Electromyographic Median Frequency Research Articles

Lower limb muscle fatigue during walking in children with cerebral palsy.

AimTo investigate whether more prominent signs of muscle fatigue occur during self‐paced walking in children with cerebral palsy (CP) compared to typically developing peers.MethodIn this case–control study, 13 children with CP (four males, nine females; mean age [SD] 11y 4mo [3y 8mo]; nine in Gross Motor Function Classification System [GMFCS] level I, three in GMFCS level II, and one in GMFCS level III) and 14 typically developing peers (nine males, five females; mean age [SD] 9y 10mo [1y 10mo]) walked 5 minutes overground at a self‐selected walking speed. Electromyography (EMG) median frequency and root mean square (RMS) were identified per gait cycle from EMG recordings of the tibialis anterior, gastrocnemius medialis, soleus, rectus femoris, and semitendinosus. Rate of change in those variables was analysed using mixed linear model analyses.ResultsThe decrease in EMG median frequency of gastrocnemius medialis and soleus and increase in EMG‐RMS of tibialis anterior, gastrocnemius medialis, and soleus were significantly larger in the most affected leg of children with CP compared with typically developing peers.InterpretationIncreased selective muscle fatigue of the lower leg muscles was observed during self‐paced walking in children with mild‐to‐moderate severe CP. This could contribute to and account for limited walking capacity.What this paper adds Children with cerebral palsy (CP) show more signs of lower leg muscle fatigue than typically developing peers.No signs of muscle fatigue were observed in upper leg muscles of children with CP.

The Effect of Repetitive Rugby Scrummaging on Force Output and Muscle Activity

During rugby scrummaging, front row forwards encounter high levels of force that has been suggested to cause transient fatigue and is likely to reduce subsequent performance. However, little is known about the effect of repetitive scrummaging on force output and onset of fatigue. Twelve male front row forwards (21.5±2.3 yr; height 185.7±4.4 cm; body mass 108.5±7.1 kg) each performed three sets of five maximal-effort isometric scrums for 10 s, with 40 s rest separating each repetition; 2 min recovery was provided between each set. Force output and electromyography (EMG) of the right medial gastrocnemius (MG), biceps femoris (BF), gluteus maximus (GM), erector spinae (ES), rectus abdominis (RA), external oblique (EO), internal oblique (IO), and rectus femoris (RF) were assessed. There was no significant force decrement from performing 15 scrums and no fatigue was detected from EMG median frequency and mean amplitude. For training and practice purposes, coaches and trainers can be confident that 15 individual repetitive static scrums against a machine are unlikely to cause a reduction in force production and promote fatigue. However, the effect of rugby-related activities in conjunction with scrummaging requires further research to determine if transient fatigue is causal to scrummaging for subsequent performance.

Muscle Activity Adaptations to Spinal Tissue Creep in the Presence of Muscle Fatigue.

AimThe aim of this study was to identify adaptations in muscle activity distribution to spinal tissue creep in presence of muscle fatigue.MethodsTwenty-three healthy participants performed a fatigue task before and after 30 minutes of passive spinal tissue deformation in flexion. Right and left erector spinae activity was recorded using large-arrays surface electromyography (EMG). To characterize muscle activity distribution, dispersion was used. During the fatigue task, EMG amplitude root mean square (RMS), median frequency and dispersion in x- and y-axis were compared before and after spinal creep.ResultsImportant fatigue-related changes in EMG median frequency were observed during muscle fatigue. Median frequency values showed a significant main creep effect, with lower median frequency values on the left side under the creep condition (p≤0.0001). A significant main creep effect on RMS values was also observed as RMS values were higher after creep deformation on the right side (p = 0.014); a similar tendency, although not significant, was observed on the left side (p = 0.06). A significant creep effects for x-axis dispersion values was observed, with higher dispersion values following the deformation protocol on the left side (p≤0.001). Regarding y-axis dispersion values, a significant creep x fatigue interaction effect was observed on the left side (p = 0.016); a similar tendency, although not significant, was observed on the right side (p = 0.08).ConclusionCombined muscle fatigue and creep deformation of spinal tissues led to changes in muscle activity amplitude, frequency domain and distribution.

Relative Importance of Four Muscle Groups for Indoor Rock Climbing Performance.

