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Objective . Muscle quality has received considerable attention within the literature due to its influence on health and performance. However, it has been assessed by various measures (e.g. ultrasound imaging, normalized strength), contributing to a lack of a consensus definition. The purpose of this study was to investigate the association between common muscle quality measures: vastus lateralis echo intensity (EI) and peak torque (PT) and power (PP) normalized to thigh lean mass (TLM) and thigh fat mass (TFM). Approach . Participants' ( n  = 39; age = 32.7 ± 8.2 years; %BF = 24.1% ±8.1%) whole body and leg composition was assessed via dual-energy x-ray absorptiometry and custom thigh analyses. Subcutaneous fat-corrected muscle EI was assessed via ultrasonography. Maximal PT and PP of the dominant leg extensors were examined on a calibrated dynamometer and were normalized to both TLM and TFM, respectively. Pearson product-moment correlations were used to examine the associations between EI and PT/TLM, PT/TFM, PP/TLM, and PP/TFM. Main results . Greater muscle EI was significantly related with lower PT/TFM and PP/TFM ( r  = -0.74 to -0.70, P  < 0.001), but unrelated to PT/TLM or PP/TLM ( P  ≥ 0.205). Significance . These findings suggest that ultrasound imaging (muscle EI) and normalized strength and power may not be used interchangeably to define muscle quality, and muscle EI may be more sensitive to the adiposity of the limb than TLM. Future research should consider using separate and consistent definitions when referring to imaging-derived or normalized strength and power values of muscle quality., (© 2021 Institute of Physics and Engineering in Medicine.)

The purpose of this study was to compare the independent and combined effects of high-intensity interval training (HIIT) and essential amino acids (EAA) on lean mass, muscle characteristics of the quadriceps, and 24-hr whole-body protein turnover (WBPT) in overweight and obese adults. An exploratory aim was to evaluate potential modulatory effects of sex. Sixty-six adults (50% female; Age: 36.7 ± 6.0 yrs; %BF: 36.0 ± 7.8%) were assigned to 8 wks of: (a) HIIT, 2 days/wk; (b) EAA supplementation, 3.6 g twice daily; (c) HIIT + EAA; or (d) control. At baseline, 4 wks, and 8 wks, total body, thigh LM and muscle characteristics were measured via dual-energy x-ray absorptiometry and B-mode ultrasound, respectively. In a subsample, changes in WBPT was measured using [N 15 ]alanine. Differences between groups were assessed using linear mixed models adjusted for baseline values, followed by 95% confidence intervals on adjusted mean change scores (Δ). HIIT and HIIT + EAA improved thigh LM (Δ: +0.17 ± 0.05 kg [0.08, 0.27]; +0.22 ± 0.05 kg [0.12,0.31]) and vastus lateralis cross-sectional area (Δ: +2.73 ± 0.52 cm 2 [1.69,3.77]; +2.64 ± 0.53 cm 2 [1.58,3.70]), volume (Δ: +54.50 ± 11.69 cm 3 [31.07, 77.92]; +62.39 ± 12.05 cm 3 [38.26, 86.52]), and quality (Δ: -5.46 ± 2.68a.u. [-10.84, -0.09]; -7.97 ± 2.76a.u.[-13.49, -2.45]). Protein synthesis, breakdown, and flux were greater with HIIT + EAA and EAA compared to HIIT (p < .05). Sex differences were minimal. Compared to women, men tended to respond more to HIIT, with or without EAA. For women, responses were greater with HIIT + EAA than HIIT. In overweight and obese adults, 8 weeks of HIIT, with or without EAA, improved thigh LM size and quality; EAA may enhance muscular adaptation via increases in protein turnover, supporting greater improvements in muscular size and quality., (© 2020 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

The purpose of this study was to determine if muscular dimensional changes with increases in torque production are influenced by age- and obesity-related increases in intramuscular fat, and its relationship to percent body fat (%BF), echo intensity (EI), strength, and maximum walking speed. Sixty-six healthy men were categorized into 3 groups based on age and body mass index status (young normal weight [YNW], older normal weight [ONW], and older obese [OB]). Participants underwent %BF assessments, resting ultrasonography to determine muscle size (cross-sectional area [CSA]) and EI of the superficial quadriceps, and a 10-m maximum walking speed assessment. Maximal and submaximal (rest-100% MVC in 10% increments) isometric leg extension strength was assessed while changes in rectus femoris (RF) CSA, width, and depth were obtained with ultrasonography. Echo intensity and %BF were different among all groups (p ≤ .007), with the YNW and OB groups exhibiting the lowest and highest %BF and EI values, respectively. The RF increased in depth and decreased in width with increases in torque intensity for all groups. The ONW group demonstrated no change (-0.08%) in RF CSA across torque intensities, whereas the YNW group (-11.5%) showed the greatest decrease in CSA, and the OB group showed a more subtle decrease (-4.6%). Among older men, a greater change in RF CSA was related to poorer EI (r = -0.355) and higher %BF (r = -0.346), while a greater decrease in RF width was associated with faster walking speeds (r = -0.431). Examining muscular dimensional changes during contraction is a unique model to investigate the influence of muscle composition on functional performance., (© The Author(s) 2020. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

