Isokinetic Leg Extension Research Articles

Effects of Creatine Supplementation and Three Days of Resistance Training on Muscle Strength, Power Output, and Neuromuscular Function

Previous studies have demonstrated increases in peak torque (PT) and decreases in acceleration time (ACC) after only 2 days of resistance training, and other studies have reported improvements in isokinetic performance after 5 days of creatine supplementation. Consequently, there may be a combined benefit of creatine supplementation and short-term resistance training for eliciting rapid increases in muscle strength, which may be important for short-term rehabilitation and return-to-play for previously injured athletes. The purpose of this study, therefore, was to examine the effects of 3 days of isokinetic resistance training combined with 8 days of creatine monohydrate supplementation on PT, mean power output (MP), ACC, surface electromyography (EMG), and mechanomyography (MMG) of the vastus lateralis muscle during maximal concentric isokinetic leg extension muscle actions. Twenty-five men (mean age +/- SD = 21 +/- 3 years, stature = 177 +/- 6 cm, and body mass = 80 +/- 12 kg) volunteered to participate in this 9-day, double-blind, placebo-controlled study and were randomly assigned to either the creatine (CRE; n = 13) or placebo (PLA; n = 12) group. The CRE group ingested the treatment drink (280 kcal; 68 g carbohydrate; 10.5 g creatine), whereas the PLA group received an isocaloric placebo (70 g carbohydrate). Two servings per day (morning and afternoon) were administered in the laboratory on days 1-6, with only 1 serving on days 7-8. Before (pre; day 1) and after (post; day 9) the resistance training, maximal voluntary concentric isokinetic leg extensions at 30, 150, and 270 degrees x s(-1) were performed on a calibrated Biodex System 3 dynamometer. Three sets of 10 repetitions at 150 degrees x s(-1) were performed on days 3, 5, and 7. Peak torque increased (p = 0.005; eta(2) = 0.296), whereas ACC decreased (p < 0.001; eta(2) = 0.620), from pretraining to posttraining for both the CRE and PLA groups at each velocity (30, 150, and 270 degrees x s(-1)). Peak torque increased by 13% and 6%, whereas ACC decreased by 42% and 34% for the CRE and PLA groups, respectively, but these differences were not statistically significant (p > 0.05). There were no changes in MP, EMG, or MMG amplitude; however, EMG median frequency (MDF) increased, and MMG MDF increased at 30 degrees x s(-1), from pretraining to posttraining for both the CRE and PLA groups. These results indicated that 3 days of isokinetic resistance training was sufficient to elicit small, but significant, improvements in peak strength (PT) and ACC for both the CRE and PLA groups. Although the greater relative improvements in PT and ACC for the CRE group were not statistically significant, these findings may be useful for rehabilitation or strength and conditioning professionals who may need to rapidly increase the strength of a patient or athlete within 9 days.

The Effects of Three Days of Velocity-Specific Isokinetic Training on Strength in the Trained and Untrained Limb

PURPOSE: To examine the effects of three days of velocity-specific isokinetic training on peak torque (PT) in the trained and untrained limbs. METHODS: Twenty-seven adult females were randomly assigned to a slow velocity training (S VT; n = 9), fast velocity training (FVT; n = 9), or control (CON; n = 9) group. All subjects performed maximal, concentric isokinetic leg extension and leg flexion muscle actions at 30, 150, and 270 deg/s on a Cybex II dynamometer for the determination of PT on visits 1 (pre-test) and 5 (post-test). The training groups performed 4 sets of 10 reciprocal leg extension and leg flexion repetitions with the nondominant limb at 30 deg/s (SVT group) or 270 deg/s (FVT group) on visits 2, 3, and 4. RESULTS: For the SVT group, leg extension PT of the trained limb increased from pre-test to post-test at 30 deg/s, 150 deg/s, and 270 deg/s. The increase in leg extension PT at 30 deg/s (21.8%) was greater than at 150 deg/s (4.8%) and 270 deg/s (9.0%). For the FVT group, leg extension PT of the trained limb increased at 270 deg/s (43.2%) only. For the CON group, there were no significant changes in leg extension PT of the trained limb at either velocity. There were no significant pre-test to post-test changes in leg extension PT for any group at any velocity in the untrained limb, or for leg flexion PT for any group at any velocity, for either limb. CONCLUSIONS: The results indicated that three sessions of slow velocity (30 deg/s) isokinetic training resulted in an increase in leg extension, but not leg flexion, PT at slow, intermediate, and fast velocities (30 deg/s, 150 deg/s, and 270 deg/s) for the trained limb, while fast velocity training (270 deg/s) led to the largest increase in PT, but at the training velocity only.

