Onset Of Muscle Activity Research Articles

Relationship Between Hamstring Flexibility and Extensor Muscle Activity During a Trunk Flexion Task

ObjectiveThe purpose of this study was to investigate the relationship between hamstring flexibility and electromyography (EMG) muscle parameters in back and lower limb extensor muscles during a trunk flexion task. MethodsThirty healthy women aged 18 to 30 years with normal hip movement were recruited for this study. Hamstring muscle flexibility was measured with the 90-90 active straight leg raise test. Surface EMG activities were simultaneously recorded from the lumbar erector spinae, gluteus maximus, biceps femoris, semitendinosus, lateral gastrocnemius, and medial gastrocnemius muscles during forward bending. Muscle activity onset and offset, amplitude, and duration were calculated with technical computer software (MATLAB, version 1.6.0). Linear regression analysis was used to investigate the relationships between hamstring flexibility test results and EMG parameters during trunk flexion. In addition, the Friedman test was used to determine the recruitment activity pattern in women with low versus normal hamstring flexibility. ResultsDuring flexion, the back extensor muscles in individuals with lower hamstring flexibility test scores were activated and deactivated later, which can lead to delayed flexion-relaxation. Regression analysis did not disclose any significant correlations between hamstring flexibility and other EMG parameters (duration and amplitude) in back extensor muscles. Activation and deactivation recruitment patterns differed between the groups with normal and low hamstring flexibility. ConclusionThe findings of this study suggest that hamstring flexibility plays an important role in the patterns of trunk and lower limb muscle activity onset, offset, and recruitment.

Knee joint kinematics and neuromuscular responses in female athletes during and after multi-directional perturbations.

The purpose of this study was to investigate weight-bearing knee joint kinematic and neuromuscular responses during lateral, posterior, rotational, and combination (simultaneous lateral, posterior, and rotational motions) perturbations and post-perturbations phases in 30° flexed-knee and straight-knee conditions. Thirteen healthy female athletes participated. Knee joint angles and muscle activity of vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), semitendinosus (ST), lateral gastrocnemius (LG), and medial gastrocnemius (MD) muscles were computed. Knee abducted during lateral perturbations, whereas it adducted during the other perturbations. It was internally rotated during flexed-knee and externally rotated during straight-knee perturbations and post-perturbations. VL and VM's mean and maximum activities during flexed-knee perturbations were greater than those of straight-knee condition. BF's mean activities were greater during flexed-knee perturbations compared with straight-knee condition, while its maximum activities observed during combination perturbations. ST's maximum activities during combination perturbations were greatest compared with the other perturbations. LG and MG's activities were greater during straight-knee conditions. Compared with the perturbation phase, the mean and maximum muscles' activities were significantly greater during post-perturbations. The time of onset of maximum muscle activity showed a distinctive pattern among the perturbations and phases. The perturbation direction is an important variable which induces individualized knee kinematic and neuromuscular response.

PROLIFIC: A Fast and Robust Profile-Likelihood-Based Muscle Onset Detection in Electromyogram Using Discrete Fibonacci Search

A stochastic scheme, namely, PLM-Lap, has recently been propounded, which relies on the profile likelihood (PL) constructed with a Laplace distribution for estimating muscle activation onsets (MAOs) in surface electromyographic (sEMG) data. The MAO detection accuracy and robustness of the PLM-Lap have been empirically shown to be better than those of several state-of-the-art approaches. The algorithm designates the data point index associated with the maximum of the PL function as an onset occurrence by regarding every sEMG data point as a candidate onset and hence exhaustively evaluating the objective function. This article concerns an expedient and faster approach premised on the discrete Fibonacci search (DFS) to locate the maximum of the discrete PL function. The experimental results support that both the exhaustive and DFS procedures are equivalent in a statistical sense, whereas the latter offers impressive computational savings by a factor of approximately 90. Owing to the speed-up, the accuracy of MAO estimation may further be enhanced by modeling the sEMG data with a set of PL functions, each one built using a suitable probability distribution, and picking the estimate from the best model. Three statistical criteria, i.e., Kolmogorov-Smirnov, Lilliefors, and Anderson-Darling test, for choosing the probability distribution are recommended. A freely downloadable MATLAB package, namely PROLIFIC, meant for sEMG onset detection is available on MATLAB File Exchange from the following link: https://www.mathworks.com/matlabcentral/fileexchange/76495-prolific-profile-likelihood-based-on-fibonacci-search.

