Maximum Voluntary Isometric Contraction Testing Research Articles

Ipsilateral and Contralateral Torque Responses to Bilateral and Unilateral Maximal, Fatiguing, Isokinetic Leg Extensions

Background: Few studies have compared performance fatigability (PF) for bilateral versus unilateral isokinetic tasks. Objectives: The purpose of this study was to examine: Mode-specific testing responses to isokinetic fatigue, differences in PF between bilateral and unilateral leg extensions, and the effects of fatiguing, unilateral, dynamic leg extensions on contralateral isokinetic peak torque (PT) and maximal voluntary isometric contraction (MVIC). Methods: Eight men (mean ± SD: age= 22.5 ± 2.5 yr.) completed pre- and post-testing for PT and MVIC following 50 bilateral, unilateral right or left leg maximal, isokinetic leg extensions at 180°·s-1, on three separate days. Fatigue-induced decreases in PT and MVIC were used to quantify PF. The data were analyzed with a 4-way repeated measures ANOVA, follow up, and post-hoc analyses. Results: The results indicated that there were no differences (p > 0.05) in PF for the bilateral versus unilateral fatiguing tasks, decreases in PT (p < 0.001 - 0.016; d = 0.54 - 2.58) and MVIC (p < 0.001 - 0.006; η2p = 0.682 - 0.962) for the exercised legs during unilateral fatigue, and a contralateral increase (p = 0.007) in PT following the right leg fatiguing task. Conclusion: The results indicated that PT was more sensitive to fatiguing isokinetic tasks than was MVIC. In addition, there was a facilitation of PT in the contralateral leg following unilateral right leg fatigue. The differences in PT and MVIC testing may be attributable to the timing and/or relative contributions of peripheral and central fatigue.

Normalizing gastrocnemius muscle EMG signal: An optimal set of maximum voluntary isometric contraction tests for young adults considering reproducibility

BackgroundEven though most studies normalize the surface EMG signal of the gastrocnemius muscle using a single position of maximum voluntary isometric contraction (MVIC), several studies tend to indicate that several positions are in fact needed to obtain a maximal voluntary activation (MVA) for most of the subjects. However, no combination of positions has already been described. Research questionA combination of MVIC positions to normalize the EMG signal of the gastrocnemius muscle is investigated. the influence of using several positions on the reproducibility of the normalization process is evaluated. MethodsTwenty healthy volunteers (45 % female – 55 % male, 25.4 years (SD 4.3), 72.6 kg (SD 13.9), 1.78 m (SD 0.12)) were recruited. Six positions for MVIC were compared and the effect of several normalization combinations on a functional task (gait) was evaluated. ResultsSeveral positions are needed to obtain at least 90 % of the MVA for 90 % of the volunteers even though the use of a single well-chosen position (unipodal standing position with knee fully extended and ankle fully plantar-flexed) will lead to no statistically significant differences of the gait evaluation during stance phase. For each position, five repetitions of the MVIC are recommended to obtain a valid MVA. SignificanceThis study confirms that using several MVIC positions is recommended when possible to normalize the gastrocnemius muscle EMG signal. However, in the situation of a patient where limited MVIC attempts are possible, using a single well-chosen position should not significantly influence the amplitude and the reproducibility of the measures.

Changes in the Plantar Flexion Torque of the Ankle and in the Morphological Characteristics and Mechanical Properties of the Achilles Tendon after 12-Week Gait Retraining.

Purpose: Although the Achilles tendon (AT) is the largest and strongest tendon, it remains one of the most vulnerable tendons among elite and recreational runners. The present study aims to explore the effects of 12-week gait retraining (GR) on the plantar flexion torque of the ankle and the morphological and mechanical properties of the AT. Methods: Thirty-four healthy male recreational runners (habitual rearfoot strikers) who never tried to run in minimal shoes were recruited, and the intervention was completed (20 in the GR group vs. 14 in the control (CON) group). The participants in the GR group were asked to run in minimal shoes (INOV-8 BARE-XF 210) provided by the investigators with forefoot strike patterns during the progressive 12-week GR. Meanwhile, the participants in the CON group were instructed to run in their own running shoes, which they were familiar with, with original foot strike patterns and intensities. The morphological properties of the AT, namely, length and cross-sectional area (CSA), were obtained by using an ultrasound device. A dynamometer was utilized simultaneously to measure and calculate the plantar flexion torque of the ankle, the rate of torque development, the peak force of the AT, and the stress and strain of the AT. Results: After 12-week GR, the following results were obtained: (1) A significant time effect in the peak ankle plantarflexion torque was observed (p = 0.005), showing a 27.5% increase in the GR group; (2) A significant group effect in the CSA was observed (p = 0.027), specifically, the increase in CSA was significantly larger in the GR group than the CON group; (3) A significant time effect in the peak AT force was observed (p = 0.005), showing a 27.5% increase in the GR group. Conclusion: The effect of 12 weeks of GR is an increase in AT CSA, plantar flexor muscle strength of the ankle, and peak AT force during a maximal voluntary isometric contraction test. These changes in AT morphology and function could be positive for tendon health and could prevent future AT injury.

