vastus lateralis muscle, and MMG amplitude and MPF values were computed for each corresponding percentage of the MVC. Polynomial regression analyses indicated that the composite MMG amplitude versus isometric torque relationship was best fit with a linear model (r 2 =0.980) for the LS group and a cubic model (r 2 =0.994) for the HS group. The composite MMG MPF versus isometric torque relationships were best fit with linear models for both the LS (r 2 =0.529) and HS (r 2 =0.591) groups. However, only 66% of the individuals exhibited the same linear MMG amplitude patterns as the composite relationship for the LS group, whereas only 33% of the individual relationships were cubic for the HS group. Only one subject exhibited a positive linear (r 2 =0.681) relationship for the MMGMPF versus isometric torque relationship for either the LS or HS groups. These findings suggested that strength differences do not affect the patterns of responses for MMG amplitude or MPF. The lack of consistency between the individual and composite patterns of responses suggested some degree of inter-individual variability. Therefore, future studies should examine the individual patterns of response to draw conclusions about motor control strategies. [Copyright &y& Elsevier]

The purpose of this study was to examine the effects of 28 days of beta-alanine (b-Ala) and creatine monohydrate (CrM) supplementation on the onset of neuromuscular fatigue by using the physical working capacity at neuromuscular fatigue threshold (PWCFT) test in untrained men. Fifty-one men (mean age ± SD = 24.5 ± 5.3 years) volunteered to participate in this 28-day, double-blind, placebo-controlled study and were randomly assigned to 1 of 4 groups: placebo (PLA; 34 g dextrose; n = 13), CrM (5.25 g CrM plus 34 g dextrose; n = 12), b-Ala (1.6 g b-Ala plus 34 g of dextrose; n = 12), or b-Ala plus CrM (CrBA; 5.25 g CrM plus 1.6 g b-Ala plus 34 g dextrose; n = 14). The supplement was ingested 4 times per day for 6 consecutive days, then twice per day for 22 days before posttesting. Before and after the supplementation, subjects performed a continuous incremental cycle ergometry test while a surface electromyographic signal was recorded from the vastus lateralis muscle to determine PWCFT. The adjusted mean posttest PWCFT values (covaried for pretest PWCFT values) for the b-Ala and CrBA groups were greater than those for the PLA group (p ≤ 0.05). However, there were no differences between the CrM vs. PLA, CrBA vs. b-Ala, CrM vs. b-Ala, or CrM vs. CrBA groups (p > 0.05). These findings suggested that b-Ala supplementation may delay the onset of neuromuscular fatigue. Furthermore, there appeared to be no additive or unique effects of CrM vs. b-Ala alone on PWCFT. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and mean power output (MP) during maximal, voluntary concentric isokinetic leg extensions at 60 and 300°·s-1 in National Collegiate Athletic Association Division I Women's Basketball players. Eleven members of a women's basketball team volunteered to perform maximal concentric isokinetic leg extensions at 60 and 300°·s-1 on a calibrated Biodex System 3 dynamometer. After the initial isokinetic testing, the dominant leg extensors were stretched using 1 unassisted and 3 assisted static stretching exercises. The poststretching isokinetic assessments were repeated at 5, 15, 30, and 45 minutes after the static stretching (post-5, post-15, post-30, and post-45). PT (N·m) and MP (W) were recorded by dynamometer software. The results indicated no stretching-related changes in PT (p = 0.161) or MP (p = 0.088) from pre- to poststretching for any of the testing intervals (post-5, post-15, post-30, and post-45). These findings indicated that the static stretching had no impact on PT or MP during maximal, voluntary concentric isokinetic muscle actions in collegiate women's basketball players. In conjunction with previous studies, these findings suggested that trained athletes may be less susceptible to the stretching-induced force deficit than untrained, nonathletes. [ABSTRACT FROM AUTHOR]

