Surface Electromyography Amplitude Research Articles

Passive activity enhances residual control ability in patients with complete spinal cord injury

Abstract Patients with complete spinal cord injury retain the potential for volitional muscle activity in muscles located below the spinal injury level. However, because of prolonged inactivity, initial attempts to activate these muscles may not effectively engage any of the remaining neurons in the descending pathway. A previous study unexpectedly found that a brief clinical round of passive activity significantly increased volitional muscle activation, as measured by surface electromyography. In this study, we further explored the effect of passive activity on surface electromyographic signals during volitional control tasks among individuals with complete spinal cord injury. Eleven patients with chronic complete thoracic spinal cord injury were recruited. Surface electromyography data from eight major leg muscles were acquired and compared before and after the passive activity protocol. The results indicated that the passive activity led to an increased number of activated volitional muscles and an increased frequency of activation. Although the cumulative root mean square of surface electromyography amplitude for volitional control of movement showed a slight increase after passive activity, the difference was not statistically significant. These findings suggest that brief passive activity may enhance the ability to initiate volitional muscle activity during surface electromyography tasks and underscore the potential of passive activity for improving residual motor control among patients with motor complete spinal cord injury.

Comparative Electromyographic Study of Scapular Stabilizing Muscles During Five Main Rehabilitation Exercises.

The aim of the study is to compare the surface electromyographic amplitude, activation ratio, and onset latency of the main scapular stabilizing muscles between five typical rehabilitative exercises. Twenty-seven healthy participants performed five scapular exercises (wall slide, wall push-up plus, prone horizontal abduction with external rotation, external rotation in side lying, and low row) while simultaneously recording surface electromyographic of serratus anterior, middle trapezius, lower trapezius, and upper trapezius. Surface electromyographic amplitudes, onset latencies, and activation ratios were calculated. Prone horizontal abduction with external rotation showed an excellent upper trapezius/middle trapezius (0.43) and upper trapezius/lower trapezius (0.30) muscle balance with high (>50% maximum voluntary isometric contraction) middle trapezius and lower trapezius amplitudes, a low (<20% maximum voluntary isometric contraction) upper trapezius amplitude, and an early activation of the scapular stabilizing muscles (-474.7 to 89.9 ms) relative to upper trapezius. External rotation in side lying showed excellent upper trapezius/serratus anterior (0.26), upper trapezius/middle trapezius (0.32), and upper trapezius/lower trapezius (0.21) activation ratios and, along with low row and wall slide, showed early activation of the scapular stabilizing muscles (-378.1 to -26.6 ms). Prone horizontal abduction with external rotation presented optimal scapular neuromuscular control. Although external rotation in side lying, low row, and wall slide did not meet all the criteria associated with optimal scapular neuromuscular control, these exercises could be used in early stages of shoulder rehabilitation because they favor early activation of the scapular stabilizing muscles.

EFFECTIVENESS OF POSTERIOR PELVIC TILT EXERCISE ON STABLE AND UNSTABLE SURFACE IN PATIENTS WITH CHRONIC LOW BACK PAIN

Purpose: The objective of this study was to assess and evaluate the efficacy of posterior pelvic tilt exercises on pain reduction, functional disability, muscle strength, and lumbopelvic angle in patients with Chronic Low Back Pain (CLBP). These exercises were conducted on stable and unstable surfaces. Methods: This was a single-blinded randomized two-group pre-test and post-test experimental study. Men and women with CLBP, with an age between 18 and 50 years, were divided into two groups at random. Group A performed the exercises on a stable surface, and Group B performed the exercises on an unstable surface. The Numerical Pain Rating Scale (NPRS), Oswestry Disability Index (ODI) for functional disability, Flexi Ruler for measuring lumbar lordosis angle, and Surface Electromyography (SEMG) for Transverse Abdominis (TA) and Rectus Abdominis (RA) muscles were used for pre- and post-treatment analysis. Results: Significant improvements in SEMG activity of TA and RA muscles were observed in both intervention groups following conventional exercises (p &lt; 0.05). However, the unstable surface group had a higher increase in SEMG amplitude during Maximal Voluntary Isometric Contraction (MVIC) and the percentage of MVIC for the TA muscles. Conclusion: Posterior pelvic tilt exercises performed on stable and unstable surfaces effectively reduced pain, decreased the angle of lumbar lordosis, improved functional disability, and enhanced activity and strength of the pelvic muscles in patients with CLBP.

