Age-Related Increases in the Shoulder Strength of High School Wrestlers

This is the publisher's version, also found at http://ehis.ebscohost.com/ehost/detail?vid=4&sid=34ab1967-2aea-457b-b261-e90e7b05e38c%40sessionmgr11&hid=2&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=s3h&AN=20752108The purpose of this investigation was to examine age-related differences in absolute and relative isokinetic shoulder strength of high school wrestlers. A total of 122 high school wrestlers (Mage = 16.31 ± 1.18 yrs) volunteered to be measured for arm flexion and extension strength at the shoulder joint using a Cybex II dynamometer at 30, 180, and 300°-s"'. The sample was divided into four age groups: 13.75-15.00 (n=22), 15.08-16.00 (n=27). 16.08-17.00 (n=34), and 17.08-18.83 years (n=39). The results ofthis study indicated significant increases in absolute and relative arm flexion and extension strength across age when covaried for BW and FFW. In addition, comparisons with previously published data indicated differences between muscle groups in the pattern of strength gains that were dependent upon the speed of muscular contraction and may have been influenced by fiber type distribution characteristics

Isokinetic Peak Torque in Young Wrestlers

This is the publisher's version, also found at http://ehis.ebscohost.com/ehost/detail?vid=3&sid=34ab1967-2aea-457b-b261-e90e7b05e38c%40sessionmgr11&hid=2&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=s3h&AN=20752369The purpose of the present study was to examine age-related changes in isokinetic leg flexion and extension peak torque (PT), PT/body weight (PT/ BW), and F*T/fat-free weight (PT/FFW) in young wrestlers. Male wrestlers (A^ = 108; age M ± SD = 11.3 + 1.5 years) volunteered to be measured for peak torque at 30, 180, and 300° • s'. In addition, underwater weighing was performed to determine body composition characteristics. The sample was divided into six age groups (8.1-8.9, n = 10; 9.0-9.9, n= 11; 10.0-10.9, n = 25; 11.0-11.9, n = 22; 12.0-12.9, n = 28; 13.0-13.9, n= 12), and repeated measures ANOVAs with Tukey post hoc comparisons showed increases across age for PT, PT/BW, and PT/FFW. The results of this study indicated that there were age-related increases in peak torque that could not be accounted for by changes in BW or FFW. It is possible that either an increase in muscle mass per unit of FFW, neural maturation, or both, contributes to the increase in strength across age in young male athletes

Time Course of Changes in Neuromuscular Responses at 30% versus 70% 1 Repetition Maximum during Dynamic Constant External Resistance Leg Extensions to Failure

International Journal of Exercise Science 10(3): 365-378, 2017. The purpose of the current study was to examine the time course of changes in neuromuscular responses from the vastus medialis (VM) during low versus high intensity dynamic constant external resistance (DCER) leg extension muscle actions to failure. Thirteen men performed DCER leg extensions to failure at 30% and 70% 1-repetition maximum (1-RM) as well as 1-RM measurements pretest and posttest. Electromyogaphy and mechanomyographic signals were measured from the VM. There were no differences in neuromuscular responses pretest versus posttest 1-RM. There were time-dependent differences between the 30% and 70% 1-RM protocols. The initial phase of the 30% 1-RM protocol exhibited increases in electromyographic-amplitude and mechanomyographic amplitude, but no changes at 70% 1-RM. The middle phases indicated decreases in mechanomyographic amplitude at 30% 1-RM, but increases in mechanomyographic amplitude at 70% 1-RM. The 70% 1-RM protocol had earlier decrease in mechanomyographic frequency than 30% 1-RM. Both protocols in the final phases exhibited increases in electromyographic amplitude and mechanomyogrpahic-amplitude, but decreases in electromyographic frequency and mechanomyographic frequency. Low and high intensity DCER leg extensions to failure have time-dependent differences in neuromuscular responses during the process of fatigue which suggested that motor unit activation strategies may by influenced by the intensity of a fatiguing workbout. Thus, examining the time course of changes in neuromuscular responses during a fatiguing workbout allowed for the identification of the time-points associated with the onset of fatigue

Applications of the Critical Power Model to Dynamic Constant External Resistance Exercise: A Brief Review of the Critical Load Test