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 < .05). The middle age groups exhibited an overall preservation of early RTD, and a potential enhancement of early normalized RTD (P = .06 for middle young vs. controls, for RTDnorm50). The RTD50/PT ratio was higher in the middle young (P < .05) compared to both the young groups. Generally, the RVD declined more linearly and exhibited worse preservation at mid-life than the early absolute or normalized RTD variables. All absolute torque-time variables were correlated (r = 0.43-0.73, P < .001) to the RVD for all groups combined. These findings showed distinct age-related declines occurred for different muscle function parameters unique to specific stages of the lifespan. Normalized RTD variables may reveal plausible mechanisms of age-related neuromuscular changes and the RTD50/PT ratio may be a useful tool for determining relative deficiencies, such that mid-life adults (45-64 yrs) should address their relative limitation of PT by enhancing strength at mid-life, whereas older adults (65+ yrs) may need more emphasis on RTD improvements. In addition, both mid-life and older men should seek to improve rapid limb velocity capacities due to the susceptibility of RVD to decline more incrementally across the lifespan. Such information may help to improve anti-aging strategies by countering age-specific muscle function deficiencies and may improve mid-life adults' ability to transition better functionally into old age., (Copyright © 2019 Elsevier Inc. All rights reserved.)

New Findings: What is the central question of this study? Are differences in muscle size and motor unit properties between normal weight and overfat children muscle specific? What is the main finding and its importance? Muscle cross-sectional area and motor unit action potential amplitudes and firing rates were similar between overfat and normal weight children for both the medial gastrocnemius and vastus lateralis muscles. There was no evidence that the chronic mechanical overload provided by the greater body mass resulted in significant hypertrophy of contractile tissue or motor units that would be used during lower-to-moderate intensity activities., Abstract: This study examined the possible differences in muscle cross-sectional area (mCSA), motor unit action potential amplitudes (MUAP AMPS ) and interspike intervals (ISIs) of the firing instances of the medial gastrocnemius (MG) and vastus lateralis (VL) between normal weight (NW) and overfat (OF) children aged 7-10 years. Fourteen NW (age = 8.6 ± 1.1 years, BMI = 15.8 ± 1.4 kg m -2 ) and 12 OF (age = 8.8 ± 0.9 years, BMI = 21.8 ± 2.4 kg m -2 ) children performed isometric trapezoidal muscle actions at 40% of maximal voluntary contraction of the plantar flexors and knee extensors. Surface electromyography was recorded from the MG and VL and decomposed into the firing events of motor units (MUs). Statistical procedures were performed on the composite recruitment thresholds (RTs), ISIs and MUAP AMPS of recorded MUs collapsed across subjects and the y-intercepts and slopes calculated from each subject's ISI and MUAP AMP vs. RT relationships. Ultrasound was used to assess mCSA, echo intensity (mEI), and subcutaneous fat (sFAT) of the MG and VL. The OF had greater mCSAs, mEI and sFAT (P = 0.004-0.024), but there were no differences in mCSA when accounting for mEI for the MG (P = 0.506) and VL (P = 0.326). The NW children had significantly greater composite MUAP AMPS for the VL and MG (P < 0.001), but only significantly larger MUAP AMPS of the VL remained for the NW (P < 0.001) when subjects were matched for sFAT. There were no differences between groups for the ISI or MUAP AMP vs. RT relationships (P > 0.05). These findings suggest that the OF children did not undergo significant muscle or MU hypertrophy that would be routinely activated during activities of daily living., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