Little research is available to guide training programs for rock climbers. To help meet this need, we sought to determine the relative importance of 4 muscle groups for rock climbing performance. Eleven male climbers were familiarized with an indoor climbing route before 5 separate days of testing. On testing days, subjects were randomly assigned to climb with no prefatiguing exercise (control climb) or after a prefatiguing exercise designed to specifically target the digit flexors (DF), shoulder adductors (SA), elbow flexors (EF), or lumbar flexors (LF). Immediately after the prefatiguing exercise, the subject climbed the route as far as possible without rest until failure. The number of climbing moves was recorded for each climb. Surface electromyography of the target muscles was recorded during the prefatigue. Fewer climbing moves were completed after prefatigue of the DF (50 ± 18%) and EF (78 ± 22%) (p ≤ 0.05) compared with the control climb. The number of moves completed after prefatigue of the LF and SA were not statistically significant compared with the control climb (p > 0.05). The short time lapse between the end of prefatiguing exercise and the start of climbing (transit time), which may have allowed for some recovery, was not different among trials (p > 0.05). Electromyography median frequency was reduced from beginning to end of each prefatiguing exercise. These results suggest that among the muscle groups studied in men, muscular endurance of DF and EF muscle groups is especially important for rock climbing on 40° overhanging terrain.

EMG Assessment of Muscle Fatigue in Elite Paralympic Athletes

PURPOSE: The Paralympic Research and Sport Science Consortium (PRSSC) has identified electromyography (EMG) analysis of wheelchair sport performance to be a major research need. EMG analysis can be used to design evidence-based training programs through the understanding of sport-specific fatigue.The purpose of the current study was to document fatigue and associated compensation among push and recovery muscles during a Paralympic Rugby training camp. METHODS: Wheelchair rugby players were recruited from a Paralympic training facility (Lakeshore Foundation, Birmingham, AL, USA). Three national team wheelchair rugby players completed 5 training sessions (3 hours each) over 2 training days. A 16-channel Noraxon EMG system 1400A (Scottsdale, AZ) with telemetry (Telemyo DTS) was used to assess EMG data of the pectoralis major (PM), anterior deltoid (AD), posterior deltoid (PD), upper trapezius (UT), biceps (B), triceps (T), and latissimus dorsi (LD). To assess fatigue, changes in EMG median frequency and mean amplitude across each training session and each training day were examined. IRB approval and informed consent were obtained prior to the study. RESULTS: Fatigue of the PM was most substantial, approaching 30% within an hour of training activity. A 25% fatigue of the AD was also present during the first training session. Some fatigue was demonstrated in BB and T during the first training session (<8%) but these muscles recovered over a training day and generated greater force production over additional training sessions. Increased force production was demonstrated in the UT throughout a training day to compensate for shoulder flexor fatigue. Function of the PD and LD were varied across participants. CONCLUSIONS: In the current study, Paralympic rugby athletes demonstrated fatigue in shoulder flexors, namely pectoralis major and anterior deltoid. Fatigue was demonstrated within the first training session of a prolonged training camp and was typically present across a training day. Whereas shoulder joint muscles fatigued, the elbow joint muscles demonstrated recovery and ultimately increased force output across a training day to compensate. This finding is typical in wheelchair users as force production moves from the shoulder joint to elbow and wrist joints when the prime movers become fatigued.

Carbohydrate Mouth Rinse Counters Fatigue Related Strength Reduction.

The purpose was to determine the effect of carbohydrate (CHO) mouth rinse on maximal voluntary contraction (MVC) and neuromuscular output in a fatigued state. It was hypothesized that CHO mouth rinse would potentiate torque output in a fatigued state. In a double-blind, cross-over design, 12 competitive male athletes (9 rowers, 1 cyclist, 1 runner and 1 volleyball player) initially performed 3 × 5 s MVC isometric knee extensions followed by a 50% MVC contraction until volitional exhaustion, with quadriceps muscle activity measured via electromyography (EMG). Immediately after, either an 8% CHO maltodextrin (WASH), or noncaloric artificial sweetener (PLA) was mouth rinsed for 10sec, before 3 × 5 s final MVCs. Fatigue caused a significant decline in post fatigue MVC trial 1 for 3 s average torque (p = .03) and peak torque (p = .02) for PLA. This fatigue related decline in torque was not noticed for WASH, with a 2.5% and 3.5% less attenuation in peak and average torque, respectively in post fatigue MVC1 compared with PLA. The effect size for MVC trial 1 between WASH/PLA was seen to be small positive (ES = 0.22; 55% likelihood of positive). Overall for EMG RMS, there were no significant differences between PLA and WASH among all muscles. EMG median frequency showed comparable results between conditions with significant reductions due to fatigue. Taken together, this evidence suggests that the attenuation of torque post fatigue was less for CHO mouth rinse than a placebo. Even though the gains were marginal, these discoveries may play an important role in sport performance, as small performance effects can have significant outcomes in real-world competitions.