Effects of Transcranial Direct Current Stimulation Over Primary Motor Cortex on the Onset Time of Upper Extremity Muscles’ Activities for Forward Reaching Performance: A Preliminary Study

Purpose: This study aimed to investigate the effect of transcranial direct current stimulation (tDCS) on the onset of upper extremity muscle activities during forward reaching performance. Methods: Fifteen healthy men (age, 24.2±1.55y) participated in this randomized double-blind crossover study. Each participant received both a sham and 2-mA stimulation over M1 bilaterally for 20 min, with a minimum washout period of 4 days. Muscle activation was evaluated for all the participants during the task of reaching out for a marked target as fast as possible, using electromyography (EMG) before and immediately after tDCS application. Results: For the within arm-length reaching performance in the 2-mA stimulation session, the muscle activities of the anterior deltoid (AD), posterior deltoid (PD), biceps brachii (BB), and inferior spinatus (IS) were decreased significantly during, immediately after, and 20 min after the tDCS period compared with the baseline values (p for all values ＜0.05). The pectoralis major (Pec) muscle showed a significant decrease only in the 20-min period after tDCS compared with the baseline values (p=0.001). For the beyond arm-length reaching performance, the 2-mA application on the AD, PD, BB, and IS showed significant decreases in onset time in all the periods after tDCS as compared with the baseline (p for all values ＜0.05). The onset of the triceps brachii muscle activity significantly decreased immediately and 20 min after the tDCS periods. For the Pec muscle, the onset time of muscle activation significantly changed only in the 20 min after the tDCS period compared with the baseline values. Conclusion: The present study demonstrated that bilateral tDCS over M1 facilitates muscle activation rapidly during the reaching performance, regardless of the reaching target distance.

Effects of a Pilates protocol in individuals with non-specific low back pain compared with healthy individuals: Clinical and electromyographic analysis

BackgroundElectromyography may be useful for assessing and understanding trunk muscle activation, and Pilates is commonly used as a treatment for low back pain. The objective of this study was to verify electromyography of trunk muscles after a Pilates protocol in individuals with non-specific low back pain and in healthy individuals. MethodsVolunteers were divided into two groups: non-specific low back pain (n = 19) and clinically healthy (n = 16) groups. Clinical assessments, classification of patients into subgroups, electromyography evaluations of the right lumbar extensor and right transverse abdominal/internal oblique muscle of the abdomen were performed before and after an 8-week Pilates protocol. FindingsComparisons were made before and after the protocol and with the control group. There was significant improvement in pain, flexibility, resistance and strength of trunk muscles. In addition, after the Pilates, there was a decrease in the time elapsed between the onset and peak of lumbar muscle activation during the evaluation of trunk extension in the low back pain group, coming closer to the time of the abdominal muscle, as it also occurred in the control group. InterpretationPilates caused clinical improvement and balanced trunk muscle activation in the low back group, becoming similar to that of the control group. Furthermore, the effects of the proposed protocol were the same between the groups. Thus, Pilates may be indicated for management of non-specific low back pain.

Neuromuscular training for children with developmental coordination disorder: A randomized controlled trial.