Context: Isokinetic and isotonic resistance training exercises are commonly used to increase strength during musculoskeletal rehabilitation programs. Our study was designed to examine the efficacy of isokinetic and isotonic muscle actions using surface electromyographic (EMG) amplitude-to-work ratios (EMG/WK) and to extend previous findings to include a range of isokinetic velocities and isotonic loads. Objective: To examine work (WK), surface EMG amplitude, and EMG/WK during concentric-only maximal isokinetic muscle actions at 60, 120, 180, 240, and 300 degrees and isotonic muscle actions at 10%, 20%, 30%, 40%, and 50% of the maximal voluntary isometric contraction (MVIC) torque during leg extension exercises. Design: A randomized, counterbalanced, cross-sectional, repeated-measures design. Setting: A university-based human muscle physiology research laboratory. Patients or Other Participants: Ten women (mean age =22.0 +/- 2.6 years) and 10 men (mean age = 20.8 +/- 1.7 years) who were apparently healthy and recreationally active. Intervention(s): Using the dominant leg, each participant performed 5 maximal voluntary concentric isokinetic leg extension exercises at randomly ordered angular velocities of 60,120, 180, 240, and 300 degrees and 5 concentric isotonic leg extension exercises at randomly ordered loads of 10%, 20%, 30%,40%, and 50% of the isometric MVIC. Main Outcome Measure(s): Work was recorded by a Biodex System 3 dynamometer, and surface EMG was recorded from the superficial quadriceps femoris muscles (vastus lateralis, rectus femoris, and vastus medialis) during the testing and was normalized to the MVIC. The EMG/WK ratios were calculated as the quotient of EMG amplitude (Vrms) and WK (J) during the concentric phase of each exercise. Results: Isotonic EMG/WK remained unchanged (P > .05)from 10% to 50% MVIC, but isokinetic EMG/WK increased (P< .05) from 60 to 300 degrees. Isotonic EMG/WK was greater (P >.05) than isokinetic EMG/WK for 50% MVIC versus 60 degrees, 40% MVIC versus 120 degrees, and 30% MVIC versus 180 degrees; however,no differences were noted (P > .05) between 20% MVIC versus 240 degrees or 10% MVIC versus 300 degrees. An 18% decrease in active range of motion was seen for the isotonic muscle actions, from 10% to 50% MVIC, and a 3% increase in range of motion for the isokinetic muscle actions from 60 to 300 degrees was also observed. Furthermore, the peak angular velocities for the isotonic muscle actions ranged from 272.9 to 483.0 degrees for 50% and 10%MVIC, respectively. Conclusions: When considering EMG/WK, peak angular velocity,and range of motion together, our data indicate that maximal isokinetic muscle actions at 240 degrees or controlled-velocity isotonic muscle actions at 10%, 20%, or 30% MVIC may maximize the amount of muscle activation per unit of WK done during the early stages of musculoskeletal rehabilitation. These results may be useful to allied health professionals who incorporate open-chain resistance training exercises during the early phases of rehabilitation and researchers who use isotonic or isokinetic modes of resistance exercise to examine muscle function. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and the joint angle at PT during maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors at 60 and 1808·s-1 for the stretched and unstretched limbs in women. Thirteen women (mean age ± SD = 20.8 ± 0.8 yr; weight ± SD = 63.3 ± 9.5 kg; height ± SD = 165.9 ± 7.9 cm) volunteered to perform separate maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors with the dominant and nondominant limbs on a Cybex 6000 dynamometer at 60 and 1808·s-1. PT (Nm) and the joint angle at PT (8) were recorded by the dynamometer software. Following the initial isokinetic assessments, the dominant leg extensors were stretched (mean stretching time ± SD = 21.2 ± 2.0 minutes) using 1 unassisted and 3 assisted static stretching exercises. After the stretching (4.3 ± 1.4 minutes), the isokinetic assessments were repeated. The statistical analyses indicated no changes (p > 0.05) from pre- to poststretching for PT or the joint angle at PT. These results indicated that static stretching did not affect PT or the joint angle at PT of the leg extensors during maximal, voluntary, eccentric isokinetic muscle actions at 60 and 1808·s-1 in the stretched or unstretched limbs in women. In conjunction with previous studies, these findings suggested that static stretching may affect torque production during concentric, but not eccentric, muscle actions. [ABSTRACT FROM AUTHOR]

Context: Stretching is commonly used as a technique for injury prevention in the clinical setting. Our findings may improve the understanding of the neuromuscular responses to stretching and help clinicians make decisions for rehabilitation progression and return to play. Objective: To examine the short-term effects of static and proprioceptive neuromuscular facilitation stretching on peak torque (PT), mean power output (MP), active range of motion (AROM), passive range of motion (PROM), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis and rectus femoris muscles during voluntary maximal concentric isokinetic leg extensions at 60 and 300°⋅s-1. Design: A randomized, counterbalanced, cross-sectional, repeated-measures design. Setting: A university human research laboratory. Patients or Other Participants: Ten female (age, 23 ± 3 years) and 9 male (age, 21 ± 3 years) apparently healthy and recreationally active volunteers. Intervention(s): Four static or proprioceptive neuromuscular facilitation stretching exercises to stretch the leg extensor muscles of the dominant limb during 2 separate, randomly ordered laboratory visits. Main Outcome Measure(s):The PT and MP were measured at 60 and 300°⋅s-1, EMG and MMG signals were recorded, and AROM and PROM were measured at the knee joint before and after the stretching exercises. Results: Static and proprioceptive neuromuscular facilitation stretching reduced PT (P = .051), MP (P = .041), and EMG amplitude (P = .013) from prestretching to poststretching at 60 and 300°⋅s-1 ( P < .05). The AROM ( P < .001) and PROM ( P = .001) increased as a result of the static and proprioceptive neuromuscular facilitation stretching. The MMG amplitude increased in the rectus femoris muscle in response to the static stretching at 60°⋅s-1 (P = .031), but no other changes in MMG amplitude were observed (P > .05). Conclusions: Both static and proprioceptive neuromuscular facilitation stretching caused similar deficits in strength, power output, and muscle activation at both slow (60°⋅s-1) and fast (300°⋅s-1) velocities. The effect sizes, however, corresponding to these stretching-induced changes were small, which suggests the need for practitioners to consider a risk-to-benefit ratio when incorporating static or proprioceptive neuromuscular facilitation stretching. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the effects of static stretching on concentric, isokinetic leg extension peak torque (PT) at 60 and 240°.s-1 in the stretched and unstretched limbs. The PT of the dominant (stretched) and nondominant (unstretched) leg extensors were measured on a calibrated Cybex 6000 dynamometer. Following the prestretching PT assessments, the dominant leg extensors were stretched using 1 active and 3 passive stretching exercises. After the stretching, PT was reassessed. The results of the statistical analyses indicated that PT decreased following the static stretching in both limbs and at both velocities (60 and 240°.s-1). The present findings suggested that the stretching-induced decreases in PT may be related to changes in the mechanical properties of the muscle, such as an altered length-tension relationship, or a central nervous system inhibitory mechanism. Overall, these findings, in conjunction with previous studies, indicated that static stretching impairs maximal force production. Strength and conditioning professionals should consider this before incorporating static stretching in preperformance activities. Future studies are needed to identify the underlying mechanisms that influence the time course of stretching-induced decreases in maximal force production for athletes and nonathletes across the age span. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in males and females during maximal, concentric isokinetic muscle actions. Subjects performed maximal leg extensions at 60° s−1, 120° s−1, 180° s−1, 240° s−1, 300° s−1, 360° s−1, 420° s−1, and 480° s−1. No gender differences were obser-ved, but there were muscle-specific differences for the patterns of MMG MPF, EMG amplitude, and EMG MPF. The MP and MMG amplitude increased to 180–240° s−1, plateaued, and then decreased to 480° s−1. MMG MPF for the VL and VM remained unchanged to 300° s−1, but then increased to 480° s−1. The EMG amplitude for the RF and EMG MPF for the VL decreased across velocity. Overall, these findings indicated that there were muscle-specific, velocity-related differences in the associations among motor control strategies (EMG amplitude and MPF) and the mechanical aspects of isokinetic muscular activity (MMG amplitude and MPF). [ABSTRACT FROM AUTHOR]

