Quadriceps femoris electromyogram during concentric, isometric and eccentric phases of fatiguing dynamic knee extensions

Effect of rest duration between sets on fatigue and recovery after short intense plyometric exercise

Plyometric training is characterized by high-intensity exercise which is performed in short term efforts divided into sets. The purpose of the present study was twofold: first, to investigate the effects of three distinct plyometric exercise protocols, each with varying work-to-rest ratios, on muscle fatigue and recovery using an incline-plane training machine; and second, to assess the relationship between changes in lower limb muscle strength and power and the biochemical response to the three exercise variants employed. Forty-five adult males were randomly divided into 3 groups (n = 15) performing an exercise of 60 rebounds on an incline-plane training machine. The G0 group performed continuous exercise, while the G45 and G90 groups completed 4 sets of 15 repetitions, each set lasting 45 s with 45 s rest in G45 (work-to-rest ratio of 1:1) and 90 s rest in G90 (1:2 ratio). Changes in muscle torques of knee extensors and flexors, as well as blood lactate (LA) and ammonia levels, were assessed before and every 5 min for 30 min after completing the workout. The results showed significantly higher (p < 0.001) average power across all jumps generated during intermittent compared to continuous exercise. The greatest decrease in knee extensor strength immediately post-exercise was recorded in group G0 and the least in G90. The post-exercise time course of LA changes followed a similar pattern in all groups, while the longer the interval between sets, the faster LA returned to baseline. Intermittent exercise had a more favourable effect on muscle energy metabolism and recovery than continuous exercise, and the work-to-rest ratio of 1:2 in plyometric exercises was sufficient rest time to allow the continuation of exercise in subsequent sets at similar intensity.

Lower limb muscle activation pattern in male soccer players with lumbar hyperlordosis

OBJECTIVE

the aim of the current study was to compare the lower limb muscle activation pattern in soccer players with and without lumbar hyperlordosis during single-leg squat performance.

METHODS

thirty male collegiate soccer players (15 with and 15 without lumbar hyperlordosis) performed the SLS task. Surface EMG was used to record the activation of eleven lower limb muscles. The activation of these muscles reduces to 100 points during the SLS cycle, where 50% demonstrates the maximum knee flexion, and 0% and 99% demonstrate the maximum knee extension.

RESULTS

soccer players with lumbar hyperlordosis had higher muscle activation than those with normal lumbar lordosis in gluteus maximus, biceps femoris, and medial gastrocnemius. By contrast, they had lower gluteus medius, vastus medialis oblique, rectus femoris, soleus, and medial gastrocnemius (only in the final ascent phase of the SLS) muscle activity than the normal group during the SLS.

CONCLUSION

this alteration may negatively affect targeted muscle performance during the SLS. Subsequent study is required to specify whether such an alteration in the lower limb muscle could be accompanied by injury in soccer players and change in their athletic performance.

Alteration of quadriceps muscle activity during functional step tasks after extended sitting session

BACKGROUND

Prolonged sitting with high knee flexion is a common activity that may affect patellofemoral joint compression and quadriceps length. Exploring the quadriceps activation after sitting may help to explain the mechanism underlying muscle changes and the resulting patellofemoral pain.

OBJECTIVES

To examine changes in quadriceps activity after prolonged sitting in cross-legged sitting, side-sitting, and sitting on a chair.

DESIGN

Laboratory observational study.

METHOD

Thirty healthy women participated and were randomly allocated to three groups of different sitting positions (n = 10/group). Electromyography (EMG) of the vastus medialis (VM), rectus femoris (RF), and vastus lateralis (VL) was performed before and after 15 min after sitting. EMG was conducted during step-up and step-down tests and was reported as %MVIC. The results were analysed using Wilcoxon signed-rank test and Kruskal-Wallis ANOVA.

RESULTS

VM activity and EMG activity during the step-down test after sitting increased significantly in the cross-legged group (p = 0.01). Sitting postures significantly influenced (p = 0.02) muscle activity changes in the VL and VM during the step-up test. Pairwise comparisons revealed significant differences between the cross-legged sitting and sitting on a chair groups.

CONCLUSIONS

Prolonged cross-legged sitting and side-sitting caused changes in VM and VL activity during step tasks in healthy young women. After cross-legged sitting, the VM exhibited a significantly higher activity in descending control, and changes in VM and VL activity increased significantly during the step-up task. Increased VM and VL activation possibly controls the patellofemoral joint. Therefore, they may fatigue more easily when many step tasks or squatting exercises are performed.

Neuromuscular Fatigue Responses of Endurance- and Strength-Trained Athletes during Incremental Cycling Exercise

This study explored the development of neuromuscular fatigue responses during progressive cycling exercise. The sample comprised 32 participants aged 22.0 ± 0.54 years who were assigned into three groups: endurance-trained group (END, triathletes, n = 10), strength-trained group (STR, bodybuilders, n = 10) and control group (CG, recreationally active students, n = 12). The incremental cycling exercise was performed using a progressive protocol starting with a 3 min resting measurement and then 50 W workload with subsequent constant increments of 50 W every 3 min until 200 W. Surface electromyography (SEMG) of rectus femoris muscles was recorded during the final 30 s of each of the four workloads. During the final 15 s of each workload, participants rated their overall perception of effort using the 20-point rating of the perceived exertion (RPE) scale. Post hoc Tukey’s HSD testing showed significant differences between the END and STR groups in median frequency and mean power frequency across all workloads (p < 0.001 and p < 0.01, respectively). Athletes from the END group had significantly lower electromyogram amplitude responses than those from the STR (p = 0.0093) and CG groups (p = 0.0006). Increasing RPE points from 50 to 200 W were significantly higher in the STR than in the END group (p < 0.001). In conclusion, there is a significant variation in the neuromuscular fatigue profiles between athletes with different training backgrounds when a cycling exercise is applied. The approximately linear trends of the SEMG and RPE values of both groups of athletes with increasing workload support the increased skeletal muscle recruitment with perceived exertion or fatiguing effect.

Blood Pressure Responses to Static and Dynamic Knee Extensor Exercise between Sexes: Role of Absolute Contraction Intensity

PURPOSE

Males have larger blood pressure (BP) responses to relative-intensity static handgrip exercise compared with females. Controlling for absolute load (maximal voluntary contraction (MVC)) abolishes these differences. Whether similar observations exist during large muscle mass exercise or dynamic contractions, and the mechanisms involved, remains unknown.