Background:Adaptive balance control is often compromised in children with developmental coordination disorder (DCD). Neuromuscular training (NMT) is commonly used in clinical settings to improve neuromuscular control and hence balance performance in these children. However, its effectiveness has not been proven scientifically. This randomized controlled study aimed to explore the effectiveness of NMT for improving adaptive balance performance and the associated leg muscle activation times in children with DCD.Methods:Eighty-eight children with DCD were randomly assigned to the NMT or control group (44 per group). The NMT group received two 40-minute NMT sessions/week for 3 months, whereas the control group received no intervention. The outcomes were measured at baseline and 3 and 6 months. The primary outcome was the sway energy score (SES) in both the toes-up and toes-down conditions as derived using the Adaptation Test (ADT). Secondary outcomes included the medial gastrocnemius, medial hamstring, tibialis anterior and rectus femoris muscle activation onset latencies during ADT, measured using surface electromyography and accelerometry. Data were analyzed using a repeated measures analysis of covariance based on the intention-to-treat principle.Results:At 3 months, no significant within-group or between-group differences were noted in the SESs for either group. At 6 months, the toes-down SES decreased by 6.8% compared to the baseline value in exclusively the NMT group (P = .004). No significant time, group or group-by-time interaction effects were observed in any leg muscle activation outcomes.Conclusions:Short-term NMT failed to improve adaptive balance performance and leg muscle activation times in children with DCD. Further studies should explore the clinical applications of longer-term task-specific interventions intended to improve the adaptive balance performance of these children.

Muscle activity during backward perturbation response in patients with clinical vertebral compression fractures

The present study examined muscle activity in response to backward perturbation in patients with clinical vertebral compression fracture (CVCF). The subjects were 32 patients aged 65 years and above consisting of 16 each with (CVCF group) and without (control group) CVCF. The time to peak activity, and time of onset of muscle activity of the anterior tibial, vastus medialis, and rectus abdominis muscles when unexpected backward perturbation was applied were evaluated by surface electromyography. The strength of perturbation was 4% or 6% of the subject’s body weight. In addition, the presence of the stepping reaction to perturbation, severity of low back pain, and vertebral alignment were evaluated. Each item was compared between the two groups. In the CVCF group, kyphosis and severity of low back pain were significantly more severe, the time to peak activity of the anterior tibial muscle after the application of perturbation at 6% of the body weight was significantly shorter, and the time of onset of activity of the rectus abdominis muscle was significantly delayed. This suggests that the time to peak activity of the anterior tibial muscle is shortened and the time of onset of activity of the rectus abdominis muscle is delayed in unexpected backward perturbation in patients with CVCF.

Reactive stepping after a forward fall in people living with incomplete spinal cord injury or disease

Cross sectional. To compare the reactive stepping ability of individuals living with incomplete spinal cord injury or disease (SCI/D) to that of sex- and age-matched able-bodied adults. A tertiary SCI/D rehabilitation center in Canada. Thirty-three individuals (20 with incomplete SCI/D) participated. Participants assumed a forward lean position in standing whilst 8-12% of their body weight was supported by a horizontal cable at waist height affixed to a rigid structure. The cable was released unexpectedly, simulating a forward fall and eliciting one or more reactive steps. Behavioral responses (i.e., single step versus non-single step) were compared using a Chi-square test. The following temporal parameters of reactive stepping were compared using t-tests: the onset of muscle activation in 12 lower extremity muscles (six per limb) and step-off, step contact and swing time of the stepping leg. Behavioral responses were significantly different between groups (χ2 = 13.9 and p < 0.01) with participants with incomplete SCI/D showing more non-single step responses (i.e., multi-steps and falls). The onsets of muscle activation were more variable in participants with incomplete SCI/D, but only the stepping tibialis anterior showed a significantly slower onset in this group compared with able-bodied adults (t = -2.11 and p = 0.049). Movement timing of the stepping leg (i.e., step-off, step contact, and swing time) was not significantly different between groups. Reactive stepping ability of individuals with incomplete SCI/D is impaired; however, this impairment is not explained by temporal parameters. The findings suggest that reactive stepping should be targeted in the rehabilitation of ambulatory individuals with SCI/D.

