Erector Spinae Activity Research Articles

Effect of seat tilting on biomechanics of L4 in tractor drivers

The tilting of the tractors' seat during deep tillage operations affects the drivers' sitting position, which can lead to lumbar spine injuries. To investigate the effect of seat tilting on the driver's L4 biomechanics, we built a tractor-driver musculoskeletal model in AnyBody™. The maximum activity of the driver's erector spinae at different tilted angles were measured by sEMG and compared with the simulation results to validate the model. The spatial position of the driver's spine at different tilted angles were obtained by 3 D motion capture. The model simulated the driver's spine posture during the actual tilt and investigated the effects of different tilted angles and vibration on the biomechanics of the driver's L4 . The results showed that as the tilt angle of the tractor increased, the load on the driver's L4 also increased, especially the shear force increased at a faster rate than the axial and normal forces, with the shear force on the driver's L4 increasing from 0 N to 138.7 N when the tractor was tilted from 0° to 15°. When vibration was applied to the musculoskeletal model, the maximum value of the shear force on the driver became progressively greater as the angle of tilt of the tractor increased. Overall, tilting the tractor can have a large impact on the biomechanics of the driver's L4, and tilting the tractor may be an important cause of lumbar spine injuries for tractor drivers.

Effect of side-sling plank exercise on trunk and hip muscle activation in subjects with gluteus medius weakness.

The effectiveness of side-sling plank (SSP) exercises on trunk and hip muscle activation in subjects with gluteus medius (Gmed) weakness is unclear. To quantify muscle activation of the rectus abdominis (RA), external oblique (EO), erector spinae (ES), lumbar multifidus (LM), Gmed, gluteus maximus (Gmax), and tensor fasciae latae (TFL) during SSP with three different hip rotations compared to side-lying hip abduction (SHA) exercise in subjects with Gmed weakness. Twenty-two subjects with Gmed weakness were recruited. SHA and three types of SSP exercises were performed: SSP with neutral hip (SSP-N), hip lateral rotation (SSP-L), and hip medial rotation (SSP-M). Surface electromyography was used to measure the activation of the trunk and hip muscles. The trunk and hip muscles activations were generally significantly higher level during three SSP than SHA. SSP-M showed significantly lower EO activation while significantly higher ES and LM activation than SSP-L. Gmed activation was significantly higher during SSP-M than during SSP-L. TFL activation was significantly lower during SSP-M than during SSP-N and SSP-L. SSP could be prescribed for patients who have reduced Gmed strength after injuries. Especially, SSP-M could be applied for patients who have Gmed weakness with dominant TFL.

Effects of passive exoskeleton on trunk and gluteal muscle activity, spinal and hip kinematics and perceived exertion for physiotherapists in a simulated chair transfer task: A feasibility study

Despite being a topic of increasing concern, work-related musculoskeletal disorders (WMSDs) among physiotherapists, have not been comprehensively explored. This study evaluated the effects of using a passive exoskeleton on biomechanics (i.e. muscle activity of back and hip extensors) and kinematics (trunk and hip flexion angles) during a simulated chair transfer task. A simulated patient was used for the chair transfer task. Twenty working physiotherapists performed the chair transfer task with or without using a passive exoskeleton. The biomechanics and kinematics during the tasks were measured using surface electromyography (sEMG) and motion sensors, respectively. Change in exertion level was examined using the Borg CR-10 scale, and an acceptance questionnaire was adopted from previous studies and used in investigating user acceptance of the exoskeleton. Results revealed that (1) using a passive exoskeleton in performing transfer tasks significantly decreased the sEMG activities of thoracic erector spinae, lumbar erector spinae and gluteal muscles, decreasing the maximum voluntary isometric contraction by 7.78%–10.95%; (2) no significant differences in the maximal flexion angles of thoracic and lumbar spines and trunk between performing the task with and without the exoskeleton; (3) a nonsignificant decrease in exertion level when performing the transfer task with the exoskeleton; and (4) no significant between-group differences in the score of acceptance questionnaire. These findings suggested that using the exoskeleton may help alleviate loading on the back by decreasing back extensor and hip extensor muscle activities while not considerably changing sagittal plane kinematics at the trunk and hip.

Spatial distribution of erector spinae activity is related to task-specific pain-related fear during a repetitive object lifting task

Fear-avoidance beliefs, particularly the fear of lifting with a flexed spine, are associated with reduced spinal motion during object lifting. Low back pain patients thereby also showed potentially clinically relevant changes in the spatial distribution of back muscle activity, but it remains unknown whether such associations are also present in pain-free individuals. This cross-sectional observational study investigated the relationship between fear-avoidance beliefs and the spatial distribution of lumbar paraspinal muscle activity in pain-free individuals during a repetitive lifting task. Thirty participants completed two pain-related fear questionnaires and performed 25 repetitions of lifting a 5 kg-box from a lower to an upper shelf and back, while multi-channel electromyographic signals were recorded bilaterally from the lumbar erector spinae muscles. Changes in spatial distribution were defined as the differences in vertical position of the weighted centroids of muscle activity (centroid shift) between the first and last few repetitions. Linear regression analyses were performed to examine the relationships between centroid shift and fear-avoidance belief scores. Fear of lifting an object with a flexed spine was negatively associated with erector spinae activity centroid shift (R2 adj. = 0.1832; p = 0.045), which might be an expression of behavioral alterations to prevent the back from possible harm.

