Maximal Voluntary Isometric Knee Extension Research Articles

Developmental changes in motor unit activity patterns: child-adult comparison using discrete motor unit analysis.

Using global surface electromyography (sEMG) and the sEMG threshold it has been suggested that children activate their type-II motor unit (MU) to a lesser extent compared with adults. However, when age-related differences in discrete MU activation are examined using sEMG decomposition this phenomenon is not observed. Furthermore, findings from these studies are inconsistent and conflicting. Therefore, the purpose of this study was to examine differences in discrete MU activation of the vastus lateralis (VL) between boys and men during moderate-intensity knee extensions. Seventeen boys and 20 men completed two laboratory sessions. Following a habituation session, maximal voluntary isometric knee extension (MVIC) torque was determined before completing trapezoidal contractions at 70% MVIC. sEMG of the VL was captured and mathematically decomposed into individual MU action potential trains. Motor unit action potential amplitude (MUAPamp), recruitment threshold (RT), and MU firing rates (MUFR) were calculated. We observed that MUAPamp-RT slope was steeper in men compared with boys (p<0.05) even after accounting for fat thickness and quadriceps muscle depth. The mean MUFR and y-intercept of the MUFR-RT relationship were significantly (p<0.001) lower in boys than in men. The slope of the MUFR-RT relationship tended to be steeper in men, but the differences did not reach statistical significance (p=0.056). Overall, our results suggest that neural strategies used to produce torque are different among boys and men. Such differences may be related, in part, to boys' lower MUFR and lesser ability to activate their higher-threshold MUs. Although, other factors (e.g., muscle composition) likely also play a role.

Maximal Lower Limb Strength in Patellar Tendinopathy: A Systematic Review With Meta-Analysis.

To investigate whether lower limb strength is reduced in people with patellar tendinopathy (PT) compared with asymptomatic control individuals or the asymptomatic contralateral limb. MEDLINE, PubMed, Scopus, and Web of Science. To be included in the systematic review and meta-analysis, studies were required to be peer reviewed, published in the English language, and case control investigations; include participants with a clinical diagnosis of PT and an asymptomatic control or contralateral limb group; and include an objective measure of lower limb maximal strength. We extracted descriptive statistics for maximal strength for the symptomatic and asymptomatic limbs of individuals with PT and the limb(s) of the asymptomatic control group, inferential statistics for between-groups differences, participant characteristics, and details of the strength-testing protocol. The risk of bias was assessed using the Joanna Briggs Institute critical appraisal tool for analytical cross-sectional studies. Of the 23 included studies, 21 reported knee strength, 3 reported hip strength, and 1 reported ankle strength. Random-effects models (Hedges g) were used to calculate the pooled effect sizes (ESs) of muscle strength according to the direction of joint movement and type of contraction. The pooled ESs (95% CI) for maximal voluntary isometric contraction knee-extension strength, concentric knee-extension strength, and concentric knee-flexion strength were 0.54 (0.27, 0.80), 0.78 (0.30, 1.33), and 0.41 (0.04, 0.78), respectively, with all favoring greater strength in the asymptomatic control group. Researchers of 2 studies described maximal eccentric knee-extensor strength with no differences between the PT and asymptomatic control groups. In 3 studies, researchers measured maximal hip strength (abduction, extension, and external rotation), and all within-study ESs favored greater strength in the asymptomatic control group. Isometric and concentric knee-extensor strength are reduced in people with PT compared with asymptomatic control individuals. In contrast, evidence for reduced eccentric knee-extension strength in people with PT compared with asymptomatic control individuals is limited and inconsistent. Although evidence is emerging that both knee-flexion and hip strength may be reduced in people with PT, more examination is needed to confirm this observation.

Recovery of Quadriceps Strength and Knee Function Using Adjuvant EMG-BF After Primary ACL Reconstruction

Introduction: Immobility and limited usage of operated limbs lead to weakness and atrophy of the muscle after anterior cruciate ligament (ACL) reconstruction. However, training programs for preventing biomechanical risk factors such as lower limb alignment and increased muscular contraction are very limited. Thus, the current study was carried out to evaluate the recovery of quadriceps muscle strength and the improvement of knee function using adjuvant electromyographic biofeedback (EMG-BF) after ACL reconstruction. Methods: This prospective randomized controlled trial was conducted among 40 patients (20=EMG-BF group, 20=Control group) with ACL reconstruction, who were referred to Akhtar Hospital from 2021 to 2022. In the EMG-BF group, EMG BFB was added to the standard rehabilitation protocol, and in the control group, the standard rehabilitation protocol with full postoperative weight-bearing, knee brace (zero degree of extension, 90 degrees of flexion), and electrical stimulation with maximal voluntary isometric knee extension was performed. Each group was intervened for 4 weeks and three sessions of 30 minutes per week. It should be noted that each patient participated in 16 outpatient physiotherapy sessions after surgery. Nicholas Hand-Held Dynamometer (HHD) was used for measuring quadriceps strength, and Knee Outcome Survey-Activities of Daily Living (KOS-ADLs) and Knee Outcome Survey Sports Activities Scale (KOS-SAS) questionnaires were used for assessing the knee function. Results: Four weeks after the treatment, the EMG-BF group showed a significant increase in quadriceps strength (P=0.0001). Quadriceps strength had a significant difference before and after 4 weeks of intervention (P=0.0001), but in the control group, no significant difference was observed (P=0.368). The EMG-BF group had a significant increase in KOS-ADLs and KOS-SAS scores after 4 weeks of intervention (P=0.0001). Conclusion: In our study, isometric strengthening of quadriceps with adjuvant EMG-BF significantly increased the strength of quadriceps and knee function during 4 weeks. EMG-BF is a low risk, low cost, and less invasive intervention and has high safety and adjustment ability. It is a valuable adjuvant method for achieving better functional recovery in a shorter time.