Comparison of a cluster-based foot model with the Oxford foot model and Rizzoli foot model to measure pronation-related kinematics

The Hybrid Assistive Limb Lumbar Type (HAL) is an active exoskeleton that provides motion according to the wearer’s voluntary drive. It was developed to support back muscles during repetitive lifting tasks. The purpose of this paper was to determine if the myoelectric activity of the back muscles is reduced or altered when using the HAL and to investigate a possible influence of its use on the cardiovascular system. Fourteen healthy young men without lower back pain underwent a freestyle, symmetrical-lifting protocol. Participants lifted a 17.05 kg handled-box for 10 min. with and without HAL support. Surface electromyography (sEMG) signals were recorded at thoracic (TES) and lumbar erector spinae (LES) and quadriceps femoris (QF). Heart rate was recorded from electrocardiogram. The subjects rated their level of physical exertion using the Borg Rating of Perceived Exertion (BORG) scale. Additionally they commented on sites of discomfort, perceptions of force, and loss of range of motion. The root mean square and integrated sEMG value was significantly reduced at the LES and TES. Heart rate variability output variables did not show any significant difference. The BORG-Scale showed no difference, with a mean score of 2.5. The HAL decreased the magnitude and onset of muscle activity and force in the lower back in a repetitive lifting task. Reduction of the muscle force and activity required during the lifting process is meaningful regarding lower back pain prevention, and the HAL may contribute to reducing the incidence of lower back pain in the working population.

Altered Cortical and Postural Response to Balance Perturbation in Traumatic Brain Injury - An EEG Pilot Study.

30-60% of traumatic brain injury (TBI) patients suffer from long-term balance deficit. Even though motor preparation and execution are altered and slowed in TBI, their relative contribution and importance to posture instability remain poorly understood. This study investigates the impaired cortical dynamics and neuromuscular response in TBI in response to balance perturbation and its relation to balance deficit. 12 TBI and 6 healthy control (HC) participants took the Berg Balance Scale (BBS) test and participated in a balance perturbation task where they were subjected to random anterior/posterior translation, while brain (EEG), muscle (EMG) activities, and center of pressure (COP) were continuously recorded. Using independent component analysis (ICA), the component most responsible for the N1 component of the perturbation evoked potential (PEP) was selected and its amplitude and latency were extracted. Balance task performance was measured by computing the COP displacement during the task. TBI had a significantly lower BBS, larger COP displacement and lower N1 amplitude compared to the HC group. No group differences was found for N1 latency and muscle activity onset delay to the perturbation. BBS was correlated with the COP displacement and N1 amplitude, and COP displacement was correlated with N1 latency. TBI balance deficit may be associated with more impaired than delayed cortical response to balance perturbation.

Characterizing gait abnormalities in patients with cervical spondylotic myelopathy: a neuromuscular analysis

Background ContextGait impairment is a hallmark of cervical spondylotic myelopathy (CSM). It has been shown to affect quality of life but has not been well defined. Further electromyographic (EMG) characterization of the gait cycle may help elucidate the true neuromuscular pathology with implications on prognosis and rehabilitation techniques. PurposeThis study compares neuromuscular activity in patients with CSM to that of healthy age-matched controls. Study DesignNonrandomized, prospective, concurrent control cohort study. MethodsNeuromuscular activity was measured in 40 patients with symptomatic CSM during a series of over-ground gait trials at a self-selected speed before surgical intervention. External oblique, multifidus, erector spinae, rectus femoris, semitendinosus, tibialis anterior, medial gastrocnemius, and medial deltoid were assessed. Identical measurements were taken in 25 healthy control patients. Differences in time of muscle onset, peak EMG, time to peak EMG, and integrated electromyography (iEMG) were assessed using one-way ANOVA. ResultsThere were no significant differences between patients with CSM and healthy controls with respect to time of muscle contraction onset. Peak EMG muscle activity was significantly higher in the medial deltoid of patients with CSM (39.3% vs. 23.3% sMVC, p=.042), but no other differences were seen in the remaining muscles tested. They also demonstrated significantly longer time to peak EMG muscle activity compared with controls in 5 of the 8 muscles tested, including the multifidus (20.2 vs. 16.8 ms, p=.050), erector spinae (18.2 vs. 8.9 ms, p<.001), semitendinosis (26.3 vs. 22.4 ms, p=.037), tibialis anterior (14.7 vs. 11.0 ms, p=.050), and medial deltoid (24.2 vs. 9.2 ms, p<.001). Compared with controls, patients with CSM demonstrated significantly higher iEMG activity in the semitendinosis (586.5% vs. 272.5 sMVC, p=.047) and medial deltoid (87.62% vs. 22.5% sMVC, p=.008). ConclusionsThe onset of muscle activity is not delayed in CSM patients, but many key muscles take longer to fully contract. This produces a situation in which patients with CSM are unable to fully fire their muscles with sufficient speed to maintain a normal gait. The core and lower extremity muscles do not contract with increased peak amplitude in response, but the deltoid and hamstring muscles are more active, suggesting compensatory activity as patients attempt to maintain balance. The end result is less efficient ambulation. These findings provide a more nuanced understanding of gait in individuals suffering from CSM and may have implications on rehabilitation protocols.

