Maximal Eccentric Isokinetic Muscle Actions Research Articles

Velocity-Dependent Changes in Electrical Efficiency of the Leg Extensors during Eccentric Isokinetic Muscle Actions.

The mechanisms underlying velocity-specific decreases in torque production during eccentric muscle actions remain unclear. Therefore, the purpose of the present study was to examine electrical efficiency at 60 and 180°·s -1 during fatiguing, maximal eccentric isokinetic muscle actions of the leg extensors. Thirteen men visited the lab on two occasions and randomly performed 30 repeated maximal eccentric isokinetic muscle actions of the leg extensors at 60 and 180°·s - ¹ through a 90° range of motion. Polynomial regression analyses and separate repeated measures ANOVAs were used to examine the composite patterns of responses for electromyographic amplitude, eccentric torque, and electrical efficiency across the 60 and 180°·s - ¹ protocols. Eccentric torque remained unchanged across the 30 maximal eccentric muscle actions performed at 60 and 180°·s -1. Electromyographic amplitude and electrical efficiency, however, increased linearly across the 180°·s -1 protocol, but there were no changes for either electromyographic amplitude or electrical efficiency during the 60°·s -1 fatiguing protocol. These findings indicated that performing eccentric muscle actions at a fast velocity (i. e., 180°·s -1) was characterized by greater efficiency (i. e., decreased electrical efficiency) compared to eccentric muscle actions performed at a slow velocity (i. e., 60°·s -1). Thus, it is possible that eccentric muscle actions performed at fast velocities are more robust to fatigue due, in part, to greater efficiency compared to slow-velocity eccentric muscle actions.

Differential Effects of Unilateral Concentric Vs. Eccentric Exercise on the Dominant and Nondominant Forearm Flexors.

The purpose of this study was to compare the electromyographic (EMG) intensity patterns after unilateral concentric vs. eccentric exercise in the dominant (DOM) and nondominant (NONDOM) forearm flexors. Twenty-six men (mean ± SD: age, 24.0 ± 3.7 years) volunteered to perform a maximal isometric muscle action of the DOM and NONDOM forearm flexors before (PRE) and immediately after (POST) a series of maximal concentric isokinetic or maximal eccentric isokinetic muscle actions of the DOM forearm flexors. The concentric isokinetic and eccentric isokinetic muscle actions were performed on separate days that were randomly ordered. However, in both cases, the subjects performed 6 sets of 10 maximal muscle actions. A bipolar surface EMG signal was detected from the biceps brachii of the DOM and NONDOM limbs during the PRE and POST isometric muscle actions. The signals were then analyzed with a wavelet analysis, and the resulting intensity patterns were classified with a paired pattern classification procedure. The results indicated that the EMG intensity patterns could be correctly classified into their respective PRE vs. POST categories with an accuracy rate that was significantly better than random (20 of 26 patterns = 76.9% accuracy) but only for the DOM limb following the eccentric muscle actions. All other classifications were not significantly better than random. These findings indicated that eccentric exercise had a significant influence on the muscle activation pattern for the forearm flexors. It is possible that the muscle damage resulting from eccentric exercise affects muscle spindle or golgi tendon organ or both activity, thereby altering the muscle activation pattern.

The Rate of Torque Development: A Unique, Non-invasive Indicator of Eccentric-induced Muscle Damage?

This study examined the time courses of recovery for isometric peak torque and rate of torque development (RTD) after eccentric-induced muscle damage. 18 men completed 6 sets of 10 maximal eccentric isokinetic muscle actions at 30° · s(-1). Peak torque, peak RTD and RTD at 10 (RTD10), 50 (RTD50), 100 (RTD100) and 200 ms (RTD200), serum creatine kinase and lactate dehydrogenase were measured before (PRE), immediately after (POST), 24, 48 and 72 h after eccentric exercise. Creatine kinase and lactate dehydrogenase increased from 139 to 6 457 and from 116 to 199 IU · L(-1) from PRE to 72 h, respectively. Peak torque and all RTDs decreased at POST. Peak torque and RTD200 remained lower than PRE through 72 h. Peak RTD remained lower than PRE through 48 h, but was not different from PRE at 72 h. RTD10 and RTD100 were lower than PRE through 24 h, but were not different from PRE at 48 and 72 h. RTD50 decreased at POST, but was not different from PRE at 24 h. Early phase RTDs recovered more quickly than PT and RTD200. Early phase RTDs may reflect neural mechanisms underlying eccentric-induced force decrements, while late RTDs may describe the same physiological mechanisms as PT.

Effects of anatabine and unilateral maximal eccentric isokinetic muscle actions on serum markers of muscle damage and inflammation

The purpose of this study was to examine the effects of anatabine supplementation in conjunction with unilateral, maximal eccentric isokinetic muscle actions on serum markers of muscle damage and pro-inflammatory cytokines in humans. Seventeen men (mean±S.D. age=22.4±3.2 yrs) participated in this double-blinded, placebo-controlled, crossover study. Participants were randomly assigned to two 10-day conditions (anatabine and placebo) separated by a 2–4 week washout period. After seven days of supplementation, blood was sampled immediately prior to PRE, immediately following POST, and 24, 48, and 72h after 6 sets of 10 repetitions of unilateral, maximal eccentric isokinetic forearm flexion exercise. Concentrations of serum creatine kinase, lactate dehydrogenase, myoglobin, high sensitivity c-reactive protein, and TNF-α were measured. Creatine kinase, myoglobin, and lactate dehydrogenase increased (P<0.05), while high sensitivity c-reactive protein and TNF-α did not change (P>0.05) after the eccentric exercise during both conditions. Lactate dehydrogenase was higher (P<0.05) during the anatabine condition. The primary findings of this study were two-fold: (a) anatabine had no beneficial effects on traditional markers of muscle damage (creatine kinase, lactate dehydrogenase, and myoglobin) compared to placebo after the eccentric exercise protocol, and (b) the eccentric exercise protocol did not elicit increase in the pro-inflammatory cytokines (c-reactive protein and TNF-α). Future studies are needed to examine the effects of anatabine on naturally-occurring inflammation that is common with aging or obesity. Furthermore, additional research is needed to examine the relationship between muscle damage and inflammation after eccentric exercises of different modes, durations, and intensities.