Acute Effects of Static Stretching on Peak Torque and Mean Power Output in National Collegiate Athletic Association Division I Women's Basketball Players

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and mean power output (MP) during maximal, voluntary concentric isokinetic leg extensions at 60 and 300 degrees .s(-1) in National Collegiate Athletic Association Division I Women's Basketball players. Eleven members of a women's basketball team volunteered to perform maximal concentric isokinetic leg extensions at 60 and 300 degrees .s(-1) on a calibrated Biodex System 3 dynamometer. After the initial isokinetic testing, the dominant leg extensors were stretched using 1 unassisted and 3 assisted static stretching exercises. The poststretching isokinetic assessments were repeated at 5, 15, 30, and 45 minutes after the static stretching (post-5, post-15, post-30, and post-45). PT (N.m) and MP (W) were recorded by dynamometer software. The results indicated no stretching-related changes in PT (p = 0.161) or MP (p = 0.088) from pre- to poststretching for any of the testing intervals (post-5, post-15, post-30, and post-45). These findings indicated that the static stretching had no impact on PT or MP during maximal, voluntary concentric isokinetic muscle actions in collegiate women's basketball players. In conjunction with previous studies, these findings suggested that trained athletes may be less susceptible to the stretching-induced force deficit than untrained, nonathletes.

Neuromuscular Responses to Three Days of Velocity-Specific Isokinetic Training

The purpose of this investigation was to examine the effects of 3 days of velocity-specific isokinetic training on peak torque (PT) and the electromyographic (EMG) signal. Thirty adult women were randomly assigned to a slow-velocity training (SVT), fast-velocity training (FVT), or control (CON) group. All subjects performed maximal, concentric, isokinetic leg extension muscle actions at 30 and 270 degrees .s(-1) for the determination of PT on visits 1 (pretest) and 5 (posttest). Electromyographic signals were recorded from the vastus lateralis, rectus femoris, and vastus medialis muscles during each test. The training groups performed 4 sets of 10 maximal repetitions at 30 degrees .s(-1) (SVT group) or 270 degrees .s(-1) (FVT group) on visits 2, 3, and 4. For the SVT group, PT increased from pretest to posttest at 30 and 270 degrees .s(-1). The increase in PT at 30 degrees .s(-1) was greater than at 270 degrees .s(-1). For the FVT group, PT increased at 270 degrees .s(-1) only. For the CON group, there were no changes in PT at either velocity. There were no pretest to posttest changes in EMG amplitude or mean power frequency (MPF) for any group at any velocity, with the exception of an increase in EMG MPF from the vastus medialis muscle at 270 degrees .s(-1) for the FVT group. The results indicated that 3 sessions of slow velocity (30 degrees .s(-1)) isokinetic training resulted in an increase in PT at slow and fast velocities (30 and 270 degrees .s(-1)), whereas training at the fast velocity (270 degrees .s(-1)) increased PT only at 270 degrees .s(-1). The lack of consistent increases in EMG amplitude or MPF suggested that the training-induced increases in leg extension PT were not caused by increased activation of the superficial muscles of the quadriceps femoris. The important implication for coaches, trainers, and physical therapists is that significant muscular performance gains may be achieved even after very short training periods, but determination of the specific physiological adaptation(s) underlying these performance gains requires further investigation.