A comparison of neural control of the biarticular gastrocnemius muscles between knee flexion and ankle plantar flexion.

We aimed to determine whether the neural control of the biarticular gastrocnemius medialis (GM) and lateralis (GL) muscles is joint-specific, that is, whether their control differs between isolated knee flexion and ankle plantar flexion tasks. Twenty-one male participants performed isometric knee flexion and ankle plantar flexion tasks while we recorded high-density surface electromyography (HDsEMG). First, we estimated the distribution of activation both within- and between muscles using two complementary approaches: surface EMG amplitude and motor unit activity identified from HDsEMG decomposition. Second, we estimated the level of common synaptic input between GM and GL motor units using a coherence analysis. The distribution of EMG amplitude between GM and GL was not different between tasks, which was confirmed by the analysis of motor units' discharge rate. Even though there was a significant proximal shift in GM and GL EMG amplitude during knee flexion compared with ankle plantar flexion, the magnitude of this shift was small and not confirmed via the inspection of the spatial distribution of motor unit action potentials. A significant coherence between GM and GL motor units was only observed for four (knee flexion) and three (ankle plantar flexion) participants, with no difference in the level of coherence between the two tasks. We were able to track only a few motor units across tasks, which raises the question as to whether the same motor units were activated across tasks. Our results suggest that the neural control of the GM and GL muscles is similar across their two main functions.NEW & NOTEWORTHY Several studies have focused on the neural strategies used to control the gastrocnemius medialis (GM) and lateralis (GL) during plantar flexion. However, their secondary function, i.e., knee flexion, is not often explored. We observed a robustness of the GM and GL activation strategy across tasks, which was confirmed with an analysis of the motor unit discharge characteristics. The level of common synaptic input between GM and GL motor units was low, regardless of the task.

Immediate effect of craniocervical flexion exercise and Mulligan mobilisation in patients with mechanical neck pain- A randomised clinical trial.

Mechanical neck pain (MNP) is one of the most prevalent musculoskeletal pathologies in the present time. Physiotherapy management strategies comprising manual therapy and exercise therapy are routinely administered in patients with MNP. To compare the immediate effect of craniocervical flexion (CCF) exercise and Mulligan mobilisation on pain, active cervical range of motion (CROM) and CCF test performance in patients with MNP. This prospective, randomised, single-blinded study involved 26 patients with MNP (16 females; mean age; years) randomised to a single session of active CCF exercise (3 sets of 10 repetitions) or Mulligan mobilisation (3 sets of 6-10 repetitions). Pain intensity was measured on a numerical pain rating scale (NPRS), active CROM was measured using CROM device, and CCF test performance with surface electromyography (EMG) from bilateral sternocleidomastoid (SCM) and anterior scalene (AS) muscles recorded pre- and immediately post-intervention by an assessor blinded to the treatment groups. Mann-Whitney U test was used to analyse between groups and Wilcoxon signed rank test was used to analyse within-group significance for pain and CROM, Cochran-Mantel-Haenszel correlation test was used to analyse the CCF test performance on EMG from the bilateral SCM and AS muscles. Comparison between pre- and post-intervention readings revealed statistically significant within-group () and no between-group significant difference for pain, ROM, and CCF test performance, indicating both interventions were equally effective. Patients with MNP who received active CCF exercise or Mulligan mobilisation exhibited similar reduction in pain intensity and increased CROM and CCF test performance post-intervention. Surprisingly, AS surface EMG amplitudes were increased post-intervention in both groups warranting further exploration of its role in neck pain.

Characteristics of submental muscles function and hyoid bone movement in patients with dysphagia after stroke.