The Immediate Effect of Spinal Manipulation on Ball Velocity and Neuromuscular Function During an Instep Kick in Former Varsity Soccer Players: A Feasibility Study.

Corso, M, Liang, L, Tran, S, Howitt, S, Srbely, J, and Mior, SA. The immediate effect of spinal manipulation on ball velocity and neuromuscular function during an instep kick in former Varsity soccer players: a feasibility study. J Strength Cond Res 36(9): 2558-2565, 2022-Spinal manipulation (SM) has been shown to increase ball velocity (BV) in soccer players. Evidence suggests that SM modulates responses at spinal or cortical levels to enhance force production in asymptomatic populations. No studies have explored the underlying neuromuscular mechanisms contributing to changes in BV post-SM in soccer players. We assessed the feasibility of measuring change in BV and neuromuscular function after SM in former Varsity level soccer players with a pre-post study design. Three to 5 maximal instep kicks were performed before and after SM at the L3-5 level. Ball velocity was measured using high-speed camera. Activation of lower limb and trunk musculature was recorded with electromyography. Outcomes included ease of recruitment, scheduling and data capture, as well as expectation and perception of SM effect and adverse events (AE). Fifteen potential subjects were recruited over 1.5 months. Eleven were scheduled (24-31 years; 8 females, 3 males). Two subjects reported mild AE after maximal voluntary isometric contraction testing. A significant increase in BV (mean change: 1.75 m·s -1 [95% confidence interval: 0.5-3.0]) and a trend to increased peak-activation of knee extensors (90.7%) were observed post-SM. Findings suggest that our recruitment strategy and methodology are feasible in a larger trial with some modifications. Our preliminary findings support previous research by suggesting that increased BV may be mediated through increased activation of knee extensors during the kick. Our findings may offer additional insight into the underlying neuromuscular mechanisms contributing to immediate change in BV post-SM.

How Do Different Forms Of Feedback Effect Maximal Voluntary Force In The Forearm Flexors?

Biofeedback provides a unique stimulus enhancement to the maximal voluntary isometric contraction (MVIC) ability in several muscle groups. However, limited research has investigated the use of biofeedback in the upper extremities specifically, the forearm flexors (FF). PURPOSE: The purpose of this study was to examine whether different methods of biofeedback affect the maximal force achieved during the FF MVIC test. METHODS: Twenty subjects (10 Male) consented to participate in this randomized counter-balanced experiment. In a single visit, subjects were exposed to the following conditions whilst performing the FF MVIC test. These included, 1) Visual and verbal feedback (VIVE); 2) Verbal feedback only (VE); 3) Visual feedback only (VI); and 4) no feedback at all (NOVIVE). Real-time force output was displayed on a monitor for VIVE and VI, and loud standardized verbal encouragement of ‘pull, pull, pull’ was utilized for VIVE and VE. For each condition, a total of three, 5-second MVIC trials were completed with a two-minute rest between each trial. In addition, a 5-minute rest was provided between consecutive conditions. A 4 x 2 repeated measures ANOVA was performed using the peak MVIC (in Newton) with a significance level set at 0.05. Condition (VIVE vs. VE vs. VI vs. NOVIVE) was a within subject factor and sex (Male vs. Female) was a between subject factor. RESULTS: A significant main effect for condition (p<.001) but no interaction was revealed, with follow-up Bonferroni-adjusted pairwise comparisons demonstrating significantly greater force production in the VIVE compared to VE (mean + standard error (SE): 330.80 + 16.09 vs. 310.62 + 15.51, p=.006), and NOVIVE (mean + SE: 330.80 + 16.09 vs. 304.42 + 15.88, p=.001) conditions; as well as, significantly greater force production in the VI compared to VE (mean + SE: 327.24 + 15.84 vs. 310.62 + 15.51, p<.001), and NOVIVE (mean + SE: 327.24 + 15.84 vs. 304.42 + 15.88, p=.004) conditions. CONCLUSIONS: The main finding is that both VIVE and VI biofeedback provide the most effective form of encouragement during FF MVIC tests by demonstrating the greatest force output. Many studies commonly include VE feedback only, however, here we demonstrate the importance of providing VI biofeedback. Therefore, it is suggested that future studies include VIVE feedback during MVIC trials in the FF.