Relationship Between Quadriceps Rate Of Torque Development And Knee Joint Power During Jumping Post-acl Reconstruction

Relationship Between Quadriceps Rate Of Torque Development and Knee Joint Power During Jumping Post-ACL Reconstruction.Kelsey A. Reeves, Darren L. Johnson, Chris Fry, Brian Noehren. University of Kentucky, Lexington, KYThe inability to generate knee joint power after an anterior cruciate ligament (ACL) reconstruction limits athletic performance and contributes to low return to sports rates. However, the underlying factors contributing to a lack of knee joint power in the injured limb remain unclear. Rate of torque development (RTD) of the quadriceps may play a critical role in the development of knee joint power. To date, there is no work on the relationship between early and late stage RTD and knee joint power. Late stage RTD may be more relevant for concentric (CON) movements because of the time it takes to generate power in the knee. PURPOSE: To evaluate the relationship between RTD and knee joint power during the CON phase of a drop vertical jump (DVJ) in patients who were 6 months post ACL reconstruction. METHODS: Three DVJs were recorded for each subject (n = 20, age 20.5 ± 6, BMI 24.0 ± 3.4, 9 female) using instrumented 3D motion analysis. Knee joint power was calculated during the CON phase of the DVJ using custom computer code. RTD was obtained from the subject’s maximal voluntary isometric knee extension strength using an isokinetic dynamometer. Early and late stage RTD were defined as 0-100 ms and 100-200 ms from muscle activation onset, respectively. Relationships between variables were determined using Pearson Product Moment Correlations. RESULTS: Average peak knee joint power was 3.0 ± 1.3 W/kg. Average early and late stage RTD were 6.4 ± 3.6 Nm/kg/s and 2.9 ± 1.3 Nm/kg/s, respectively. Late stage RTD was significantly correlated with knee joint power (r = 0.75, p = 0.000) whereas early stage RTD was not (r = 0.27, p = 0.243). CONCLUSION: Late stage RTD is an important contributing factor to the development of knee joint power during athletic movements such as a jump following an ACL reconstruction. Interventions should look to target late stage RTD to help restore an athlete’s ability to generate power and safely return to sport.

Muscle quality indices separately associate with joint-level power-related measures of the knee extensors in older males

PurposeThe purpose of this study was to investigate associations of muscle quality indices with joint-level power-related measures in the knee extensors of thirty-two older males (65–88 years).MethodsMuscle quality indices included: echo intensity, ratio of intracellular- to total water content (ICW/TW), and specific muscle strength. Echo intensity was acquired from the rectus femoris (EIRF) and vastus lateralis (EIVL) by ultrasonography. ICW/TW was computed from electrical resistance of the right thigh obtained by bioelectrical impedance spectroscopy. Specific muscle strength was determined as the normalized maximal voluntary isometric knee extension (MVIC) torque to estimated knee extensor volume. Isotonic maximal effort knee extensions with a load set to 20% MVIC torque were performed to obtain the knee extension power-related measures (peak power, rate of power development [RPD], and rate of velocity development [RVD]). Power and RPD were normalized to MVIC.ResultsThere were no significant correlations between muscle quality indices except between EIRF and EIVL (|r|≤ 0.253, P ≥ 0.162). EIRF was negatively correlated with normalized RPD and RVD (r ≤ − 0.361, P ≤ 0.050). ICW/TW was positively correlated with normalized peak power (r = 0.421, P = 0.020). Specific muscle strength was positively correlated with absolute peak power and RPD (r ≥ 0.452, P ≤ 0.012).ConclusionKnee extension power-related measures were lower in participants with higher EI, lower ICW/TW, and lower specific muscle strength, but the muscle quality indices may be determined by independent physiological characteristics.

Older Compared With Younger Adults Performed 467 Fewer Sit-to-Stand Trials, Accompanied by Small Changes in Muscle Activation and Voluntary Force.