Dysphagia is one of the common complications after stroke. Dysphagia significantly increases the probability of serious adverse consequences. The purpose of this study was to compare the characteristics of submental muscles electromyography and hyoid motion parameters between patients with dysphagia after stroke and healthy controls, and whether there is a synergistic effect between the function of the submental muscles and the movement of the hyoid. Fifteen patients with post-stroke dysphagia and fifteen healthy adults simultaneously underwent the videofluoroscopic and surface electromyography of the submental muscles while swallowing 5ml of concentrated liquid barium sulphate. The electromyographic signal of the submental muscles was analysed along with parameters of hyoid movement. Stage transition duration and duration of surface electromyographic activity were extended significantly in post-stroke dysphagia patients(P<0.05). Surface electromyography amplitude and hyoid movement were significantly reduced in patients (P<0.05). There was a significant correlation between the maximum hyoid movement distance and the peak sEMG amplitude in healthy controls (r=0.660, P=0.014), but not in patients with dysphagia after stroke (r=0.425, P=0.148). Submental muscles electromyographic signal changes in patients may be the result of uncoordinated muscle contractions and decreased muscle strength. Furthermore, the reduced hyoid movement distance may be due to impaired function of the submental muscles. In addition, the submental muscles and hyoid movement or other swallowing structures functions were impaired to varying degrees, resulting in the disappearance of the correlation between the maximum movement distance of the hyoid and the peak amplitude.

Variability in Normalization Methods of Surface Electromyography Signals in Eccentric Hamstring Contraction

In human movement analysis, normalization of a surface electromyography signal is a crucial step; therefore, parameter selection for this procedure must be adequately justified. The aim of this research was to determine the variability of electromyography signals in eccentric hamstring contraction under different normalization parameters. Cross-sectional study. Nine university rugby players (age 21.50 [3.61]y; body mass index 21.50 [4.95]) and no history of recent hamstring injury. Values from maximum voluntary isometric contraction protocol and task related (ie,Nordic hamstring exercise) were used for surface electromyography signal normalization. Intersubject and intrasubject variation coefficients were used for normalization method variability and for signal reproducibility, respectively. Intrasubject variation coefficient value indicates acceptable reproducibility of surface electromyography (less than 12%) for all normalization procedures. Lower values of intersubject variation coefficient value were achieved for normalization procedures using task-related values. Parameters extracted from task execution provided less variability for surface electromyography amplitude normalization in eccentric hamstring muscle contractions.

The facilitation of trunk muscles by abdominal bracing during walking in chronic low back pain patients

Walking is known to be beneficial for chronic low back pain (LBP) patients and fast walking recruits more trunk muscles. Abdominal bracing has also been shown to improve LBP and facilitate several trunk muscles. We aimed to investigate the effects of walking velocity and abdominal bracing on the activation of trunk muscles in chronic LBP patients during walking. Forty-six volunteers with chronic LBP underwent walking exercise on the treadmill without (“non-braced walking”) and with abdominal bracing (“braced walking”) at speeds of 4, 5, and 6 km/h, with the surface electrodes placed on their trunk muscles to measure muscle activity. The root mean square values of the surface electromyography amplitude data were obtained at the multifidus of lower (ML) and upper lumbar (MU), erector spinae of lower lumbar (EL) and thoracic (ET), rectus abdominis (RA), and external oblique (EO). All muscles activated significantly more at faster walking. The “braced walking” facilitated the ET and RA significantly more than the “non-braced walking”. The interaction between the walking speed and abdominal bracing was significant at ML, MU, and RA. The increase in muscle activation observed at lower speed diminished as speed increased. Since “braced walking” seems to additionally facilitate the trunk muscles especially at slower gait speeds, patients who cannot walk fast may still be able to train their muscles by “braced walking.”

Effects of whole-body electromyostimulation training on upper limb muscles strength and body composition in moderately trained males: A randomized controlled study.