Passenger muscle responses in lane change and lane change with braking maneuvers using two belt configurations: Standard and reversible pre-pretensioner

Objective: The introduction of integrated safety technologies in new car models calls for an improved understanding of the human occupant response in precrash situations. The aim of this article is to extensively study occupant muscle activation in vehicle maneuvers potentially occurring in precrash situations with different seat belt configurations.Methods: Front seat male passengers wearing a 3-point seat belt with either standard or pre-pretensioning functionality were exposed to multiple autonomously carried out lane change and lane change with braking maneuvers while traveling at 73 km/h. This article focuses on muscle activation data (surface electromyography [EMG] normalized using maximum voluntary contraction [MVC] data) obtained from 38 muscles in the neck, upper extremities, the torso, and lower extremities. The raw EMG data were filtered, rectified, and smoothed. All muscle activations were presented in corridors of mean ± one standard deviation. Separate Wilcoxon signed ranks tests were performed on volunteers’ muscle activation onset and amplitude considering 2 paired samples with the belt configuration as an independent factor.Results: In normal driving conditions prior to any of the evasive maneuvers, activity levels were low (<2% MVC) in all muscles except for the lumbar extensors (3–5.5% MVC). During the lane change maneuver, selective muscles were activated and these activations restricted the sideway motions due to inertial loading. Averaged muscle activity, predominantly in the neck, lumbar extensor, and abdominal muscles, increased up to 24% MVC soon after the vehicle accelerated in lateral direction for all volunteers. Differences in activation time and amplitude between muscles in the right and left sides of the body were observed relative to the vehicle’s lateral motion. For specific muscles, lane changes with the pre-pretensioner belt were associated with earlier muscle activation onsets and significantly smaller activation amplitudes than for the standard belt (P < .05).Conclusions: Applying a pre-pretensioner belt affected muscle activations; that is, amplitude and onset time. The present muscle activation data complement the results in a preceding publication, the volunteers’ kinematics and the boundary conditions from the same data set. An effect of belt configuration was also seen on previously published volunteers’ kinematics with lower lateral and forward displacements for head and upper torso using the pre-pretensioner belt versus the standard belt. The data provided in this article can be used for validation and further improvement of active human body models with active musculature in both sagittal and lateral loading scenarios intended for simulation of some evasive maneuvers that potentially occur prior to a crash.

Effects of the head lift exercise and neuromuscular electrical stimulation on swallowing muscles activity in healthy older adults: a randomized pilot study.

