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.

Acute Effects of Concentric vs. Eccentric Exercise on Force Steadiness and Electromyographic Responses of the Forearm Flexors

The purpose of this study was to examine the acute effects of concentric (CON) vs. eccentric (ECC) exercise on isometric strength, force steadiness, and surface electromyographic (EMG) responses of the forearm flexors. Fifteen resistance-trained men (mean ± SD: age = 23.7 ± 3.5 years; height = 178.9 ± 4.7 cm; body weight = 86.2 ± 9.8 kg) performed 6 sets of 10 maximal CON isokinetic or ECC isokinetic muscle actions using the dominant forearm flexors on 2 separate experimental visits. Before and immediately after the exercise interventions, isometric strength testing and submaximal trapezoid isometric contractions were performed, with bipolar EMG signals detected from the biceps brachii. The coefficient of variation of the force output from the mid 8-second portion of each submaximal trapezoid isometric contraction was calculated to assess force steadiness. In addition, the EMG signal was selected from the same portion as the force signal. The results showed that both CON and ECC caused similar isometric strength losses, but ECC caused a greater loss of force steadiness than CON. In addition, EMG amplitude increased similarly after both exercise interventions, but the magnitude of the increase in EMG mean frequency after ECC tended to be smaller, when compared with that after CON. These findings suggested that, even for resistance-trained individuals that are more resistant to ECC exercise-induced muscle damage than untrained individuals, their ability to maintain a steady submaximal force can be impaired after a bout of ECC exercise.

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.

The effects of anatabine on non-invasive indicators of muscle damage: a randomized, double-blind, placebo-controlled, crossover study

BackgroundAnatabine (ANA), a minor tobacco alkaloid found in the Solanaceae family of plants, may exhibit anti-inflammatory activity, which may be useful to aid in recovery from exercise-induced muscle damage. The purpose of this study, therefore, was to examine the effects of ANA supplementation on the recovery of isometric strength and selected non-invasive indicators of muscle damage.MethodsA double-blinded, placebo-controlled, crossover design was used to study eighteen men (mean ± SD age = 22.2 ± 3.1 yrs; body mass = 80.3 ± 15.7 kg) who participated in two randomly-ordered conditions separated by a washout period. The ANA condition consisted of consuming 6–12 mg anatabine per day for 10 days, while testing took place during days 7–10. The placebo (PLA) condition was identical except that the PLA supplement contained no ANA. Maximal voluntary isometric peak torque (PT) of the forearm flexors, arm circumference, hanging joint angle, and subjective pain ratings were measured before (PRE), immediately after (POST), and 24, 48, and 72 h after six sets of 10 maximal, eccentric isokinetic forearm flexion muscle actions. Resting heart rate and blood pressure were measured at PRE and 72 h in each condition.ResultsFor PT, hanging joint angle, arm circumference, and subjective pain ratings, there were no condition x time (p > 0.05) interactions, there were no main effects for condition (p > 0.05), but there were main effects for time (p < 0.001). There were no condition x time (p > 0.05) interactions and no main effects for condition (p > 0.05) or time (p > 0.05) for blood pressure or resting heart rate.ConclusionsANA supplementation had no effect on the recovery of muscle strength, hanging joint angle, arm swelling, or subjective pain ratings after a bout of maximal eccentric exercise in the forearm flexors. Therefore, ANA may not be beneficial for those seeking to improve recovery from heavy eccentric exercise. Future studies should examine the effects of ANA on the pro-inflammatory cytokine responses to exercise-induced muscle damage and the chronic low-grade inflammation observed in obese and elderly individuals.

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.

Torque-related changes in mechanomyographic intensity patterns for the superficial quadriceps femoris muscles

The purpose of this study was to investigate changes in mechanomyographic (MMG) intensity patterns for the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) during submaximal to maximal concentric isokinetic, eccentric isokinetic and isometric muscle actions of the leg extensors. Eleven men (mean ± SD age = 20.1 ± 1.1 years) performed concentric, eccentric and isometric muscle actions of the dominant leg extensors on 3 separate days. Surface MMG signals were detected from the VL, RF and VM, processed with a wavelet analysis and examined with a trend plot. The results indicated that the trend plot was capable of tracking systematic changes in MMG amplitude and frequency with an increase in torque. However, these changes were statistically significant in only 26% of the cases. There were also no consistent differences between muscles or contraction types for the significance of the trend plots.