The feasibility of whole body vibration in institutionalised elderly persons and its influence on muscle performance, balance and mobility: a randomised controlled trial [ISRCTN62535013

BackgroundFatigue or lack of interest can reduce the feasibility of intensive physical exercise in nursing home residents. Low-volume exercise interventions with similar training effects might be an alternative. The aim of this randomised controlled trial was to investigate the feasibility of Whole Body Vibration (WBV) in institutionalised elderly, and its impact on functional capacity and muscle performance.MethodsTwenty-four nursing home residents (15 female, 9 male; mean age 77.5 ± 11.0 years) were randomised (stratification for age, gender and ADL-category) to 6 weeks static WBV exercise (WBV+, N = 13) or control (only static exercise; N = 11). Outcome measures were exercise compliance, timed up-and-go, Tinetti-test, back scratch, chair sit-and-reach, handgrip strength and linear isokinetic leg extension.ResultsAt baseline, WBV+ and control groups were similar for all outcome variables. Twenty-one participants completed the program and attended respectively 96% and 86% of the exercise sessions for the WBV+ and control groups. Training-induced changes in timed up-and-go and Tinetti-test were better for WBV+ compared to control (p = 0.029 for timed up-and-go, p = 0.001 and p = 0.002 for Tinetti body balance and total score respectively). In an alternative analysis (Worst Rank Score & Last Observation Carried Forward) the differences in change remained significant on the Tinetti body balance and total score. No other significant differences in change between both groups were observed.ConclusionIn nursing home residents with limited functional dependency, six weeks static WBV exercise is feasible, and is beneficial for balance and mobility. The supplementary benefit of WBV on muscle performance compared to classic exercise remains to be explored further.

Early signaling responses to divergent exercise stimuli in skeletal muscle from well‐trained humans

Skeletal muscle from strength- and endurance-trained individuals represents diverse adaptive states. In this regard, AMPK-PGC-1alpha signaling mediates several adaptations to endurance training, while up-regulation of the Akt-TSC2-mTOR pathway may underlie increased protein synthesis after resistance exercise. We determined the effect of prior training history on signaling responses in seven strength-trained and six endurance-trained males who undertook 1 h cycling at 70% VO2peak or eight sets of five maximal repetitions of isokinetic leg extensions. Muscle biopsies were taken at rest, immediately and 3 h postexercise. AMPK phosphorylation increased after cycling in strength-trained (54%; P<0.05) but not endurance-trained subjects. Conversely, AMPK was elevated after resistance exercise in endurance- (114%; P<0.05), but not strength-trained subjects. Akt phosphorylation increased in endurance- (50%; P<0.05), but not strength-trained subjects after cycling but was unchanged in either group after resistance exercise. TSC2 phosphorylation was decreased (47%; P<0.05) in endurance-trained subjects following resistance exercise, but cycling had little effect on the phosphorylation state of this protein in either group. p70S6K phosphorylation increased in endurance- (118%; P<0.05), but not strength-trained subjects after resistance exercise, but was similar to rest in both groups after cycling. Similarly, phosphorylation of S6 protein, a substrate for p70 S6K, was increased immediately following resistance exercise in endurance- (129%; P<0.05), but not strength-trained subjects. In conclusion, a degree of "response plasticity" is conserved at opposite ends of the endurance-hypertrophic adaptation continuum. Moreover, prior training attenuates the exercise specific signaling responses involved in single mode adaptations to training.

Biochemical Changes in Response to Intensive Resistance Exercise Training in the Elderly

Background: It is assumed that low-grade inflammation, characterized by increased circulating IL-6 and TNF-α, is related to the development of sarcopenia. Physical exercise, especially high intensity resistance training, has been shown to be effective in restoring the strength deficit in the elderly. Intensive exercise is accompanied by significant release of IL-6 and TNF-α into the blood circulation, but does not result in muscle wasting. Exercise-induced changes in heat-shock protein (Hsp), responsible for cellular protection during stressful situations, might interfere with the acute phase reaction and muscle adaptation. Objective: To investigate if intensive strength training in elderly persons induces changes in Hsp70 expression, and if these changes are related to changes in the acute phase reaction or muscle adaptation. Methods: 31 elderly persons (aged 68.4 ± 5.4 years) performed 6 weeks’ intensive strength training. At baseline and after 6 weeks, muscle strength, functional performance (physical activity profile, 6-min walk, 30- second chair stand, grip strength, chair sit & reach and back scratch), linear isokinetic leg extension, circulating IL-6, TNF-α, IL-10 and TGF-β, and Hsp70 in monocytes (M) and lymphocytes (L) immediately after sampling (IAS), after incubation at 37 and 42°C were determined. In 12 participants, cytokines were determined in untrained and trained conditions before and after a single training session. Results: After 6 weeks’ training, muscle strength and functional performance improved significantly, together with decreased Hsp70 IAS and Hsp70 37°C and increased Hsp70 42°C (all p < 0.05). Strength gains correlated positively with baseline Hsp70 37°C and training-induced changes of Hsp70 42°C in M and L. In an untrained condition, training induced an increase of IL-6 (p < 0.05) and a tendency of IL-10 to decrease (p = 0.06). In a trained condition the decrease of IL-10 disappeared. Baseline physical activity and 6-min walk distance correlated negatively with circulating IL-6 (p < 0.05); except for a negative correlation between TGF-β and Hsp70 37°C L (p < 0.05), no significant relationships were found between cytokines and Hsp70. After the training program, Hsp70 37°C was negatively related to circulating TNF-α, IL-10 and TGF-β. Conclusion: Strength training in the elderly induces changes in Hsp70 expression, associated to strength gains and circulating cytokines.