Resistance training has been known to have a positive effect on muscle performance in exercisers. Whole-body electromyostimulation (WB-EMS) is advertised as a smooth, time-efficient, and highly individualized resistance training technology. The purpose of this study is to evaluate the effects of WB-EMS training on maximum isometric elbow muscle strength and body composition in moderately trained males in comparison to traditional resistance training. The study was a randomized controlled single-blind trial. Twenty, moderately trained, male participants (25.15 ± 3.84, years) were randomly assigned to the following groups: a WB-EMS training group (n = 11) and a traditional resistance training group (the control group [CG]: n = 9). Both training intervention programs consisted of 18 training sessions for six consecutive weeks. All subjects performed dynamic movements with the WB-EMS or external weights (CG). The primary outcome variables included maximum isometric elbow flexor strength (MIEFS), maximum isometric elbow extensor strength (MIEES) and surface electromyography amplitude (sEMGRMS). Secondary outcomes involved lean body mass, body fat content, arm fat mass, and arm lean mass. ANOVAs, Friedman test and post hoc t-tests were used (P = 0.05) to analyze the variables development after the 6-week intervention between the groups. Significant time × group interactions for MIEFS (η2 = 0.296, PBonferroni = 0.013) were observed, the increase in the WB-EMS group were significantly superior to the CG [23.49 ± 6.48% vs. 17.01 ± 4.36%; MD (95% CI) = 6.48 (1.16, 11.80); d = 1.173, P = 0.020]. There were no significant differences were observed between interventions regarding MIEES, sEMGRMS and body composition. These findings indicate that in moderately trained males the effects of WB-EMS were similar to a traditional resistance training, with the only exception of a significantly greater increase in elbow flexor strength. WB-EMS can be considered as an effective exercise addition for moderately trained males.

How does multi-set high-load resistance exercise impact neuromuscular function in normoxia and hypoxia?

ABSTRACT This study examined whether hypoxia during multi-set, high-load resistance exercise alters neuromuscular responses. Using a single-blinded (participants), randomised crossover design, eight resistance-trained males completed five sets of five repetitions of bench press at 80% of one repetition maximum in moderate normobaric hypoxia (inspiratory oxygen fraction = 0.145) and normoxia. Maximal isometric bench press trials were performed following the warm-up, after 10 min of altitude priming and 5 min post-session (outside, inside and outside the chamber, respectively). Force during pre-/post-session maximal voluntary isometric contractions and bar velocity during exercise sets were measured along with surface electromyographic (EMG) activity of the pectoralis major, anterior deltoid and lateral and medial triceps muscles. Two-way repeated measures ANOVA (condition×time) were used. A significant time effect (p = 0.048) was found for mean bar velocity, independent of condition (p = 0.423). During sets of the bench press exercise, surface EMG amplitude of all studied muscles remained unchanged (p > 0.187). During maximal isometric trials, there were no main effects of condition (p > 0.666) or time (p > 0.119), nor were there any significant condition×time interactions for peak or mean forces and surface EMG amplitudes (p > 0.297). Lower end-exercise blood oxygen saturation (90.9 ± 1.8 vs. 98.6 ± 0.6%; p < 0.001) and higher blood lactate concentration (5.8 ± 1.4 vs. 4.4 ± 1.6 mmol/L; p = 0.007) values occurred in hypoxia. Acute delivery of systemic normobaric hypoxia during multi-set, high-load resistance exercise increased metabolic stress. However, only subtle neuromuscular function adjustments occurred with and without hypoxic exposure either during maximal isometric bench press trials before versus after the session or during actual exercise sets. Highlights Performing multi-set, high-load bench press resistance exercise in hypoxia accentuates metabolic stress, as evidenced by lower arterial oxygen saturation and higher blood lactate concentration, compared to normoxia. Acute hypoxic exposure doesn’t alter neuromuscular responses during the execution of the sets since mean bar velocity dropped similarly in both conditions from set 2 to set 5 with no difference in peak velocity and surface EMG amplitude of the prime movers during the bench press. Only subtle adjustments in peak or mean force and accompanying surface EMG activity occur with and without hypoxic exposure during maximal isometric bench press trials after a 10-min hypoxic priming period and 5 min after the session in reference to post-warm-up.