A 90 min Daytime Nap Opportunity Is Better Than 40 min for Cognitive and Physical Performance.

This study examined the effects of different nap durations on attention and physical performance as well as mood states, sleepiness, perceived exertion (RPE), recovery (PRS), and muscle soreness (DOMS) in trained men. Fourteen amateur team sport players (age: 20.3 ± 3.0 years, height: 173.1 ± 6.7 cm, body-mass: 68.1 ± 6.6 kg) performed a maximal voluntary isometric contraction (MVIC) test, 5-m shuttle run, and the digit-cancellation (i.e., attention) test after a no-nap (N0) and 40-min (N40) and 90-min (N90) of nap opportunities. Subjective measurement of mood states, RPE, PRS and DOMS were determined. Compared to N0, both nap durations enhanced attention, MVIC, total distance (TD), and higher distance (HD) (p < 0.001), with a higher gain after N90 compared to N40 for attention (Δ = +3), MVIC (Δ = +30 N) and TD (Δ = +35 m) (p < 0.001). Total mood scores were better after N40 and N90 compared to N0 (p < 0.05), with lower scores after N90 compared to N40 (p < 0.05). DOMS and RPE scores were significantly lower and PRS was significantly higher after N40 and N90 compared to N0 and after N90 compared to N40 (p < 0.05). Although both nap opportunity durations were beneficial, N90 was better than N40 for improving physical performances and attention as well as the perception of recovery, reducing fatigue perception, muscle soreness, and negative mood states.

Effects of knee flexion angles in supine bridge exercise on trunk and pelvic muscle activity

ABSTRACT This study investigated the activity of surface electromyography (sEMG) on trunk and pelvic muscles during supine bridge exercise (SBE) with different knee flexion angles. Twenty-five physically active males participated in this study. Subjects received maximum voluntary isometric contraction (MVIC) tests followed by four SBEs with different knee flexion angles (40°, 60°, 90° and 120°) in random. sEMG activities of rectus abdominis (RA), erector spinae (ER), gluteus medius (GMed), superior gluteus maximus (SGMax), inferior gluteus maximus (IGMax), biceps femoris (BF) long head, and the ratio of SGMax/BF and IGMax/BF on the dominant side were measured. Non-clinical magnitude-based inference was performed to compare the effect. The results indicated a substantial change of muscle activity, especially between SBE with 40° and 120° knee flexion. With respect to ER and BF, moderate effect (−0.70 ± 0.17) and extremely large effect (−4.78 ± 0.51) were recorded, whereas very large effect for SGMax/BF (2.68 ± 0.23) and IGMax/BF (2.95 ± 0.26) was observed, respectively. Both ER and BF worked better with smaller knee flexion angles (40° > 60° > 90° > 120°), while SGMax and IGMax were more favourable to SBE with large knee flexion angles (90° = 120° > 60° > 40°).

Exercícios isométricos possuem alta responsividade para membros inferiores

Introdução: Para a reabilitação pós-cirúrgica do ligamento cruzado anterior, os vastos medial e lateral precisam ser trabalhados visando uma boa recuperação. Discute-se a respeito dos exercícios isométricos e isotônicos a serem utilizados na fase de reabilitação, tendo seus resultados divergentes na literatura. Objetivo: Assim, o objetivo do presente estudo é comparar a ativação dos vastos medial e lateral em exercícios isométricos e isotônicos. Métodos: Participaram deste estudo 11 sujeitos (sete homens e quatro mulheres), fisicamente ativos e com experiência em musculação. Foi realizada a anamnese, a avaliação antropométrica, o teste de carga de 10 repetições máximas (RM), o teste de contração voluntária isométrica máxima e o teste de agachamento. Resultados: No vasto lateral da coxa direita, a atividade eletromiográfica foi significativamente maior na contração voluntária isométrica máxima em relação ao agachamento dinâmico (p&lt;0,05). O mesmo foi observado na coxa esquerda (p&lt;0,05). Conclusão: O recrutamento dos vastos medial e lateral em exercícios isométricos é maior em relação a exercícios isotônicos.

Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

BackgroundRecent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass (UWM) affects the muscular activity of the shoulder stabilizers. Aim of the study was to assess neuromuscular activity of dynamic shoulder stabilizers under four conditions of stable and UWM during three shoulder exercises. It was hypothesized that a combined condition of weight with UWM would elicit greater activation due to the increased stabilization demand.MethodsSixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 s.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different exercise conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root-mean-square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; p ≤ 0.05; Bonferroni adjusted α = 0.008).ResultsPWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p > 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles.ConclusionHigher weight generated greater muscle activation whereas an UWM raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an UWM increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.

Assessment of Hamstring: Quadriceps Coactivation without the Use of Maximum Voluntary Isometric Contraction

This study aimed to study the coactivation patterns of the hamstring and quadriceps muscle groups during submaximal strength exercises commonly used in injury prevention in soccer without the use of maximum voluntary isometric contraction testing. This was used to compare: (i) the inter-limb differences in muscle activation; (ii) the intra-muscular group activation pattern and (iii) the activation pattern during different phases of the exercise. Muscle activation was recorded by surface electromyography in 19 elite, male, youth soccer players. Participants performed the following: Bulgarian squat, lunge and squat. Electrical activity was recorded for the rectus femoris, vastus medialis, vastus lateralis, biceps femoris and semitendinosus. No significant inter-limb differences were found (F1, 13 = 619; p = 0.82; η2 = 0.045). Significant differences were found in the muscle activation between individual muscles within the quadriceps and hamstrings muscle group for each of the exercises: Bulgarian squat (F1,18 = 331: p &lt; 0.001; η2 = 0.80), lunge (F4,72 = 114.5; p &lt; 0.001; η2 = 0.86) and squat (F1,16 = 247.31; p &lt; 0.001; η2 = 0.93). Differences were found between the different phases of each of the exercises (F2,26 = 52.27; p = 0.02; η2 = 0.80). The existence of an activation pattern of each of the muscles in the three proposed exercises could be used for muscle assessment and as a tool for reconditioning post-injury.

Outcome measures in a cohort of ambulatory adults with spinal muscular atrophy.

With the advent of disease-altering therapies for spinal muscular atrophy (SMA), there is a requirement to better characterize outcome measures, particularly in milder forms of disease. Maximal voluntary isometric contraction testing and 6-minute walk test (6MWT) performed in ambulatory SMA adults as part of the SMA-VALIANT trial were analyzed. Test-retest reliability and correlation with other candidate biomarkers and outcomes were investigated. Maximal voluntary isometric contraction testing and 6MWT showed good test-retest reliability (intraclass correlation coefficient = 0.98 and 0.85, respectively). Maximal voluntary isometric contraction testing and 6MWT demonstrated very strong correlation (r = 0.83, P <. 0001), and each correlated with the SMA Functional Rating Scale (r = 0.7, P < .0001 and r = 0.65, P = .0001, respectively), lean muscle mass (r = 0.68, P < .0001 and r = 0.56, P = .001, respectively), and ulnar compound muscle action potential (r = 0.57, P = .0008 and r = 0.47, P = .008, respectively). Maximal voluntary isometric contraction testing and 6MWT are suitable outcomes for use in ambulatory adults with SMA. Maximal voluntary isometric contraction testing may be preferable because of superior test-retest reliability and closer associations with other outcomes and biomarkers of neuromuscular function.

Isometric Exercise with Large Muscle Mass Improves Redox Balance and Blood Pressure in Hypertensive Adults.