METHODS

BP, heart rate, muscle oxygenation (near-infrared spectroscopy), and rectus femoris EMG were recorded in 28 males and 17 females during 10% and 30% MVC static (120 s) and isokinetic dynamic (180 s; 1:2 work-to-rest ratio; angular velocity, 60°·s-1) knee extensor exercise. Static and dynamic exercises were completed on separate visits, in a randomized order. Sex differences were examined with and without statistical adjustment of MVC (ANCOVA).

RESULTS

Males had larger systolic BP responses (interaction, P < 0.0001) and muscle deoxygenation (interaction, P < 0.01) than did females during 10% static exercise, with no difference in EMG (interaction, P = 0.67). Peak systolic BP was correlated with MVC (r = 0.55, P = 0. 0001), and adjustment for MVC abolished sex differences in systolic BP (interaction, P = 0.3). BP, heart rate, muscle oxygenation/deoxygenation, and EMG responses were similar between sexes during 30% static exercise (interaction; all, P > 0.2), including following adjustment for MVC (all, P > 0.1). Males had larger systolic BP responses during dynamic exercise at 10% and 30% (interaction; both, P = 0.01), which were abolished after adjustment for MVC (interaction; both, P > 0.08). Systolic BP responses were correlated with absolute MVC and stroke volume responses during 10% (r = 0.31, P = 0.04; r = 0.61, P < 0.0001, respectively) and 30% (r = 0.48, P = 0.001; r = 0.59, P < 0.0001, respectively).

CONCLUSIONS

Absolute contraction intensity can influence systolic BP responses to 10% but not 30% MVC static, as well as 10% and 30% MVC dynamic knee extensor exercise, and should be considered in cross-sectional comparisons of exercise BP.

Safety, Fear and Neuromuscular Responses after a Resisted Knee Extension Performed to Failure in Patients with Severe Haemophilia

Background: low–moderate intensity strength training to failure increases strength and muscle hypertrophy in healthy people. However, no study assessed the safety and neuromuscular response of training to failure in people with severe haemophilia (PWH). The purpose of the study was to analyse neuromuscular responses, fear of movement, and possible adverse effects in PWH, after knee extensions to failure. Methods: twelve severe PWH in prophylactic treatment performed knee extensions until failure at an intensity of five on the Borg CR10 scale. Normalised values of amplitude (nRMS) and neuromuscular fatigue were determined using surface electromyography for the rectus femoris, vastus medialis, and vastus lateralis. After the exercise, participants were asked about their perceived change in fear of movement, and to report any possible adverse effects. Results: Patients reported no adverse effects or increased fear. The nRMS was maximal for all the muscles before failure, the median frequency decreased, and wavelet index increased during the repetitions. The vastus lateralis demonstrated a higher maximum nRMS threshold and earlier fatigue, albeit with a lower and more progressive overall fatigue. Conclusions: severe PWH with adequate prophylactic treatment can perform knee extensions to task failure using a moderate intensity, without increasing fear of movement, or adverse effects.

Electromyographic activity in the gluteus medius, gluteus maximus, biceps femoris, vastus lateralis, vastus medialis and rectus femoris during the Monopodal Squat, Forward Lunge and Lateral Step-Up exercises

The Monopodal Squat, Forward Lunge and Lateral Step-Up exercises are commonly performed with one's own body weight for rehabilitation purposes. However, muscle activity evaluated using surface electromyography has never been analyzed among these three exercises. Therefore, the objectives of the present study were to evaluate the amplitude of the EMG activity of the gluteus medius, gluteus maximus, biceps femoris, vastus lateralis, vastus medialis and rectus femoris muscles in participants performing the Lateral Step-Up, Forward Lunge and Monopodal Squat exercises. A total of 20 physically active participants (10 men and 10 women) performed 5 repetitions at 60% (5 repetition maximum) in each of the evaluated exercises. The EMG amplitude was calculated in percentage of the maximum voluntary contraction. The Monopodal Squat exercise showed a higher EMG activity (p ≤ 0.001) in relation to the Lateral Step-Up and Forward Lunge exercises in all of the evaluated muscles (d > 0.6) except for the rectus femoris. The three exercises showed significantly higher EMG activity in all of the muscles that were evaluated in the concentric phase in relation to the eccentric one. In the three evaluated exercises, vastus lateralis and vastus medialis showed the highest EMG activity, followed by gluteus medius and gluteus maximus. The Monopodal Squat, Forward Lunge and Lateral Step-Up exercises not only are recommended for their rehabilitation purposes but also should be recommended for performance objectives and strength improvement in the lower limbs.

The effect of 10 weeks of strength training on the electromyographic response of quadriceps portions

Abstract This study investigate the effect of 10-week strenght training on the amplitude of the electromyographic (EMG) signal of vastus medialis, vastus lateralis and rectus Femoris. Twenty three untrained volunteers performed 3-5 sets (3 sets - weeks 1 and 2; 4 series - weeks 3 and 4; 5 series weeks 5 to 10) with 6 repetitions, intensity of 50% of 1 repetition maximum (1RM), 3 min rest between sets and 6 s repetition duration at the knee extensor exercise. One group (5:1) performed concentric action of 5 s and eccentric of 1 s and the other (3:3) performed concentric of 3 s and eccentric of 3 s. The VM, VL and RF EMG (RMS) activities were recorded in each repetition of the three series at the first training session and the first three series at the last session. The protocol 5:1 led to EMG reduction in all portions, with a greater number of repetitions presenting differences at the VL and RF. VM and RF presented similar results at Group 3:3. It was verified that all the differences occurred in the second half of the series. It was also verified differences in EMG ratios just in group 3:3 and only in VM/VL and VM/RF. These results suggest that the coordination was not affected when equivalent repetitions of series were compared. It was also suggested that these results were influenced by the reduced degrees of freedom of the exercise and the training load progression adopted.

Effect of knee joint angle on the neuromuscular activation of the quadriceps femoris during repetitive fatiguing contractions

We assessed the effect of knee joint angle on the EMG amplitude and frequency of the four individual muscles in the quadriceps femoris during repetitive fatiguing maximum voluntary contractions (MVCs). Fifteen healthy men and women performed two fatiguing tasks consisting of 40 MVCs in flexion (80°) and extension (140˚) (full extension = 180˚). Neuromuscular activation of the vastus intermedius (VI), vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was recorded using surface electrodes, and median frequency (MF) and root mean square (RMS) of electromyographic (EMG) signals (normalized by pre-test MVCs) were calculated. MVCs significantly decreased from the 10th to the 40th repetition in both flexion and extension. The MFs of VI and VM in flexion and that of RF flexion and extension were significantly decreased after the 10th repetition. There were no significant changes in normalized EMG amplitude in any muscles specific to knee angle. Stepwise regression analysis suggested that predictive synergistic action may occur in RF/VM and RF/VI in flexion and in RF/VM in extension. This suggest that EMG MF of RF/VM is independent, but that of RF/VI and RF/VL is dependent upon knee joint angle, which may, in part, explain joint angle-specific muscle fatigue.