Background: Repetitive sit-to-stand (rSTS) is a fatigue perturbation model to examine the age-effects on adaptability in posture and gait, yet the age-effects on muscle activation during rSTS per se are unclear. We examined the effects of age and exhaustive rSTS on muscle activation magnitude, onset, and duration during ascent and descent phases of the STS task.Methods: Healthy older (n = 12) and younger (n = 11) adults performed rSTS, at a controlled frequency dictated by a metronome (2 s for cycle), to failure or for 30 min. We assessed muscle activation magnitude, onset, and duration of plantar flexors, dorsiflexors, knee flexors, knee extensors, and hip stabilizers during the initial and late stages of rSTS. Before and after rSTS, we measured maximal voluntary isometric knee extension force, and rate of perceived exertion, which was also recorded during rSTS task.Results: Older vs. younger adults generated 35% lower maximum voluntary isometric knee extension force. During the initial stage of rSTS, older vs. younger adults activated the dorsiflexor 60% higher, all 5 muscle groups 37% longer, and the hip stabilizers 80% earlier. Older vs. younger adults completed 467 fewer STS trials and, at failure, their rate of perceived exertion was ~17 of 20 on the Borg scale. At the end of the rSTS, maximum voluntary isometric knee extension force decreased 16% similarly in older and younger, as well as the similar age groups decline in activation of the dorsiflexor and knee extensor muscles (all p < 0.05).Conclusion: By performing 467 fewer STS trials, older adults minimized the potential effects of fatigability on muscle activation, voluntary force, and motor function. Such a sparing effect may explain the minimal changes in gait after rSTS reported in previous studies, suggesting a limited scope of this perturbation model to probe age-effects on muscle adaptation in functional tasks.

Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial.

Inclusion body myositis is the most frequent myositis in patients older than 50 years. Classical immunosuppressants are ineffective in treating inclusion body myositis, and to date there are no recommendations for pharmacological approaches to treatment. When used after organ transplantation, sirolimus can block the proliferation of effector T cells, while preserving T regulatory cells, and induce autophagy, all of which are processes that are impaired in inclusion body myositis. In this pilot study, we aimed to test the efficacy of sirolimus in patients with inclusion body myositis. This randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial was done at a single hospital in Paris, France. The study included men and women (aged 45-80 years) who had a defined diagnosis of inclusion body myositis according to established criteria. Eligible participants were randomly assigned (1:1) to receive once-daily oral sirolimus 2 mg or placebo. Centralised balanced block randomisation (blocks of four) was computer generated without stratification. The study comprised a 15-day screening period (days -15 to 0) and a 52-week treatment period (day 0 to month 12). The primary endpoint was the relative percentage change from baseline to month 12 in maximal voluntary isometric knee extension strength. Secondary endpoints included the following assessments at months 6 and 12: 6-min walking distance, isometric muscle strength for hand grip (finger flexors), knee flexion and elbow flexion and extension, forced vital capacity, muscle replacement with fat measured by quantitative nuclear MRI, Inclusion Body Myositis Weakness Composite Index (IBMWCI), Inclusion Body Myositis Functional Rating Scale (IBMFRS), Health Assessment Questionnaire without Disability Index (HAQ-DI), and analyses of T-cell subpopulations by mass cytometry. The primary analysis was done on the intention-to-treat population. The trial is registered at ClinicalTrials.gov, NCT02481453. Between July 15, 2015, and May 13, 2016, we screened 285 patients, 44 of whom were randomly allocated to sirolimus (22 patients) or placebo (22 patients). We observed no difference in the primary outcome of relative percentage change from baseline to month 12 of the maximal voluntary isometric knee extension strength (median difference 3·78, 95% CI -10·61 to 17·31; p=0·85). For secondary outcomes, differences between the groups were not significant for changes in strength of other muscle groups (grip, elbow flexion and extension, or knee flexion), IBMWCI, IBMFRS, and lower limb muscle fat fraction. However, we observed significant differences in favour of sirolimus between the study groups for HAQ-DI, forced vital capacity, thigh fat fraction, and 6-min walking distance. Ten (45%) of 22 patients in the sirolimus group had a serious adverse event compared with six (27%) of 22 patients in the placebo group. Four (18%) patients in the sirolimus group stopped their treatment because of adverse events (severe mouth ulcers, aseptic pneumonia, renal insufficiency, and peripheral lower limb oedema), which resolved after treatment discontinuation. Canker sores were the most frequent side-effect and were mainly mild or moderate in ten patients. We found no evidence for efficacy of sirolimus for treating inclusion body myositis based on maximal voluntary isometric knee extension strength and other muscle strength measures, and the side-effects of treatment were substantial for some patients. However, we believe there was enough evidence of benefit in certain secondary outcomes to pursue a multicentre phase 3 trial to further assess the safety and efficacy of sirolimus. Institut national de la santé et de la recherche médicale, Direction générale de l'offre de soins, and Association Française contre les Myopathies.