Shoemaker, ME, Smith, CM, Gillen, ZM, and Cramer, JT. Sex differences in test-retest reliability of near-infrared spectroscopy during postocclusive reactive hyperemia of the vastus lateralis. J Strength Cond Res 38(2): e40-e48, 2024--The purpose of this study was to determine test-retest reliability for vascular reactivity measures and ranges for normalization of near-infrared spectroscopy (NIRS) variables from the vastus lateralis using postocclusive reactive hyperemia (PORH) procedure in male subjects, female subjects, and combined. Concentrations of oxygenated hemoglobin (Hb) + myoglobin (Mb) (O2Hb) and deoxygenated Hb + Mb (HHb) to derive total Hb + Mb (THb), difference in Hb + Mb signal (Hbdiff), and muscle tissue oxygen saturation (StO2) from the vastus lateralis were measured during the PORH in 12 male subjects (age: 23.17 6 1.77 years; stature: 180.88 6 4.59 cm; and mass: 81.4769.68 kg) and 10 female subjects (age: 23.8062.07 years; stature: 165.9564.92 cm; and mass: 70.93610.55 kg) on 2 separate days. Adipose tissue thickness at the NIRS site was measured with ultrasonography. There were no significant differences between the mean values from visit 1 to visit 2 (p. 0.076-0.985). In the composite sample, intraclass correlation coefficient (ICC) and coefficient of variation (CV) ranged from 0.35 to 0.91 and 4.74 to 39.18%, respectively. In male subjects, ICC and CV values ranged from 0.57 to 0.89 and 2.44 to 28.55%, respectively. In female subjects, ICC and CV values ranged from 2 0.05 to 0.75 and 7.83 to 61.19%, respectively. Although NIRS variables were overall reliable during PORH, when separated by sex, reliability in male subjects generally increased, whereas female subjects were not reliable, suggesting adipose tissue thickness may be a contributing factor. Understanding sex differences in reliability is important when using this technique for normalization or examining vascular reactivity during athletic performance. With greater utilization of NIRS monitoring in athletes to examine training adaptations, it is important for practitioners to understand the capabilities and potential limitations of the tool. [ABSTRACT FROM AUTHOR]

Furthermore, substrate utilization and fuel adaptability are positively associated with exercise performance [[6]], while numerous dietary and training interventions have been explored to either quantify or manipulate these outcome variables [[7], [9]]. Metabolic flexibility can be defined as the ability of the skeletal muscle to adjust its utilization of substrate pathways [[1]]. Thus, to appropriately adjust substrate utilization in response to nutritional and/or exercise stress (i.e., glucose mobilization via insulin), increasing skeletal muscle quality and/or quality should be prioritized. Skeletal muscle is necessary for movement and exercise; however, it also has an important role in metabolism, as skeletal muscle accounts for 60-80% of the response of glucose to insulin [[1], [5]]. [Extracted from the article]