Separate and combined effects of local and systemic hypoxia in resistance exercise

PURPOSES

This study quantified performance, physiological, and perceptual responses during resistance exercise to task failure with blood flow restriction (BFR), in systemic hypoxia, and with these stimuli combined.

METHODS

Fourteen young men were tested for 1-repetition maximum (1RM) in the barbell biceps curl and lying triceps extension exercises. On separate visits, subjects performed exercise trials (4 sets to failure at 70% 1RM with 90 s between sets) in six separate randomized conditions, i.e., in normoxia or hypoxia (fraction of inspired oxygen = 20.9% and 12.9%, respectively) combined with three different levels of BFR (0%, 45%, or 60% of resting arterial occlusion pressure). Muscle activation and oxygenation were monitored via surface electromyography and near-infrared spectroscopy, respectively. Arterial oxygen saturation, heart rate, and perceptual responses were assessed following each set.

RESULTS

Compared to set 1, the number of repetitions before failure decreased in sets 2, 3, and 4 for both exercises (all P < 0.001), independently of the condition (P > 0.065). Arterial oxygen saturation was lower with systemic hypoxia (P < 0.001), but not BFR, while heart rate did not differ between conditions (P > 0.341). Muscle oxygenation and activation during exercise trials remained unaffected by the different conditions (all P ≥ 0.206). A significant main effect of time, but not condition, was observed for overall perceived discomfort, difficulty breathing, and limb discomfort (all P < 0.001).

CONCLUSION

Local and systemic hypoxic stimuli, or a combination of both, did not modify the fatigue-induced change in performance, trends of muscle activation or oxygenation, nor exercise-related sensations during a multi-set resistance exercise to task failure.

The effects of instrument-assisted soft tissue mobilization on active range of motion, functional fitness, flexibility, and isokinetic strength in high school basketball players

Although many studies have focused on stretching techniques for athletes, no comprehensive studies have investigated the use of the instrument-assisted soft tissue mobilization (IASTM) technique in young basketball players. The active properties of muscle and subjective reporting of functional ability were used to identify the effects of IASTM on the calf muscle. Active range of motion (AROM), functional fitness, and isokinetic lower strength in the knees and ankles were measured in 40 healthy young basketball players. They were divided into the IASTM group (n= 20) and a control group (CG, n= 20). Twenty asymptomatic young basketball players were treated with IASTM six times per week for 8 weeks. The remaining 20 participants did not receive a treatment intervention between tests and served as the control. Ankle AROM (two knee positions of 0∘ and 45∘ flexion), functional fitness at the knee and ankle (side-step and vertical jump), and isokinetic peak torque were determined during ankle dorsiflexion (DF) and plantar flexion (PF) and knee extension (EX) and flexion (FX). The data were analyzed using repeated-measures analysis of variance. Significant differences were observed between the two groups in IASTM and control AROM 0∘ knee flexion (right: DF; p< 0.001 and PF; p< 0.001; left: DF; p< 0.001 and PF; p= 0.011), AROM 45∘ knee flexion (right: DF; p< 0.001 and PF; p= 0.009; left: DF; p< 0.001 and PF; p= 0.001), functional fitness (side step; p= 0.001, sit and reach; p= 0.025, vertical jump; p= 0.001), ankle isokinetic strength 30∘/sec (right: DF; p= 0.001 and PF; p= 0.001; left: DF; p< 0.001 and PF; p= 0.002), ankle isokinetic strength 120∘/sec (right: DF; p= 0.049 and PF; p= 0.001; left: DF; p= 0.023 and PF; p< 0.001), knee isokinetic strength 60∘/sec (right: EX; p= 0.001, FX; p= 0.001 and hamstring and quadriceps ratio [H/Q]; p= 0.001, left: EX; p= 0.001, FX; p= 0.001 and H/Q; p= 0.001), and knee isokinetic strength 180∘/sec (right: EX; p= 0.001, FX; p= 0.001 and H/Q; p= 0.001; left: EX; p= 0.001, FX; p= 0.010 and H/Q; p= 0.001). These results suggest that IASTM improves functional fitness and lower body muscle strength in young basketball players.

The effects of taurine on repeat sprint cycling after low or high cadence exhaustive exercise in females

This study investigated the effects of taurine on repeated sprint exercise, performed after fixed incremental ramp exercise to exhaustion at isokinetic high (90 r/min) or low (50 r/min) cadences. In a double-blind, repeated measures design, nine females completed an incremental ramp test to volitional exhaustion, followed by 2 min active recovery and 6 × 10 s sprints on a cycle ergometer, in one of four conditions: high cadence (90 r/min) + taurine (50 mg/kg body mass); high cadence + placebo (3 mg/kg body mass maltodextrin); low cadence (50 r/min) + taurine; low cadence + placebo. Heart rate (HR) and blood lactate concentration B[La] were measured before and after the ramp test and after the sprints. Taurine lowered HR vs. placebo prior to the ramp test (P = 0.004; d = 2.1). There was an effect of condition on ramp performance (P < 0.001), with higher end-test power (d = 3.7) in taurine conditions. During repeated sprints, there was a condition × time interaction (P = 0.002), with higher peak sprint power in the placebo conditions compared to taurine (sprint 2-6; P < 0.05). B[La] was higher in taurine compared to placebo post-ramp (P = 0.004; d = 4.7). Taurine-lowered pre-exercise HR and improved incremental end-test power output, with subsequent detrimental effects on sprint performance, independent of cadence. Short endurance performance can be acutely enhanced after taurine ingestion but this effect might not be maintained across longer periods of exercise or induce the need for longer recovery periods.