Greater neuromuscular fatigue following low-load blood flow restriction than non-blood flow restriction resistance exercise among recreationally active men.

The purpose of this study was to examine the acute effects of low-load blood flow restriction (LLBFR) and low-load non-BFR (LL) on neuromuscular function after a bout of standardized fatiguing leg extension muscle actions. Fourteen men (mean age ± SD = 23 ± 4 yr) volunteered to participate in this investigation and randomly performed LLBFR and LL on separate days. Resistance exercise consisted of 75 isotonic unilateral leg extension muscle actions performed at 30% of one-repetition maximum. Before (pretest) and after (posttest) performance of each bout of exercise, strength and neural assessments were determined. There were no pretest to posttest differences between LLBFR and LL for maximal voluntary isometric contraction (MVIC) torque or V wave/M wave responses (muscle compound action potentials assessed during a superimposed MVIC muscle action), which exhibited decreases (collapsed across condition) of 41.2% and 26.2%, respectively. There were pretest to posttest decreases in peak twitch torque (36.0%) and surface electromyography amplitude (sEMG) (29.5%) for LLBFR but not LL and larger decreases in voluntary activation for LLBFR (11.3%) than for LL (4.5%). These findings suggested that LLBFR elicited greater fatigue-induced decreases in several indexes of neuromuscular function relative to LL. Despite this, both LLBFR and LL resulted in similar decrements in performance as assessed by maximal strength.NEW & NOTEWORTHY The application of blood flow restriction induces greater acute neuromuscular fatigue relative to nonrestricted conditions. Resistance exercise with blood flow restriction elicited a greater reduction in twitch responses. These neuromuscular differences might explain the more favorable adaptations achieved with blood flow restriction that are likely a function of metabolic stress and subsequent changes in efferent neural drive.

Can a Short-term Daily Oral Administration of Propolis Improve Muscle Fatigue and Recovery?

This study investigated the effect of 1-week oral administration of propolis on muscle fatigue and recovery after performing a fatigue task (total 100 maximal voluntary concentric knee extension repetitions). In this placebo-controlled, double-blind study, 18 young men consumed a formulation with high Brazilian green propolis dose (H-BGP), a formulation with low Brazilian green propolis dose, or a placebo, for 1 week before performing the fatigue task (an interval between each intervention: 1-2 weeks). Maximal voluntary contraction torque, central fatigue (voluntary activation and root mean square values of the surface electromyography amplitude), and peripheral fatigue (potentiated triplet torque) were assessed before, immediately after, and 2 minutes after the fatigue task. Maximal voluntary contraction torque decreased immediately after the fatigue task in all conditions (P<0.001); however, it recovered from immediately after to 2 minutes after the fatigue task only in the H-BGP condition (P<0.001). Furthermore, there was a significant decrease in voluntary activation (P<0.001) and root mean square values of the surface electromyography amplitude (P≤0.035) only in the placebo condition. No significant difference was observed in the time-course change in potentiated triplet torque between the conditions. These results suggest that oral administration of propolis promotes muscle fatigue recovery by reducing central fatigue.

Velocity-based resistance training: do women need greater velocity loss to maximize adaptations?

