Evaluating the Relationship Between Surface and Intramuscular-Based Electromyography Signals: Implications of Subcutaneous Fat Thickness

Intramuscular (iEMG) and surface electromyographic (sEMG) signals have been compared previously using predictive regression equations, finite element modeling, and correlation and cross-correlation analyses. Although subcutaneous fat thickness (SCFT) has been identified as a primary source of sEMG signal amplitude attenuation and low-pass filter equivalence, few studies have explored the potential effect of SCFT on sEMG and iEMG signal characteristics. The purpose of this study was to investigate the relationship between normalized submaximal iEMG and sEMG signal amplitudes collected from 4 muscles (rectus femoris, vastus lateralis, infraspinatus, and erector spinae) and determine whether SCFT explains more variance in this relationship. The effect of sex was also explored. Linear regression models demonstrated that the relationship between sEMG and iEMG was highly variable across the muscles examined (adjusted coefficient of determination [Adj R2] = .02-.74). SCFT improved the model fit for vastus lateralis, although this relationship only emerged with the inclusion of sex as a covariate. Thus, this research suggests that SCFT is not a prominent factor affecting the linearity between sEMG and iEMG. Researchers should investigate other parameters that may affect the linearity between sEMG and iEMG signals.

Relationship between onset of trunk muscle activities and pelvic kinematics in individuals with and without chronic low back pain

BACKGROUND

Lumbopelvic movement patterns during prone hip extension has been proposed as a clinical screening method for trunk muscle dysfunction in patients with chronic low back pain (CLBP). However, correlations between trunk muscle onset and pelvic kinematics have not been investigated.

OBJECTIVE

To examine the correlation between trunk muscle onset and pelvic kinematics during prone hip extension in participants with CLBP.

METHODS

Fifteen patients with CLBP and 15 healthy individuals participated. We evaluated the muscle activities of the lumbar multifidus, the longissimus, and the semitendinosus via electromyogram and the displacement angles of the pelvic tilt, oblique and rotation.

RESULTS

The onset of the multifidus at the ipsilateral side of hip extension was significantly delayed in the patients with CLBP compared to the control group (P< 0.001). The onset of the ipsilateral multifidus in the control group was significantly correlated with increased anterior pelvic tilt angle (P= 0.019, r= 0.597), whereas no significant correlation was observed in the CLBP group (P= 0.810, r=-0.068).

CONCLUSION

The results suggest that pelvic kinematics during prone hip extension does not predict the delayed trunk muscle onset in patients with CLBP.

Effect of Adding Diaphragmatic Breathing Exercises to Core Stabilization Exercises on Pain, Muscle Activity, Disability, and Sleep Quality in Patients With Chronic Low Back Pain: A Randomized Control Trial

Objective

The purpose of this study was to test the effect of adding diaphragmatic breathing exercises (DBEs) to core stabilization exercises (CSEs) for patients with chronic low back pain (CLPB).

Methods

Twenty-two patients with CLPB were randomly allocated to the experimental (DBE + CSE) or control group (CSE only). They were given 12 treatment sessions 3 times a week for 4 weeks. Patients were evaluated before and after the 12 sessions. Surface electromyography of transverse abdominis, Oswestry Disability Index, Fear Avoidance Belief Questionnaire, Pittsburgh Sleep Quality Index, Numeric Pain Rating Scale, and chest expansion were used as outcome measures for pain, muscle activity, disability, and sleep quality.

Results

The outcome measure scores showed statistical significance of (P = .01) in time effect on muscle activity, sleep quality, disability score, pain score, fear-avoidance belief of patients and chest expansion; and group effect on Fear Avoidance Belief Questionnaire and physical activity parameter (P = .05). An interaction effect (time x group) on muscle activity for right transverse abdominus during tuck in (P = .01) and chest expansion (P = .01) was also found; however, no significant difference was found related to other parameters.

Conclusion

The combination of DBE and CSE interventions compared to CSE alone showed improvement in the measured parameters for patients with CLBP. Incorporating DBE with CSE also improved muscle activation and chest expansion.