Skin temperature response to unilateral training measured with infrared thermography

This study aimed to identify the skin temperature (Tsk) behavior to understand the acute cross-effect after unilateral training of lower-limbs. Seventeen healthy young men (weight, 75.2±5.5 kg; height, 1.8±0.1 m; age, 22.5±1.6 years) were divided into two groups: high-trained (n=8) and low-trained (n=9). All participants performed: (a) one-repetition maximum (1RM) testing protocol on the leg press, (b) a unilateral training protocol (4×10 repetitions at 70% of 1RM for leg press and 4×10 repetitions at 50% of 1RM for knee extension). Pre- and posttraining thermal images were recorded. The main results showed that independent of the limb (exercised vs. nonexercised), differences between low- and high-trained were observed for all regions of interest (ROI) except for the anterior knee: posttraining, 30-min and 60-min posttraining in nonexercised limb. The increase of contralateral Tsk was more than 50% on the ROIs corresponding to the exercises muscles 30-min post-training in low-trained but was not so high in high-trained (P<0.05). Low-trained subjects incremented more the Tsk than high-trained in both legs after exercise. In conclusion, we observed an acute contralateral Tsk effect to unilateral training on the Tsk of the nonexercised limb, reliant on the training level of the subject.

Strength Training to Contraction Failure Increases Voluntary Activation of the Quadriceps Muscle Shortly After Total Knee Arthroplasty: A Cross-sectional Study

OBJECTIVE

The objective of this study was to investigate voluntary activation of the quadriceps muscle during one set of knee extensions performed until contraction failure in patients shortly after total knee arthroplasty.

DESIGN

This was a cross-sectional study of 24 patients with total knee arthroplasty. One set of knee extensions was performed until contraction failure, using a predetermined 10 repetition maximum loading. In the operated leg, electromyographic (EMG) activity of the lateral and medial vastus, semitendinosus, and biceps femoris muscles was recorded during the set. Muscle activity (%EMGmax) and median power frequency of the EMG power spectrum were calculated for each repetition decile (10%-100% contraction failure).

RESULTS

Muscle activity increased significantly over contractions from a mean of 90.0 and 93.6 %EMGmax (lateral vastus and medial vastus, respectively) at 10% contraction failure to 99.3 and 105.5 %EMGmax at 100% contraction failure (P = 0.009 and 0.004). Median power frequency decreased significantly over contractions from a mean of 66.8 and 64.2 Hz (lateral vastus and medial vastus, respectively) at 10% contraction failure to 59.9 and 60.1 Hz at 100% contraction failure (P = 0.0006 and 0.0187).

CONCLUSION

In patients shortly after total knee arthroplasty, 10 repetition maximum-loaded knee extensions performed in one set until contraction failure increases voluntary activation of the quadriceps muscle during the set.

CLINICAL TRIALS

Gov-identifier: NCT01713140 to the abstract to increase trial transparency.

ELECTROMYOGRAPHIC ANALYSIS OF LEG EXTENSION EXERCISE DURING DIFFERENT ANKLE AND KNEE POSITIONS

The imbalance between vastus medialis oblique (VMO) and vastus lateralis (VL) strength is one of the main factor for patellofemoral pain syndrome (PFPS) onset, related to improper alignment of the patella. The aim of this paper is to investigate the effects of knee flexion, knee rotation and ankle flexion attitudes on the activity of the VMO and VL muscles during unilateral maximal voluntary isometric contraction (MIVC) of the quadriceps femoris. Eighteen healthy subjects volunteered for the study. Five conditions for two different knee flexion angles (90°; 30°) were tested using leg extension machine: Neutral (N) condition, maximal knee medial rotation (MR), maximal knee lateral rotation (LR), maximal ankle plantarflexion (PF) and maximal ankle dorsiflexion (DF). Data were normalized in order to calculate the normalized VMO/VL ratio. The normalized VMO/VL ratio for all the conditions occurred at 90° of knee flexion was higher than the same conditions at 30° of knee flexion (p = 0.02). No statistical differences between conditions at the same knee angle and for angle x condition interaction were observed (p > 0.05). These findings suggest that knee flexion should be the first variable to be managed during isometric knee extension movement performed by leg extension machine, in order to increase VMO/VL ratio.

Time-course of performance changes and underlying mechanisms during and after repetitive moderately weight-loaded knee extensions

The purpose of this study was to investigate the mechanisms of fatigue development induced by isoload (IL) fatiguing knee extensions. Nine physically active males (age=23±2years, height=179±7cm, mass=76±7kg) performed repetitive ballistic knee extensions at 30% of the isometric maximal voluntary peak torque. Fatigue development was assessed throughout the fatiguing exercise by quantifying changes in peak torque, agonist and antagonist electromyographic activity (EMG) and torque- and EMG-angle relationships. Before and after the fatiguing exercise, isometric maximal voluntary contractions were performed to measure peak torque (MVIC torque), voluntary activation (VA) and resting twitch torque. IL peak torque decreased from the middle of the fatiguing exercise while the agonist and antagonist EMG amplitude increased consistently during the entire exercise (P<.005). The pattern of the torque-angle relationship changed with fatigue (P<.005) reflecting a change in torque production strategy even if the EMG-angle relationships were not modified. Post-exercise testing revealed a decrease in MVIC torque (-31%; P<.005). VA was unchanged (P=.60) while the resting twitch torque was impaired to a great extent (-46%; P<.005) suggesting that local muscular mechanisms but not neural drive were altered during single-joint IL fatiguing task.

Early progressive strength training to enhance recovery after fast-track total knee arthroplasty: a randomized controlled trial

OBJECTIVE

To compare 7 weeks of supervised physical rehabilitation with or without progressive strength training (PST) commenced early after fast-track total knee arthroplasty (TKA) on functional performance.

METHODS

In total, 82 patients with a unilateral primary TKA were randomized to 2 different interventions: 7 weeks of supervised physical rehabilitation with PST (PST group) and without PST (CON group) commenced early after fast-track TKA. The primary outcome was the maximal distance walked in 6 minutes (6-minute walk test). Secondary outcomes were lower extremity strength and power, knee joint effusion and range of motion, knee pain, and self-reported disability and quality of life. All outcome measures were assessed before TKA (baseline) and 4, 8, and 26 weeks after TKA.

RESULTS

There was no statistically significant difference between the PST and CON groups in the change score from baseline to the 8-week postoperative assessment (primary end point) for the 6-minute walk test with unadjusted baseline scores (mean difference between groups: -11.3 meters [95% confidence interval -45.4, 22.7]; analysis of variance P = 0.51). There were no statistically significant or clinically meaningful differences between groups in change scores from baseline to any other time point for all secondary outcomes. The secondary outcome knee extension strength did not reach the level recorded before surgery in both groups.

CONCLUSION

Seven weeks of supervised physical rehabilitation with PST was not superior to 7 weeks of supervised physical rehabilitation without PST in improving functional performance, measured as the maximal walking distance in 6 minutes, at the primary end point 8 weeks after fast-track TKA.