Neuromuscular function in young overweight/obese (OF) children is not well described., Aim: This study examined isometric and isokinetic leg extensor strength, muscle size (mCSA) and tissue composition as measured via echo intensity (mEI), and motor unit (MU) firing rates in normal weight (NW) and OF children aged 7-10 years., Methods: Fourteen NW (eight girls and six boys, BMI: 15.8 ± 1.4 kg/m 2 ) and 15 OF (10 girls and five boys, BMI: 20.8 ± 2.3 kg/m 2 ) children volunteered to perform this study. Percentage body fat (%BF) was measured, and mCSA, mEI, and subcutaneous fat (sFAT) of the vastus lateralis (VL) was assessed. MU mean firing rates (MFRs) in relation to recruitment threshold (RT) of the VL were assessed during submaximal isometric contractions. Maximal isokinetic contractions were performed at 1.05 and 4.20 rad/s. The 95% confidence intervals (CI) from the statistical tests are presented., Results: The OF children had greater %BF (95% CI = -15.1 to -7.2), mCSA (95% CI = -4.1 to -1.2), mEI (95% CI = -22.3 to -5.9), and sFAT (95% CI = -0.5 to -0.1), greater rate of strength loss with increasing isokinetic velocities (95% CI = 0.4 to 5.4), and a smaller range of MFRs (95% CI = 0.007 to 7.136) at the steady torque than the NW children., Conclusions: The OF children had poorer muscle tissue composition, greater velocity-related impairments in muscle strength, and a smaller range of MFRs at the targeted torque that may suggest altered MU recruitment strategies. Interventions in OF children should include exercises and recruit higher-threshold MUs, such as high-intensity resistance exercises., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background Declines in the ability to rapidly generate quadriceps muscle torque may underlie disability in individuals with tibiofemoral osteoarthritis. Objective To determine whether quadriceps rate of torque development (RTD) predicts self-reported disability and physical performance outcomes in individuals with tibiofemoral osteoarthritis. Methods This controlled laboratory, cross-sectional study assessed quadriceps strength and RTD in 76 individuals (55% female; mean ± SD age, 61.83 ± 7.11 years) with symptomatic and radiographic tibiofemoral osteoarthritis. Early (0-50 milliseconds), late (100-200 milliseconds), and overall peak RTDs were quantified in the symptomatic (involved) and contralateral limbs and used to calculate bilateral average values. Disability was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) function subscale and 3 physical performance tests, including the (1) 20-m fast-paced walk, (2) 30-second chair stand, and (3) timed stair climb. Separate univariate regression models were used to determine the unique associations among measures of quadriceps RTD, WOMAC function score, and physical performance outcomes after accounting for quadriceps strength (change in R 2 ). Results Greater involved-side late RTD and greater bilateral average early RTD were associated with faster walking (change in R 2 = 0.05, P = .013 and change in R 2 = 0.05, P = .043, respectively). Greater bilateral average late RTD was associated with faster walking (change in R 2 = 0.20, P<.001) and faster stair climb (change in R 2 = 0.11, P = .001). No quadriceps RTD variable was significantly associated with WOMAC function score (change in R 2 range, <0.01-0.017). Conclusion Involved-limb quadriceps RTD was weakly associated with physical performance outcomes, but not self-reported disability, in individuals with tibiofemoral osteoarthritis. Bilateral average quadriceps RTD was moderately associated with walking speed. Level of Evidence Prognosis, level 2b. J Orthop Sports Phys Ther 2018;48(9):694-703. Epub 22 May 2018. doi:10.2519/jospt.2018.7898.

Background: The purpose of this study was to determine associations between self-reported function (International Knee Documentation Committee Index), isometric quadriceps strength and rate of torque development in individuals with a unilateral anterior cruciate ligament reconstruction., Methods: Forty-one individuals [31% male, BMI mean 25 (SD 4) kg/m 2 , months post anterior cruciate ligament reconstruction mean 49 (SD 40)] completed the self-reported function and isometric quadriceps function testing. Rate of torque development was assessed at 0-100ms (early), 100-200ms (late) ms, and peak following the onset of contraction. Associations were examined between rate of torque development, strength, and self-reported function. Linear regression was used to determine the unique amount of variance explained by the combination of rate of torque development and strength., Findings: Higher rate of torque development 100-200ms is weakly associated with higher self-reported function in individuals with a unilateral anterior cruciate ligament reconstruction (r=0.274, p=0.091); however, rate of torque development 100-200ms does not predict a significant amount of variance in self-reported function after accounting for strength (ΔR 2 =0.003, P=0.721)., Interpretation: Quadriceps strength has a greater influence on self-reported function compared to rate of torque development in individuals with an anterior cruciate ligament reconstruction with time from surgery., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Context:   Individuals with anterior cruciate ligament reconstruction (ACLR) have quadriceps dysfunction that contributes to physical disability and posttraumatic knee osteoarthritis. Quadriceps function in the ACLR limb is commonly evaluated relative to the contralateral uninjured limb. Bilateral quadriceps dysfunction is common in individuals with ACLR, potentially biasing these evaluations., Objective:   To compare quadriceps function between individuals with ACLR and uninjured control participants., Design:   Cross-sectional study., Setting:   Research laboratory., Patients or Other Participants:   Twenty individuals with unilateral ACLR (age = 21.1 ± 1.7 years, mass = 68.3 ± 14.9 kg, time since ACLR = 50.7 ± 21.3 months; females = 14; Tegner Score = 7.1 ± 0.3; 16 patellar tendon autografts, 3 hamstrings autografts, 1 allograft) matched to 20 control participants (age = 21.2 ± 1.2 years, mass = 67.9 ± 11.3 kg; females = 14; Tegner Score = 7.1 ± 0.4) on age, sex, body mass index, and Tegner Activity Scale., Main Outcome Measure(s):   Maximal voluntary isometric knee extension was performed on an isokinetic dynamometer. Peak torque (PT), rate of torque development (RTD), electromyographic (EMG) amplitude, central activation ratio (CAR), and hamstrings EMG amplitude were assessed during maximal voluntary isometric knee extension and compared between groups using independent-samples t tests. Relationships between hamstrings co-activation and quadriceps function were assessed using Pearson correlations., Results:   Participants with anterior cruciate ligament reconstruction displayed lesser quadriceps PT (1.86 ± 0.74 versus 2.56 ± 0.37 Nm/kg, P = .001), RTD (39.4 ± 18.7 versus 52.9 ± 16.4 Nm/s/kg, P = .03), EMG amplitude (0.25 ± 0.12 versus 0.37 ± 0.26 mV, P = .04), and CAR (83.3% ± 11.1% versus 93.7% ± 3.2%, P = .002) and greater hamstrings co-activation (27.2% ± 12.8% versus 14.3% ± 3.7%, P < .001) compared with control participants. Correlations were found between hamstrings co-activation and PT (r = -0.39, P = .007), RTD (r = -0.30, P = .03), and EMG amplitude (r = -0.30, P = .03)., Conclusions:   Individuals with ACLR possessed deficits in PT, RTD, and CAR compared with control participants. Peak torque is the net result of all agonist and antagonist activity, and lesser PT in individuals with ACLR is partially attributable to greater hamstrings co-activation.