PurposeSwallowing physiology exhibits several changes in advanced ages. The present study aimed to investigate and compare effects of a period of the head lift exercise (HLE) and neuromuscular electrical stimulation (NMES) on swallowing muscles activity in healthy elderly.Patients and methodsA total of 23 older adults were randomized to either the HLE or NMES group for ten therapy sessions. They received pre- and post-therapy surface electromyography (sEMG) during water swallowing.ResultsFor the HLE group, duration of suprahyoid muscles activity was significantly reduced at post-intervention compared to pre-intervention (p=0.036). Moreover after treatments, duration and latency between onset and peak amplitude of suprahyoid muscles activity was significantly shorter in the HLE group compare to the NMES group (respectively, p=0.007 and p=0.003).ConclusionOur findings suggest that the HLE, against the NMES, may be effective in reducing some aging effects on the suprahyoid muscles activity, especially in elders who demonstrate prolonged duration and latency between onset and peak of the suprahyoid muscles activity during swallowing.

Changes in oxygen and carbon dioxide in the genesis of sleep bruxism: a mechanism study

PurposeRhythmic masticatory muscle activity (RMMA), a biomarker of sleep bruxism (SB), has been associated with mild hypoxia and/or big breaths in some adults with non-sleep-disordered breathing. The purpose of this study was to investigate that concurrent oxygen and carbon dioxide fluctuations are among the physiological variables that contribute to RMMA onset. MethodsTwelve subjects (5 female, 7 male, mean age: 43 ± 11) underwent polysomnography recording in a sleep laboratory. RMMA index and apnea-hypopnea index were calculated. Oxygen saturation (SpO2) was estimated by finger pulse oximeter and end-tidal CO2 (ETCO2) by nasal airflow cannula before and after RMMA onset. Given the expected response time delay between actual arterial hypoxemia and fingertip pulse detection, we adjusted the SpO2 desaturation onset to the onset of masseter muscle activity using a 17 s criterion based on ETCO2 shifts. ResultsSpO2 was slightly but significantly lower than at baseline (max: −0.6%) in the 6–4 s before RMMA onset and significantly higher in the 6–18 s after onset (0.9%; p < 0.05). Although ETCO2 before RMMA onset did not differ from baseline, it decreased at 8–10 s after onset (−1.7 mmHg: p < 0.05). No changes in SpO2 or ETCO2 in relation to RMMA onset reached a critical clinical threshold. ConclusionsThe mild transient hypoxia observed before RMMA onset was not associated with a change in ETCO2. The mild and brief oxygen fluctuations before RMMA onset may reflect a physiological response that seems to have little influence on SB genesis.

Stumbling Reactions in Partial Gravity - Neuromechanics of Compensatory Postural Responses and Inter-Limb Coordination During Perturbation of Human Stance.

Spontaneous changes in gravity play a significant role in interplanetary space missions. To preserve the astronauts’ capability to execute mission-critical tasks and reduce the risk of injury in transit and on planetary surfaces, a comprehensive understanding of the neuromuscular control of postural responses after balance deterioration in hypo- or hyper-gravity conditions is essential. Therefore, this study aimed to evaluate the effect of acute gravitational variation on postural adjustments in response to perturbations. Gravitational changes were induced using parabolic flight. Postural set was manipulated by randomly providing unilateral left, bilateral or split perturbations which require balance corrections to restore postural stability. In six subjects, postural reactions were recorded after anterior and posterior surface perturbations for progressively increased gravitational conditions spanning from 0.25 to 1.75 g. Ankle and knee joint kinematics and electromyograms (EMG) of eight leg muscles were recorded prior (PRE) and after perturbation onset. Muscle activation onset latencies and amplitudes in the short-, medium-, and long-latency responses (SLR, MLR, LLR) were assessed. Results demonstrate an increased muscle activity (p < 0.05) and co-contraction in the lower extremities (p < 0.05) prior to perturbation in hypo- and hyper-gravity. After perturbation, reduced muscle onset latencies (p < 0.05) and increased muscle activations in the MLR and LLR (p < 0.05), concomitant with an increased co-contraction in the SLR, were manifested with a progressive rise in gravity. Ankle and knee joint deflections remained unaffected, whereas angular velocities increased (p < 0.05) with increasing gravitation. Effects were more pronounced in bi- compared to unilateral or split perturbations (p < 0.05). Neuro-mechanical adaptations to gravity were more distinct and muscle onset latencies were shorter in the displaced compared to the non-displaced leg. In conclusion, the timing and magnitude of postural reflexes involved in stabilization of bipedal stance are gravity-dependent. The approximately linear relationship between gravity and impulse-directed EMG amplitudes or muscle onset latencies after perturbation indicates that the central nervous system correctly predicts the level of gravity. Moreover, it accurately governs contractions in the antigravity musculature to counterbalance the gravitational pull and to regain upright posture after its disturbance. Importantly, unilateral perturbations evoked fast reflex responses in the synergistic muscles of the non-displaced contralateral leg suggesting a synchronized inter-limb coordination mediated by spinal circuitries.