Neural Contributions to Concentric vs. Eccentric Exercise–Induced Strength Loss

The purpose of this study was to examine the strength, electromyographic (EMG), and mechanomyographic (MMG) responses after workouts designed to elicit fatigue and muscle damage vs. only fatigue. Thirteen men (mean ± SD age = 23.7 ± 2.2 years) performed 6 sets of 10 maximal concentric isokinetic (CONexercise) or eccentric isokinetic (ECCexercise) muscle actions of the dominant forearm flexors on 2 separate days. Before (PRE) and after (POST) these workouts, peak torque (PT), surface EMG, and MMG signals were measured during maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the forearm flexors. The subjects also visited the laboratory for a control (CTL) visit with quiet resting between the PRE and POST measurements, rather than performing the CONexercise or ECCexercise. The results showed that there were significant 26 and 25% decreases in PT after the CONexercise and ECCexercise, respectively, and these decreases were statistically equivalent for the concentric, eccentric, and isometric muscle actions. There were also 19 and 23% reductions in normalized EMG amplitude after the CONexercise and ECCexercise, respectively, but no changes in EMG mean frequency (MNF), MMG amplitude, or MMG MNF. These findings demonstrated a neural component(s) to the strength decrement after CONexercise and ECCexercise. It is possible that after these 2 types of exercise, activation of free nerve endings that are sensitive to muscle damage and pH changes resulted in inhibition of alpha motor neurons, causing decreased muscle activation and torque. These findings suggest that training programs designed to minimize strength loss during competition should consider the fact that at least some of this loss is because of neural factors.

Vastus lateralis oxygenation dynamics during maximal fatiguing concentric and eccentric isokinetic muscle actions

The present study aimed to assess whether high intensity exhaustive eccentric (ECC) exercise was associated with a greater decrease in muscle oxygenation compared to high intensity exhaustive concentric (CON) exercise during maximal isokinetic knee extensions. On two separate days, ten recreationally active participants performed maximal isokinetic concentric (KE CON) and eccentric (KE ECC) knee extension exercises at 60° s −1 until exhaustion. Muscle oxygenation profile and activity were acquired continuously from the vastus lateralis (VL) muscle using near-infrared spectroscopy, along with surface electromyography (sEMG). The torque output was significantly greater during KE ECC ( P < 0.01). Total time to exhaustion was longer in ECC condition ( P < 0.01). The decrease in tissue oxygenation index observed between the beginning and end-exercise values was significantly greater during KE ECC than during KE CON ( P < 0.05) while total haemoglobin volume did not differ significantly. KE ECC resulted in a significant increase in end-exercise integrated sEMG ( P < 0.05). We propose that the associated higher intramuscular pressure may have compressed blood vessels and led to a greater decrease in tissue oxygenation index. The observed end-exercise increase in neural drive during KE ECC may have occurred to prevent from muscle performance decrease. These results suggest that, over time, repeated maximal ECC actions induce a greater O 2 extraction compared to maximal CON actions.

An examination of mechanomyographic signal stationarity during concentric isokinetic, eccentric isokinetic and isometric muscle actions

The purpose of the present study was to examine the stationarity of surface mechanomyographic (MMG) signals from the vastus lateralis, rectus femoris and vastus medialis during concentric isokinetic, eccentric isokinetic and isometric muscle actions of the leg extensors. Eleven healthy men (mean ± SD age = 20.1 ± 1.1 years) performed submaximal to maximal concentric isokinetic, eccentric isokinetic and isometric muscle actions of the leg extensors, and surface MMG signals were detected from the vastus lateralis, rectus femoris and vastus medialis. All surface MMG signals were tested for stationarity with a procedure that examined changes in the mean value, variance, mean frequency and standard deviation of the power spectrum over time. The results showed that the three muscle action types resulted in similar levels of signal nonstationarity. Thus, despite the fact that the isometric muscle actions were performed at a constant force level and with no change in muscle length, the level of signal nonstationarity was similar to that for the concentric and eccentric isokinetic muscle actions. Future studies need to be done to identify the mechanism(s) causing MMG signal nonstationarity during isometric muscle actions.