Quadriceps Strength And Rate Of Torque Development Are Associated With Countermovement Jump Knee Kinetics Post-aclr

Quadriceps neuromuscular dysfunction is ubiquitous after anterior cruciate ligament reconstruction (ACLR) and can impair knee function during athletic activities. While peak quadriceps strength is often measured, time-dependent metrics such as rate of torque development may be important to sports performance. PURPOSE: To determine the relationships between quadriceps strength, rate of torque development, time since surgery, and knee joint kinetics during jumping in collegiate athletes up to 2 years post-ACLR. METHODS: 31 Division I athletes (age 20.3±1.3, BMI 26.1±3.9 kg/m2, 17 female) performed countermovement jumps (CMJ) on force plates while whole body kinematics were recorded and completed maximal and rapid voluntary isometric knee extension (KE) contractions. Sagittal plane KE impulses were computed for concentric (CON) and landing (LAND) CMJ phases; KE peak torque (PT) and rate of torque development from 20-80% of peak torque (RTD) were extracted from isometric KE efforts. Limb symmetry indices (LSI) were computed and clinically relevant cutoffs of 90% LSI were investigated. A mixed effects model accounted for repeated measurements and assessed the relationships of PT, RTD, and time from surgery with CON and LAND. All possible pairwise interactions were tested. RESULTS: Among 31 athletes, 81 tests were completed 4-24 months post-surgery. PT and RTD were significantly correlated with CON (PT: p=.001, RTD: p=.044) and LAND (PT: p=.009, RTD: p=.008). No significant pairwise interactions between PT, RTD, and time from surgery were detected. Among 24 instances of PT LSI ≥ 90%, mean CON and LAND LSI were 87.3% and 94.2%, respectively. In comparison, among 15 occurrences of RTD LSI ≥ 90%, mean CON and LAND LSI were 93.0% and 102.2%. Among the 22 assessments completed ≥ 1 year post-surgery, mean CON and LAND LSI were 82.4%, and 83.3%, respectively. However, when CON and LAND LSI were ≥ 90%, mean PT was 94.5-94.7% and mean RTD was 85.1-85.3%. CONCLUSIONS: Both peak and rapid knee extensor torque development are strongly associated with symmetrical sagittal plane CMJ knee mechanics. CMJ knee kinetic asymmetries did not resolve over time, independent from quadriceps function. Restoring maximal and rapid quadriceps torque capacity appears to be an important step in recovering symmetrical CMJ mechanics post-ACLR.

Mechanical and Material Tendon Properties in Patients With Proximal Patellar Tendinopathy.

IntroductionThe effect of chronic patellar tendinopathy on tissue function and integrity is currently unclear and underinvestigated. The aim of this cohort comparison was to examine morphological, material, and mechanical properties of the patellar tendon and to extend earlier findings by measuring the ability to store and return elastic energy in symptomatic tendons.MethodsSeventeen patients with chronic (>3 months, VISA-P < 80), inferior pole patellar tendinopathy (24 ± 4 years; male = 12, female = 5) were carefully matched to controls (25 ± 3 years) for training status, pattern, and history of loading of the patellar tendon. Individual knee extension force, patellar tendon stiffness, stress, strain, Young’s modulus, hysteresis, and energy storage capacity, were obtained with combined dynamometry, ultrasonography, magnetic resonance imaging, and electromyography.ResultsAnthropometric parameters did not differ between groups. VISA-P scores ranged from 28 to 78 points, and symptoms had lasted from 10 to 120 months before testing. Tendon proximal cross-sectional area was 61% larger in the patellar tendinopathy group than in the control group. There were no differences between groups in maximal voluntary isometric knee extension torque (p = 0.216; d < −0.31) nor in tensile tendon force produced during isometric ramp contractions (p = 0.185; d < −0.34). Similarly, tendon strain (p = 0.634; d < 0.12), hysteresis (p = 0.461; d < 0.18), and strain energy storage (p = 0.656; d < 0.36) did not differ between groups. However, patellar tendon stiffness (−19%; p = 0.007; d < −0.74), stress (−27%; p< 0.002; d < −0.90) and Young’s modulus (−32%; p = 0.001; d < −0.94) were significantly lower in tendinopathic patients compared to healthy controls.DiscussionIn this study, we observed lower stiffness in affected tendons. However, despite the substantial structural and histological changes occurring with tendinopathy, the tendon capacity to store and dissipate energy did not differ significantly.

Routine monitoring of isometric knee extension strength in patients with muscle impairments using a new portable device: cross-validation against a standard isokinetic dynamometer