Muscular fatigue of the lower limb and subsequent joint angle adaptations during a 16.1km cycling time trial

Background: Effective muscular recruitment during cycling is crucial to optimising performance.  As such, much research has examined when muscles are active during the pedal revolution and how muscle co-activation may influence pedalling technique but little evidence associated with the effect of fatigue on lower limb joint angles and its subsequent effect on power output and muscle recruitment.  Purpose: Are changes in muscular recruitment patterns and changes in lower limb kinematics detrimental to performance?  Methods: A preliminary case study of a well-trained veteran cyclist (V I‡O2peak  49.9 ml . kg-1 . min-1 and PPO of 400W) conducted a 16.1km simulated cycling time trial on a Wattbike Pro at 80% PPO with a cadence of 98 rpm.  Bilateral surface EMG were employed using pairs of Ag/AgCl electrodes adhered to both right and left vastus medialis (VM), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (GM).  Intervals of sixty seconds in duration, of 3D kinematic and electromyography (EMG) data were synchronised using a Vicon motion capture system throughout the time trial.  Ten consecutive pedal revolutions per 60 s interval were processed for subsequent analysis.    Kinematic and EMG data signals were imported into Visual 3D v.5 and Matlab for processing.  Results: There were statistically significant changes (p<0.05) in all kinematic data across nine time points.  Fundamental changes occurred between minute 10-12 with a decrease in flexion angle for the left hip (z = -9.56, p<0.05, r = 0.55), and the right hip, (z = -7.67, p<0.05, r = 0.44).  The left ankle starts to have a greater planter flexion (z = -9.69, p<0.05, r = 0.56) between minutes 10-12 and this continues to have a significant change between time points for the remainder of the trial.  The magnitude of EMG data revealed that there were statistically significant changes (p<0.05) in all muscles across seven time points.  Decreases in the magnitude of activation were observed between minutes 8-10 for both the left (z = -9.17, p<0.05, r = 0.53) and right (z = -8.21, p<0.0005, r = 0.48) TA.  The frequency domain EMG analysis indicated a trend towards lower frequencies being recorded for the left and right TA and GM with a trend towards higher frequencies being recorded for the left and right VM.  Analysis of the Wattbike data indicated that there were statistically significant differences from minutes 1 to 20 between left and right angle to peak force applied to the crank (t(19) = 20.89, p<0.05) with no statistical significance between left and right limb percentage use (95% CI 2.81, 3.31%).  Indications showed that there was a higher magnitude of activation for the left leg across all muscles tested and the Wattbike data indicates greater power generation on the left side of the pedal revolution.  Discussion: Based on the results from this study there were decreases in the ankles range of motion (ROM) with increases in hip flexion from minute 10-12 with changes in neuromuscular activity between minutes 8-10 then there were smaller effect changes for the remainder of the time trial.  The alterations in the EMG median frequency indicated a trend towards muscular fatigue for TA and GM with increases in neuromuscular activity in both VM’s possibly counteracting fatigue.  The ankle’s decrease in ROM may be a product of fatigue associated with the TA and GM but by becoming stiffer it may optimise the foot/pedal interface.  Even with these changes in kinematic and EMG data the power output remained constant.  Conclusion: As this was a case study further work in this area needs to be considered in establishing variability in joint angles and how they may be beneficial/detrimental in generating the same level of power output when fatigued.  An association of muscular fatigue in cycling and changes to lower limb joint angle variability requires further investigation examining joint coupling patterns, independent pedal power analysis and cross reference to physiological parameters for fatigue to establish strategies that may be beneficial in improving cycling performance.