Resistance training interventions aimed at increasing lower body power and rates of force development have produced varying results. Potentially, the use of WBLFV in between sets of resistance training may increase high-threshold motor unit recruitment and synchronization leading to greater adaptations in both isometric and dynamic performance. The relationship between isometric force/time characteristics and dynamic performance and their respective changes in response to resistance training is of practical importance to strength and conditioning practitioners. To determine the effects of applying whole body vibration prior to and then intermittently between sets of Smith Machine squats upon training induced changes in isometric and dynamic performance and their relationships to one another. Twenty four recreationally resistance trained men were randomly assigned to one of two groups, resistance only (SQT n = 11), or resistance plus whole body vibration (SQTV n = 13). An isometric squat test as well as Squat Jumps (SQJ) and Depth Jumps (DJ) were performed prior to, and following a six-week, periodized Smith Machine squat program. WBLFV was applied 180 s prior to the first work set (50Hz 2-4mm, 30 s) and intermittently (50Hz 4-6mm, 3 × 10 s, 60s between exposures) within a 240s inter-set rest period. Subjects were instructed to assume a quarter squat posture while positioning their feet directly under their center of mass which was modified using a hand held goniometer to a knee angle of 135 ± 5°. Measures of isometric force (N) and isometric rates of force development (N·s-1) were recorded from the onset of contraction (F0) to time points corresponding to F30ms, F80ms, F250ms, Force at initial peak (Finitial), Force at 50% of MVC (MVC50) Time Finitial (ms) as well as the Peak Isometric Force (MVCp) and Peak Isometric Rate of Force Development (PISORFD). Squat jumps were performed with a 20kg Olympic barbell with a linear position transducer attached while the DJ utilized body mass as resistance while dropping from a height of 30cm onto a switch mat. Measures recorded during jumps included jump height (cm) peak power (PMax,W), peak power per kg of body mass (PMax/kg, W/kg) and mean power (Pav,W) for both jump conditions. Correlation matrices matching isometric force/time variables and dynamic (SQJ, DJ) performance within group between weeks 1 and 7(Pre- Post training) revealed multiple significant positive, and negative correlations (p = ∗<.05 and∗∗<.001, range, r = -.624 to .859). A greater total amount of positive correlations were seen for SQTV (24) compared to SQT (2). Correlation coefficients (r) calculated between percent change (%Δ) scores for similar variables revealed small to moderate r values with the only significant correlation seen for the SQTV group between F30ms and DJ height (cm) (r = -.589, R2 = -.347, p <.05). More positive correlations were seen for isometric and dynamic %Δ variables that for SQTV (9) compared to SQT (7). The addition of WBLFV to the SQTVgroup appeared to effect neuro-muscular training adaptation differently from SQT as reflected in the percent change relationship between isometric and dynamic performance measures following six weeks of exposure. WBLFV may help facilitate early phase adaptations to resistance exercise with a tendency to improve early force time components of isometric and dynamic performance. [ABSTRACT FROM AUTHOR]

A response by Joel T. Cramer and Eric D. Ryan to a letter to the editor about their article "Do practical durations of stretching alter muscle strength? A dose-response study," that was published in a previous issue.

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]

BACKGROUND: Low-load resistance training with blood flow restriction (LL + BFR) attenuated delayed onset muscle soreness (DOMS) under some conditions. OBJECTIVE: The purpose of this study examined the effects of reciprocal concentric-only elbow flexion-extension muscle actions at 30% of peak torque on indices of DOMS. METHODS: Thirty untrained women (mean ± SD; 22 ± 2.4 years) were randomly assigned to 6 training days of LL + BFR (n = 10), low-load non-BFR (LL) (n = 10), or control (n = 10). Participants completed 4 sets (1 × 30, 3 × 15) of submaximal (30% of peak torque), unilateral, isokinetic (120 ∘ s - 1 ) muscle actions. Indices of DOMS including peak power, resting elbow joint angle (ROM), perceived muscle soreness (VAS), and pain pressure threshold (PPT) were assessed. RESULTS: There were no changes in peak power, ROM, or VAS. There was a significant interaction for PPT. Follow-up analyses indicated PPT increased for the LL + BFR condition (Day 5 > Day 2), but did not decrease below baseline. The results of the present study indicated LL + BFR and LL did not induce DOMS for the elbow extensors in previously untrained women. CONCLUSION: These findings suggested LL + BFR and LL concentric-only resistance training could be an effective training modality to elicit muscular adaptation without inducing DOMS. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this exploratory study was to quantify the test-retest reliability, intertrial variability and correlations between variables calculated during voluntary and evoked muscle actions. Methods: During three separate trials of isometric leg extension muscle actions with 14 men [mean age (±SD) = 21·9 (±3·2) years; height = 179·2 (±8·0) cm; mass = 77·7 (±10·9) kg], peak torque (PTV), time to peak torque (TPTV), rate of torque development (RTDV), time to peak rate of torque development (TRTDV), electromechanical delay (EMDV) and EMG amplitude (EMGRMS) were quantified for voluntary muscle actions. Peak twitch torque (PTE), time to peak twitch torque (TPTE), rate of torque development (RTDE), time to peak raTE of torque Development (TRTDE), electromechanical DElay (EMDE), peak-to-peak M-wave (Mp-p) and M-wave area (Marea) were calculated for evoked twitches. All electromyographic measurements were recorded over the vastus lateralis. Results: Voluntary intraclass correlation coefficients (ICC) were 0·84-0·96, except for TRTDV (0·30) and EMDV (0·74). Evoked ICC were 0·80-0·95, except for EMDE (0·52). Relative standard errors of measurement for TPT and TRTD were greater for voluntary than evoked, whereas the value for PTE was greater than PTV. There were low to moderate correlations (r = -0·41-0·51) between common voluntary and evoked variables. Conclusions: Evoked variables showed lower intertrial variability than voluntary. Overall, voluntary and evoked muscle actions provide unique, complimentary information regarding neuromuscular function that cannot be used interchangeably. [ABSTRACT FROM AUTHOR]