The study and application of the critical power (CP) concept has spanned many decades. The CP test provides estimates of two distinct parameters, CP and W0 , that describe aerobic and anaerobic metabolic capacities, respectively. Various mathematical models have been used to estimate the CP and W0 parameters across exercise modalities. Recently, the CP model has been applied to dynamic constant external resistance (DCER) exercises. The same hyperbolic relationship that has been established across various continuous, whole-body, dynamic movements has also been demonstrated for upper-, lower-, and whole-body DCER exercises. The asymptote of the load versus repetition relationship is defined as the critical load (CL) and the curvature constant is L0 . The CL and L0 can be estimated from the same linear and non-linear mathematical models used to derive the CP. The aims of this review are to (1) provide an overview of the CP concept across continuous, dynamic exercise modalities; (2) describe the recent applications of the model to DCER exercise; (3) demonstrate how the mathematical modeling of DCER exercise can be applied to further our understanding of fatigue and individual performance capabilities; and (4) make initial recommendations regarding the methodology for estimating the parameters of the CL test

Muscle- and Mode-Specific Responses of the Forearm Flexors to Fatiguing, Concentric Muscle Actions

Background: Electromyographic (EMG) and mechanomyographic (MMG) studies of fatigue have generally utilized maximal isometric or dynamic muscle actions, but sport- and work-related activities involve predominately submaximal movements. Therefore, the purpose of the present investigation was to examine the torque, EMG, and MMG responses as a result of submaximal, concentric, isokinetic, forearm flexion muscle actions. Methods: Twelve men performed concentric peak torque (PT) and isometric PT trials before (pretest) and after (posttest) performing 50 submaximal (65% of concentric PT), concentric, isokinetic (60°·s-1), forearm flexion muscle actions. Surface EMG and MMG signals were simultaneously recorded from the biceps brachii and brachioradialis muscles. Results: The results of the present study indicated similar decreases during both the concentric PT and isometric PT measurements for torque, EMG mean power frequency (MPF), and MMG MPF following the fatiguing workbout, but no changes in EMG amplitude (AMP) or MMG AMP. Conclusions: These findings suggest that decreases in torque as a result of fatiguing, dynamic muscle actions may have been due to the effects of metabolic byproducts on excitation–contraction coupling as indicated by the decreases in EMG MPF and MMG MPF, but lack of changes in EMG AMP and MMG AMP from both the biceps brachii and brachioradialis muscles

Effects of intensity on muscle-specific voluntary electromechanical delay and relaxation electromechanical delay

The purposes of this study were to examine: 1) the potential muscle-specific differences in voluntary electromechanical delay (EMD) and relaxation electromechanical delay (R-EMD), and 2) the effects of intensity on EMD and R-EMD during step incremental isometric muscle actions from 10 to 100% maximal voluntary isometric contraction (MVIC). EMD and R-EMD measures were calculated from the simultaneous assessments of electromyography, mechanomyography, and force production from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) during step isometric muscle actions. There were no differences between the VL, VM, and RF for the voluntary EMDE-M (onsets of the electromyographic to mechanomyographic signals), EMDM-F (onsets the mechanomyographic to force production), or EMDE-F (onsets of the electromyographic signal to force production) as well as R-EMDE-M (cessation of electromyographic to mechanomyographic signal), R-EMDM-F (cessation of mechanomyographic signal to force cessation), or R-EMDE-F (cessation of electromyorgraphic signal to force cessation) at any intensity. There were decreases in all EMD and R-EMD measures with increases in intensity. The relative contributions from EMDE-M and EMDM-F to EMDE-F as well as R-EMDE-M and R-EMDM-F to R-EMDE-F remained similar across all intensities. The superficial muscles of the quadriceps femoris shared similar EMD and R-EMD measurements

Co-Activation, Estimated Anterior and Posterior Cruciate Ligament Forces, and Motor Unit Activation Strategies during the Time Course of Fatigue

This study aimed to combine co-activation as well as anterior and posterior cruciate ligament force estimations with the motor unit activation strategies employed by the primary muscles that are involved in the movement at the knee joint. Fourteen male subject performed 25 maximal concentric isokinetic leg extension muscle actions at 120 s-1. Electromyographic and mechanomyographic signals from the vastus lateralis and bicep femoris, as well as force, were used to measure co-activation, and estimated anterior and posterior ligament forces during the time course of fatigue. There were decreases in quadriceps force and increases in hamstring force during the 25 leg extensions. The posterior cruciate ligament force was greater than the anterior cruciate ligament force during each leg extension. Both the posterior and anterior cruciate ligament forces decreased during the 25 leg extensions. Each muscle indicated unique neuromuscular responses, which may explain the decreases in quadriceps force and increases in the hamstring force. The combination of anterior and posterior cruciate ligament force estimation and motor unit activation strategies helped to provide a better understanding of the fatigue-related mechanism that was utilized to avoid injury and increase or maintain joint stability during the time course of fatigue

The Contributions of Arterial Cross‑Sectional Area and Time‑Averaged Flow Velocity to Arterial Blood Flow