Introduction: The purpose of this study was to compare the effect of whole body vibration (WBV) and local muscle vibration (LMV) on quadriceps function., Methods: Sixty adults were randomized to WBV, LMV, or control groups. Quadriceps function [Hoffmann (H)-reflex, active motor threshold (AMT), motor evoked potential (MEP) and electromyographic amplitude, peak torque (PT), rate of torque development (RTD), and central activation ratio (CAR)] was assessed before and immediately after and 10 and 20 minutes after interventions., Results: WBV improved PT, CAR, AMT, EMG, and MEP amplitude, and EMG amplitude and CAR were greater than control after application. LMV improved EMG amplitude and AMT, and EMG amplitude was greater than control after application. AMT remained lower 10 and 20 minutes after WBV and LMV. No differences were noted between LMV and WBV. Vibration did not influence H-reflex or RTD., Conclusions: WBV and LMV increased quadriceps function and may be used to enhance the efficacy of strengthening protocols. Muscle Nerve 54: 469-478, 2016., (© 2016 Wiley Periodicals, Inc.)

Objective: To determine the immediate effects of a single session of whole-body vibration (WBV) and local muscle vibration (LMV) on quadriceps function in individuals with anterior cruciate ligament reconstruction (ACLR)., Design: Singe-blind, randomized crossover trial., Setting: Research laboratory., Participants: Population-based sample of individuals with ACLR (N=20; mean age ± SD, 21.1±1.2y; mean mass ± SD, 68.3±14.9kg; mean time ± SD since ACLR, 50.7±21.3mo; 14 women; 16 patellar tendon autografts, 3 hamstring autografts, 1 allograft)., Interventions: Participants performed isometric squats while being exposed to WBV, LMV, or no vibration (control). Interventions were delivered in a randomized order during separate visits separated by 1 week., Main Outcome Measures: Quadriceps active motor threshold (AMT), motor-evoked potential (MEP) amplitude, Hoffmann reflex (H-reflex) amplitude, peak torque (PT), rate of torque development (RTD), electromyographic amplitude, and central activation ratio (CAR) were assessed before and immediately after a WBV, LMV, or control intervention., Results: There was an increase in CAR (+4.9%, P=.001) and electromyographic amplitude (+16.2%, P=.002), and a reduction in AMT (-3.1%, P<.001) after WBV, and an increase in CAR (+2.7%, P=.001) and a reduction in AMT (-2.9%, P<.001) after LMV. No effect was observed after WBV or LMV in H-reflex, RTD, or MEP amplitude. AMT (-3.7%, P<.001), CAR (+5.7%, P=.005), PT (+.31Nm/kg, P=.004), and electromyographic amplitude (P=.002) in the WBV condition differed from the control condition postapplication. AMT (-3.0% P=.002), CAR (+3.6%, P=.005), and PT (+.30Nm/kg, P=.002) in the LMV condition differed from the control condition postapplication. No differences were observed between WBV and LMV postapplication in any measurement., Conclusions: WBV and LMV acutely improved quadriceps function and could be useful modalities for restoring quadriceps strength in individuals with knee pathologies., (Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