Reliability of telemetric electromyography and near-infrared spectroscopy during high-intensity resistance exercise

This study quantified the inter- and intra-test reliability of telemetric surface electromyography (EMG) and near infrared spectroscopy (NIRS) during resistance exercise. Twelve well-trained young men performed high-intensity back squat exercise (12 sets at 70–90% 1-repetition maximum) on two occasions, during which EMG and NIRS continuously monitored muscle activation and oxygenation of the thigh muscles. Intra-test reliability for EMG and NIRS variables was generally higher than inter-test reliability. EMG median frequency variables were generally more reliable than amplitude-based variables. The reliability of EMG measures was not related to the intensity or number of repetitions performed during the set. No notable differences were evident in the reliability of EMG between different agonist muscles. NIRS-derived measures of oxyhaemoglobin, deoxyhaemoglobin and tissue saturation index were generally more reliable during single-repetition sets than multiple-repetition sets at the same intensity. Tissue saturation index was the most reliable NIRS variable. Although the reliability of the EMG and NIRS measures varied across the exercise protocol, the precise causes of this variability are not yet understood. However, it is likely that biological variation during multi-joint isotonic resistance exercise may account for some of the variation in the observed results.

Shifts in EMG spectral power during fatiguing dynamic contractions

We examined the etiology of the electromyographic (EMG) spectral shift during dynamic fatigue. Nineteen subjects (mean ± SD age = 22.4 ± 1.6 years) performed 50 consecutive maximal concentric isokinetic contractions of dominant leg extensors. Surface EMG signals were detected from the vastus lateralis, rectus femoris, and vastus medialis during each contraction, processed with a wavelet analysis, and the resulting spectra were decomposed with a nonparametric spectral decomposition procedure. The results indicated that the decreases in EMG frequency during the 50 contractions were generally due to reductions in high-frequency power and increases in low-frequency power. In addition, the spectral shifts were most pronounced for the rectus femoris, followed by the vastus lateralis, and then the vastus medialis. The spectral decomposition procedure is much more sensitive for tracking dynamic fatigue than is EMG mean frequency or median frequency.

Fatigue and muscle activation during submaximal elbow flexion in children with cerebral palsy

The purpose of this study was to investigate whether children with cerebral palsy (CP), like typically developing peers, would compensate for muscle fatigue by recruiting additional motor units during a sustained low force contraction until task failure.Twelve children with CP and 17 typically developing peers performed one submaximal isometric elbow flexion contraction until the task could no longer be sustained at on average 25% (range 10–35%) of their maximal voluntary torque. Meanwhile surface electromyography (EMG) was measured from the biceps brachii and triceps brachii, and acceleration variations of the forearm were detected by an accelerometer. Slopes of the change in EMG amplitude and median frequency and accelerometer variation during time normalised to their initial values were calculated.Strength and time to task failure were similar in both groups. Children with CP exhibited a lower increase in EMG amplitude of the biceps brachii and triceps brachii during the course of the sustained elbow flexion task, while there were no significant group differences in median frequency decrease or acceleration variation increase. This indicates that children with CP do not compensate muscle fatigue with recruitment of additional motor units during sustained low force contractions.

On the Functional Capacity and Quality of Life of Patients with Acromegaly: Are They Candidates for Rehabilitation Programs?

[Purpose] This study compared patients having active acromegaly with those having controlled acromegaly in terms of peripheral muscle strength, body composition, and functional capacity. We also examined the associations between these measures. [Methods] A total of 14 patients with active acromegaly, 12 patients with controlled acromegaly, and 12 healthy controls were subjected to isometric dynamometry, surface electromyography, electrical bioimpedance, and a six-minute walk test. [Results] The active acromegaly group exhibited significantly more fat-free mass than the control group. With respect to the peripheral muscle performance, the controlled acromegaly group presented a significantly lower electromyographic median frequency than the control group. The quadriceps maximum strength was significantly lower in the controlled acromegaly group than in the control group. The fat-free mass was significantly correlated with the quadriceps maximum strength. The global scores of the Acromegaly Quality of Life Questionnaire were significantly correlated with the six-minute walk distance. [Conclusion] Patients with acromegaly have more fat-free mass, less peripheral muscle strength, and greater fatigability than healthy control subjects. These findings depend on the degree of hormonal control. In acromegalic patients, peripheral muscle strength is related to body composition, and functional capacity is correlated with quality of life.