Objective: Muscle strength is a critical clinical hallmark in both health and disease. The current study introduces a novel portable device prototype (MyoQuad) for assessing and monitoring maximal voluntary isometric knee extension torque (MVIT). Approach: Fifty-six patients with inclusion body myositis were studied. Knee extension weakness is a key feature in this inflammatory muscle disease. Cross-validation with an isokinetic dynamometer (Biodex System 3 Pro) was performed. Between-day reproducibility and ability to monitor changes in muscle strength over time compared to the gold standard method as a reference, were also investigated. Main results: The measurement was feasible even in the weakest patients. Agreement between methods was excellent (standard error of measurement (SEM) was 3.8 Nm and intra-class correlation coefficient (ICC) was 0.973). Least significant difference (LSD) was 4.9 and 5.3 Nm for the MyoQuad and the Biodex, respectively Measurements using the MyoQuad exhibited excellent between-day reproducibility (SEM was 2.4 Nm and ICC was 0.989 versus 2.6 Nm and 0.988 using the Biodex). Changes in MVIT at 6 and 12 months were similar between methods (timepoint × method interaction was not significant; all p > 0.19); strength changes classified according to LSD at 6 and 12 months were consistent between methods (>70% consistent classification)). Significance: The measurement of MVIT using the MyoQuad offers a cost-effective, portable and immediate alternative for the routine measurement of maximal voluntary isometric strength of the quadriceps. The MyoQuad offers a comfort and stability that cannot be provided by standard hand-held dynamometers. These results support quantitative muscle strength assessment using fixed yet flexible dynamometry within clinical routine and multicenter trials.

Impact of daily protein and energy intake and distribution on muscle mass and strength in Danish older individuals-The CALM study

AbstractThe importance of dietary protein for the maintenance of muscle mass and strength is heavily discussed. However, adequate energy intake is an underlying assumption but often not considered. In this study, we investigated the impact of daily intake and meal distribution of both protein and energy on muscle mass and strength. In a cross-sectional study, a total of 184 older individuals (gender: 86F/98M, age: 70.2 ± 3.9 yrs, BMI: 25.4 ± 3.7 kg/m2; means ± SD) were recruited. Participants underwent a 3-day weighed dietary record, Dual-energy X-ray Absorptiometry (DXA) scan, hand-grip strength, and Maximal Voluntary Isometric knee-extension Contraction (MVIC). Participants were divided into two categories: lower (LOW; &lt; 0.83 g/adjusted(a)BW/day) or higher (HIGH; ≥ 1.1 g/aBW/day) protein intake levels analysed by gender to characterize a daily protein and energy intake pattern. Main meal protein and energy intake distributions were calculated, and correlations were made. Further, energy intake at breakfast and lunch divided by total energy intake (energy ratio) was correlated with appendicular skeletal muscle index (ASMI), hand-grip strength, and MVIC were determined using the LOW/HIGH-protein-intake categorization. Further, gender-specific ASMI, hand-grip strength and knee extension were compared based on the following four distinct daily protein intake ranges: &lt; 0.66; ≥ 0.66- &lt; 0.83; ≥ 0.83- &lt; 1.1; ≥ 1.1 g/aBW/day. A positive correlation appeared between protein and energy intake in all main meals (r ≥ 0.57, p &lt; 0.0001). In the LOW category, positive correlations were found between energy ratio and ASMI (r = 0.16, p = 0.048), hand-grip strength (r = 0.40, p = 0.0009), and MVIC (r = 0.36, p = 0.0019), whereas no associations were found in the HIGH category. ASMI, hand grip, and MVIC were similar regardless of the protein intake ranges, though with women being lower than men (p &lt; 0.05) in all outcomes. These results show that total daily protein intake did not affect muscle mass and strength in our cohort. However, our data demonstrate that greater energy intake in breakfast and lunch relative to total energy intake is associated with higher muscle mass and strength, particularly when protein intake is lower than 0.83 g/aBW/day, indicating the potential importance of meal energy content at lower intakes of protein.

Intra- and Post-match Time-Course of Indicators Related to Perceived and Performance Fatigability and Recovery in Elite Youth Soccer Players.

PurposeOur aims were to examine (i) the internal load during simulated soccer match-play by elite youth players; and (ii) the time-course of subsequent recovery from perceived and performance fatigability.MethodsEleven male youth players (16 ± 1 years, 178 ± 7 cm, 67 ± 7 kg) participated in a 2 × 40-min simulated soccer match, completing 30 rounds (160 s each) with every round including multidirectional and linear sprinting (LS20m), jumping (CMJ) and running at different intensities. During each round, LS20m, CMJ, agility, heart rate (HR), oxygen uptake (VO2), energy expenditure (EE), substrate utilization and perceived exertion RPE were assessed. In addition, the blood level of lactate (Lac) was obtained after each of the five rounds. Creatine kinase (CK) concentration, maximal voluntary isometric knee extension and flexion, CMJ, number of skippings in 30 s, and subjective ratings on the Acute Recovery and Stress Scale (ARSS) were examined before and immediately, 24 and 48 h after the simulation.ResultsDuring the game %HRpeak (p < 0.05, d = 1.08), %VO2peak (p < 0.05; d = 0.68), Lac (p < 0.05, d = 2.59), RPEtotal (p < 0.05, d = 4.59), and RPElegs (p < 0.05, d = 4.45) all increased with time during both halves (all p < 0.05). Agility improved (p < 0.05, d = 0.70) over the time-course of the game, with no changes in LS20m (p ≥ 0.05, d = 0.34) or CMJ (p ≥ 0.05, d = 0.27). EE was similar during both halves (528 ± 58 vs. 514 ± 61 kcal; p = 0.60; d = 0.23), with 62% (second half: 65%) carbohydrate, 9% (9%) protein and 26% (27%) fat utilization. With respect to recovery, maximal voluntary knee extension (p ≥ 0.05, d = 0.50) and flexion force (p ≥ 0.05, d = 0.19), CMJ (p ≥ 0.05, d = 0.13), number of ground contacts (p ≥ 0.05, d = 0.57) and average contact time (p ≥ 0.05, d = 0.39) during 30-s of skipping remained unaltered 24 and 48 h after the game. Most ARSS dimensions of load (p < 0.05, d = 3.79) and recovery (p < 0.05, d = 3.22) returned to baseline levels after 24 h of recovery. Relative to baseline values, CK was elevated immediately and 24 h after (p < 0.05, d = 2.03) and normalized 48 h later.ConclusionIn youth soccer players the simulated match evoked considerable circulatory, metabolic and perceptual load, with an EE of 1042 ± 118 kcal. Among the indicators of perceived and performance fatigability examined, the level of CK and certain subjective ratings differed considerably immediately following or 24–48 h after a 2 × 40-min simulated soccer match in comparison to baseline. Accordingly, monitoring these variables may assist coaches in assessing a U17 player’s perceived and performance fatigability in connection with scheduling training following a soccer match.