Residual Physiological And Functional Benefits Following A Year Of Resistance Training In Older Adults

Long term participation in home-based exercise training programs using household items, resistance tubing, exercise balls, and hand exercisers have been shown to provide significant health benefits for older adults. However, little is known about the long term impact of these exercise interventions on older individuals. PURPOSE The goal of this study was to assess the residual effects 12 months following a year long moderate intensity resistance training program in older adults. METHODS Thirty two retired individuals over 55 years of age were recruited to participate in a year long monitored home-based moderate intensity resistance training program. Pre- and post-testing included anthropometric, physical, physiological and functional testing. At the completion of the study, each participant was provided information and retained the Thera-Band ® equipment to continue to perform the exercises at home. After completion of the 12 month training program, no monitoring was provided. One year after the post-testing, participants were invited to return to the lab for follow up testing and 26 agreed. At the initial assessment, these 11 males and 15 females were, on average 65.6±7.53 years, weighed 70.2±10.3 kg, and measured 167.3±8.9 cm (means ± SD). The effects of the year long training program and the 12 month follow up period were assessed using a repeated measures ANOVA. Significance was accepted at p<0.05. RESULTS Grip strength and isokinetic leg flexion and extension torques were significantly increased by training and maintained at follow up. Systolic blood pressure decreased significantly after training and was also reduced at follow up. Fast self-paced walking speed and functional reach were unchanged by training but were improved at follow up. Body mass, sum of skinfolds, resting heart rate, diastolic blood pressure, sit and reach, timed up and go and 6 minute walk test results were unchanged following training and at follow up testing. CONCLUSION These results demonstrate that there are significant residual benefits one year after the completion of a long term, monitored exercise training program. Implementation of long duration behavior modification strategies to increase strength and physical activity in older individuals, like this monitored home-based resistance exercise training program, are likely to have significant residual benefits on the health and quality of life of the participants. Supported by EKM Health Foundation, Nova Scotia Health Research Foundation and Thera-Band®.

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.

Mechanomyographic and Electromyographic Responses of the Vastus Medialis Muscle During Isometric and Concentric Muscle Actions

The purpose of this study was to examine the patterns for the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) vs. torque relationships during submaximal to maximal isometric and isokinetic muscle actions. Seven men (mean +/- SD age, 22.4 +/- 1.3 years) volunteered to perform isometric and concentric isokinetic leg extension muscle actions at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC) and peak torque (PT) on a Cybex II dynamometer. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes on the vastus medialis. Polynomial regression and separate 1-way repeated-measures analysis of variance were used to analyze the EMG amplitude, MMG amplitude, EMG MPF, and MMG MPF data for the isometric and isokinetic muscle actions. For the isometric muscle actions, EMG amplitude (R(2) = 0.999) and MMG MPF (R(2) = 0.946) increased to MVC, mean MMG amplitude increased to 60% MVC and then plateaued, and mean EMG MPF did not change (p > 0.05) across torque levels. For the isokinetic muscle actions, EMG amplitude (R(2) = 0.988) and MMG amplitude (R(2) = 0.933) increased to PT, but there were no significant mean changes with torque for EMG MPF or MMG MPF. The different torque-related responses for EMG and MMG amplitude and MPF may reflect differences in the motor control strategies that modulate torque production for isometric vs. dynamic muscle actions. These results support the findings of others and suggest that isometric torque production was modulated by a combination of recruitment and firing rate, whereas dynamic torque production was modulated primarily through recruitment.