The purpose of this study was to examine the influence of lower extremity muscular size and quality on stair-climb performance (SCP) in career firefighters. Forty-six male career firefighters (age = 37.0 ± 7.2 years; stature = 180.2 ± 6.9 cm; body mass = 108.0 ± 19.8 kg) volunteered for this study. Panoramic ultrasound images of the vastus lateralis and rectus femoris were obtained to determine cross-sectional area (CSA) and echo intensity (EI) of each muscle. The CSA of each muscle was then summed together and normalized to body mass (CSA/BM [QCSA]). Additionally, EI was averaged across both muscles (QEI). Participants then performed a timed and weighted SCP assessment where they ascended and descended 26 stairs 4 times as quickly as possible while wearing a weighted vest (22.73 kg) to simulate the weight of their self-contained breathing apparatus and turnout gear. Bivariate correlations and stepwise regression analyses were used to examine the relationships among variables and the relative contributions of QCSA and QEI to SCP. Partial correlations were used to examine the relationship between QCSA and SCP and QEI and SCP while controlling for age and body mass index (BMI). The results indicated that QCSA and QEI were significantly related to SCP before (r = -0.492, p = 0.001; r = 0.363, p = 0.013, respectively) and after accounting for age and BMI (r = -0.324, p = 0.032; r = 0.413, p = 0.005, respectively). Both QCSA and QEI contributed significantly to the prediction of SCP (r = 0.560, p < 0.001). These findings indicate that lower extremity muscle size and quality are important contributors to critical firefighting tasks, which have been shown to be improved with resistance training.

Introduction: Quadriceps voluntary activation, assessed via the superimposed burst technique, has been extensively studied in a variety of populations as a measure of quadriceps function. However, a variety of stimulus delivery techniques have been employed, which may influence the level of voluntary activation as calculated via the central activation ratio (CAR). The purpose was to determine the effect of visual feedback, stimulus delivery, and perceived discomfort on maximal voluntary isometric contraction (MVIC) peak torque and the CAR., Methods: Quadriceps CAR was assessed in 14 individuals on two days using three stimulus delivery methods; (1) manual without visual feedback, (2) manual with visual feedback, and (3) automated with visual feedback., Results: MVIC peak torque and the CAR were not different between the automated with visual feedback (MVIC=3.25, SE=0.14Nm/kg; CAR=88.63, SE=1.75%) and manual with visual feedback (MVIC=3.26, SE=0.13Nm/kg, P=0.859; CAR=89.06, SE=1.70%, P=0.39) stimulus delivery methods. MVIC (2.99, SE=0.12Nm/kg) and CAR (85.32, SE=2.10%) were significantly lower using manual without visual feedback compared to manual with visual feedback and automated with visual feedback (CAR P<0.001; MVIC P<0.001). Perceived discomfort was lower in the second session (P<0.05)., Conclusion: Utilizing visual feedback ensures participant MVIC, and may provide a more accurate assessment of quadriceps voluntary activation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The purposes of the present study were to examine the effects of electrode placements over, proximal, and distal to the innervation zone (IZ) on electromyographic (EMG) amplitude (RMS) and frequency (MPF) responses during: (1) a maximal voluntary isometric contraction (MVIC), and; (2) a sustained, submaximal isometric muscle action. A linear array was used to record EMG signals from the vastus lateralis over the IZ, 30mm proximal, and 30mm distal to the IZ during an MVIC and a sustained isometric muscle action of the leg extensors at 50% MVIC. During the MVIC, lower EMG RMS (p>0.05) and greater EMG MPF (p<0.05) values were recorded over the IZ compared to away from the IZ, however, no differences in slope coefficients for the EMG RMS and MPF versus time relationships over, proximal, and distal to the IZ occurred. Thus, the results of the present study indicated that during an MVIC, EMG RMS and MPF values recorded over the IZ are not comparable to those away from the IZ. However, the rates of fatigue-induced changes in EMG RMS and MPF during sustained, submaximal isometric muscle actions of the leg extensors were the same regardless of the electrode placement locations relative to the IZ., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This study examined the effects of electromyographic (EMG) recording methods and innervation zone (IZ) on the mean power frequency (MPF)-torque relationships. Nine subjects performed isometric ramp muscle actions of the leg extensors from 5% to 100% of maximal voluntary contraction with an eight channel linear electrode array over the IZ of the vastus lateralis. The slopes were calculated from the log-transformed monopolar and bipolar EMG MPF-torque relationships for each channel and subject and 95% confidence intervals (CI) were constructed around the slopes for each relationship and the composite of the slopes. Twenty-two to 55% of the subjects exhibited 95% CIs that did not include a slope of zero for the monopolar EMG MPF-torque relationships while 25-75% of the subjects exhibited 95% CIs that did not include a slope of zero for the bipolar EMG MPF-torque relationships. The composite of the slopes from the EMG MPF-torque relationships were not significantly different from zero for any method or channel, however, the method and IZ location slightly influenced the number of significant slopes on a subject-by-subject basis. The log-transform model indicated that EMG MPF-torque patterns were nonlinear regardless of recording method or distance from the IZ., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Purpose: Vibratory stimuli enhance muscle activity and may be used for rehabilitation and performance enhancement. Efficacy of vibration varies with the frequency of stimulation, but the optimal frequency is unclear. The purpose of this study was to examine the effects of 30 Hz and 60 Hz local muscle vibration (LMV) on quadriceps function., Methods: Twenty healthy volunteers (age = 20.4 ± 1.4 years, mass = 68.1 ± 11.0 kg, height = 170.1 ± 8.8 cm, males = 9) participated. Isometric knee extensor peak torque (PT), rate of torque development (RTD), and electromyography (EMG) of the quadriceps were assessed followed by one of the three LMV treatments (30 Hz, 60 Hz, control) applied under voluntary contraction, and again immediately, 5, 15, and 30 min post-treatment in three counterbalanced sessions. Dependent variables were analyzed using condition by time repeated-measures ANOVA., Results: The condition × time interaction was significant for EMG amplitude (p = 0.001), but not for PT (p=0.324) or RTD (p = 0.425). The increase in EMG amplitude following 30 Hz LMV was significantly greater than 60 Hz LMV and control., Conclusions: These findings suggest that 30 Hz LMV may elicit an improvement in quadriceps activation and could be used to treat quadriceps dysfunction resulting from knee pathologies., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The purpose of this study was to examine muscle characteristics of the vastus lateralis (VL) and body composition of National Collegiate Athletic Association (NCAA) Division I football players. Sixty-nine Division I football players (mean ± SD; age: 20.0 ± 1.1 years; height: 186.2 ± 7.0 cm; body mass: 106.3 ± 21.1 kg; %fat: 17.8 ± 4.6%) were stratified by player position, race, year, and starter status. A panoramic scan of the VL was performed using a GE Logiq-e B-mode ultrasound. Muscle cross-sectional area (mCSA) and echo intensity (EI) were determined using Image-J software from the VL scan. Body composition measures were determined using dual-energy x-ray absorptiometry (DXA). For mCSA, defensive linemen (DL: 46.7 ± 4.2 cm) had significantly greater CSA (p ≤ 0.05) than wide receivers (WR), linebackers (LB), defensive backs (DB), punters/kickers (PK), and running backs (RB). There were no significant differences for EI (p > 0.05) between positions. Offensive linemen and DL had significantly greater %fat than WR, LB, DB, PK, and RB (p ≤ 0.05); greater lean mass than all other positions (p ≤ 0.05); and more fat mass than quarterbacks, WR, LB, DB, PK, and RB (p ≤ 0.05). There were no muscle or body composition differences for race, year, or starter status. Because no differences between positions were observed for EI measures, it may indicate that competitive athletes have increased muscle quality regardless of body composition differences. Ultrasound and DXA measures may be useful to identify muscle characteristics and imbalances if a player gains or loses weight, suffers an injury, or declines in performance.