Neuromuscular fatigue and tibiofemoral joint biomechanics when transitioning from non-weight bearing to weight bearing

CONTEXT

Fatigue is suggested to be a risk factor for anterior cruciate ligament injury. Fatiguing exercise can affect neuromuscular control and laxity of the knee joint, which may render the knee less able to resist externally applied loads. Few authors have examined the effects of fatiguing exercise on knee biomechanics during the in vivo transition of the knee from non-weight bearing to weight bearing, the time when anterior cruciate ligament injury likely occurs.

OBJECTIVE

To investigate the effect of fatiguing exercise on tibiofemoral joint biomechanics during the transition from non-weight bearing to early weight bearing.

DESIGN

Cross-sectional study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Ten participants (5 men and 5 women; age = 25.3 ± 4.0 years) with no previous history of knee-ligament injury to the dominant leg.

INTERVENTION(S)

Participants were tested before (preexercise) and after (postexercise) a protocol consisting of repeated leg presses (15 repetitions from 10°-40° of knee flexion, 10 seconds' rest) against a 60% body-weight load until they were unable to complete a full bout of repetitions.

MAIN OUTCOME MEASURE(S)

Electromagnetic sensors measured anterior tibial translation and knee-flexion excursion during the application of a 40% body-weight axial compressive load to the bottom of the foot, simulating weight acceptance. A force transducer recorded axial compressive force.

RESULTS

The axial compressive force (351.8 ± 44.3 N versus 374.0 ± 47.9 N; P = .018), knee-flexion excursion (8.0° ± 4.0° versus 10.2° ± 3.7°; P = .046), and anterior tibial translation (6.7 ± 1.7 mm versus 8.2 ± 1.9 mm; P < .001) increased from preexercise to postexercise. No significant correlations were noted.

CONCLUSIONS

Neuromuscular fatigue may impair initial knee-joint stabilization during weight acceptance, leading to greater accessory motion at the knee and the potential for greater anterior cruciate ligament loading.

Neuromuscular response differences to power vs strength back squat exercise in elite athletes

The study's aim was to establish the neuromuscular responses in elite athletes during and following maximal 'explosive' regular back squat exercise at heavy, moderate, and light loads. Ten elite track and field athletes completed 10 sets of five maximal squat repetitions on three separate days. Knee extension maximal isometric voluntary contraction (MIVC), rate of force development (RFD) and evoked peak twitch force (Pt) assessments were made pre- and post-session. Surface electromyography [root mean square (RMS)] and mechanical measurements were recorded during repetitions. The heavy session resulted in the greatest repetition impulse in comparison to moderate and light sessions (P < 0.001), while the latter showed highest repetition power (P < 0.001). MIVC, RFD, and Pt were significantly reduced post-session (P < 0.01), with greatest reduction observed after the heavy, followed by the moderate and light sessions accordingly. Power significantly reduced during the heavy session only (P < 0.001), and greater increases in RMS occurred during heavy session (P < 0.001), followed by moderate, with no change during light session. In conclusion, this study has shown in elite athletes that the moderate load is optimal for providing a neuromuscular stimulus but with limited fatigue. This type of intervention could be potentially used in the development of both strength and power in elite athletic populations.

Exploratory study of electromyographic behavior of the vastus medialis and vastus lateralis at neuromuscular fatigue onset

This study aimed to determine and analyze the neuromuscular fatigue onset by median frequency (MDF) and the root mean square (RMS) behavior of an electromyographic signal (EMG). Eighteen healthy men with no prior knee problems initially performed three maximum voluntary isometric contractions (MVIC). After two days of MVIC test, participants performed a fatiguing protocol in which they performed submaximal knee-extension contractions at 20% and 70% MVIC held to exhaustion. The MDF and RMS values from the EMG signals were recorded from the vastus medialis (VM) and the vastus lateralis (VL). Analysis of the MDF and RMS behavior enabled identification of neuromuscular fatigue onset for VM and VL muscles in 20% and 70% loads. Alterations between the VM and VL in the neuromuscular fatigue onset, at 20% and 70% MVIC, were not significant. These findings suggest that the methodology proposal was capable of indicating minute differences sensible to alterations in the EMG signals, allowing identification of the moment when the MDF and the RMS showed significant changes in behavior. The methodology used was also a viable one for describing and identifying the neuromuscular fatigue onset by means of the analysis of EMG signals.

Surface Electromyography Assessments of the Vastus medialis and Rectus femoris Muscles and Creatine Kinase after Eccentric Contraction Following Glutamine Supplementation

Purpose

L-glutamine is the most abundant amino acid found in human muscle and plays an important role in protein synthesis and can reduce the levels of inflammation biomarkers and creatine kinase (CK) after training sessions. Delayed onset muscle soreness (DOMS) develops after intense exercise and is associated with an inflammatory response. The purpose of this study was to investigate the effect of glutamine supplementation on surface electromyography activity of the vastus medialis muscle (VMM) and rectus femoris muscle (RFM) and levels of creatine kinase after an eccentric contraction.

Methods

Seventeen healthy men (age: 22.35±2.27yr; body mass: 69.91± 9.78kg; height: 177.08±4.32cm) were randomly assigned to experimental (n=9) and control groups (n=8) in a double-blind manner. In both groups, subjects were given L-glutamine supplementation (0.1g.kg^-1) or placebo three times a week for 4 weeks. Median frequency (MDF) and mean power frequency (MPF) for VMM and RFM muscles and also CK measurements were performed before, 24h and 48 h after a resistance training session. The resistance training included 6 sets of eccentric leg extensions to exhaustion with 75% of 1RM.

Results

There was no significant difference between groups for MDF or MPF in VMM and RFM. The difference of CK level between the groups was also not significant.

Conclusion

The results of this study indicate that glutamine supplementation has no positive effect on muscle injury markers after a resistance training session.