The acute effects of static stretching on peak torque, mean power output, electromyography, and mechanomyography

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240 degrees x s(-1) of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3) years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240 degrees x s(-1). Surface EMG (muVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P< or =0.05) from pre- to post-stretching for the stretched limb at 60 and 240 degrees x s(-1) and for the unstretched limb at 60 degrees x s(-1). EMG amplitude of the VL and RF also decreased (P< or =0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.

Mechanomyographic Responses of the Vastus Medialis to Isometric and Eccentric Muscle Actions

The mechanomyographic (MMG) signal may be used to examine the motor control strategies used to modulate torque during various types of muscle actions. Therefore, the purpose of this study was to examine the MMG amplitude and mean power frequency (MPF) versus torque relationships during isometric and eccentric isokinetic muscle actions. Eleven adults (mean age +/- SD = 20.8 +/- 1.4 yr) volunteered to perform isometric and eccentric isokinetic leg extension muscle actions at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of peak torque on a Cybex 6000 dynamometer. A piezoelectric crystal contact sensor was placed on the vastus medialis to detect the MMG signal. Polynomial regression analyses indicated that for the isometric muscle actions, the relationships for MMG amplitude (r2 = 0.984) and MPF (r2 = 0.989) versus torque were linear. For the eccentric isokinetic muscle actions, the relationships for MMG amplitude (r2 = 0.580) and MPF (r2 = 0.961) versus torque were also linear. The patterns for MMG amplitude and MPF may reflect the motor control strategies that modulate torque production for isometric and eccentric isokinetic muscle actions. Based on the results of this and previous studies, it appears that for the vastus medialis, torque is modulated in a similar manner for isometric, concentric, and eccentric isokinetic muscle actions. Specifically, these findings suggest that gradation of torque involves increases in recruitment and firing rate to 100% voluntary torque production.

ACUTE EFFECTS OF STATIC STRETCHING ON PEAK TORQUE IN WOMEN

The purpose of this study was to examine the effects of static stretching on concentric, isokinetic leg extension peak torque (PT) at 60 and 240°.s-1 in the stretched and unstretched limbs. The PT of the dominant (stretched) and nondominant (unstretched) leg extensors were measured on a calibrated Cybex 6000 dynamometer. Following the prestretching PT assessments, the dominant leg extensors were stretched using 1 active and 3 passive stretching exercises. After the stretching, PT was reassessed. The results of the statistical analyses indicated that PT decreased following the static stretching in both limbs and at both velocities (60 and 240°.s-1). The present findings suggested that the stretching-induced decreases in PT may be related to changes in the mechanical properties of the muscle, such as an altered length-tension relationship, or a central nervous system inhibitory mechanism. Overall, these findings, in conjunction with previous studies, indicated that static stretching impairs maximal force production. Strength and conditioning professionals should consider this before incorporating static stretching in preperformance activities. Future studies are needed to identify the underlying mechanisms that influence the time course of stretching-induced decreases in maximal force production for athletes and nonathletes across the age span.

THE ACUTE EFFECTS OF STATIC STRETCHING ON PEAK TORQUE AND EMG OF THE STRETCHED AND UNSTRETCHED (CONTRALATERAL) VASTUS LATERALIS MUSCLES