The Influence of Anticipation of Movement Starting Time on Feedforward Activation of Trunk Muscles During Rapid Shoulder Joint Movements

This study aimed to clarify the differences in the onset of trunk muscle activity with and without anticipation of the movement starting time during rapid shoulder movements. Ten healthy men in a relaxed upright position performed rapid 135° flexion, 135° abduction, and 45° extension of the shoulder on the dominant hand side with and without anticipation of the movement starting time. They moved their shoulder joints following a 3-s countdown and a light stimulus in the anticipation and non-anticipation conditions, respectively. Electromyography of the anterior and posterior quadratus lumborum, transversus abdominis, internal oblique, external oblique, rectus abdominis, lumbar multifidus, lumbar erector spinae on the non-dominant hand side, and the middle deltoid on the dominant hand side were measured. The onset of activity of each trunk muscle relative to the onset of the middle deltoid was calculated. Two-way analysis of variance (eight trunk muscles × two anticipation conditions) was used to compare the onset of electromyographic activity of the trunk muscles in each direction of the shoulder movement. There were significant interactions between the muscles and anticipation conditions during shoulder abduction and extension. The onset of activity in the anterior and posterior quadratus lumborum, transversus abdominis, and internal oblique occurred earlier with anticipation of the movement starting time than without anticipation during shoulder abduction and extension. The anticipation of movement starting time may contribute to a reliable center of mass control within the support base and improve lumbar spine stability by hastening the onset of activity of the deep trunk muscles.

Human-Robot Cooperative Strength Training Based on Robust Admittance Control Strategy

A stroke is a common disease that can easily lead to lower limb motor dysfunction in the elderly. Stroke survivors can effectively train muscle strength through leg flexion and extension training. However, available lower limb rehabilitation robots ignore the knee soft tissue protection of the elderly in training. This paper proposes a human-robot cooperative lower limb active strength training based on a robust admittance control strategy. The stiffness change law of the admittance model is designed based on the biomechanics of knee joints, and it can guide the user to make force correctly and reduce the stress on the joint soft tissue. The controller will adjust the model stiffness in real-time according to the knee joint angle and then indirectly control the exertion force of users. This control strategy not only can avoid excessive compressive force on the joint soft tissue but also can enhance the stimulation of quadriceps femoris muscles. Moreover, a dual input robust control is proposed to improve the tracking performance under the disturbance caused by model uncertainty, interaction force and external noise. Experiments about the controller performance and the training feasibility were conducted with eight stroke survivors. Results show that the designed controller can effectively influence the interaction force; it can reduce the possibility of joint soft tissue injury. The robot also has a good tracking performance under disturbances. This control strategy also can enhance the stimulation of quadriceps femoris muscles, which is proved by measuring the muscle electrical signal and interaction force. Human-robot cooperative strength training is a feasible method for training lower limb muscles with the knee soft tissue protection mechanism.

A guide for standardized interpretation of lumbar multifidus ultrasonography; an observational study

Background

Inconsistent descriptions of Lumbar multifidus (LM) morphology were previously identified, especially in research applying ultrasonography (US), hampering its clinical applicability with regard to diagnosis and therapy. The aim of this study is to determine the LM-sonoanatomy by comparing high-resolution reconstructions from a 3-D digital spine compared to standard LM-ultrasonography.

Methods

An observational study was carried out. From three deeply frozen human tissue blocks of the lumbosacral spine, a large series of consecutive photographs at 78 μm interval were acquired and reformatted into 3-D blocks. This enabled the reconstruction of (semi-)oblique cross-sections that could match US-images obtained from a healthy volunteer. Transverse and oblique short-axis views were compared from the most caudal insertion of LM to L1.

Results

Based on the anatomical reconstructions, we could distinguish the LM from the adjacent erector spinae (ES) in the standard US imaging of the lower spine. At the lumbosacral junction, LM is the only dorsal muscle facing the surface. From L5 upwards, the ES progresses from lateral to medial. A clear distinction between deep and superficial LM could not be discerned. We were only able to identify five separate bands between every lumbar spinous processes and the dorsal part of the sacrum in the caudal anatomical cross-sections, but not in the standard US images.

Conclusion

The detailed cross-sectional LM-sonoanatomy and reconstructions facilitate the interpretations of standard LM US-imaging, the position of the separate LM-bands, the details of deep interspinal muscles, and demarcation of the LM versus the ES. Guidelines for electrode positioning in EMG studies should be refined to establish reliable and verifiable findings. For clinical practice, this study can serve as a guide for a better characterisation of LM compared to ES and for a more reliable placement of US-probe in biofeedback.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05590-5.