Acute Effects of Transcranial Direct Current Stimulation on Knee Extensor Torque-Producing Capabilities

Transcranial direct current stimulation (tDCS) is a method of neuromodulation aimed to increase cortical excitability. Recently, tDCS has been utilized as a modality treatment in various medical conditions (e.g. stroke rehabilitation); however, few investigations have examined its effect on motor function. PURPOSE: To examine the acute effects of tDCS on torque producing capabilities of the knee extensors. METHODS: Thirty-two recreationally active females (Age = 21.8 ± 2.6; Height = 165.3 ± 6.3cm; Weight = 68.1 ± 11.6kg) participated in this single-blind investigation. Participants were required to report to the laboratory on two separate occasions to receive two randomized conditions, tDCS or sham stimulation. During the initial visit, participants were familiarized with maximal voluntary isometric knee extension (MVIC; 120° knee extension) testing procedures via an isokinetic dynamometer, which was utilized to assess peak torque (PT) and peak rate of torque development (pRTD). Subsequently, participants underwent a 5-minute low-intensity warm-up via a cycle ergometer prior to data acquisition. Participants performed two MVICs with a 2-minute rest period between contractions. Following initial isometric testing procedures, participants were outfitted with a set of commercially available headphones designed to deliver tDCS to the primary motor cortex for a duration of 21 minutes, during which, they performed various low-intensity dynamic movements. Participants then completed an additional series of MVICs identical to pre-testing following “stimulation”. RESULTS: Two separate 2x2 (time x condition) repeated-measures ANOVAs were conducted to assess differences in pre- to post-stimulation PT and pRTD within conditions. No differences were observed in PT for either condition (p > 0.05). pRTD revealed no interaction effect (p > 0.05); however, a main effect of time was observed (F1,31 = 9.97, p = .004). Follow-up paired-samples t-tests revealed decreases in pRTD from pre- to post-stimulation within the tDCS condition (t31 = 2.643, p = 0.013). CONCLUSIONS: Although tDCS does not appear to alter PT production, our findings suggest that tDCS may negatively affect an individual’s ability to rapidly produce force.

Whole-Body Vibration Improves Early Rate of Torque Development in Individuals With Anterior Cruciate Ligament Reconstruction

Pamukoff, DN, Pietrosimone, B, Ryan, ED, Lee, DR, Brown, LE, and Blackburn, JT. Whole body vibration improves early rate of torque development in individuals with anterior cruciate ligament reconstruction. J Strength Cond Res 31(11): 2992-3000, 2017-The purpose of this study was to compare the effect of whole-body vibration (WBV) and local muscle vibration (LMV) on early and late quadriceps rate of torque development (RTD), and electromechanical delay (EMD) in individuals with anterior cruciate ligament reconstruction (ACLR). Twenty individuals with ACLR were recruited for this study. Participants performed isometric squats while being exposed to WBV, LMV, or no vibration (control) in a randomized order during separate visits. Early and late quadriceps RTD and EMD were assessed during a maximal voluntary isometric knee extension before and immediately after WBV, LMV, or control. There was a significant condition by time interaction for early RTD (p = 0.045) but not for late RTD (p = 0.11) or EMD of the vastus medialis (p = 0.15), vastus lateralis (p = 0.17), or rectus femoris (p = 0.39). Post hoc analyses indicated a significant increase in early RTD after WBV (+5.59 N·m·s·kg; 95% confidence interval, 1.47-12.72; p = 0.007). No differences were observed in the LMV or control conditions, and no difference was observed between conditions at posttest. The ability to rapidly produce knee extension torque is essential to physical function, and WBV may be appropriate to aid in the restoration of RTD after ACLR.