The aim of this study was to investigate the hemodynamic, oxidative stress (OS), and nitric oxide (NO) responses to a submaximal isometric exercise session (IES) involving large muscle mass. Fourteen hypertensive (HTG: age = 35.9 ± 8.1 yr, height = 1.73 ± 0.10 m, total body mass = 78.0 ± 15.8 kg) and 10 normotensive (NTG: age = 41.1 ± 9.4 yr, height = 1.71 ± 0.12 m, total body mass = 82.3 ± 22.4 kg) participants performed two experimental sessions in the leg press and bench press: (i) control session and (ii) 8 sets × 1 min contraction at 30% maximal voluntary isometric contraction with 2-min rest interval. Blood pressure (BP) was measured at rest and during 60 min postexercise. Blood samples were collected at rest, immediately after the session, and 60 min postexercise. NO was obtained through the Griess reaction method. OS parameters were analyzed using commercial kits. A repeated-measures ANOVA with Bonferroni post hoc test was used to analyze all dependent variables. A significant decrease in systolic BP was observed only for HTG at 45 and 60 min postexercise (baseline vs 45 min: P = 0.03, Δ% = 4.44%; vs 60 min: P = 0.018, Δ% = 5.58%). NO increased immediately postexercise only for HTG (P = 0.008, Δ% = 16.44%). Regarding OS parameters, thiobarbituric acid reactive substances presented a significant reduction 60 min after the IES for NTG and HTG; catalase increased in both groups. The data showed that only 8 min of IES with a large muscle mass elicits an elevated pro-oxidant activity leading to a greater NO bioavailability, increases antioxidant reaction, and consequently reduces BP in hypertensive patients.

Assessment of neuromuscular activity during maximal isometric contraction in supine vs standing body positions

BackgroundWhen comparing neuromuscular activity between different individuals or different conditions by use of surface electromyography (sEMG) it is necessary to apply standardized assessment protocol. Most frequently used method is the maximum voluntary isometric contraction (MVIC). However, the influence of body posture on sEMG activity during MVIC testing remains largely unknown. AimTo evaluate the MVIC method for sEMG normalization in supine versus standing positions for selected muscles of the lower extremity and trunk. MethodsTwelve healthy individuals participated; five females and seven males (age 22–51 yrs). sEMG signals were recorded bilaterally from mm tibialis anterior, gluteus medius, adductor longus, rectus abdominus, external oblique and internal oblique/transversus abdominus according to standardized test protocol. Two different body positions were used: supine and standing position. ResultsMVIC peak sEMG signal amplitudes did not differ systematically between supine and standing test positions. Pronounced inter-subject variability in MVIC reference sEMG activity were observed between participants, during both supine and standing test positions. ConclusionPresent data demonstrate that MVIC EMG normalization is a biomechanically stable procedure that can be performed in a reproducible manner for the major leg and trunk muscles when comparing supine vs. standing test positions.

Determining the optimal maximal and submaximal voluntary contraction tests for normalizing the erector spinae muscles.

BackgroundThis study aimed to identify which maximum voluntary isometric contraction (MVIC) and sub-MVIC tests produce the highest activation of the erector spinae muscles and the greatest reduction in inter-individual variability, to put them forward as reference normalization maneuvers for future studies.MethodsErector spinae EMG activity was recorded in 38 healthy women during five submaximal and three maximal exercises.ResultsNone of the three MVIC tests generated the maximal activation level in all the participants. The maximal activation level was achieved in 68.4% of cases with the test performed on the roman chair in the horizontal position (96.3 ± 7.3; p < 0.01). Of the five submaximal maneuvers, the one in the horizontal position on the roman chair produced the highest percentage of activation (61.1 ± 16.7; p < 0.01), and one of the lowest inter-individual variability values in the normalized signal of a trunk flexion-extension task.ConclusionsA modified Sorensen MVIC test in a horizontal position on a roman chair and against resistance produced the highest erector spinae activation, but not in 100% of participants, so the execution of several normalization maneuvers with the trunk at different inclinations should be considered to normalize the erector spinae EMG signal. A modified Sorensen test in a horizontal position without resistance is the submaximal maneuver that produces the highest muscle activation and the greatest reduction in inter-individual variability, and could be considered a good reference test for normalization.