PurposeMen and women typically display different neuromuscular characteristics, force–velocity relationships, and differing strength deficit (upper vs. lower body). Thus, it is not clear how previous recommendations for training with velocity-loss resistance training based on data in men will apply to women. This study examined the inter-sex differences in neuromuscular adaptations using 20% and 40% velocity-loss protocols in back squat and bench press exercises.MethodsThe present study employed an 8-week intervention (2 × week) comparing 20% vs. 40% velocity-loss resistance training in the back squat and bench press exercises in young men and women (~ 26 years). Maximum strength (1-RM) and submaximal-load mean propulsive velocity (MPV) for low- and high-velocity lifts in squat and bench press, countermovement jump and vastus lateralis cross-sectional area were measured at pre-, mid-, and post-training. Surface EMG of quadriceps measured muscle activity during performance tests.ResultsAll groups increased 1-RM strength in squat and bench press exercises, as well as MPV using submaximal loads and countermovement jump height (P < 0.05). No statistically significant between-group differences were observed, but higher magnitudes following 40% velocity loss in 1-RM (g = 0.60) and in low- (g = 1.42) and high-velocity (g = 0.98) lifts occurred in women. Training-induced improvements were accompanied by increases in surface EMG amplitude and vastus lateralis cross-sectional area.ConclusionSimilar increases in strength and power performance were observed in men and women over 8 weeks of velocity-based resistance training. However, some results suggest that strength and power gains favor using 40% rather than 20% velocity loss in women.

Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy.

Surface electromyography amplitudes are commonly measured in acute sports and exercise science studies to make inferences about muscular strength, performance, and hypertrophic adaptations that may result from different exercises or exercise-related variables. Here, we discuss the presumptive logic and assumptions underlying these inferences, focusing on hypertrophic adaptations for simplicity's sake. We present counter-evidence for each of its premises and discuss evidence both for and against the logical conclusion. Given the limited evidence validating the amplitude of surface electromyograms as a predictor of longitudinal hypertrophic adaptations, coupled with its weak mechanistic foundation, we suggest that acute comparative studies that wish to assess stimulus potency be met with scrutiny.

Acute Neuromuscular Response to Team Sports-Specific Running, Resistance, and Concurrent Training: A Crossover Study.

This study aimed to examine the changes in muscle contractile function, voluntary activation, and muscle damage after lower limb resistance training (RT), intermittent sprint exercise, and concurrent training (CT). Ten male, recreational team sport athletes with a history of RT participated in a randomized crossover study involving an intermittent sprint protocol (ISP), lower limb RT, and CT (ISP and RT separated by 1 h). Before (PRE), immediately after (POST), 24 h and 48 h after each exercise condition, quadriceps muscle activation, voluntary activation, muscle contractile function (evoked twitch responses), creatine kinase, muscle soreness, and Profile of Mood States (POMS)-fatigue were recorded. Quadriceps contractile function was hampered in all conditions, with a significantly greater decline observed POST RT (58.4% ± 18.0%) and CT (54.8% ± 8.6%) compared with ISP (35.9% ± 10.7%, P < 0.05), recovering at 48 h after all exercise conditions. POMS-fatigue ratings increased at POST in all conditions with CT and ISP eliciting the greatest increase, returning to baseline 48 h after all exercise conditions. Quadriceps muscle soreness remained elevated from PRE at 48 h after all exercise conditions. No changes across time were observed for voluntary activation and quadriceps surface EMG amplitude after any exercise condition. The volume and load lifted in the RT session was unaffected by previous intermittent exercise (ISP) in CT. RT impairs contractile function, which is not exacerbated when performed 1 h after the ISP. Contractile function after all exercise conditions displayed the same recovery profile (48 h) despite the postexercise decrement being smaller after the ISP compared with RT and CT. Previous intermittent sprint exercise does not negatively affect the volume of exercise performed in a lower limb RT session.

Investigation of surface electromyography amplitude values during stair climbing task in children with Duchenne muscular dystrophy.