Effect of prolonged vibration to synergistic and antagonistic muscles on the rectus femoris activation during multi-joint exercises

PurposeUnique neuromuscular activation of the quadriceps femoris is observed during multi-joint leg extensions: lower activation of the biarticular rectus femoris (RF) than monoarticular vasti muscles. As one of the potential mechanisms for the lower RF activation, Ia afferent-mediated inhibitory connections between synergistic muscles and/or between agonist and antagonist muscles have been proposed. If this is the major factor, it is hypothesized that RF activation during multi-joint leg extensions increases after prolonged vibration to synergistic and/or antagonist muscles. This study tested the hypothesis.MethodsFourteen men exerted maximal voluntary isometric knee extension and flexion and performed submaximal parallel squat before and after one of the following three interventions on different days: prolonged vibration to the vastus lateralis (VL, synergist) or biceps femoris (BF, antagonist), or quiet sitting for 30 min. Muscle activations of the quadriceps femoris and hamstrings were determined using surface electromyography.ResultsAfter prolonged VL or BF vibration, VL (21%) or BF (30%) activation during isometric contractions significantly decreased, which was significantly correlated with the reduction of the maximal isometric knee extension or flexion strength. The magnitude of RF activation during squat was significantly lower than those of VL and the vastus medialis. No significant increase in RF activation during squat was observed after vibrations.ConclusionThe findings suggest that lower biarticular RF activation compared with the monoarticular vasti muscles during multi-joint exercises does not result from the modulation by peripheral inhibitory input from Ia afferents originating from synergist and/or antagonist muscles.

Oral contraceptive pill use and the susceptibility to markers of exercise-induced muscle damage

PurposeFirstly, to establish whether oral contraceptive pill (OCP) users are more susceptible to muscle damage compared to non-users, and secondly, to establish whether differences can be attributed to differences in patella tendon properties.MethodsNine female OCP users and 9 female non-users participated in the investigation. Combining dynamometry, electromyography and ultrasonography, patella tendon properties and vastus lateralis architectural properties were measured pre and during the first of 6 sets of 12 maximal voluntary eccentric knee extensions. Serum oestrogen levels were measured on the 7th day of the pill cycle and the 14th day of menstrual cycle in OCP users and non-users, respectively. Maximal voluntary isometric knee extension torque loss, creatine kinase and muscle soreness were measured 48 h pre-damage, post-damage, and 48, 96 and 168 h post-damage.ResultsOestrogen levels were significantly lower in OCP users compared to non-users (209 ± 115 and 433 ± 147 pg/ml, respectively, p = 0.004). Proposed determinants of muscle damage, patella tendon stiffness and maximal eccentric torque did not differ between OCP users and non-users. The change in creatine kinase from pre to peak was significantly higher in OCP users compared to non-users (962 ± 968 and 386 ± 474 Ul, respectively, p = 0.016). There were no other differences in markers of muscle damage.ConclusionAlthough our findings suggest that, when compared to non-users, the OCP may augment the creatine kinase response following eccentric exercise, it does not increase the susceptibility to any other markers of muscle damage.

Relationships Among and Differences between Muscle Quality and Functional Performance in Younger and Older Women

The quality of skeletal muscle has been identified as an important factor that is used to describe intramuscular changes associated with muscle function in aging. Traditionally, muscle quality (MQ) has been calculated as maximal muscle strength expressed per unit of muscle mass. More recently, however, the echo intensity (EI) of skeletal muscle ultrasound images has been used as a surrogate measure of muscle quality. PURPOSE: The purpose of this study was to examine the relationships among and differences between commonly-used measures of MQ and functional performance in younger (YW) and older women (OW). METHODS: 15 YW (mean ± SD: 22 ± 2 yrs) and 15 OW (74 ± 5 yrs) completed this study. Muscle cross section area (mCSA) and EI of the rectus femoris were measured from ultrasound scans at the midpoint of the thigh. Each participant completed two maximal voluntary isometric knee extension contractions (MVICs) to determine MVIC strength. Each participant also completed three maximal velocity sit-to-stand movements, during which power and movement velocity were measured. MQ was calculated as MVIC strength ÷ mCSA. Independent samples t-tests were used to analyze differences between YW and OW and Pearson’s correlation coefficients were also used to analyze the relationships among the dependent variables in the YW and OW. RESULTS: MVIC strength (166 ± 37 vs 105 ± 28 Nm), mean velocity (0.6 ± 0.1 vs 0.4 ± 0.1 m/s), peak velocity (0.9 ± 0.2 vs 0.7 ± 0.1), mean power (435 ± 81 vs 299 ± 57 W), peak power (1070 ± 265 vs 597 ± 127 W) were greater and EI (39 ± 8 vs 52 ± 10 au) was lower in the YW than OW, respectively. There was no difference in muscle quality (p = 0.96). EI and MQ were not significantly related (r = 0.12) in the YW, but were significantly related in the OW (r = 0.54). EI was inversely related to mCSA in the YW (r = -0.53) and OW (r = -0.54). In addition, MVIC was significantly related to mCSA (r = 0.75) in the OW, and was not significantly related to EI or MQ in either the YW or OW. CONCLUSION: There were age-related differences in muscle strength, muscle size, echo intensity, and functional performance, but no age-related difference in traditionally measured MQ. EI was related to MQ in the OW, but not the YW. Although EI has been used as a surrogate for MQ, these data suggest that MQ and EI may reflect different qualities of skeletal muscle in aging.