INTRODUCTION: As virtual education becomes more widespread, particularly considering the recent COVID-19 pandemic, studies that assess the impact of online teaching strategies are vital. Current anatomy curriculum at Paul L. Foster School of Medicine consists of self-taught PowerPoint material, clinical vignette-centered team-based learning (dry lab), and prosection-based instruction (wet lab). This study examined the impact of video-based muscle model (VBMM) instruction using a student-designed forearm muscle model on anatomy quiz scores and student perceptions of its effectiveness with regards to learning outcomes. METHODS: Students divided into Group 1 (54 students) and Group 2 (53 students) were assessed prior to and following a 3.5-minute video on anterior forearm compartment musculature using the muscle model. Group 1 began by completing a pretest, then received VBMM instruction, and then completed a posttest prior to participating in the standard dry lab and 1 hour wet lab. Group 2 completed the wet lab, then received the pretest, VBMM instruction, and posttest prior to participating in the dry lab. Both groups took an identical five-question quiz covering locations and functions of various anterior forearm muscles each time. RESULTS: Mean scores were higher than no formal intervention with exposure to VBMM instruction alone (0.73 points, P =.01), wet lab alone (0.88 points, P =.002), and wet lab plus VBMM instruction (1.35 points, P = <.001). No significant difference in scores was found between instruction with VBMM versus wet lab alone (P = 1.00), or between either instruction method alone compared to a combination of the two methods (P =.34,.09). Student survey opinions on the VBMM instruction method were positive. CONCLUSION: VBMM instruction is comparable to prosection-based lab with regards to score outcomes and was well received by students as both an independent learning tool and as a supplement to cadaveric lab. When compared to either instruction method alone, the supplementation of VBMM with cadaveric prosection instruction was best. VBMM instruction may be valuable for institutions without access to cadaveric specimens, or those looking to supplement their current anatomy curriculum. [ABSTRACT FROM AUTHOR]

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]

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 article presents the results of a study which investigated the degree to which plantar flexor muscle fatigue affected muscular force generation in men. An overview of related previous research is provided, along with details of the experimental protocol, which measured maximal voluntary muscle activation and peak torque.

Abstract: The purpose of this study was to use a wavelet-based signal processing technique to examine the influence of electrode placement over the innervation zone (IZ) on the shape of the electromyographic (EMG) frequency spectrum. Ten healthy males (mean±SD age=23.6±3.0years) performed isometric muscle actions of the dominant leg extensors at 10%, 40%, 70%, and 100% of the maximum voluntary contraction (MVC). Surface EMG signals were detected simultaneously from the vastus lateralis with two bipolar electrode arrangements. One of the electrode arrangements had its center point located directly over the IZ, while the other arrangement had its center point distal to the IZ (i.e., 20mm away). All EMG signals were processed with a wavelet-based procedure. The results showed that for all isometric torque levels, the EMG signals from the distal electrode arrangement demonstrated greater total intensity values than those for the IZ arrangement for frequencies ranging from approximately 2 to 110Hz. There were no consistent differences, however, between the IZ and distal electrode arrangements for total EMG intensity values above 110Hz. Thus, these findings indicated that electrode placement over the IZ affected primarily the low-, rather than the high-frequency portion of the EMG frequency spectrum. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to examine the influence of interelectrode distance (IED) over the estimated innervation zone (IZ) for the vastus lateralis muscle and normalization on the torque-related patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the leg extensors. Eight men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously with two bipolar electrode arrangements in single differential configuration (20 and 40mm IEDs) placed over the estimated IZ for the vastus lateralis muscle and a third electrode arrangement in single differential configuration (20mm IED) placed distal to the estimated IZ. The results indicated that there were only a few (six of 90 statistical comparisons) significant (p <0.05) mean differences among the three electrode arrangements for absolute EMG amplitude. There were no mean differences among the three electrode arrangements for absolute or normalized EMG MPF values or normalized EMG amplitude for the three types of muscle actions. Thus, it may be possible to reduce the potential influence of the IZ on amplitude and spectral parameters of the EMG signal through normalization. [Copyright &y& Elsevier]

The article presents a study which examines the influence of the innervation zone (IZ) on electromyographic (EMG) signals from different bipolar electrodes arrangements that have their center point directly over the IZ. It also investigates the effects of normalization on EMG amplitude and mean power frequency (MPF) values over the IZ. The subject of the study performed isometric muscle action of the dominant leg extensors, and four separate bipolar surface EMG signals were detected simultaneously from the vastus lateralis muscle. The results of the study demonstrated that the patterns for absolute and normalized EMG amplitude and MPF versus isometric torque relationships for the vastus lateralis were affected by electrode location rather than by the IZ.