The purpose of this study was to examine the effects of 2 different types of protein supplementation on thigh muscle cross-sectional area (CSA), blood markers, muscular strength, endurance, and body composition after 8 weeks of low- or moderate-volume resistance training in healthy, recreationally trained, college-aged men. One hundred and six men were randomized into 5 groups: low-volume resistance training with bioenhanced whey protein (BWPLV; n = 22), moderate-volume resistance training with BWP (BWPMV; n = 20), moderate-volume resistance training with standard whey protein (SWPMV; n = 22), moderate-volume resistance training with a placebo (PLA; n = 21), or moderate-volume resistance training with no supplementation (CON; n = 21). Except for CON, all groups consumed 1 shake before and after each exercise session and one each on the nontraining day. The BWPLV, BWPMV, and SWPMV groups received approximately 20 g of whey protein per shake, whereas the BWP groups received 5 g of additional polyethylene glycosylated (PEG) leucine. Resistance training sessions were performed 3 times per week for 8 weeks. There were no interactions (p > 0.05) for muscle strength and endurance variables, body composition, muscle CSA, and safety blood markers, but the main effects for training were observed (p ≤ 0.05). However, the Albumin:Globulin ratio for SWPMV was lower (p = 0.037) than BWPLV and BWPMV. Relative protein intake (PROREL) indicated a significant interaction (p < 0.001) with no differences across groups at pre; however, BWPLV, BWPMV, and SWPMV had a greater intake than did PLA or CON at post (p < 0.001). This study indicated that 8 weeks of resistance training improved muscle performance and size similarly among groups regardless of supplementation.