The aims of this study were (a) to examine the surface electromyography (sEMG) amplitude values of the lower limb muscles during stair climbing both between different functional levels of Duchenne muscular dystrophy (DMD), in comparison with healthy children, and (b) to investigate the relationships between sEMG amplitudes and physical performance. sEMG amplitudes of the lower limbs of twenty-one children with DMD between levels I and III according to the Brooke Lower Extremity Functional Classification Scale and eleven healthy peers were evaluated by using sEMG during stair climbing task. Physical performance was evaluated by 6-min walk test and ascending 4-step timed performance test. The lower limb sEMG amplitude values of children with DMD were statistically higher than healthy children (p < 0.001). sEMG amplitudes of the right (p = 0.01) and left (p = 0.003) biceps femoris, the right (p < 0.001) and left (p = 0.001) gastrocnemius medialis, and the right vastus lateralis (p = 0.02) muscles were higher in children with levels 2-3 than those in level 1. Moderate-to-strong relations were found between the gastrocnemius medialis and biceps femoris sEMG amplitudes and physical performance assessments (p < 0.05). Increased sEMG amplitude values in the lower limbs during stair climbing task are thought to be caused by the effort to compensate for progressive muscle weakness and are associated with lower physical performance in children with DMD. Further, sEMG amplitude values are determined to increase as the functional level deteriorates. NCT04287582 ( https://clinicaltrials.gov/ct2/show/NCT04287582?term=merve+bora&draw=2&rank=1 ).

Acute effects of different rest intervals between agonist-antagonist paired-sets in the neuromuscular system performance of young adults

IntroductionThe agonist-antagonist paired-sets (APS) is a resistance training that involves alternating between exercises for agonist/antagonist muscles of a joint, with little or no rest between then. There is evidence that APS is more strenuous than traditional methods, but evidence on the optimal RI between agonist-antagonist actions is unknown. ObjectiveThe aim of this study was to compare different rest intervals between agonist-antagonist actions during APS in young adults. MethodFifty healthy men (mean age 23.2 ± 2.8 years; 1.76 ± 0.1m height, 78.03 ± 8.1 kg) were included and performed three different agonist-antagonist paired-sets protocols separated by 72h, consisting of 4 sets of 10 repetitions. The protocols differed in terms of the rest interval between the knee flexion and extension movements: 0s (no rest); 60s and 120s. The rest intervals between exercise sets were standardized at 60s. Total work, peak torque, neuromuscular efficiency, surface EMG amplitude (sEMG, root mean square) and fatigue index obtained by processing of sEMG signal, were compared between rest intervals and exercise sets within each protocol. ResultsThere were no significant differences between rest intervals for total work, peak torque and neuromuscular efficiency (P > 0.05), but significant differences were found for sEMG and fatigue (P < 0.01), in which the protocol with 60s interval resulted in greater fatigue. ConclusionWe showed that peak torque, total work and neuromuscular efficiency were not different between RI. The 60s RI showed a lower sEMG and a greater muscle fatigue. Although there were no significant differences, the NME was higher in the 60s interval.

Temporal and spatial relationship between gluteal muscle Surface EMG activity and the vertical component of the ground reaction force during walking.

Optimized temporal and spatial activation of the gluteal intermuscular functional unit is essential for steady gait and minimized joint loading. To analyze the temporal relationship between spatially resolved surface EMG (SEMG) of the gluteal region and the corresponding ground reaction force (GRF). Healthy adults (29♀; 25♂; age 62.6±7.0 years) walked at their self-selected slow, normal, and fast walking speeds on a 10 m walkway (ten trials/speed). Bilateral paired eight-electrode strips were horizontally aligned at mid-distance of the vertical line between greater trochanter and iliac crest. Concerning the ventral to dorsal direction, the center of each strip was placed on this vertical line. Initially, these signals were monopolarly sampled, but eight vertically oriented bipolar channels covering the whole gluteal region from ventral to dorsal (P1 to P8) were subsequently calculated by subtracting the signals of the corresponding electrodes of each electrode strip for both sides of the body. Three vertical bipolar channels represented the tensor fasciae latae (TFL; P2), gluteus medius (Gmed, SENIAM position; average of P4 and P5), and gluteus maximus muscles (Gmax; P7). To determine the interval between SEMG and corresponding GRF, the time delay (TD) between the respective first amplitude peaks (F1) in SEMG and vertical GRF curves was calculated. Throughout the grand averaged SEMG curves, the absolute amplitudes significantly differed among the three walking speeds at all electrode positions, with the amplitude of the F1 peak significantly increasing with increasing speed. In addition, when normalized to slow, the relative SEMG amplitude differences at the individual electrode positions showed an impressively homogeneous pattern. In both vertical GRF and all electrode SEMGs, the F1 peak occurred significantly earlier with increasing speed. Also, the TD between SEMG and vertical GRF F1 peaks significantly decreased with increasing speed. Concerning spatial activation, the TD between the respective F1 peaks in the SEMG and vertical GRF was significantly shorter for the ventral TFL position than the dorsal Gmed and Gmax positions, showing that the SEMG F1 peak during this initial phase of the gait cycle occurred earlier in the dorsal positions, and thus implying that the occurrence of the SEMG F1 peak proceeded from dorsal to ventral. Tightly regulated spatial and temporal activation of the gluteal intermuscular functional unit, which includes both speed- and position-dependent mechanisms, seems to be an essential requirement for a functionally optimized, steady gait.