PURPOSE To examine the acute effects of static stretching on peak torque (PT) and electromyographic (EMG) amplitude from the vastus lateralis (VL) muscle of the stretched (dominant) and unstretched (contralateral) things during leg extension exercises. METHODS Fourteen females (mean age ± SD = 22 ± 1 yr) volunteered to perform separate maximal, concentric isokinetic leg extensions of the dominant and non-dominant (contralateral) limbs on a calibrated Cybex 6000 isokinetic dynamometer at 60 and 240°•s−1. A bipolar surface EMG electrode arrangement was placed over the longitudinal axes of both VL muscles. The EMG (μ V) signals were expressed as root mean square (rms) amplitude values, while PT (Nm) was recorded by the dynamometer. Following the initial PT and EMG measurements, the dominant leg extensors were stretched for approximately 20 min using one unassisted and three assisted static stretching exercises. After the stretching and 10 min of quiet sitting, PT and EMG measurements were repeated. RESULTS For PT and EMG amplitude, there were no significant (p> 0.05) interactions involving the pre- vs. post-stretch factor (STRETCH), but significant main effects (p ≤ 0.05) for STRETCH. The pre-stretch marginal means for PT and EMG amplitude collapsed across limb and velocity were PT ± SEM = 144.6 ± 11.1 Nm and EMG amplitude ± SEM = 478.1 ± 37.7 μVrms, while the post-stretch marginal means collapsed across limb and velocity were PT ± SEM = 140.2 ± 10.6 Nm and EMG amplitude ± SEM = 447.1 ± 37.9 μVrms. CONCLUSIONS These results indicated that the patterns of decrease for PT and EMG amplitude as a result of the static stretching were the same in both the stretched and unstretched limbs at 60 and 240°•s−1. It is possible, therefore, that the 3% mean decrease in PT and the 6.5% mean decrease in EMG amplitude may have been due, in part, to a bilateral central nervous system inhibitory mechanism affecting both the stretched and unstretched (contralateral) muscles. In addition, these findings provide useful information regarding the neural component underlying the stretch-induced force deficit.

FREQUENCY CHANGES IN EMG AND MMG SIGNALS DURING FATIGUING ISOKINETIC MUSCLE ACTIONS

PURPOSE Fourier transformation procedures are frequently used to determine the power density spectrum of electromyographic (EMG) and mechanomyographic (MMG) signals. One assumption of Fourier transformations is that of stationarity (no change in signal characteristics), which cannot be assumed during dynamic muscle actions. Continuous wavelet transformations (CWT) do not require signal stationarity. The purpose of this study was to compare the patterns of frequency responses of EMG and MMG signals calculated from discrete Fourier transformation (DFT) and CWT procedures during fatiguing isokinetic muscle actions. METHODS Five subjects (mean age ± SD = 21 ± 2 years) performed 50 consecutive, maximal, concentric, isokinetic leg extension muscle actions on a Cybex II dynamometer at 180°s−1. EMG and MMG signals were recorded simultaneously from the vastus lateralis muscle every fifth repetition. DFT analyses were used to calculate the mean power frequencies (MPF) and CWT analyses were used to determine the instantaneous mean frequencies (IMF) for the EMG and MMG signals. The average of the IMF (AIMF) across the muscle action was used to represent the center frequency of the signal for the CWT analyses. RESULTS Regression analyses indicated that both normalized EMG MPF (slope = −0.402) and EMG AIMF (slope = −0.508) decreased linearly across the repetitions with no significant (p > 0.05) difference between the slope coefficients. There were no changes (p > 0.05) in normalized MMG MPF or MMG AIMF across the repetitions. CONCLUSIONS The results indicated that both DFT and CWT identified the fatigueinduced decrease in the center frequency of the EMG signal, as well as the lack of change in the MMG signal. These findings suggested that DFT was robust to the stationarity assumption.

Power Output, Mechanomyographic, and Electromyographic Responses to Maximal, Concentric, Isokinetic Muscle Actions in Men and Women

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitudes, and mean power frequencies (MPFs) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in men and women during dynamic muscle actions. Twelve women (mean ± SD age = 22 ± 3 years) and 11 men (22 ± 3 years) performed maximal, concentric, isokinetic leg extensions at velocities of 60, 120, 180, 240, and 300°·1 on a Cybex 6000 dynamometer. Piezoelectric MMG-recording sensors and bipolar surface EMG electrodes were placed over the VL, RF, and VM muscles. No sex-related differences were found among the velocity-related patterns for PT, MP, MMG amplitude, MMG MPF, or EMG MPF. There were, however, sex-related differences in the patterns of EMG amplitude across velocity. The results indicated similar velocity-related patterns of increase of MP and MMG amplitude for all 3 muscles and of EMG amplitude for the VL and VM in the women. Velocity-related decreases (p < 0.05) were found for PT and EMG MPF for the VL. EMG amplitude for all muscles in the men and for the RF in the women as well as EMG MPF for the RF and VM remained unchanged (p > 0.05) across velocity. MMG MPF increased (p ≤ 0.05) only between 240 and 300°·s-1. Overall, these findings suggested that there were sex- and muscle-specific, velocity-related differences in the associations among motor unit activation strategies (EMG amplitude and MPF) and the mechanical aspects of muscular activity (MMG amplitude and MPF). With additional examination and validation, however, MMG may prove useful to practitioners for monitoring training-induced changes in muscle power output.