Lower Extremity Neuromuscular Control Immediately After Fatiguing Hip-Abduction Exercise

Fatigue of the gluteus medius (GMed) muscle might be associated with decreases in postural control due to insufficient pelvic stabilization. Men and women might have different muscular recruitment patterns in response to GMed fatigue. To compare postural control and quality of movement between men and women after a fatiguing hip-abduction exercise. Descriptive laboratory study. Controlled laboratory. Eighteen men (age = 22 ± 3.64 years, height = 183.37 ± 8.30 cm, mass = 87.02 ± 12.53 kg) and 18 women (age = 22 ± 3.14, height = 167.65 ± 5.80 cm, mass = 66.64 ± 10.49 kg) with no history of low back or lower extremity injury participated in our study. Participants followed a fatiguing protocol that involved a side-lying hip-abduction exercise performed until a 15% shift in electromyographic median frequency of the GMed was reached. Baseline and postfatigue measurements of single-leg static balance, dynamic balance, and quality of movement assessed with center-of-pressure measurements, the Star Excursion Balance Test, and lateral step-down test, respectively, were recorded for the dominant lower extremity (as identified by the participant). We observed no differences in balance deficits between sexes (P > .05); however, we found main effects for time with all of our postfatigue outcome measures (P ≤ .05). Our findings suggest that postural control and quality of movement were affected negatively after a GMed-fatiguing exercise. At similar levels of local muscle fatigue, men and women had similar measurements of postural control.

Hip flexor muscle fatigue in patients with symptomatic femoroacetabular impingement

Patients with symptomatic femoroacetabular impingement (FAI) have considerable hip muscle weakness, in particular, hip flexion and hip adduction. In addition, they experience disabilities while performing prolonged dynamic tasks. It was therefore postulated that, besides hip flexor muscle weakness, patients with symptomatic FAI would show greater hip flexor fatigue compared with healthy controls. Hip flexor fatigue was evaluated in two different experiments. Fifteen patients with symptomatic FAI and 15 age-matched healthy controls were tested in each experiment. In the first one, changes in hip flexor torque fluctuations and electromyographic (EMG) activity were measured during a sustained submaximal isometric contraction. In the second experiment, hip flexor torque decline was measured during a series of 20 maximal dynamic contractions. Patients with FAI exhibited hip flexor weakness under both isometric (P = 0.02) and isokinetic conditions (P = 0.03). Fatigue-induced changes in isometric hip flexor torque fluctuations, EMG root mean square and median frequency did not differ significantly between patients and controls (P > 0.05). Similarly, isokinetic hip flexor torque decline was comparable in patients with FAI and controls (P > 0.05). None of the hip flexor fatigue outcomes considered here differed between patients with symptomatic FAI and controls. Therefore, the disabilities that patients experience while performing prolonged dynamic tasks do not seem to be caused by exaggerated hip flexor muscle fatigue.

Variation in Neuromuscular Activation of Loaded Explosive Movement

To understand the neuromuscular activation pattern of the elbow flexor muscle under different loads during explosive movements, the electromyography (EMG) signals were induced under different loads with movement. Twenty-one young male physical education students or collegiate sport players were voluntarily participated in this study. Each subject performed fast concentric movement of the elbow flexor muscle under 15%, 30%, 45%, 60%, 75%, 90%, and 105% of maximal voluntary contraction. A loadcell, goniometer and the Biovision EMG system were used to collect the signals for force, elbow angular displacement and EMG. After the data were processed, the SPSS software was used to calculate the values of the parameters, and simple regression was used to determine the relationship between loads and EMG amplitude as well as the relationship between loads and EMG median frequency (MDF). The significance level was set at .05. The results demonstrated that the EMG amplitudes of explosive movement remained high because of the maximal effort exerted when the loads were changed. In other words, the diversity of EMG amplitudes was independent of the variation in the loads. On the other hand, EMG MDF showed a linear positive correlation with load. These results suggest that explosive movement with a heavy load might be suitable for power training to improve the rate of force development by enhancing the efficiency of activation frequency, even though its movement velocity was not higher than that of explosive movement with a light load.