Change in the activity of trunk and lower limb muscles during 2000-m rowing

This study aimed to clarify the changes in the activity of the trunk and lower limb muscles during 2000-m rowing. Ten male rowers performed a 2000-m race simulation on a rowing ergometer. Electromyography results of the abdominal muscles, back muscles, gluteus maximus (GMax), biceps femoris (BF), and rectus femoris (RF) were recorded. The electromyographic activity during the three strokes after the start (initial stage), at 1000m (middle stage), and before the end (final stage) were analyzed. From the handle position, the rowing motion was divided into five phases (early-drive, middle-drive, late-drive, early-recovery, and late-recovery). The peak activities of the abdominal muscles, back muscles, GMax, and BF in each stroke of the rowing motion were delayed at the middle and final stages compared to the initial stage (P<0.05). The peak activity of the RF was observed in the late-drive phase at the initial stage, whereas a high RF activity was observed in the middle-drive phase at the middle and final stages (P<0.05). Considering the results of the activity of the back muscles and RF, RF muscular endurance enhancement may lead to a decrease in the load on the back muscles and help prevent muscular low back pain in rowers. J. Med. Invest. 69 : 45-50, February, 2022.

Coordinate activity of the quadratus lumborum posterior layer, lumbar multifidus, erector spinae, and gluteus medius during single-leg forward landing

This study aimed to clarify the differences in electromyographic activity between the quadratus lumborum anterior (QL-a) and posterior layers (QL-p), and the relationship among trunk muscles and gluteus medius (GMed) activities during forward landing. Thirteen healthy men performed double-leg and single-leg (ipsilateral or contralateral sides as the electromyography measurement of trunk muscles) forward landings from a 30 cm-height-box. The onset of electromyographic activity in pre-landing and the electromyographic amplitude of the unilateral QL-a, QL-p, abdominal muscles, lumbar multifidus (LMF), erector spinae (LES), and bilateral GMed were recorded. Two-way ANOVA was used to compare the onset of electromyographic activity (3 landing leg conditions × 10 muscles) and electromyographic amplitude among (3 landing leg conditions × 2 phases). The onset of QL-p was significantly earlier in contralateral-leg landing than in the double-leg and ipsilateral-leg landings. The onset of LMF and LES was significantly earlier than that of the abdominal muscles in contralateral-leg landing. QL-p activity and GMed activity on the contralateral leg side in the pre-landing were significantly higher in contralateral-leg landing than in the other leg landings. To prepare for pelvic and trunk movements after ground contact, LMF, LES, QL-p on non-support leg side, and GMed on support leg side showed early or high feedforward activation before ground contact during single-leg forward landing.

Differences in the activity of the shoulder girdle and lower back muscles owing to postural alteration while using a smartphone

The purpose of this study was to clarify the influence of different postures on the activity of the shoulder girdle and lower back muscles while using a smartphone. Sixteen healthy male participants maintained two postures while using a smartphone : a good posture in which the tragus and acromion were closer to the vertical line passing through the greater trochanter, and a poor posture in which the tragus and acromion were farther from the vertical line passing through the greater trochanter. The target muscles were the rhomboid major (Rhom), upper trapezius, middle trapezius, lower trapezius (LT), lumbar erector spinae (LES), and lumbar multifidus (LMF). The activities of the Rhom and LT were significantly lower with poor posture than those with good posture. The activities of LES and LMF were significantly higher with poor posture than those with good posture. The results of this study indicated that poor posture was associated with hypoactivity of the shoulder girdle muscles and hyperactivity of the lower back muscles when compared with good posture. Poor posture for prolonged periods while using a smartphone would lead to malfunction of the shoulder girdle muscles and musculofascial lower back pain. J. Med. Invest. 67 : 274-279, August, 2020.

Changes in lumbar kinematics and trunk muscle electromyographic activity during baseball batting under psychological pressure

Psychological pressure during sports competition disturbs the ideal physical movement and causes injury. Baseball batting frequently causes trunk injuries. This study aimed to examine the influence of psychological pressure on the lumbar kinematics and trunk muscle activity during the baseball batting. Fourteen collegiate baseball players participated in this study. The participants performed bat swings under three different psychological conditions (non-pressure, pressure, and emphasized pressure). The lumbar kinematics and trunk muscle activity were measured during each bat swing. One- and two-way analyses of variance were performed to compare the lumbar kinematics and trunk muscle activity among different psychological pressure conditions. The lumbar flexion angle throughout the bat swing in the swing phase, from the moment of ground contact of the lead foot to the moment of ball contact, was significantly larger under the pressure and emphasized pressure conditions than under the non-pressure condition (P<0.05). The bilateral lumbar erector spinae (LES) activities in the swing and follow-through phases were significantly higher under the emphasized pressure condition than under the non-pressure condition (P<0.05). These results indicate that the baseball batting under psychological pressure influenced the lumbar kinematics and bilateral LES activities and may be related to the development of low back pain.