Abstract: The purposes of this investigation were to examine the effects of electrode placement and innervation zone (IZ) location on: (a) the torque-related patterns of responses for absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) and (b) the mean absolute and normalized EMG amplitude and MPF values. In addition, the present study examined the variability between subjects for the location of the IZ for the vastus lateralis (VL). Eight men (mean±SD age=23.0±4.3yr) performed submaximal to maximal isometric muscle actions of the dominant leg extensors. During each muscle action, fifteen channels of bipolar surface EMG signals were detected from the vastus lateralis using a linear electrode array aligned with the long axis of the muscle fibers. The results indicated that there were differences among channels 1–15 for the patterns of responses and mean values for absolute and normalized EMG amplitude and MPF versus isometric torque. Thus, normalized EMG amplitude and MPF values from different individuals cannot be compared if the EMG signals were detected from different locations over the muscle. In addition, absolute and relative (to femur length) estimates of IZ location for the VL resulted in similar inter-subject variability. [Copyright &y& Elsevier]

Abstract: The purpose of the present study was to: (a) examine the influence of the innervation zone (IZ) for the vastus medialis on EMG signals from bipolar electrode arrangements that have their center point directly over the IZ, 10mm distal to the IZ, 10mm proximal to the IZ, and 20mm distal to the IZ, and (b) investigate the effects of normalization on EMG amplitude and center frequency values over the IZ. Ten men (mean±S.D. age=23.6±3.0 years) performed submaximal to maximal isometric muscle actions of the dominant leg extensors, and four separate bipolar surface EMG signals were detected simultaneously from the vastus medialis. One bipolar electrode arrangement had its center point located directly over the IZ, while the other electrode arrangements had their center points 10mm proximal, 10mm distal, and 20mm distal to the IZ. The results showed that there were no consistent patterns among the four electrode arrangements for the absolute and normalized EMG amplitude and mean power frequency (MPF) versus isometric torque relationships. Generally speaking, the IZ had the greatest effect on the EMG signal when the center point of the bipolar electrode arrangement was directly over it or 10mm proximal to it. In addition, normalization reduced the influence of the IZ on the absolute EMG amplitude and MPF values. Thus, these findings supported the practice of normalization, and indicated that it is a useful technique for reducing the influence of electrode location on EMG amplitude and MPF data. Future studies should examine the potential for movement of the IZ during isometric muscle actions. [Copyright &y& Elsevier]

Abstract: The purpose of the present study was to compare monopolar and bipolar recording techniques for the patterns of responses and mean values for absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) versus isometric torque for the vastus lateralis muscle. Ten healthy men (mean±S.D. age=23.6±3.0 years; body weight=80.9±15.6kg) volunteered to perform submaximal to maximal isometric muscle actions of the dominant leg extensors. Monopolar and bipolar surface EMG signals were detected simultaneously from the vastus lateralis with an eight-channel linear electrode array. The results indicated that in 70–80% of the cases, monopolar and bipolar recording techniques resulted in the same patterns of responses for absolute and normalized EMG amplitude and MPF versus isometric torque. There were, however, differences between the two techniques for mean absolute EMG amplitude and MPF values, but not for the normalized values. Thus, these results supported the practice of normalization, and suggested that comparisons can be made between monopolar and bipolar recording methods for the patterns of responses and mean values for normalized (but not absolute) EMG amplitude and MPF versus isometric torque. [Copyright &y& Elsevier]

The article discusses the effect of the estimated innervation zone (IZ) on electromyographic (EMG) amplitude and mean power frequency (MPF). Participants performed isometric muscle actions of the leg extensors wherein the surface EMG signals were recorded from the vastus lateralis muscle placed over the estimated IZ. Results of the test show the inconsistency on the differences on the patterns of response and mean values for EMG amplitude and MPF versus isometric torque over the estimated IZ from those away from the IZ. Moreover, these differences suggest that normalized EMG amplitude values are not comparable if the EMG signals are detected from different electrode locations.

The purpose of this study was to examine the patterns for the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) vs. torque relationships during submaximal to maximal isometric and isokinetic muscle actions. Seven men (mean ± SD age, 22.4 ± 1.3 years) volunteered to perform isometric and concentric isokinetic leg extension muscle actions at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC) and peak torque (PT) on a Cybex II dynamometer. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes on the vastus medialis. Polynomial regression and separate 1-way repeated-measures analysis of variance were used to analyze the EMG amplitude, MMG amplitude, EMG MPF, and MMG MPF data for the isometric and isokinetic muscle actions. For the isometric muscle actions, EMG amplitude (R2 = 0.999) and MMG MPF (R2 = 0.946) increased to MVC, mean MMG amplitude increased to 60% MVC and then plateaued, and mean EMG MPF did not change (p > 0.05) across torque levels. For the isokinetic muscle actions, EMG amplitude (R2 = 0.988) and MMG amplitude (R2 = 0.933) increased to PT, but there were no significant mean changes with torque for EMG MPF or MMG MPF. The different torque-related responses for EMG and MMG amplitude and MPF may reflect differences in the motor control strategies that modulate torque production for isometric vs. dynamic muscle actions. These results support the findings of others and suggest that isometric torque production was modulated by a combination of recruitment and firing rate, whereas dynamic torque production was modulated primarily through recruitment. [ABSTRACT FROM AUTHOR]