Time course of low- and high-volume strength training on neuromuscular adaptations and muscle quality in older women

This study investigated the effects of low- and high-volume strength trainings on neuromuscular adaptations of lower- and upper-body muscles in older women after 6 weeks (6WE), 13 weeks (13WE), and 20 weeks (20WE) of training. Healthy older women were assigned to low-volume (LV) or high-volume (HV) training groups. The LV group performed one set of each exercise, while the HV group performed three sets, 2 days/week. Knee extension and elbow flexion one-repetition maximum (1-RM), maximal isometric strength, maximal muscle activation, and muscle thickness (MT) of the lower- and upper-body muscles, as well as lower-body muscle quality (MQ) obtained by ultrasonography, were evaluated. Knee extension and elbow flexion 1-RM improved at all time points for both groups; however, knee extension 1-RM gains were greater for the HV group after 20WE. Maximal isometric strength of the lower body for both groups increased only at 20WE, while upper-body maximal isometric strength increased after 13WE and 20WE. Maximal activation of the lower and upper body for both groups increased only after 20WE. Both groups showed significant increases in MT of their lower and upper body, with greater gains in lower-body MT for the HV group at 20WE. MQ improved in both groups after 13WE and 20WE, whereas the HV group improved more than the LV group at 20WE. These results showed that low- and high-volume trainings have a similar adaptation time course in the muscular function of upper-body muscles. However, high-volume training appears to be more efficient for lower-body muscles after 20 weeks of training.

Sex comparisons for relative peak torque and electromyographic mean frequency during fatigue

PURPOSE

This study compared the relative peak torque and normalized electromyographic (EMG) mean frequency (MNF) responses during fatiguing isokinetic muscle actions for men versus women.

METHOD

Twenty men (Mage +/- SD = 22 +/- 2 years) and 20 women (Mage +/- SD = 22 +/- 1 years) performed 50 maximal concentric isokinetic muscle actions of the leg extensors at a velocity of 180 degrees/s while surface EMG signals were detected from the vastus lateralis, rectus femoris, and vastus medialis. The dependent variables were initial, final, and average peak torque; percent decline; the estimated percentage of fast-twitch fibers for the vastus lateralis; and the linear slope coefficients and y-intercepts for normalized EMG MNF versus repetition number. The data were analyzed with independent-samples t tests and 2-way mixed-factorial analyses of variance.

RESULTS

The mean initial, final, and average peak torque values for men were greaterthan those for women. There were no mean differences for percent decline and the estimated percentage of fast-twitch fibers for the vastus lateralis. There were also no sex differences for the linear slope coefficients, but there were differences among the muscles (vastus medialis > vastus lateralis > rectus femoris). The mean y-intercept for the vastus lateralis for men was greater than that for women.

CONCLUSIONS

Men demonstrated greater peak torque values than those for women, but the declines in peak torque and normalized EMG MNF were similar between thesexes. The vastus medialis was more fatigue-resistant than both the vastus lateralis and rectus femoris.

Biomechanical changes at the knee after lower limb fatigue in healthy young women

BACKGROUND

The purpose of this study was to identify changes in knee kinematics, kinetics and stiffness that occur during gait due to lower limb neuromuscular fatigue.

METHODS

Kinematic, kinetic and electromyographic measures of gait were collected on healthy, young women (n=20) before and after two bouts of fatigue. After baseline gait analysis, two bouts of fatiguing contractions were completed. Fatigue was induced using sets of 50 isotonic knee extensions and flexions at 50% of the peak torque during a maximum voluntary isometric contraction. Fatigue was defined as a drop in knee extension or flexion maximum voluntary isometric torques of at least 25% from baseline. Gait analyses were completed after each bout of fatigue. Dynamic knee stiffness was calculated as the change in knee flexion moment divided by the change in knee flexion angle from 3 to 15% of the gait cycle. Co-activations of the biceps femoris and rectus femoris muscles were calculated from 3 to 15% and 40 to 52% of gait. Repeated measures analyses of variance assessed differences in discrete gait measures, knee torques, and electromyography amplitudes between baseline and after each bout of fatigue.

FINDINGS

Fatigue decreased peak isometric torque. Fatigue did not alter knee adduction moments, knee flexion angles, dynamic knee stiffness, or muscle co-activation. Fatigue reduced the peak knee extension moment.

INTERPRETATION

While neuromuscular fatigue of the knee musculature alters the sagittal plane knee moment in healthy, young women during walking, high intensity fatigue is not consistent with known mechanical environments implicated in knee pathologies or injuries.

The vector of quadriceps pull is directed from the patella to the femoral neck

BACKGROUND

The quadriceps is the primary extensor of the knee. Its vector, which is perpendicular to the flexion axis of the knee, is important in understanding knee function and properly aligning total knee components. Three-dimensional (3-D) imaging enables evaluation using a 3-D model of each quadriceps component.

QUESTIONS/PURPOSES

We calculated the direction and magnitude of the quadriceps vector (QV) and the precision of the measurement, and asked whether the QV bears a constant relationship to the femur and is aligned with an anatomically based axis on the femur.

METHODS

Using CT data of 14 subjects, we created a 3-D solid model of each quadriceps muscle component. Vectors (3-D direction and length) for each quadriceps component were determined using principal component analysis for muscle direction and volume for magnitude; vector addition established the directional vector of the combined muscle. The combined vector originating in the center of the patella was compared with the shaft, mechanical, and spherical (center femoral head to center medial side of the knee) axes.

RESULTS

The QV passed from the patella center proximally crossing the femoral neck between the femoral head and greater trochanter and was most closely aligned with the spherical axis.

CONCLUSIONS

The QV axis may be an important reference for alignment of total knee components.

CLINICAL RELEVANCE

The spherical axis can be used in aligning total knee components to the flexion axis of the knee.

Alternate muscle activity patterns among synergists of the quadriceps femoris including the vastus intermedius during low-level sustained contraction in men

INTRODUCTION

We quantified the alternate muscle activity among four synergists of the quadriceps femoris (QF), including the vastus intermedius (VI), during low-level sustained contraction.

METHODS

Surface electromyograms (EMGs) were recorded from the VI, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) in 11 healthy men during isometric knee extension at 2.5% maximum voluntary contraction for 60 min to determine alternate muscle activity among the four synergists of the QF.

RESULTS

Alternate activity was primarily found between the RF and VI, VL, or VM, and rarely found among the vasti muscles. Multiple muscle comparison revealed the duration of alternate activity in the RF/VI+VL+VM combination remained high throughout the experiment, although the frequency of that combination did not.

CONCLUSIONS

These results suggested that there is a fixed muscle combination, i.e., RF and the 3 vasti muscles, to perform low-intensity sustained contraction in the human QF.