Feedforward activation of the quadratus lumborum during rapid shoulder joint abduction

This study aimed to clarify the difference in the onset of EMG activity between eight trunk muscles, including the anterior (QL-a) and posterior (QL-p) layers of the quadratus lumborum during rapid shoulder joint abduction. Thirteen healthy men participated in this study. Electromyography of the QL-a, QL-p, transversus abdominis (TrA), internal oblique (IO), external oblique (EO), rectus abdominis (RA), lumbar multifidus (LMF), lumbar erector spinae (LES) on non-movement side, and middle deltoid (MD) on the movement side were measured. Subjects who were standing in a relaxed position performed rapid shoulder abduction with the dominant hand after light stimulus with or without a 3 kg wrist weight. Two-way ANOVA (muscles × weight conditions) was used to compare the onset of trunk muscles relative to that of MD. There was a significant main effect of the muscles. The onset of the QL-a, QL-p, and TrA was significantly earlier than that of the IO, EO, LMF, and LES (P < 0.01). This result suggests that the activities of the QL-a, QL-p, and TrA have a crucial role in controlling the center of mass within the base of support and stabilizing the lumbar spine in the coronal plane during shoulder abduction.

Activity of the Quadratus Lumborum and Trunk Muscles Relates to Pelvic Tilt Angle During Pelvic Tilt Exercises

OBJECTIVE

Pelvic tilt exercises are used clinically to correct lumbopelvic alignment. The anterior and posterior layers of the quadratus lumborum are important for pelvic motor control in the coronal plane. This study aimed to evaluate whether the anterior and posterior activity is related to the pelvic tilt angle during pelvic tilt exercises.

DESIGN

The study design was single-occasion repeated measures in a randomized manner. Twelve healthy men performed the four directions of the pelvic tilt exercises (anterior or posterior pelvic tilt and lateral pelvic elevation on the ipsilateral or contralateral measurement side). The electromyographies of the anterior and posterior were recorded using intramuscular fine-wire electrodes and normalized to isometric peak electromyography.

RESULTS

The activity of the anterior and posterior during lateral pelvic elevation on the ipsilateral measurement side (19.0 ± 16.0 percent of maximal voluntary isometric contraction) was significantly higher than that during other directions of the pelvic tilt exercises (P < 0.01). There was a significant positive correlation between the anterior activity and the maximum change angles of pelvic tilt during lateral pelvic elevation on the ipsilateral measurement side (r = 0.674, P = 0.016).

CONCLUSIONS

The anterior activity was related to a large lateral pelvic elevation angle on the ipsilateral side during pelvic tilt exercises.

Muscle Synergy of the Underwater Undulatory Swimming in Elite Male Swimmers

Improving the performance of underwater undulatory swimming (UUS) improves swimming time, so it is important to identify the pattern of muscle coordination in swimmers with fast UUS. This study aimed to identify muscular coordination in the trunk and lower limb during UUS in elite swimmers. Nine swimmers (aged 20 ± 2 years; height, 1.74 ± 0.03 m; weight, 73.0 ± 4.4 kg) participated in this study. Measurements were taken by electromyography of eight muscles: rectus abdominis (RA), internal abdominal muscle (IO), rectus femoris (RF), erector spinae (ES), multifidus (MF), tibialis anterior (TA), and thigh biceps (BF), and gastrocnemius (GS). For evaluation of muscle coordination, “muscle synergy” and “activation coefficient” were calculated using non-negative matrix factorization from electromyographic data. Kick frequency, kick amplitude, swim velocity, and kinematics of the pelvis were also calculated. Kick cycle was divided into two kick phases: downward kick (from the highest toe vertical coordinate to the lowest point) and upward kick (from the lowest point to the highest point). Kick frequency, kick amplitude, and swimming velocity were 1.9 ± 0.3 Hz, 0.45 ± 0.6 m, and 1.8 ± 0.2 m·s ⁻¹, respectively. The maximum backward pelvic tilt was 94.4 ± 4.5° and the minimum (forward) was 90.8 ± 5.7°. Three muscle synergy values were extracted from each swimmer during UUS: those involved in the transition from upward kick to downward kick (Synergy 1), downward kick (Synergy 2), and upward kick (Synergy 3). Synergy 1 involved mainly the RF, IO, and RA, which were activated during the turn from the upward to the downward phase. Synergy 2 involved mainly the MF, ES, and TA in the downward kick. Synergy 3 corresponded to the coordination of the BF and GS, which were active in the upward kick. In UUS by elite swimmers, both the upward kick and downward kick followed the trunk muscles involved in the pelvic forward–backward tilt movement, and lower limb muscles were activated. Muscle coordination based on pelvic forward-backward tilt during UUS is expected to contribute to the coaching field for elite swimmer development.