Background: Ultrasound has been used for noninvasive assessments of endothelial function in both clinical and athletic settings and to identify changes in muscle blood flow in response to exercise, nutritional supplementation, and occlusion. The purposes of the present study were to examine the reliability and relative contributions of arterial cross‑sectional area and time‑averaged flow velocity to predict muscle blood flow as a result of fatiguing exercise in men and women. Methods: Eighteen healthy men and 18 healthy women performed 50 consecutive eccentric repetitions of the elbow flexors at 60% of their pretest eccentric peak torque at a velocity of 180° s−1. Test‑retest reliability and stepwise linear regression analyses were performed to determine the ability of arterial cross‑sectional area and time‑averaged flow velocity to predict brachial artery muscle blood flow for the men, women, and combined sample. Results: There was no systematic test versus retest mean differences (P \u3e 0.05) for any of the ultrasound determined variables. The two‑variable regression models significantly improved the ability to predict muscle blood flow and were associated with smaller standard error of the estimates (3.7%–10.1% vs. 16.8%–37.0% of the mean baseline muscle blood flow values) compared to the one‑variable models. Conclusions: The findings of the present study supported the use of ultrasound for reliable assessments of arterial diameter, arterial cross‑sectional area, time‑averaged flow velocity, and muscle blood flow from the brachial artery in men and women. Furthermore, time‑averaged flow velocity was a more powerful predictor of muscle blood flow than arterial cross‑sectional area

Effects of fatiguing constant versus alternating intensity intermittent isometric muscle actions on maximal torque and neuromuscular responses

Objective: To determine the effects of constant versus alternating applications of torque during fatiguing, intermittent isometric muscle actions of the leg extensors on maximal voluntary isometric contraction (MVIC) torque and neuromuscular responses. Methods: Sixteen subjects performed two protocols, each consisting of 50 intermittent isometric muscle actions of the leg extensors with equal average load at a constant 60% MVIC or alternating 40 then 80% (40/80%) MVIC with a work-to-rest ratio of 6-s on and 2-s off. MVIC torque as well as electromyographic signals from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) and mechanomyographic signals from the VL were recorded pretest, immediately posttest, and 5-min posttest. Results: The results indicated that there were no time-related differences between the 60% MVIC and 40/80% MVIC protocols. The MVIC torque decreased posttest (22 to 26%) and remained depressed 5-min posttest (9%). There were decreases in electromyographic frequency (14 to 19%) and mechanomyographic frequency (23 to 24%) posttest that returned to pretest levels 5-min posttest. There were no changes in electromyographic amplitude and mechanomyogrpahic amplitude. Conclusions: These findings suggested that these neuromuscular parameters did not track the fatigue-induced changes in MVIC torque after 5-min of recovery

The validity of the EMG and MMG techniques to examine muscle hypertrophy

Objective: The purpose of this investigation was to examine the ability of the electromyographic (EMG) and mechanomyographic (MMG) amplitude versus torque relationships to track group and individual changes in muscle hypertrophy as a result of resistance training. Approach: Twelve women performed four weeks of forearm flexion blood flow restriction (BFR) resistance training at a frequency of three times per week. The training was performed at an isokinetic velocity of 120°∙s−1 with a training load that corresponded to 30% of concentric peak torque. Muscle hypertrophy was determined using ultrasound-based assessments of muscle cross-sectional area from the biceps brachii. Training-induced changes in the slope coefficients of the EMG amplitude and MMG amplitude versus torque relationships were determined from the biceps brachii during incremental (10%–100% of maximum) isometric muscle actions. Main results: There was a significant (p \u3c 0.001; d = 2.15) mean training-induced increase in muscle cross-sectional area from 0 week (mean ± SD = 5.86 ± 0.65 cm2) to 4 weeks (7.42 ± 0.80 cm2), a significant (p = 0.023; d = 0.36) decrease in the EMG amplitude versus torque relationship (50.70 ± 20.41 to 43.82 ± 17.76 μV∙Nm−1), but no significant (p = 0.192; d = 0.17) change in the MMG amplitude versus torque relationship (0.018 ± 0.009 to 0.020 ± 0.009 m∙s−2∙Nm−1). There was, however, great variability for the individual responses for the EMG and MMG amplitude versus torque relationships. Significance: The results of the present study indicated that the EMG amplitude, but not the MMG amplitude versus torque relationship was sensitive to mean changes in muscle cross-sectional area during the early-phase of resistance training. There was, however, great variability for the individual EMG amplitude versus torque relationships that limits its application for identifying individual changes in muscle hypertrophy as a result of BFR