Concentric and eccentric isokinetic muscle activity separated by paired pattern classification of wavelet transformed mechanomyograms

It was hypothesized that concentric and eccentric isokinetic muscle actions should yield detectable differences in the mechanomyograms, which may reflect properties of the contraction and relaxation phases of the muscles. A paired pattern classification technique was adapted to determine whether wavelet transformed mechanomyograms from the three superficial quadriceps muscles were different during maximal concentric and eccentric isokinetic muscle actions. Mechanomyograms for this study were recorded from eleven healthy men (mean ± SD age = 20.1 ± 1.1 yrs) who performed maximal concentric and eccentric isokinetic muscle actions of the dominant leg extensors at a velocity of 30° s −1. The results indicated that the paired pattern classification accurately classified the MMG intensity patterns in approximately 94% of the cases as being from a concentric or eccentric movement. Thus, it can be concluded that the differences in the intensity patterns recorded from concentric and eccentric muscle actions were significant. These findings indicated that the combined MMG wavelet analysis and pattern classification techniques could potentially be useful in situations where muscle activity during concentric muscle actions must be distinguished from that during eccentric muscle actions.

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.

The effects of interelectrode distance over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus concentric, eccentric, and isometric torque relationships for the vastus lateralis muscle

The purpose of this study was to examine the influence of interelectrode distance (IED) over the estimated innervation zone (IZ) for the vastus lateralis muscle and normalization on the torque-related patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the leg extensors. Eight men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously with two bipolar electrode arrangements in single differential configuration (20 and 40 mm IEDs) placed over the estimated IZ for the vastus lateralis muscle and a third electrode arrangement in single differential configuration (20 mm IED) placed distal to the estimated IZ. The results indicated that there were only a few (six of 90 statistical comparisons) significant ( p < 0.05) mean differences among the three electrode arrangements for absolute EMG amplitude. There were no mean differences among the three electrode arrangements for absolute or normalized EMG MPF values or normalized EMG amplitude for the three types of muscle actions. Thus, it may be possible to reduce the potential influence of the IZ on amplitude and spectral parameters of the EMG signal through normalization.

A New Wavelet-based Technique For Analyzing Surface Mechanomyographic Signals

PURPOSE: Wavelet-based signal processing methods have become popular techniques for analyzing nonstationary electromyographic (EMG) signals. The purpose of this study was to introduce a new wavelet analysis designed specifically for processing surface mechanomyographic (MMG) signals. METHODS: The MMG wavelet analysis uses a filter bank of eleven nonlinearly scaled wavelets that maintain a nearly constant relationship between time and frequency resolution across the entire frequency range for MMG. The analysis was tested on nonstationary MMG signals recorded during concentric and eccentric isokinetic muscle actions, as well as a nonstationary MMG test signal. The results from the MMG wavelet analysis were also compared with those from the short-time Fourier transform (STFT), Wigner-Ville transform, and continuous wavelet transform (CWT). RESULTS: The results indicated that unlike the STFT, Wigner-Ville transform, and CWT, the MMG wavelet analysis resolved the intensity, timing, and frequencies of events in the MMG signals without generating interference terms. Furthermore, the MMG wavelet spectra were similar in shape to those calculated with Fourier-based algorithms, such as the discrete Fourier transform (DFT) and fast Fourier transform (FFT). CONCLUSIONS: The results from this study indicated that the MMG wavelet analysis provided advantages over the STFT, Wigner-Ville transform, and CWT. Specifically, the MMG wavelet analysis resolved the intensity, timing, and frequencies of the events in nonstationary MMG signals without generating interference terms. Thus, the analysis is well suited for processing nonstationary MMG signals, such as those recorded during concentric and eccentric isokinetic muscle actions, isometric ramp muscle actions, and cycle ergometry.

The influence of electrode placement over the innervation zone on electromyographic amplitude and mean power frequency versus isokinetic torque relationships

The purpose of this investigation was to examine the influence of electrode placement over the estimated innervation zone (IZ) for the vastus lateralis, as well as proximal and distal to the estimated IZ, on the torque-related patterns for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric and eccentric isokinetic muscle actions of the leg extensors. Eleven men performed randomly ordered, submaximal to maximal concentric and eccentric isokinetic muscle actions of the dominant leg extensors in 10% increments from 10 to 90% peak torque (PT). Surface EMG signals were recorded simultaneously from the vastus lateralis muscle with bipolar electrode arrangements placed over the estimated IZ, as well as proximal and distal to the estimated IZ. The results indicated that there were no consistent differences among the proximal, IZ, and distal electrode placement sites for the patterns of responses for absolute and normalized EMG amplitude and MPF versus torque, or the mean absolute and normalized EMG amplitude and MPF values. Thus, these findings suggested that during concentric and eccentric isokinetic muscle actions of the leg extensors, electrode placement over the estimated IZ for the vastus lateralis had no effect on the patterns of responses or mean values for absolute and normalized EMG amplitude and MPF versus torque.