The effects of visual feedback and verbal encouragement as modes of psychological motivation on isokinetic concentric leg extension test results

The effects of visual feedback and verbal encouragement as modes of psychological motivation on isokinetic concentric leg extension test results

Power Output, Mechanomyographic, and Electromyographic Responses to Maximal, Concentric, Isokinetic Muscle Actions in Men and Women

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitudes, and mean power frequencies (MPFs) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in men and women during dynamic muscle actions. Twelve women (mean +/- SD age = 22 +/- 3 years) and 11 men (22 +/- 3 years) performed maximal, concentric, isokinetic leg extensions at velocities of 60, 120, 180, 240, and 300 degrees x s(-1) on a Cybex 6000 dynamometer. Piezoelectric MMG-recording sensors and bipolar surface EMG electrodes were placed over the VL, RF, and VM muscles. No sex-related differences were found among the velocity-related patterns for PT, MP, MMG amplitude, MMG MPF, or EMG MPF. There were, however, sex-related differences in the patterns of EMG amplitude across velocity. The results indicated similar velocity-related patterns of increase of MP and MMG amplitude for all 3 muscles and of EMG amplitude for the VL and VM in the women. Velocity-related decreases (p <or = 0.05) were found for PT and EMG MPF for the VL. EMG amplitude for all muscles in the men and for the RF in the women as well as EMG MPF for the RF and VM remained unchanged (p > 0.05) across velocity. MMG MPF increased (p < or = 0.05) only between 240 and 300 degrees x s(-1). Overall, these findings suggested that there were sex- and muscle-specific, velocity-related differences in the associations among motor unit activation strategies (EMG amplitude and MPF) and the mechanical aspects of muscular activity (MMG amplitude and MPF). With additional examination and validation, however, MMG may prove useful to practitioners for monitoring training-induced changes in muscle power output.

The Effect of Concentric Isokinetic Strength Training of the Quadriceps Femoris on Electromyography and Muscle Strength in the Trained and Untrained Limb

The purpose of the present investigation was to examine the effects of unilateral concentric isokinetic leg extension training on peak torque (PT) and electromyographic (EMG) responses in the trained and untrained limbs. Twenty adult men were randomly assigned to a training (TRN, n = 11) or control (CTL, n = 9) group. The TRN group performed 6 sets of 10 leg extensions 3 days per week for 12 weeks at a velocity of 90°s−1. All subjects were tested every 4 weeks for PT and EMG responses of both legs at a velocity of 90°s−1. The 3-way mixed factorial analysis of variance (ANOVA) indicated a significant (p < 0.05) increase in PT over the 12 weeks in both the trained and untrained limb for the TRN group but no significant change in PT in either limb for the CTL group. The results of the 3-way ANOVA for the EMG data indicated no significant change in EMG amplitude in the trained or untrained limb for the TRN or CTL group. The increase in PT in the absence of a change in EMG may result from hypertrophic factors and/or changes in the other muscles or muscle groups involved in leg xtension.

The Effect of Concentric Isokinetic Strength Training of the Quadriceps Femoris on Electromyography and Muscle Strength in the Trained and Untrained Limb

The purpose of the present investigation was to examine the effects of unilateral concentric isokinetic leg extension training on peak torque (PT) and electromyographic (EMG) responses in the trained and untrained limbs. Twenty adult men were randomly assigned to a training (TRN, n = 11) or control (CTL, n = 9) group. The TRN group performed 6 sets of 10 leg extensions 3 days per week for 12 weeks at a velocity of 90 degrees.s(-1). All subjects were tested every 4 weeks for PT and EMG responses of both legs at a velocity of 90 degrees.s(-1). The 3-way mixed factorial analysis of variance (ANOVA) indicated a significant (p < 0.05) increase in PT over the 12 weeks in both the trained and untrained limb for the TRN group but no significant change in PT in either limb for the CTL group. The results of the 3-way ANOVA for the EMG data indicated no significant change in EMG amplitude in the trained or untrained limb for the TRN or CTL group. The increase in PT in the absence of a change in EMG may result from hypertrophic factors and/or changes in the other muscles or muscle groups involved in leg extension.