Eccentric exercise does not affect common drive in the biceps brachii

The purpose of this study was to investigate the effects of eccentric exercise on common drive. Eleven men, age 23.6 ± 2.1 (mean ± SD) years, performed trapezoid isometric muscle actions of the dominant forearm flexors immediately before and after 1 of 2 interventions: (a) 6 sets of 10 maximal eccentric isokinetic muscle actions of the forearm flexors; or (b) 10 minutes of quiet resting. Surface electromyographic signals were recorded from the biceps brachii and decomposed into individual motor unit action potential trains. Mean firing rate patterns were calculated for each motor unit, and all possible combinations were cross-correlated to measure common drive. The peak cross-correlation coefficients were generally in the 0.2-0.5 range and occasionally as high as 0.7. These coefficients were not, however, affected by the eccentric exercise, despite a 19.5% decrease in strength, indicating that the eccentric exercise did not affect common drive. Muscle Nerve, 2012.

Effect of Magnesium Supplementation in Isokinetic Knee-Flexion in Elite Volleyball Players

Magnesium is involved in various processes that affect muscle function including energy production and electrolyte balance. The relationship between magnesium status and exercise has received significant attention in the past decade, and supplementation, in order to improve performance, is a discussed subject. PURPOSE: To evaluate if magnesium supplementation improves muscle strength in well trained athletes. METHODS: Nine male athletes (23+2yrs), from a professional volleyball adult team, were randomly assigned to two experimental groups, double-blind: magnesium supplementation (500mg magnesium oxide capsules per day, five athletes) and control (500mg maltodextrin capsules per day, four athletes) during a four-week period. At t=0 and t=30days the athletes performed maximal eccentric isokinetic muscle actions of the dominant and nondominant knee extensor muscles at 60 degrees x s(-1) on a isokinetic dynamometer (Biodex). RESULTS: After the experimental period the supplemented group had left and right knee flexion peak torque greater than the control (196+19 vs. 170+13N·m, p=0.06) and (202+19 vs. 176+20N·m, p=0.11) respectively. CONCLUSIONS: The magnesium supplementation indicates an increase in the performance when evaluated for isokinetic knee-flexion. These differences had statistical significance (at the 0.15 level of significance), what recommends an evaluation with a larger sample. This study was supported by CNPq, grant nr. 142618/2005-5.

Mechanomyographic and Electromyographic Responses During Submaximal to Maximal Eccentric Isokinetic Muscle Actions of the Biceps Brachii

The purpose of this investigation was to determine the mechanomyography (MMG) and electromyography (EMG) amplitude and mean power frequency (MPF) vs. eccentric isokinetic torque relationships for the biceps brachii muscle. Nine adults (mean +/- SD age = 23.1 +/- 2.9 years) performed submaximal to maximal eccentric isokinetic muscle actions of the dominant forearm flexors. After determination of isokinetic peak torque (PT), the subjects randomly performed submaximal step muscle actions in 10% increments from 10 to 90% PT. Polynomial regression analyses indicated that the MMG amplitude vs. eccentric isokinetic torque relationship was best fit with a quadratic model (R(2) = 0.951), where MMG amplitude increased from 10 to 60% PT and then plateaued from 60 to 100% PT. There were linear increases in MMG MPF (r(2) = 0.751) and EMG amplitude (r(2) = 0.988) with increases in eccentric isokinetic torque, but there was no significant change in EMG MPF from 10 to 100% PT. The results suggested that for the biceps brachii, eccentric isokinetic torque was increased to approximately 60% PT through concurrent modulation of the number of active motor units and their firing rates, whereas additional torque above 60% PT was produced only by increases in firing rates. These findings contribute to current knowledge of motor-control strategies during eccentric isokinetic muscle actions and could be useful in the design of training programs.

Mechanomyographic responses to maximal eccentric isokinetic muscle actions.

The purpose of the present investigation was to examine the mechanomyographic (MMG) responses to maximal eccentric isokinetic muscle actions. Eight adult male volunteers [age 22 +/- 2 (SD) yr] performed maximal eccentric muscle actions of the leg extensors at 60, 90, 120, and 180 degrees /s on a Cybex 6000 isokinetic dynamometer. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. Test-retest intraclass correlations ranged from R = 0.88 to 0.97 for peak torque and from R = 0.97 to 0.98 for root mean square MMG amplitude values. There was no significant (P > 0.05) velocity-related change in eccentric peak torque; however, there was a significant (P < 0.05) increase in MMG between 60 [119 +/- 44 (SE) mV] and 180 degrees/s (302 +/- 128 mV). These findings indicated a velocity-related dissociation between MMG and peak torque for maximal eccentric isokinetic muscle actions.