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.

Acute Effects of Static Stretching on Maximal Eccentric Torque Production in Women

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and the joint angle at PT during maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors at 60 and 180 degrees x s(-1) for the stretched and unstretched limbs in women. Thirteen women (mean age +/- SD = 20.8 +/- 0.8 yr; weight +/- SD = 63.3 +/- 9.5 kg; height +/- SD = 165.9 +/- 7.9 cm) volunteered to perform separate maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors with the dominant and nondominant limbs on a Cybex 6000 dynamometer at 60 and 180 degrees x s(-1). PT (Nm) and the joint angle at PT (degrees) were recorded by the dynamometer software. Following the initial isokinetic assessments, the dominant leg extensors were stretched (mean stretching time +/- SD = 21.2 +/- 2.0 minutes) using 1 unassisted and 3 assisted static stretching exercises. After the stretching (4.3 +/- 1.4 minutes), the isokinetic assessments were repeated. The statistical analyses indicated no changes (p > 0.05) from pre- to poststretching for PT or the joint angle at PT. These results indicated that static stretching did not affect PT or the joint angle at PT of the leg extensors during maximal, voluntary, eccentric isokinetic muscle actions at 60 and 180 degrees x s(-1) in the stretched or unstretched limbs in women. In conjunction with previous studies, these findings suggested that static stretching may affect torque production during concentric, but not eccentric, muscle actions.

Comparison of the fast Fourier transform and continuous wavelet transform for examining mechanomyographic frequency versus eccentric torque relationships

The purpose of this study was to compare the eccentric torque-related patterns for mechanomyographic (MMG) center frequencies (mean power frequency (MPF), median frequency (MDF), and average instantaneous mean power frequency (AIMPF)) determined by the fast Fourier transform (FFT) and continuous wavelet transform (CWT). Eight adults (mean ± S.D. age = 22.5 ± 2.4 years) performed submaximal to maximal, eccentric isokinetic muscle actions of the biceps brachii on a Cybex 6000 dynamometer. The mean MMG MPF, MDF, and AIMPF values for both the absolute and normalized data from 10 to 100% eccentric peak torque (PT) were highly intercorrelated at r = 0.908–0.985. Linear models provided the best fit for the absolute MMG MPF ( r = 0.873), MDF ( r = 0.831), and AIMPF ( r = 0.924), as well as normalized MMG MPF ( r = 0.869), MDF ( r = 0.816), and AIMPF ( r = 0.920) versus percentage eccentric PT relationships. There were no significant differences ( p > 0.05) among the linear slope coefficients for the MMG MPF, MDF, and AIMPF versus percentage eccentric PT relationships for either the absolute or normalized data. These results suggested that Fourier or wavelet transform procedures can be used to examine the patterns of MMG responses during eccentric muscle actions of the biceps brachii.

Relationships For Mechanomyographic Amplitude And Mean Power Frequency Vs. Torque During Isometric And Eccentric Isokinetic Muscle Actions

PURPOSE To examine the mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus torque relationships during isometric and eccentric isokinetic muscle actions. METHODS Eight women (mean age/SD = 20.4/1.3 y) volunteered to perform isometric and eccentric isokinetic leg extension muscle actions at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of maximal voluntary contraction (MVC) and peak torque (PT) on a Cybex 6000 dynamometer. An accelerometer (Entran, EGAS-FT-10- /V05) was placed on the vastus medialis to detect the MMG signal. The amplitude of the MMG signal was expressed as root mean square (rms), while frequency data were expressed as mean power frequency (MPF). Torque (Nm) was recorded by the dynamometer. RESULTS Polynomial regression analyses indicated that the relationship for MMG amplitude versus MVC was linear (r∧2 = 0.930) for the isometric muscle actions, but there was no significant relationship between MMG amplitude and PT for the eccentric isokinetic muscle actions. For the isometric and eccentric isokinetic muscle actions, the MMG MPF versus % MVC or % PT relationships were linear (r∧2 = 0.957 and 0.920, respectively). CONCLUSIONS The different torque-related responses for MMG amplitude and MPF may reflect differences in the motor control strategies that modulate torque production for isometric versus eccentric isokinetic muscle actions. These results suggested that isometric torque production was modulated by a combination of recruitment and firing rate, while eccentric isokinetic torque production was modulated primarily through firing rate.