Effects of paraspinal fatigue on lower extremity motoneuron excitability in individuals with a history of low back pain

Individuals with low back pain (LBP) have been shown to demonstrate decreased quadriceps activation following lumbar paraspinal fatigue. The response of other lower extremity muscles is unknown. The purpose of this study was to determine changes in motoneuron pool excitability of the vastus medialis, fibularis longus, and soleus following lumbar paraspinal fatigue in individuals with and without a history of LBP. A controlled laboratory study was used to compare motoneuron pool excitability before and after a lumbar paraspinal fatiguing exercise. Twenty individuals (10 with history of LBP) performed isometric lumbar paraspinal exercise until a 25% shift in paraspinal muscle surface electromyography median frequency occurred. Motoneuron pool excitability, using H/M ratios of the vastus medialis, fibularis longus, and soleus before and immediately after a lumbar paraspinal fatiguing exercise. There was a significant (P=.03) increase of 15% in soleus H/M ratio in both groups following lumbar paraspinal fatigue. Neither group demonstrated changes in vastus medialis (P=.80) or fibularis longus (P=.86). Soleus motoneuron pool excitability increased following lumbar paraspinal fatigue independent of group allocation and occurred in the absence of changes in vastus medialis or fibularis longus muscles. Increased soleus motoneuron pool excitability may be a postural response to preserve lower extremity function.

Experimental simulated study on the break for manual lifting task by surface electromyography and electrocardiogram

To investigate the recovery duration of manual lifting tasks. 30 college student volunteers with gender equally distributed were involved in the simulated stoop-, squart- and semi squart-lifting tasks in the laboratory. Signals of electromyography (EMG) at the back muscles (left and right thorax m. erector spinae, LT(10) and RT(10); left and right lumbar m. erector spinae, LL(3) and RL(3)) and electrocardiography (ECG) were recorded during the rest intervals. The percentage of maximum voluntary electrical activation (MVE%), EMG median frequency (MF), and heart rate (HR) were analyzed to predict the recovery time required. During the break, MVE% at 4 back muscles of all the male subjects were recovered to resting level within 5 minutes and 91.8% were within 2 minutes. Except for RL(3) after squat- and stoop-lifting task, the MVE% of female subjects went back to resting level within 3 minutes and 67.8% were within 2 minutes. The MF of male subjects were recovered in 10 minutes and 74.9% within 2 minutes, with the exception of RL(3) after stoop- and squat-lifting tasks. All the female MF were recovered in 8 minutes and 83.4% were within 2 minutes. However, during the last 20 minute break after the lifting tasks, the MVE% and MF of all male and female subjects were recovered, while HR came back to resting level within 14 and 5 minutes, respectively. For the three manual lifting tasks with 25% MVC workload lasting for 4.5 min, a break of 15 minutes is sufficient for most erectors spinae to recover from local muscle load. However, in terms of the HR, a break of 15 minutes is enough for the recovery of systematic load.

Time-Frequency Analysis of Electromyographic Signal for the Biceps Brachii during Ramp Movements

To understand the neuromuscular activation patterns of the elbow flexor under different loads during weight training movement, we examined the electromyography (EMG) signal induced under different loads with ramp movement. Twenty-one young male physical education students or collegiate sport players voluntarily participated in this study. A force transducer, goniometer, and electromyographic system were used simultaneously with a data acquisition (DAQ) system to collect the signals for force, elbow angular displacement and EMG. The obtained data were analyzed by SPSS and simple regression was used to test the relationship between loads and EMG amplitude as well as the relationship between loads and EMG median frequency (MDF). The significance level was set at .05. The results revealed that the EMG amplitudes showed a linear positive correlation with the loads. On the other hand, the EMG MDF remained stable despite an increase in the loads. Therefore, the variation in EMG MDF was independent of the variation in the loads. These findings indicated that the linear relationship between activation pattern and load during ramp movement is attributable to fiber recruitment rather than firing frequency.

A Comparison of Hypertrophy Potential between the Vastus Lateralis and Rectus Femoris during Level Walking in Combination with Vascular Restriction

Recent research has found that by compressing blood flow to working muscle during lower body exercise involving short bouts of walk training results in an increased muscle volume and improved quadriceps strength. However, the effects of vascular restriction (VR) during walking on neuromuscular adaptations as assessed by electromyography (EMG) activity may provide insight on how low intensity training with vascular restriction can be applied to various modes of exercise. PURPOSE: The purpose of this study was to explore and compare muscle activation changes of the quadriceps muscles during walking using EMG with and without blood flow restriction. METHODS: EMG electrodes were placed along the longitudinal axis of the vastus lateralis (VL) and rectus femoris (RF) of the right thigh of seven male volunteers (mean ± SD age = 22.7 ± 6.8 years; height = 178 ±5.4 cm; weight = 82.6 ± 7.7 kg). Placement of the electrode was marked at a point of 33.3% on VL, and RF 50% of the distance between the lateral femoral epicondyle and the greater trochanter. On two separate testing sessions, subjects walked on a treadmill for two, 10 minutes bouts separated by a 5 min rest period at a speed of 80.4 m*min-1 with and without blood flow restriction. RESULTS: There were significant main effects for both condition (with and without VR) and muscles (VL and RF), as well as an interaction between condition and muscles (condition*muscle) for EMG amplitude (RMS). On the other hand, there were no significant main effects or interactions for EMG median frequency (MDF). CONCLUSIONS: The findings suggest that walking with VR might cause neural adaptation in both VL and RF, but the VL might have a better potential for hypertrophic response when performing slow walking with blood flow restriction. Walking speed and the pressure used for compression during walking might change the pattern of response, therefore, both need to be given careful consideration in the design of future studies.