Change in Regional Activity of the Quadratus Lumborum During Bridge Exercises

CONTEXT

The quadratus lumborum (QL) is expected to contribute to segmental motor control of the lumbar spine to prevent low back pain. It has different layers (anterior [QL-a] and posterior [QL-p] layers), whose functional differences are becoming apparent. However, the difference between the QL-a and QL-p activities during bridge exercises utilized in rehabilitation is unclear.

OBJECTIVE

To compare QL-a and QL-p activities during bridge exercises.

DESIGN

Repeated-measurement design was used to assess electromyographic activity of trunk muscles recorded during 14 types of bridge exercises.

SETTING

University laboratory.

PARTICIPANTS

A total of 13 healthy men with no history of lumbar spine disorders participated.

INTERVENTION

The participants performed 14 types of bridge exercises (3, 3, and 8 types of side bridge, back bridge, and front bridge [FB], respectively).

MAIN OUTCOME MEASURES

Fine-wire electromyography was used for QL-a and QL-p activity measurements during bridge exercises.

RESULTS

Both QL-a and QL-p showed the highest activity during the side bridge with hip abduction  (47.3% [29.5%] and 43.0% [32.9%] maximal voluntary isometric contraction, respectively). The activity of the QL-a was significantly higher than that of the QL-p during back bridge with ipsilateral leg lift and FB elbow-toe with ipsilateral arm and contralateral leg lift (P < .05). With regard to the QL-p, the activity of the FB hand-knee with contralateral arm and ipsilateral leg lift, the FB elbow-knee with contralateral arm and ipsilateral leg lift, and the FB elbow-toe with contralateral arm and ipsilateral leg lift were significantly higher than that of the FB elbow-knee and FB elbow-toe (P < .05).

CONCLUSION

This study indicates different regional activities; the QL-a activated during the back bridge with ipsilateral leg lift and FB with ipsilateral arm lift, and the QL-p activated during the FB with ipsilateral leg lift. These results have implications for the rehabilitation of low back pain or lumbar scoliosis patients based on QL recruitment.

A Study on Trunk Muscle Activation of 2 Deep Water Running Styles (High-Knee and Cross-Country Style) and Land Walking

Context: Deep water running (DWR) is an aquatic aerobic exercise which involves running in water without the feet touching the bottom of the pool, and it may involve different activation of trunk muscles compared with running or walking on land. This form of exercise is gradually being adopted as a form of therapeutic exercise for people with low back pain. It is proposed that different types of running or walking in water may be a more comfortable form of training for the trunk and abdominal muscles compared with exercising on dry land. Objectives: This study aimed to examine the trunk muscle activation in DWR in 2 different styles—high knee style and cross-country style, and these were compared with walking on land. Participants: Eleven healthy individuals (2 females and 9 males, mean age = 24 [4.6]) were recruited for this study. Outcome Measures: Surface electromyography was used to examine the activities of the right transversus abdominis, rectus abdominis, lumbar multifidus, and lumbar erector spinae muscles in 5 conditions: static standing on land and in water, running in deep water with high knee and cross-country styles, and finally walking on a treadmill. Results: The percentage of maximal voluntary contraction of the transversus abdominis was significantly higher for both running styles in DWR, compared with that of static standing in water. Comparing directly the 2 styles, muscle activity was higher with a high knee action compared to without. The activation of transversus abdominis during high-knee DWR was comparable with that during treadmill walking and this may have clinical implications. Conclusion: The results of this study confirmed that running in deep water with a high knee action activated trunk muscles differently compared with standing or walking on land.