Having your cake and eating it: Faster responses with reduced muscular activation while learning a temporal interval

We examined how motor responses to a stimulus evolve as individuals learn to predict when a stimulus will appear, by comparing responses to a regular versus irregular stimulus train. The study was conducted with two groups of adults — one responded to the regular appearance of a visual stimulus every 3 s (R group) and the second responded to the irregular presentation of the same stimulus (IR group) at intervals varying between 2 and 4 s. Participants responded to the appearance of the stimulus by bending over to press a button that was slightly out of reach. This whole body reach requires muscular activation at the ankles. Over the course of 50 consecutive responses, the response times in the R group were found to decrease more than those for participants in the IR group. The electromyographs (EMGs) of two ankle antagonist muscles, the anterior tibialis and soleus were also modified as participants progressively learnt the temporal regularity of a sequence. Tibialis onset times for the R group were found to decrease faster. A less predictable observation was the faster reduction in post stimulus activation of the tibialis muscle for the R group. Soleus muscle deactivation is an indicator of movement preparation. EMG integrals for this muscle a little before stimulus onset showed a trend for greater decrease in the R group. In summary, our study shows that temporal expectations over repeated stimulus presentation permit the dynamic optimization of motor activity with progressively faster response times, muscle activation onset times and lower muscle activation amplitudes.

Remote muscle contraction enhances spinal reflexes in multiple lower-limb muscles elicited by transcutaneous spinal cord stimulation.

Transcutaneous spinal cord stimulation (tSCS) is a useful technique for the clinical assessment of neurological disorders. However, the characteristics of the spinal cord circuits activated by tSCS are not yet fully understood. In this study, we examined whether remote muscle contraction enhances the spinal reflexes evoked by tSCS in multiple lower-limb muscles. Eight healthy men participated in the current experiment, which required them to grip a dynamometer as fast as possible after the presentation of an auditory cue. Spinal reflexes were evoked in multiple lower-limb muscles with different time intervals (50-400ms) after the auditory signals. The amplitudes of the spinal reflexes in all the recorded leg muscles significantly increased at 50-250ms after remote muscle activation onset. This suggests that remote muscle contraction simultaneously facilitates the spinal reflexes in multiple lower-limb muscles. In addition, eight healthy men performed five different tasks (i.e., rest, hand grip, pinch grip, elbow flexion, and shoulder flexion). Compared to control values recorded just before each task, the spinal reflexes evoked at 250ms after the auditory signals were significantly enhanced by the above tasks except for the rest task. This indicates that such facilitatory effects are also induced by remote muscle contractions in different upper-limb areas. The present results demonstrate the existence of a neural interaction between remote upper-limb muscles and spinal reflex circuits activated by tSCS in multiple lower-limb muscles. The combination of tSCS and remote muscle contraction may be useful for the neurological examination of spinal cord circuits.

Landing Stiffness Between Individuals With and Without a History of Low Back Pain.