Neuromechanics of Middle-Distance Running Fatigue: A Key Role of the Plantarflexors?

This study aimed to investigate the changes in lower limb kinematics, kinetics, and muscle activation during a high-intensity run to fatigue (HIRF). Eighteen male and female competitive middle-distance runners performed a HIRF on an instrumented treadmill at a constant but unsustainable middle-distance speed (~3 min) based on a preceding maximum oxygen uptake (V˙O2max) test. Three-dimensional kinematics and kinetics were collected and compared between the start, 33%, 67%, and the end of the HIRF. In addition, the activation of eight lower limb muscles of each leg was measured with surface EMG (sEMG). Time to exhaustion was 181 ± 42 s. By the end of the HIRF (i.e., vs the start), ground contact time increased (+4.0%), whereas flight time (-3.2%), peak vertical ground reaction force (-6.1%), and vertical impulse (-4.1%) decreased (all P < 0.05), and joint angles at initial contact became more (dorsi)flexed (ankle, +1.9°; knee, +2.1°; hip, +3.6°; all P < 0.05). During stance, by the end of the HIRF: peak ankle plantarflexion moment decreased by 0.4 N·m·kg-1 (-9.0%), whereas peak knee extension moment increased by 0.24 N·m·kg-1 (+10.3%); similarly, positive ankle plantarflexion work decreased by 0.19 J·kg-1 (-13.9%), whereas positive knee extension work increased by 0.09 J·kg-1 (+33.3%; both P < 0.05) with no change in positive hip extension work. Hip extensor surface EMG amplitude increased during the late swing phase (+20.9-37.3%; P < 0.05). Running at a constant middle-distance pace led primarily to the fatigue of the plantarflexors with a compensatory increase in positive work done at the knee. Improving the fatigue resistance of the plantarflexors might be beneficial for middle-distance running performance.

Association between Oxygen Consumption and Surface Electromyographic Amplitude and Its Variation within Individual Calf Muscles during Walking at Various Speeds.

Surface electromyography (EMG) has been used to estimate muscle work and physiological burden of the whole body during human movements. However, there are spatial variations in surface EMG responses within individual muscles. The aim of this study was to investigate the relation between oxygen consumption and surface EMG responses of lower leg muscles during walking at various speeds and to quantify its spatial variation within an individual muscle. Nine young males walked on a treadmill at four speeds: preferred minus 1 km/h, preferred, preferred plus 1 km/h, and preferred plus 2 km/h, and the metabolic response was measured based on the expired gas. High-density surface EMG of the tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius, and soleus muscles was performed using 64 two-dimensional electrode grids. Correlation coefficients between oxygen consumption and the surface EMG amplitude were calculated across the gait speeds for each channel in the electrode grid and for individual muscles. Mean correlation coefficients across electrodes were 0.69–0.87 for the four individual muscles, and the spatial variation of correlation between the surface EMG amplitude and oxygen consumption within an electrode grid was significantly greater in MG muscle than in TA muscle (Quartile deviations: 0.24 for MG and 0.02 for TA, p < 0.05). These results suggest that the physiological burden of the whole body during gait at various speeds can be estimated from the surface EMG amplitude of calf muscles, but we need to note its spatial distribution within the MG muscle.