The decline in maximal and rapid isometric torque characteristics may compromise functional living abilities in aging adults while loco-motor muscle groups, such as the leg extensors and flexors, may exhibit different torque-time age related decreases. The purpose of the present study was to examine the age-related differences in maximal and rapid torque characteristics of the leg extensor and flexor muscle groups in young, middle-aged, and old men. Sixty-five healthy men were categorized by age as young (n=25; mean±SD age=24.9±3.0 years), middle-aged (n=22; age=50.6±4.0 years), and old (n=18; age=66.8±4.5 years). Participants performed maximal voluntary contractions (MVCs) of the leg extensors and flexors and an estimated thigh cross sectional area (eThighCSA) assessment. Peak torque (PT), peak rate of torque development (RTDpeak), absolute RTD and the contractile impulse (IMPULSE) were calculated at time intervals of 30, 50, 100 and 200 ms from the torque-time curve. Relative RTD was calculated at 10, 20, 30, 40 and 50% of MVC from the normalized torque-time curves. PT, RTDpeak and later rapid torque variables (RTD100, RTD200, and IMPULSE200) were greater (P≤0.05) in the young and middle-aged when compared to the old men for both muscle groups. Early (RTD30,50; IMPULSE30,50) and late (IMPULSE100) rapid torque variables were greater (P≤0.05) for the young and middle-aged than the old men for the leg extensors but not the leg flexors, except for RTD30, in which there was no difference between young and old. There were no differences for all relative RTD variables between age groups (P>0.05). eThighCSA was lower in the old compared to the young (P=0.001) and middle-aged (P=0.016) men. Maximal and rapid torque characteristics were preserved in middle-aged men but greatly reduced in older men with differential effects at early and late portions of the torque-time curve between the leg extensors and flexors. Significant decreases in absolute maximal and rapid torque production with no change in relative RTD across age groups and lower eThighCSA in old men may suggest that the loss of rapid torque producing capacities observed in older men may be largely a function of mechanisms associated with loss of muscle strength and muscle mass., (Copyright © 2012 Elsevier Inc. All rights reserved.)

We compared starters and non-starters for various isokinetic strength variables in elite women's soccer players. A convenience sample of 10 starters (mean ± s; age = 20 ± 2 years; height = 170 ± 4 cm; body mass = 65 ± 5 kg) and 7 non-starters (age = 20 ± 1 years; height = 164 ± 3 cm; body mass = 63 ± 4 kg) performed maximal voluntary muscle actions of the leg extensors (concentric) and flexors (eccentric) on an isokinetic dynamometer in order to measure concentric peak torque for the leg extensors, eccentric peak torque for the leg flexors, and the functional hamstrings:quadriceps (H:Q) ratio at 1.047 rad · s(-1) and 4.189 rad · s(-1) concentric peak torque for the leg extensors was not different between starters and non-starters. However, it was greater at 1.047 rad · s(-1) than at 4.189 rad · s(-1) in both groups. Eccentric peak torque for the leg flexors was greater for the starters versus non-starters at 4.189 rad · s(-1). Eccentric strength of the leg flexors at fast movement velocities may be used as an effective physiological profile and may discriminate between playing status in elite women's soccer players.

Citrulline malate (CitMal) and beetroot juice (BEET) are increasingly popular ergogenic aids, but few studies have rigorously investigated their effects on resistance exercise performance and underlying mechanisms. The current randomized, double-blind, crossover study evaluated the effects of CitMal and BEET supplementation on blood flow, metabolic efficiency, and performance during maximal isokinetic leg extension exercise. After familiarization, 27 recreationally active men (age: 22 ± 4 years) completed 3 visits in which subjects ingested a treatment beverage (CitMal [8 g], BEET [400-mg nitrate], or placebo [PLA]), followed by a 2-hour rest period, warm-up, and 5 sets of 30 concentric leg extensions. Before and after exercise, ultrasound was used to measure diameter (aDIAM) and blood flow (aBF) of the superficial femoral artery, along with cross-sectional area and echo intensity of the vastus lateralis. Plasma analytes (lactate, nitrate/nitrite [NOx], and urea nitrogen [BUN]) were also assessed at these times, and indirect calorimetry was used to measure energy expenditure and respiratory exchange ratio before and during exercise. Resting NOx values were higher in BEET (233.2 ± 1.1 µmol⋅L-1) compared with CitMal (15.3 ± 1.1, p < 0.0001) and PLA (13.4 ± 1.1, p < 0.0001). Postexercise NOx values, adjusted for resting differences, were higher in BEET (86.3 ± 1.2 μmol⋅L-1) than CitMal (21.3 ± 1.1, p < 0.0001) and PLA (18.1 ± 1.1, p < 0.0001). No other variables were affected by treatment (all p > 0.05). While BEET increased NOx, neither treatment was found to enhance performance, blood flow, metabolic efficiency, nor the hormonal response to leg extension exercise. [ABSTRACT FROM AUTHOR]