Reduced spinal stabilization, delayed onset of muscle activation, and increased knee joint stiffness have been reported in individuals with a history of low back pain (LBP). Biomechanical adaptations resulting from LBP may increase the risk for future injury due to suboptimal loading of the lower-extremity or lumbar spine. Assessing landing mechanics in these individuals could help identify which structures might be susceptible to future injury. To compare vertical and joint stiffness of the lower-extremity and lumbar spine between individuals with and without a previous history of LBP. Cross-sectional study. Research laboratory. There were 45 participants (24 without a previous history of LBP-age 23 [8]y, height 169.0 [8.5]cm, mass 69.8 [13.8]kg; 21 with a previous history of LBP-age 25[9]y, height 170.0 [8.0]cm, mass 70.2 [11.8]kg). Single-limb landing trials on the dominant and nondominant limb from a 30-cm box. Vertical stiffness and joint stiffness of the ankle, knee, hip, and lumbar spine. Individuals with a previous history of LBP had lower vertical stiffness (P = .04), but not joint stiffness measures compared with those without a previous history of LBP (P > .05). Overall females had lower vertical (P = .01), ankle (P = .02), and hip stiffness (P = .04) compared with males among all participants. Males with a previous history of LBP had lower vertical stiffness compared with males without a previous history LBP (P = .01). Among all individuals without a previous history of LBP, females had lower vertical (P < .01) and ankle stiffness measures (P = .04) compared with males. Landing stiffness may differ among males and females and a previous history of LBP. Comparisons between individuals with and without previous LBP should be considered when assessing landing strategies, and future research should focus on how LBP impacts landing mechanics.

Chinese Martial Art Training Failed to Improve Balance or Inhibit Falls in Older Adults.

This randomized controlled trial explored the effects of a Ving Tsun (VT) Chinese martial art training program on reactive standing balance performance, postural muscle reflex contraction latency, leg muscle performance, balance confidence and falls in community-dwelling older adults. We randomly assigned 33 healthy older adults to either a VT group (mean age = 67.5 years) or a control group (mean age = 72.1 years). The VT group received two 1-hour VT training sessions per week for three months (24 sessions). Primary outcome measures collected before and after the intervention period were electromyographic muscle activation onset latencies of the hamstring and gastrocnemius and the center of pressure path, length and movement velocity in standing (reactive balance performance). Secondary outcome measures included isometric peak force and time to isometric peak force of the knee extensors and flexors, the Activities-Specific Balance Confidence Scale score, and fall history. Results revealed that the mean gastrocnemius muscle activation onset latency was significantly longer (22.53 ms) in the VT group after the intervention. The peak force of the knee flexors significantly increased (by 1.58 kg) in the control group over time but not in the VT group. The time to reach peak force in the knee flexors was significantly longer (by 0.51 s) in the control group (but not the VT group) at posttest compared with the pretest value. No other significant group, time, or group-by-time interaction effects were noted. We discussed possible reasons for the failure of three months of martial art training to benefit fall risks among these older adults.

Effectiveness of an on-body lifting aid (HAL® for care support) to reduce lower back muscle activity during repetitive lifting tasks

The Hybrid Assistive Limb Lumbar Type (HAL) is an active exoskeleton that provides motion according to the wearer’s voluntary drive. It was developed to support back muscles during repetitive lifting tasks. The purpose of this paper was to determine if the myoelectric activity of the back muscles is reduced or altered when using the HAL and to investigate a possible influence of its use on the cardiovascular system. Fourteen healthy young men without lower back pain underwent a freestyle, symmetrical-lifting protocol. Participants lifted a 17.05 kg handled-box for 10 min. with and without HAL support. Surface electromyography (sEMG) signals were recorded at thoracic (TES) and lumbar erector spinae (LES) and quadriceps femoris (QF). Heart rate was recorded from electrocardiogram. The subjects rated their level of physical exertion using the Borg Rating of Perceived Exertion (BORG) scale. Additionally they commented on sites of discomfort, perceptions of force, and loss of range of motion. The root mean square and integrated sEMG value was significantly reduced at the LES and TES. Heart rate variability output variables did not show any significant difference. The BORG-Scale showed no difference, with a mean score of 2.5. The HAL decreased the magnitude and onset of muscle activity and force in the lower back in a repetitive lifting task. Reduction of the muscle force and activity required during the lifting process is meaningful regarding lower back pain prevention, and the HAL may contribute to reducing the incidence of lower back pain in the working population.