Influence of muscular fatigue on skiing performance during parallel turns

Muscular fatigue and muscle-activation patterns during a skiing demonstration (down a coarse around 4000 m long) was evaluated. Nine subjects participated in skiing trials and pre-training with a squat exercise. Surface electromyogram (SEMG) signals from the agonist and antagonist muscles around the knee at certain knee-joint angles were recorded. The SEMG signals showed that experienced skiers maintained their posture regardless of muscle fatigue by means of sustained muscle contractions in accordance with the change in inclination of the slope. In contrast, intermediate skiers did not maintain their posture (because of muscle fatigue) and distributed their strength over muscles to co-contract with each other. It is concluded from this result that the influence of muscle fatigue on skiing performance is related to skill level.(1).

Gait analysis using wearable sensors

Gait analysis using wearable sensors is an inexpensive, convenient, and efficient manner of providing useful information for multiple health-related applications. As a clinical tool applied in the rehabilitation and diagnosis of medical conditions and sport activities, gait analysis using wearable sensors shows great prospects. The current paper reviews available wearable sensors and ambulatory gait analysis methods based on the various wearable sensors. After an introduction of the gait phases, the principles and features of wearable sensors used in gait analysis are provided. The gait analysis methods based on wearable sensors is divided into gait kinematics, gait kinetics, and electromyography. Studies on the current methods are reviewed, and applications in sports, rehabilitation, and clinical diagnosis are summarized separately. With the development of sensor technology and the analysis method, gait analysis using wearable sensors is expected to play an increasingly important role in clinical applications.

Electromyographic normalization procedures for determining exercise intensity of closed chain exercises for strengthening the quadriceps femoris muscles

The purpose of this study was to compare the electromyographic (EMG) amplitudes of the quadriceps femoris (QF) muscles during a maximum voluntary isometric contraction (MVIC) to submaximal and maximal dynamic concentric contractions during active exercises. A secondary purpose was to provide information about the type of contraction that may be most appropriate for normalization of EMG data if one wants to determine if a lower extremity closed chain exercise is of sufficient intensity to produce a strengthening response for the QF muscles. Sixty-eight young healthy volunteers (39 female, 29 male) with no lower extremity pain or injury participated in the study. Surface electrodes recorded EMG amplitudes from the vastus medialis obliquus (VMO), rectus femoris (RF), and vastus lateralis (VL) muscles during 5 different isometric and dynamic concentric exercises. The last 27 subjects performed an additional 4 exercises from which a second data set could be analyzed. Maximum isokinetic knee extension and moderate to maximum closed chain exercises activated the QF significantly more than a MVIC. A 40-cm. lateral step-up exercise produced EMG amplitudes of the QF muscles of similar magnitude as the maximum isokinetic knee extension exercises and would be an exercise that could be considered for strengthening the QF muscles. Most published EMG studies of exercises for the QF have been performed by comparing EMG amplitudes during dynamic exercises to a MVIC. This procedure can lead one to overestimate the value of a dynamic exercise for strengthening the QF muscles. We suggest that when studying the efficacy of a dynamic closed chain exercise for strengthening the QF muscles, the exercise be normalized to a dynamic maximum muscle contraction such as that obtained with knee extension during isokinetic testing.

Delayed-onset muscle soreness alters the response to postural perturbations

INTRODUCTION

Eccentric contractions induce muscle fiber damage that is associated with delayed-onset muscle soreness and an impaired ability of the muscle to generate voluntary force. Pain and pathophysiological changes within the damaged muscle can delay or inhibit neuromuscular responses at the injured site, which is expected to have an effect on reflex activity of the muscle.

PURPOSE

The aim of the study was to investigate the reflex activity of knee muscles to rapid destabilizing perturbations, before, immediately after, and 24 and 48 h after eccentric exercise.

METHODS

Bipolar surface EMG signals were recorded from 10 healthy men with seven pairs of electrodes located on the knee extensor muscles (vastus medialis, rectus femoris, and vastus lateralis) and knee flexor muscles (the medial and lateral heads of the hamstring and the medial and lateral heads of gastrocnemius) of the right leg during rapid perturbations.

RESULTS

The maximal voluntary contraction force decreased by 24% ± 4.9% immediately after exercise and remained reduced by 21.4% ± 4.1% at 24 h and by 21.6% ± 9.9% at 48 h after exercise with respect to baseline. During the postexercise postural perturbations, the EMG average rectified value of the knee extensor muscles was significantly lower than baseline (P < 0.001). Moreover, the decrease in average rectified value over time during postexercise sustained contractions was greatest compared with the session before exercise (P < 0.0001).

CONCLUSIONS

Reflex activity in leg muscles elicited by rapid destabilizing perturbations is reduced after exercise-induced muscle soreness.

Goniometer crosstalk compensation for knee joint applications

Electrogoniometers are prone to crosstalk errors related to endblocks rotation (general crosstalk) and to the characteristics of each sensor (individual crosstalk). The aim of this study was to assess the crosstalk errors due to endblock misalignments and to propose a procedure to compensate for these errors in knee applications. A precision jig was used to simulate pure ±100° flexion/extension movements. A goniometer was mounted with various degrees of valgus/varus (±20°) and rotation (±30°) misalignments. For valgus/varus misalignments, although offset compensation eliminated the error in the valgus/varus recordings for 0° of flexion/extension and reduced it to a few degrees for small (±30°) flexion/extension angles (root mean square error = 1.1°), the individual crosstalk caused pronounced errors for large (±100°) angles (18.8°). Subsequent compensation for this crosstalk reduced these errors to 0.8° and 4.5°, respectively. For rotational misalignment, compensation for the general crosstalk by means of coordinate system rotation, in combination with compensation for the individual crosstalk, reduced the errors for small (±30°) and large (±100°) flexion/extension angles from 3.6° to 0.5° and from 15.5° to 2.4°, respectively. Crosstalk errors were efficiently compensated by the procedures applied, which might be useful in preprocessing of knee functional data, thereby substantially improving goniometer accuracy.

Effect of delayed-onset muscle soreness on muscle recovery after a fatiguing isometric contraction

An increase to above-baseline levels of electromyography (EMG) mean power spectral frequency (MPF) has been observed previously during muscle recovery following fatiguing contractions and has been explained by membrane hyperpolarization due to increased activation of the Na+-K+ pump. It is hypothesized that this membrane mechanism is impaired by muscle fiber damage following eccentric exercise. Thus, the aim of the study was to investigate surface EMG signal characteristics during recovery from fatigue after eccentric exercise. Ten healthy subjects performed sustained isometric knee extensions at 40% of the maximal torque (MVC) until task failure before, immediately after and 24 and 48 h after eccentric exercise. Bipolar surface EMG signals were recorded from six locations over the quadriceps during the sustained isometric contraction and during 3-s long contractions at 40% MVC separated by 1-min intervals for 15 min (recovery). Before the eccentric exercise, MPF of EMG signals increased to values above baseline during recovery from the fatiguing isometric contraction (P<0.001), whereas immediately after and 24 and 48 h after the eccentric task, MPF was lower than baseline during the entire recovery period (P<0.01). In conclusion, delayed-onset muscle soreness abolished the supranormal increase in EMG MPF following recovery from fatigue.