Comparison of Modular Control during Smash Shot between Advanced and Beginner Badminton Players

This study investigated muscle synergy during smash shot in badminton and compared synergies of advanced players (more than 7 years experience) and beginner players (less than 3 years experience). The dominant hand of all players was the right side. Muscle activities were recorded on both sides of the rectus abdominis, external oblique (EO), internal oblique/transversus abdominis (IO/TrA), and erector spinae. Additionally, the right side of the biceps brachii, triceps brachii, flexor carpi radialis, flexor carpi ulnaris, and flexor digitorum profundus muscle activities were recorded. All data was obtained using surface electromyography. Synergy was extracted from electromyography signals using nonnegative matrix factorization. Extracted synergies in each group were compared using scalar product (SP) which is the similarity index. As a result, two synergies were extracted in the beginner players and three synergies were extracted in advanced players. Beginner and advanced players had one synergy in common (SP = 0.86) that was mainly on the left side of the EO. It activated in the early stroke and had a role of side bending from the left to hit the shuttlecock at a higher point. Another synergy that had coactivation of the IO/TrA and forearm muscles at impact was extracted only for advanced players and it may enhance the smash shot performance in badminton.

Electromyographic and kinetic comparison of the back squat and overhead squat

The purpose of this study was to compare muscle activity and kinetics during the back squat and overhead squat performed at 3 relative intensities (60, 75, and 90% 3 repetition maximum). Fourteen subjects (age, 26 ± 7 years; height, 182.5 ± 13.5 cm; body mass, 90.5 ± 17.5 kg) performed each exercise using a within-subjects crossover design. In addition, a selection of trunk isolation exercises were included to provide additional comparisons. Squats were performed on a force platform with electromyographic activity of the anterior deltoid, rectus abdominis (RA), external oblique (EO), erector spinae (ES), gluteus maximus, vastus lateralis, biceps femoris, and lateral gastrocnemius recorded throughout. The overhead squat demonstrated significantly greater (p ≤ 0.05) activity in the anterior trunk muscles (RA and EO) during the eccentric phase. However, the magnitudes of the differences were relatively small (approximately 2-7%). In contrast, the back squat displayed significantly greater (p ≤ 0.05) activity in the posterior aspect of the trunk ES and all lower-body muscles during the concentric phase. Kinetic comparisons revealed that significantly greater peak force (p ≤ 0.05) was developed during the back squat. Electromyographic comparisons between the trunk isolation exercises and squat variations demonstrated substantially greater anterior trunk activity during the isolation exercises, whereas the highest activity in the posterior aspect of the trunk was obtained during the squats (p ≤ 0.05). The results of the study do not support the hypothesis that the overhead squat provides a substantially greater stimulus for developing the trunk musculature compared with the back squat.

Abdominal muscle activity during a standing long jump

STUDY DESIGN

Experimental laboratory study.

OBJECTIVES

To measure the activation patterns (onset and magnitude) of the abdominal muscles during a standing long jump using wire and surface electromyography.

BACKGROUND

Activation patterns of the abdominal muscles, especially the deep muscles such as the transversus abdominis (TrA), have yet to be examined during full-body movements such as jumping.

METHODS

Thirteen healthy men participated. Wire electrodes were inserted into the TrA with the guidance of ultrasonography, and surface electrodes were attached to the skin overlying the rectus abdominis (RA) and external oblique (EO). Electromyographic signals and video images were recorded while each subject performed a standing long jump. The jump task was divided into 3 phases: preparation, push-off, and float. For each muscle, activation onset relative to the onset of the RA and normalized muscle activation levels (percent maximum voluntary contraction) were analyzed during each phase. Comparisons between muscles and phases were assessed using 2-way analyses of variance.

RESULTS

The onset times of the TrA and EO relative to the onset of the RA were -0.13 ? 0.17 seconds and -0.02 ? 0.07 seconds, respectively. Onset of TrA activation was earlier than that of the EO. The activation levels of all 3 muscles were significantly greater during the push-off phase than during the preparation and float phases.

CONCLUSION

Consistent with previously published trunk-perturbation studies in healthy persons, the TrA was activated prior to the RA and EO. Additionally, the highest muscle activation levels were observed during the push-off phase.