Validity and reliability of serratus anterior hand held dynamometry

BackgroundStrength testing of the serratus anterior muscle with hand held dynamometry (HDD) in supine subjects has low reproducibility, and is influenced by compensatory activity of other muscles like the pectoralis major and upper trapezius. Previously, two manual maximum voluntary isometric contraction tests of the serratus anterior muscle were reported that recruited optimal surface electromyography (sEMG) activity in a sitting position. We adapted three manual muscle tests to make them suitable for HHD and investigated their validity and reliability.MethodsTwenty-one healthy adults were examined by two assessors in one supine and two seated positions. Each test was repeated twice. Construct validity was determined by evaluating force production (assessed with HHD) in relation to sEMG of the serratus anterior, upper trapezius and pectoralis major muscles, comparing the three test positions. Intra- and interrater reliability were determined by calculating intra-class correlation coefficients (ICC) smallest detectable change (SDC) and standard error of measurement (SEM).ResultsSerratus anterior muscle sEMG activity was most isolated in a seated position with the humerus in 90° anteflexion in the scapular plane. This resulted in the lowest measured force levels in this position with a mean force of 296 N (SEM 15.8 N). Intrarater reliability yielded an ICC of 0.658 (95% CI 0.325; 0.846) and an interrater reliability of 0.277 (95% CI -0.089;0.605). SDC was 127 Newton, SEM 45.8 Newton.ConclusionThe results indicate that validity for strength testing of the serratus anterior muscle is optimal with subjects in a seated position and the shoulder flexed at 90° in the scapular plane. Intrarater reliability is moderate and interrater reliability of this procedure is poor. However the high SDC values make it difficult to use the measurement in repeated measurements.

Mean muscle activation comparison between fastballs and curveballs with respect to the upper and lower extremity

Baseball research on muscle activity (upper and lower extremity) during the throwing motion is important to understanding pitching mechanics for the future. Therefore, it is the purpose of this research study to compare the lower extremity muscle and upper extremity muscle activation patterns associated with the curveball pitch and the fastball pitch from the stretch position. Twelve skilled (NCAA collegiate level) pitchers volunteered to be in this study, with a mean age of 22.3 ± 4.53 years, mean height of 1.74 ± 0.13 m, and mean mass of 89.0 k ± 10.97 kg. The pitchers were fitted with six surface electromyography (EMG) bipolar electrodes on the stride leg biceps femoris, medial gastrocnemius, ipsilateral side lower trapezius, upper trapezius, triceps brachii and biceps brachii. Each pitcher underwent maximum voluntary isometric contraction (MVIC) testing and then performed the fastball & curveball pitching sequence. All EMG variables of interest were normalized using MVIC data and compared between pitching type. A repeated measures ANOVA was conducted for all muscle activity as well. If significance was found a pairwise analysis (Bonferroni) was performed between pitch type, using SPSS (p 0.05). Significant differences in the mean muscle activity for the fastball and curveball pitched from the stretch were observed. A higher level of muscle activity was found for the stretch fastball when compared to the stretch curveball. This study was able to provide a baseline measurement of muscle activity; however, kinematics and kinetics should be measured in future studies.

Reliability of Motor Unit Behavior during a Maximal Voluntary Isometric Contraction of the Knee Extensors

PURPOSE: To establish the intra- and inter-day reliability of the mean firing rate (MFR) versus recruitment threshold (RT) of the vastus lateralis (VL) during a maximal voluntary isometric contraction (MVIC) of the knee extensor musculature. METHODS: Thirty-two young, healthy males (Mean ± SD; Age: 23 ± 3 years; Height: 176.4 ± 5.9 cm; Weight: 87.3 ± 13.4 kg) reported to the laboratory on three separate occasions, each separated by 6 ± 1 days. Each visit occurred at the same time of day (±1 hour) and consisted of MVIC testing and ramp contractions, during which MU behavior was recorded. Specifically, subjects completed 2 MVIC attempts each separated by approximately 2 min., in the subject’s maximal force (FMAX) was obtained. Following an additional 2 minutes of rest, subjects completed 2 maximal ramp contraction, each separated by 2 minutes of rest, during which MU behavior was recorded through surface electromyography (sEMG). The ramp contraction trajectory consisted of a 3 second quiescent period, followed by a 10 second linear increase to FMAX, a 6 second hold at FMAX, a 5 second linear decrease back to baseline and another 3 second quiescent period. Both relative intra- and inter-day reliability of the MFR versus RT relationship were examined using the intra-class correlation coefficients (ICC2,1). The standard error of measurement (SEM) was calculated as the square root of the mean square error term from the ANOVA table and expressed in the units of measurement. The coefficient of variation (CV) was also calculated by expressing the SEM relative to the grand mean (%). RESULTS: For intra- and inter-day analyses, 16 and 20 subjects met the inclusion criteria and were included in final analyses, respectively. Both intra- and inter-day reliability statistics are presented in Table 1. CONCLUSIONS: The MFR versus RT relationship of the VL demonstrates strong intra- and inter-day reliability during a maximal voluntary contraction in young, healthy men.