The purpose of this review is to examine the literature that has investigated mechanomyographic (MMG) amplitude and frequency responses during dynamic muscle actions. To date, the majority of MMG research has focused on isometric muscle actions. Recent studies, however, have examined the MMG time and/or frequency domain responses during various types of dynamic activities, including dynamic constant external resistance (DCER) and isokinetic muscle actions, as well as cycle ergometry. Despite the potential influences of factors such as changes in muscle length and the thickness of the tissue between the muscle and the MMG sensor, there is convincing evidence that during dynamic muscle actions, the MMG signal provides valid information regarding muscle function. This argument is supported by consistencies in the MMG literature, such as the close relationship between MMG amplitude and power output and a linear increase in MMG amplitude with concentric torque production. There are still many issues, however, that have yet to be resolved, and the literature base for MMG during both dynamic and isometric muscle actions is far from complete. Thus, it is important to investigate the unique applications of MMG amplitude and frequency responses with different experimental designs/methodologies to continually reassess the uses/limitations of MMG. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to compare measurements of muscle strength, size, and activation of the forearm flexors in pre- and post-pubescent males and females. Methods: Forty pre-pubescent (mean ± 95% confidence interval, age = 9.79 ± 0.35 years, n = 10 males, n = 10 females) and post-pubescent (age = 17.23 ± 0.58 years, n = 10 males, n = 10 females) youth participated. Subjects completed maximal voluntary isometric contractions (MVICs) of the forearm flexors, and submaximal isometric step muscle actions at 30, 50, and 70% of the peak MVIC. Percent voluntary activation (VA) was quantified during all isometric muscle actions. Forearm flexor (biceps brachii and brachialis) muscle cross-sectional area (CSA) was quantified from ultrasound images. Results: MVIC strength was expressed in absolute terms and normalized to CSA. Post-pubertal males were 130% stronger, had 101% greater CSA, and 17% greater maximal VA than pre-pubertal males, while post-pubertal females were 72% stronger, had 54% greater CSA, and 23% greater maximal VA than pre-pubertal females. When MVIC strength was normalized to CSA, the post-pubertal males were still 15% stronger than the pre-pubertal males, while the post-pubertal females were only 12% stronger than the pre-pubertal females. The responses for VA across intensity reflected differences in muscle activation strategies between pre- and post-pubertal males and females. Conclusion: These results suggest that muscle size may account for a greater proportion of the growth and development-related differences in strength among males, while females may be more affected by changes in muscle activation. Regardless of sex, changes in muscle size and neuromuscular function influence strength increases during growth and development. [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]

Purpose: The purpose of this investigation was to examine the individual and composite patterns of responses and time-course of changes in muscle size, strength, and edema throughout a 4 week low-load blood flow restriction (LLBFR) resistance training intervention.Methods: Twenty recreationally active women (mean ± SD; 23 ± 3 years) participated in this investigation and were randomly assigned to 4 weeks (3/week) of LLBFR (n = 10) or control (n = 10) group. Resistance training consisted of 75 reciprocal isokinetic forearm flexion-extension muscle actions performed at 30% of peak torque. Strength and ultrasound-based assessments were determined at each training session.Results: There were quadratic increases for composite muscle thickness (R2 = 0.998), concentric peak torque (R2 = 0.962), and maximal voluntary isometric contraction (MVIC) torque (R2 = 0.980) data for the LLBFR group. For muscle thickness, seven of ten subjects exceeded the minimal difference (MD) of 0.16 cm during the very early phase (laboratory visits 1-7) of the intervention compared to three of ten subjects that exceeded MD for either concentric peak torque (3.7 Nm) or MVIC (2.2 Nm) during this same time period. There was a linear increase for composite echo intensity (r2 = 0.563) as a result of LLBFR resistance training, but eight of ten subjects never exceeded the MD of 14.2 Au.Conclusions: These findings suggested that the increases in muscle thickness for the LLBFR group were not associated with edema and changes in echo intensity should be examined on a subject-by-subject basis. Furthermore, LLBFR forearm flexion-extension resistance training elicited real increases in muscle size during the very early phase of training that occurred prior to real increases in muscle strength. [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 reported test-retest reliability and evaluated collinearity for isometric leg extension and flexion peak torque (PT) and rate of torque development (RTD) in young boys and girls. Measurements of growth included height, body mass, fat-free mass, maturity offset, and leg extensor and flexor muscle cross-sectional area. Maximal isometric contractions quantified PT and RTD. Intraclass correlation coefficients (ICCs), SEM, coefficients of variation, and minimum detectable changes quantified test-retest reliability. Zero-order correlations and first-order partial correlations evaluated collinearity. Peak torque from leg extension and flexion exhibited ICCs ≥ 0.90, RTD from leg extension and flexion exhibited ICCs ≥ 0.38. Partialing out leg flexion PT reduced the relationships between leg extension PT and growth (rPText, growth.PTflex = 0.392-0.605). Partialing out leg extension PT eliminated the relationships between leg flexion PT and growth (rPTflex, growth.PText = 0.098-0.263). Partialing out leg extension RTD reduced the relationships between PT and growth (rPText, growth.RTDext = 0.516-0.775). Partialing out leg extension PT eliminated the relationships between RTD and growth (/rRTDext, growth.PText/ = 0.001-0.148). Leg extension PT was more reliable and explained the most unique variability in growth among young boys and girls. In contrast, RTD was less reliable and was fully accounted for by PT, indicating that RTD may be an unnecessary measurement in studies of young boys and girls. [ABSTRACT FROM AUTHOR]