The Relationship between Knee Related Function and Objectively Measured Physical Activity after ACL Reconstruction

Persistent quadriceps weakness and knee dysfunction have been reported after ACL reconstruction (ACLR). It is unclear if these clinical findings are related to physical inactivity among those with a history of ACLR. PURPOSE: To investigate the relationship between patient reported knee function, knee extension strength, and objectively measured physical activity in individuals with and without a history of ACLR. METHODS: 17 ACLR participants (Sex = 10F/7M, Age = 20.5 ± 1.9 yrs, BMI = 23.4 ± 3.5kg/m2, Time since surgery = 39.3 ± 18.7mo) and 17 matched controls (Sex = 10F/7M, Age = 20.5 ± 2.5 years, BMI = 23.1 ± 3.5kg/m2) enrolled. Participants completed the International Knee Documentation Committee (IKDC) form to assess knee function. Involved limb knee extension maximal voluntary isometric contraction (MVIC) strength (Nm/kg) and isokinetic knee extension strength (Nm/kg) was assessed at 60 and 180 deg/s using a multi-mode dynamometer. Moderate-to-vigorous physical activity (MVPA, min/day) was assessed with an ActiGraph GT3X-BT accelerometer worn on an elastic belt at the hip over a period of 7 days with a minimum of 4 days of wear with ≥10 hours per day. Wear time (min/day) was validated using recommendations of Choi et al and Freedson Adult VM3 cut points were used to categorize physical activity. Relationships between MVPA, knee extension strength, and IKDC score were assessed for all participants as well as within the ACLR group using Pearson’s product moment correlations (r). RESULTS: Overall, IKDC score (mean = 93.42 ± 6.95) was positively correlated with isokinetic knee extension strength at 180 deg/s (mean = 1.30 ± 0.45Nm/kg, r = 0.41, p = 0.02). In the ACLR group, IKDC score (mean = 90.19 ± 7.21) was positively correlated with knee extension MVIC strength (mean = 2.28 ± 0.78, r = 0.48, p = 0.05) as well as isokinetic knee extension strength at 180 deg/s (mean = 1.21 ± 0.55, r = 0.57, p = 0.02). There were no significant correlations between IKDC score, knee extension MVIC strength, or isokinetic knee extension strength and MVPA. CONCLUSIONS: MVPA is an important clinical outcome that may not be related to traditional patient reported or functional outcome measures after ACLR. Understanding the factors contributing to physical inactivity after ACLR may guide clinical intervention strategies aimed at promoting MVPA.

Quadriceps Function and Hamstrings Co-Activation After Anterior Cruciate Ligament Reconstruction

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. To compare quadriceps function between individuals with ACLR and uninjured control participants. Cross-sectional study. Research laboratory. 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. 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. 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). 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.

Native whey induces higher and faster leucinemia than other whey protein supplements and milk: a randomized controlled trial

BackgroundResistance exercise and protein intake are both strong stimuli for muscle protein synthesis. The potential for a protein to acutely increase muscle protein synthesis seems partly dependent on absorption kinetics and the amino acid composition. The aim of this double-blinded randomized cross-over study was to compare time dependent changes in blood amino acid concentrations after ingesting 20 g of five distinct high quality dairy protein supplements (native whey, whey protein concentrate 80, hydrolysed whey, microparticulated whey, and milk proteins). Furthermore, we investigated whether differences in time dependent changes in blood amino acid concentrations affected acute blood glucose and urea responses, and recovery of muscle function after a bout of strength training.MethodsTen young healthy, recreationally active men ingested different milk protein supplements after a whole-body strength training session on five occasions in a randomized manner. Blood concentrations of amino acids, glucose and urea was measured before and 0, 30, 45, 60, 90, 120 min, and 22 and 30 h post-exercise. Maximal voluntary isometric knee extension and counter movement jump were assessed before, immediately after, 6, 22 and 30 h after exercise.ResultsIntake of native whey induced a faster and higher leucinemia than the other protein supplements (p < 0.001). All whey protein supplements showed faster time dependent changes in blood amino acid concentrations for total essential and branched chain amino acids compared to milk. There were no major differences between trials in blood concentrations of glucose or urea, or recovery of muscle function after exercise.ConclusionNative whey induced the strongest leucinemia and appears to have a greater potential for stimulating muscle protein synthesis than other whey supplements and milk. There were no meaningful differences in blood glucose, urea or recovery of muscle function after the supplements. Future studies should investigate whether the increased leucinemia with native whey translates into greater muscle protein synthesis and muscle mass accretion over time. (NCT02882386, August 16, 2016).