Muscular Function Response to Walking Exercise in Combination with Vascular Restriction

Recent studies concluded that once-daily vascular restricted walk training produced physiologically significant increases in thigh muscle volume and knee joint strength, however the effects of vascular restriction (VR) on motor unit activation from electromyographic (EMG) activity has not been determined. Investigating the muscular function response to walking exercise with VR may help researchers to define the neuromuscular changes, if any, and to explain the adaptations occurring in skeletal muscle strength and size following training. PURPOSE: The purpose of this study was to examine the changes in EMG amplitude (RMS) and median frequency (MDF) patterns during maximum voluntary contraction (MVC) before and after walking combined with or without reduced blood flow. METHODS: Nine young healthy males (Mean ± SD age = 24.3 ± 6.5 years; height = 174.4 ±7.3 cm; weight = 81.3 ± 7.7 kg) had their pre-walk MVC determined by using Biodex. Surface EMG electrodes were placed along the longitudinal axis of the vastus lateralis (VL) and rectus femoris (RF) of the right thigh. The electrode placements on the VL were placed to a mark that was made at 33.3%, and RF 50%, of the distance from the lateral femoral epicondyle to the greater trochanter. On two separate testing sessions, each subject walked for 20 minutes (two bouts of 10 min walking) on a treadmill at a speed of 80.4 m.min-1 with and without blood flow restriction, with a 2 min rest interval between the bouts. After completing the walking exercise, each subject repeated the exact same MVC procedure using the Biodex to measure post-walk MVC. RESULTS: No significant condition (with or without VR) effect was detected (p>0.05) for the pre- and post-walk MVCs, but there was significant increases in EMG MDF from the pre- to post-walk MVC for both the VL and RF (p<0.01). There were no significant changes in EMG RMS from pre to post-walk MVC and torque values for either condition. CONCLUSIONS: Twenty minutes of walking with or without VR resulted in increases in EMG MDF values indicating increases in action potential conduction velocity of the active muscle fibers for both the VL and RF of the right leg during MVC.

A dynamic network involving M1‐S1, SII‐insular, medial insular, and cingulate cortices controls muscular activity during an isometric contraction reaction time task

Magnetoencephalographic, electromyographic (EMG), work, and reaction time (RT) were recorded from nine subjects during visually triggered intermittent isometric contractions of the middle finger under two conditions: unloaded and loaded (30% of maximal voluntary contraction). The effect of muscle fatigue was studied over three consecutive periods under both conditions. In the loaded condition, the motor evoked field triggered by the EMG onset decreased with fatigue, whereas movement-evoked fields (MEFs) increased (P < 0.01). Fatigue was demonstrated in the loaded condition, since (i) RT increased due to an increase in the electromechanical delay (P < 0.002); (ii) work decreased from Periods 1 to 3 (P < 0.005), while (iii) the myoelectric RMS amplitude of both flexor digitorum superficialis and extensor muscles increased (P < 0.003) and (iv) during Period 3, the spectral deflection of the EMG median frequency of the FDS muscle decreased (P < 0.001). In the unloaded condition and at the beginning of the loaded condition, a parallel network including M1-S1, posterior SII-insular, and posterior cingulate cortices accounted for the MEF activities. However, under the effect of fatigue, medial insular and posterior cingulate cortices drove this network. Moreover, changes in the location of insular and M1-S1 activations were significantly correlated with muscle fatigue (increase of RMS-EMG; P < 0.03 and P < 0.01, respectively). These results demonstrate that a plastic network controls the strength of the motor command as fatigue occurs: sensory information, pain, and exhaustion act through activation of the medial insular and posterior cingulate cortices to decrease the motor command in order to preserve muscle efficiency and integrity.