Principal components of frequency domain electromyograms for muscular fatigue analysis

The parameters commonly employed for muscular fatigue (MF) analysis, the mean frequency (F(mean)) and median frequency (F(median)) of surface EMG (SEMG) spectra, did not present consistent results for exercises performed at low to moderate intensities. For overcoming this limitation, the present study proposes the use of principal component (PC) analysis of SEMG spectra for MF monitoring. The SEMG from vastus lateralis muscle of 24 young male subjects were recorded during a maximal effort test in cycle ergometer. Epochs of 200 ms SEMG, extracted from each period of muscle activation of each subject were used for estimating the amplitude spectra, which were employed to obtain the first two PCs. The PC coefficients from the first 40 spectra were used as a reference for calculating the standard distance. This index presented a consistent increase along the exercise, while the values of F(mean) and F(median) did not present any pattern. Comparisons between initial and final values from all subjects show no significant changes in F(mean) and F(median) (Student t test, P > 0.05) and a significant increase (P < 10(-3)) in standard distance, indicating this index as an alternative to MF analysis in cyclical exercises.

Differentiation of power and endurance athletes based on their muscle fatigability assessed by new spectral electromyographic indices

The aim of this study was to differentiate between endurance and power athletes based on electromyographic (EMG) data analysed using new spectral indices. Nine endurance and six strength athletes were recruited to complete sets of knee extension repetitions (15 per set) until exhaustion, with each set followed by a maximal voluntary isometric knee extensor contraction. Peripheral muscle fatigue of the vastus lateralis, vastus medialis, and rectus femoris (bilaterally) was quantified by the changes in median frequency of the EMG power spectrum and a new spectral EMG fatigue index. Cluster analysis of the fatigue indices differentiated athletes into two groups: endurance (fatigue resistant) and strength (faster fatigue), whereas cluster analysis of the median EMG power spectrum frequency produced six indistinct groups. The average fatigue index for the quadriceps group increased across repetitions by 40 +/- 24% in the endurance group and by 184 +/- 12% in the strength group. The decrease in peak force and power across repetitions, and the rate of force decrease during maximal voluntary contraction per set, were significantly smaller for the endurance than for the strength group. The new spectral EMG indices effectively discriminated between strength and endurance athletes, thus providing a useful functional index that could be applied to track training adaptations as well as potentially talent identification.

Effects of a prior high-intensity knee-extension exercise on muscle recruitment and energy cost: a combined local and global investigation in humans

The effects of a priming exercise bout on both muscle energy production and the pattern of muscle fibre recruitment during a subsequent exercise bout are poorly understood. The purpose of the present study was to determine whether a prior exercise bout which is known to increase O(2) supply and to induce a residual acidosis could alter energy cost and muscle fibre recruitment during a subsequent heavy-intensity knee-extension exercise. Fifteen healthy subjects performed two 6 min bouts of heavy exercise separated by a 6 min resting period. Rates of oxidative and anaerobic ATP production, determined with (31)P-magnetic resonance spectroscopy, and breath-by-breath measurements of pulmonary oxygen uptake were obtained simultaneously. Changes in muscle oxygenation and muscle fibre recruitment occurring within the quadriceps were measured using near-infrared spectroscopy and surface electromyography. The priming heavy-intensity exercise increased motor unit recruitment (P < 0.05) in the early part of the subsequent exercise bout but did not alter muscle energy cost. We also observed a reduced deoxygenation time delay, whereas the deoxygenation amplitude was increased (P < 0.01). These changes were associated with an increased oxidative ATP cost after approximately 50 s (P < 0.05) and a slight reduction in the overall anaerobic rate of ATP production (0.11 +/- 0.04 mM min(-1) W(-1) for bout 1 and 0.06 +/- 0.11 mM min(-1) W(-1) for bout 2; P < 0.05). We showed that a priming bout of heavy exercise led to an increased recruitment of motor units in the early part of the second bout of heavy exercise. Considering the increased oxidative cost and the unaltered energy cost, one could suggest that our results illustrate a reduced metabolic strain per fibre.

Análise da fadiga muscular localizada em atletas e sedentários através de parâmetros de freqüência do sinal eletromiográfico

Embora a análise no domínio da freqüência do sinal eletromiográfico (EMG) seja empregada na caracterização do processo de fadiga muscular localizada, sua aplicação, especificamente a da freqüência mediana (Fmed), é pouco explorada no âmbito esportivo. O objetivo do presente estudo foi verificar a viabilidade da aplicação do sinal EMG, através de sua análise no domínio da freqüência, como parâmetro para determinação e diferenciação no comportamento da fadiga muscular localizada. Dois grupos de sujeitos, um caracterizado como atletas (n =12) e outro como sedentários (n =12), foram submetidos a análises baseadas em procedimentos executados em três diferentes situações experimentais, todos envolvendo a modalidade de exercício isométrico: i) teste máximo para determinação da contração isométrica voluntária máxima (CIVM); ii) teste de fadiga, sustentado por 35 seg. a 80% da CIVM; iii) teste de recuperação, sustentado por 10 seg. a 80% da CIVM; neste ultimo foi monitorado o comportamento da Fmed nos três primeiros (Fmedi) e três últimos segundos (Fmedf) do sinal EMG no músculo tibial anterior durante o teste de fadiga. Durante os 10 segundos do teste de recuperação foi calculada a Fmed referente a todo o período (Fmedr). parâmetro utilizado no cálculo do índice de recuperação muscular (IRM). Os resultados apontam que a Fmedf apresentou valor menor em relação à Fmedi em ambos os grupos (p < 0,05). Quando comparado com o grupo de sedentários, o grupo de atletas apresentou valores maiores de Fmedi e Fmedf (p < 0,05). O valor médio e desvio-padrão do IRM para o grupo de atletas foram de 62,1% ± 28,7 e, para o grupo de sedentários, de 55,2% ± 27,8 (p > 0,05). Dessa forma, os resultados apresentados neste estudo permitem inferir a viabilidade na aplicação de parâmetros no domínio da freqüência do sinal EMG para a determinação e diferenciação do comportamento da fadiga muscular localizada.