The purpose of this short report was to provide test- and position-specific normative reference values for the 10- and 20-yd split times (10YD and 20YD) during the 40-yd dash (40YD) as well as 10-yd split times during the proagility drill (PA) based on a large, nationally representative sample of high school--aged American football players in their freshman, sophomore, and junior classes. Cross-sectional 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. The sample included (n = 7,478) high school--aged American football athletes in their freshman (n = 1,185), sophomore (n = 2,514), and junior (n = 3,779) classes. Each player selfclassified their American football positions as defensive back, defensive end, defensive linemen, linebacker, offensive linemen (OL), quarterback (QB), running back, tight end, or wide receiver. The results of the freshman, sophomore, and junior class were aggregated to generate test- and position-specific normative values. Mean differences were found among classes for all positions and all measurements (p ≤ 0.05) except for OL and QB PA split time (p > 0.05). Greater percent differences for all 3 variables were observed between freshman and sophomore years than between sophomore and junior years. These normative reference values will be useful for athletes, parents, coaches, and high school strength and conditioning professionals to set realistic goals for young American football athletes. [ABSTRACT FROM AUTHOR]

Purpose: Low-load venous blood flow restriction resistance training (RT + BFR) has been demonstrated to increase muscle strength to a greater degree than low-load non-BFR resistance training (RT) during isotonic training, but no previous investigations have examined RT + BFR versus RT during isokinetic training. The purpose of the present study was to examine the effects of 4 weeks of isokinetic low-load RT + BFR versus low-load RT on indices of muscle strength, muscle size, and neural adaptations.Methods: Thirty women (mean ± SD; 22 ± 2 years) participated in this investigation and were randomly assigned to 4 weeks of either RT + BFR (n = 10), RT (n = 10), or control (n = 10) group. Resistance training consisted of 75 reciprocal forearm flexion-extension isokinetic muscle actions of the forearm flexors performed at a velocity of 120°s-1.Results: Concentric peak torque increased to a greater extent for RT + BFR after 4 weeks (36.9%) compared to RT (25.8%), but there were similar increases in isometric torque (23.3-42.1%). For both RT + BFR and RT, there were similar increases in muscle cross-sectional area and muscle thickness of the biceps brachii after 2 weeks (11.3-14.3% and 12.4-12.9%, respectively) and 4 weeks (18.7-21.9% and 19.0-20.0%, respectively). There were similar increases in mechanomyographic amplitude, mechanomyographic mean power frequency, and electromyographic mean power frequency, but no changes in electromyographic amplitude for all conditions (including control).Conclusions: These findings indicated that low-load RT + BFR elicited greater increases in concentric strength than low-load RT, but elicited comparable increases in isometric strength and muscle size. There were also no differences in any of the EMG and MMG responses among conditions. [ABSTRACT FROM AUTHOR]

Purpose: To compare measurements of muscle strength, size, and neuromuscular function among pre-adolescent and adolescent boys and girls with distinctly different strength capabilities.Methods: Fifteen boys (mean age ± confidence interval: 13.0 ± 1.0 years) and 13 girls (12.9 ± 1.1 years) were categorized as low strength (LS, n = 14) or high strength (HS, n = 14) based on isometric maximal voluntary contraction strength of the leg extensors. Height (HT), seated height, and weight (WT) determined maturity offset, while percent body fat and fat-free mass (FFM) were estimated from skinfold measurements. Quadriceps femoris muscle cross-sectional area (CSA) was assessed from ultrasound images. Isometric ramp contractions of the leg extensors were performed while surface electromyographic amplitude (EMGRMS) and mechanomyographic amplitude (MMGRMS) were recorded for the vastus lateralis (VL). Neuromuscular efficiency from the EMG and MMG signals (NMEEMG and NMEMMG, respectively) and log-transformed EMG and MMG vs. torque relationships were also used to examine neuromuscular responses.Results: HS was 99-117% stronger, 2.3-2.8  years older, 14.0-15.7 cm taller, 20.9-22.3 kg heavier, 2.3-2.4 years more biologically mature, and exhibited 39-43% greater CSA than LS (p ≤ 0.001). HS exhibited 74-81% higher NMEEMG than LS (p ≤ 0.022), while HS girls exhibited the highest NMEMMG (p ≤ 0.045). Even after scaling for HT, WT, CSA, and FFM, strength was still 36-90% greater for HS than LS (p ≤ 0.031). The MMGRMS patterns in the LS group displayed more type I motor unit characteristics.Conclusions: Neuromuscular adaptations likely influence strength increases from pre-adolescence to adolescence, particularly when examining large, force-producing muscles and large strength differences explained by biological maturity, rather than simply age. [ABSTRACT FROM AUTHOR]