Effects of previous carbohydrate supplementation on muscular fatigue: double-blind, randomized, placebo-controlled crossover study

Abstract AIMS The aim of this study was to examine the effects of previous carbohydrate supplementation on high-volume resistance exercise performance METHODS Twenty males physically independent adults aged ≥18 years participated in a double-blind randomized placebo-controlled crossover study. Sixty minutes before the experimental protocol, each participant ingested 0,6 g.kg of body mass-1 of carbohydrate supplementation or placebo. Maximum voluntary isometric contraction tests were performed before and after the dynamic fatigue induction protocol consisting of 10 sets of 8 repetitions of right leg knee extensors at 120o s-1. RESULTS Lower decrement of the isometric peak torque (p<0,001) and of the rate of torque development (p<0,001) was observed in carbohydrate supplementation after the dynamic protocol. Both concentric and eccentric peak torque differed significantly (p<0,001) between carbohydrate supplementation and placebo treatments from the second set, although the slope of the force-repetitions curve was not different between them. Additionally, the carbohydrate supplementation resulted in a lower session rating of perceived exertion (p<0,05). CONCLUSIONS Previous carbohydrate supplementation attenuates muscle fatigue and internal load exercise in a high-volume isokinetic leg protocol.

Effects of ischemic preconditioning on the isometric test variables

Summary Introduction Recent studies reported improvements in aerobic performance after ischemic preconditioning (IPC) compared to a control or placebo condition. However, the effects of IPC on both skeletal maximal muscle strength and power have not been investigated. Summary of facts and results Considering the importance of muscle strength/power production and the potential benefits of IPC, the purpose of this study was to investigate the effects of IPC on peak isometric torque and rate of force development (RFD). Ten participants performed on separated days 4 sets of either ischemic preconditioning (5 min of ischemia [250 mmHg] and 5 min of reperfusion) or placebo (5 min of placebo [10 mmHg] and 5 min of reperfusion) alternated in both lower limbs 30 min before maximal voluntary isometric contraction test. RFD was calculated over time intervals of 0–30, 0–50, and 0–200 ms and peak isometric torque was determined from the torque-time curve. Despite no significant difference, there was a moderate effect of ischemic preconditioning on rate of force development in time intervals of 0–30 ms, small effect in 0–50 ms, and trivial effect of ischemic preconditioning on rate of force development in 0–200 ms and on peak isometric torque. Conclusions Considering that RFD is a key factor of performance in tasks with limited time (

Maturation Related Change in Neuromuscular Component of Force Production in Trained and Untrained Girls

PURPOSE: the main purpose of the present study was to investigate the maturation-related change in neuromuscular components of force production in gymnasts and untrained girls during the maximal voluntary isometric contraction (MVC). METHOD: 60 girls, in two groups of gymnasts and untrained were divided into the three subgroups of preadolescents, adolescents, and adults according to Tanner’s scale. All aspects of study were explained and clarified to all subjects. Then, informed consent forms were completed by subjects (in the child’s group by their parents). After familiarity and initial measurements, each subject performed three maximal voluntary isometric contractions (MVC) of the knee extensor at five different angles to determine the optimal angle of force production. The rate of force development (RFD) was calculated using the torque data. The EMG signal of the rectus femoris muscle was recorded during the MVC test to measure voluntary activation (RMS). RESULTS: The normalization of torque based on body weight eliminated the difference in force between the age groups. These results were similarly observed in the level of RMS and RFD. However, there was a significant difference between the gymnasts and the untrained groups in all variables. CONCLUSION: It seems that the differences in body size are more likely to justify absolute force differences than the neural factors. This is partly supported by the results of RMS and the RFD. Keywords: Preadolescents, Electromyography (EMG), Rate of Force Development (RFD), Maximum Voluntary contraction (MVC) Footnotes 1*Corresponding Author (faculty member of Shahid Beheshti University, Tehran Province, Tehran, District 1, Daneshjou Boulevard, 1983969411)