Gerstner, GR, Giuliani, HK, Mota, JA, and Ryan, ED. Influence of muscle quality on the differences in strength from slow to fast velocities in career firefighters. J Strength Cond Res 32(10): 2982–2986, 2018—The purpose of this study was to examine the relationship between ultrasound-derived muscle quality and the %decrease in peak torque (PT) from slow to fast velocities in career firefighters. Thirty-nine male career firefighters (mean ± SD : age = 36.90 ± 6.87 years; stature = 180.93 ± 6.98 cm; mass = 109.30 ± 20.57 kg; and body mass index [BMI] = 33.24 ± 4.95 kg·m−2) performed 3 maximal concentric isokinetic contractions at a slow (1.05 rad·s−1) and fast (4.19 rad·s−1) velocity in random order. The velocity-related decrease in PT was calculated as the %decrease from 1.05 to 4.19 rad·s−1. Ultrasonography was used to determine subcutaneous fat corrected echo intensity (EI) to represent muscle quality before strength testing. The results indicated that there was a significant relationship between EI and %decrease in PT while adjusting for age (r partial = 0.331, p = 0.042), and age and BMI (r partial = 0.325, p = 0.050). These findings suggest that velocity-impaired isokinetic strength may be influenced by alterations in skeletal muscle tissue composition. Future studies are needed to determine whether the %decrease in PT is related to performance during critical firefighter tasks. [ABSTRACT FROM AUTHOR]

Purpose: Neuromuscular deficits and atrophy after anterior cruciate ligament reconstruction (ACLR) may be accompanied by changes in muscle composition and poor quadriceps muscle quality (QMQ). Quadriceps atrophy occurs after ACLR but improves within the first three postoperative months, yet this hypertrophy could be attributable to increases in noncontractile tissue (i.e., poor QMQ). The purposes of this study were to evaluate changes in QMQ after ACLR and to determine if changes in QMQ and cross-sectional area (CSA) occur in parallel or independently. Methods: A longitudinal prospective cohort design was implemented to evaluate QMQ and CSA in 20 individuals with ACLR and 12 healthy controls. Participants completed three testing sessions (baseline/presurgery, 1 month, and 3 months) during which ultrasound images were obtained from the vastus lateralis (VL) and rectus femoris (RF). QMQ was calculated as the echo intensity (EI) of each image, with high EI representing poorer QMQ. Anatomical CSA was also obtained from each image. Results: RF and VL EI were greater at 1 and 3 months in the ACLR limb compared with baseline and the contralateral limb and did not change between 1 and 3 months. VL and RF CSA in the ACLR limb were smaller at 1 and 3 months compared with the contralateral limb and controls (VL only) but increased from 1 to 3 months. Changes in QMQ and CSA were not correlated. Conclusions: QMQ declines within the first month after ACLR and does not improve by 3 months although hypertrophy occurs, suggesting that these morphological characteristics change independently after ACLR. Poorer QMQ represents greater concentration of noncontractile tissues within the muscle and potentially contributes to chronic quadriceps dysfunction observed after ACLR. [ABSTRACT FROM AUTHOR]

Echo intensity (EI) has gained popularity as a method for quantifying ultrasound-derived muscle quality in older adults, which may reflect non-contractile tissue accumulation. However, since water is hypo-echoic, previous authors have suggested that alterations in hydration status and/or intracellular water content (ICW) may influence EI. PURPOSE: To assess the influence of hydration status and segmental ICW on EI in older men. METHODS: Twenty normal weight, healthy, older men (mean ± SD age: 69.5 ± 2.0 yrs; body mass index: 23.6 ± 1.2 kg/m2) refrained from vigorous exercise for 48 hours and fasted for a minimum of eight hours prior to visiting the laboratory on one occasion. A clinical handheld refractometer was used to assess hydration status via urine specific gravity (USG). Panoramic brightness mode ultrasound imaging was used to determine anatomical cross-sectional area (CSA) and EI. Following a 20-minute lying rest period, one scan of each superficial quadricep muscle (vastus lateralis, rectus femoris, vastus medialis) was taken of the right thigh at 50% femur length with the leg propped and supported at 50 degrees of flexion. Cross-sectional area was summed and EI was averaged across all three muscles. Segmental bioelectrical impedance spectroscopy was used to measure ICW and extracellular water content (ECW) of the right thigh. Total body water (TBW) of the segment was determined from the sum of ICW and ECW. The ICW values were normalized to TBW prior to analyses. Pearson's product-moment correlation coefficients were used to assess the association between EI and USG and ICW/TBW. Given previous authors have suggested ICW reflects the amount of contractile tissue, a partial correlation was used to assess the association between EI and ICW/TBW while controlling for CSA. RESULTS: Echo intensity (96.9 ± 12.6 a.u.) was not associated with USG (1.016 ± 0.01) (P = 0.865). Poorer EI (higher value) was negatively associated (r = -0.527, P = 0.02) with lower ICW/TBW (0.50 ± 0.04) prior to and after accounting for CSA (29.8 ± 4.7 cm²) (r = -0.518, P = 0.02). CONCLUSIONS: Hydration status did not influence EI in a group of largely euhydrated (70%) older adults. Thigh specific segmental ICW content influences EI values in older adults. Future studies are needed to determine how ICW content influences age-related differences in EI. [ABSTRACT FROM AUTHOR]