만성 요통환자의 굽힘과 폄편향이 허리근육의 횡단면적과 근활성도에 미치는 영향

The purpose of study was to explore the influence of flexion and extension bias on the electromyographic (EMG) activities and cross-sectional area of lumbar muscles in chronic low back pain. twenty-two patients with chronic low back pain were divided into either flexion bias or extension bias groups by symptom provoking posture. The multifidus, iliopsoas, and erector spinae muscles were measured by magnetic reasoning imaging (MRI) and calculated with ratio by body of the 4th lumbar vertebra. EMG activities of multifidus and erector spinae was measured, and all the EMG amplitude were normalized into %maximum voluntary isometric contraction (%MVIC). Flexion bias group has significantly lower ratio of iliopsoas cross-sectional area than that of extension bias group (p<.05). As a result, flexion bias group has higher ratio of cross-sectional area of multifidus at the more involved side (p<.05). Flexion bias group has significantly higher %MVIC in erector spinae than extension bias group during trunk flexion and extension (p<.05). Consequently, the results of this study suggest that necessity of exercise for preventing multifidus muscle atrophy for flexion bias group.

Between/within-session reliability of spinal kinematic and lumbar muscle activity measures in patients with chronic low back pain and asymptomatic individuals

BackgroundLongitudinal research is required to better understand the role of spinal movement alterations in chronic low back pain (CLBP). To this end, it is critical to assess the between-session reliability of spinal movement measures. Research questionWhat is the within/between-session reliability of spinal movement measures in patients with CLBP and asymptomatic controls? MethodsSpinal movement was recorded prospectively during two sessions, a week apart, for 20 patients with CLBP (60% male; 40.0 ± 12.3 years old) and 20 asymptomatic individuals (55% male; 38.2 ± 10.9 years old). Sagittal-plane angular amplitude and angular velocity at the lower lumbar, upper lumbar, lower thoracic and upper thoracic joints, as well as maximal erector spinae activity were measured during five daily-activity tasks. In addition, task-independent measures were obtained by averaging the measures across tasks. The Intraclass Correlation Coefficient (ICC 2,1) and the minimal detectable change (MDC) were calculated. Pearson correlation was used to compare task-independent and task-specific measures. ResultsBetween-session ICCs in patients with CLBP were mostly moderate to good for maximal angular amplitude and erector spinae activity measures. Lower ICCs were observed for range of angular motion and angular velocity measures (42% of ICCs < 0.5). Median MDCs were 9.6°, 18.3°/s and 1.0% for angular amplitude, angular velocity and erector spinae activity measures, respectively. The reliability of task-independent and task-specific measures was strongly correlated (r = 0.91, p < 0.001). SignificanceSagittal-plane maximal angular amplitude and erector spinae activity measures during various daily-activity tasks demonstrated mostly moderate to good between-session ICCs. However, relatively large MDCs suggested that important changes are needed to be detectable. Task-independent measures reported similarly acceptable ICCs than task-specific measures, supporting their use to describe spinal movement.

The effect of low back pain on neuromuscular control in cyclists

ABSTRACT This study was designed to identify neuromuscular adaptations of low back pain (LBP) cyclists , and the impact of a cycling effort on spinal shrinkage. Forty-eight trained cyclists rode their road bike on a smart trainer for 1-hour. Surface electromyography (EMG) recorded muscle activity of the lumbar erector spinae (LES), 3D motion analysis system recorded kinematic of the trunk, and stadiometry measured spinal height. Statistical comparisons were made using repeated measure ANOVAs. The LBP group presented increase in pain levels throughout the effort (p < 0.001). A significant group difference was only observed for the thoracic angle (p = 0.03), which was less flexed for LBP. The one-hour cycling effort (time effect) significantly increased the trunk flexion (p < 0.001) and thoracic flexion (p < 0.001) for both groups. Significant lower LES activation (35% less) was observed at the end of the effort as well as a decrease in spinal height (p = 0.01) for both groups. Neuromuscular adaptations to cycling effort is identified by a decrease in LES EMG amplitude and an increase flexion of the trunk. Adaptation to pain is seen by an increase in thoracic flexion. Despite these adaptations, LBP cyclists could not ride their bike pain-free.

Pain and electromyography reduction cause of sitting upright posture, frequent break, eye rest and self-stretching during smartphone usage.

Prolonged use of the smartphone causes neck and shoulder pain. However, no study has yet evaluated the effects of sitting upright, combined with frequent breaks, eye rest and self-stretching on pain and EMG during smartphone use. The purpose of the study was to compare pain and muscle activity between the control group (rest only) and the intervention group (rest combined with correct posture, eye rest and self-stretching) in smartphone use for 41.30 minutes. Forty-four healthy females aged 18-25 years old were recruited and randomly divided into two groups. The body pain chart and Visual Analog Scale (VAS) were used to evaluate pain. Electromyography (EMG) was used to measure muscle activity of Cervical Erector Spinae (CES) and Upper Trapezius (UT) muscles. The results showed that overall pain and neck pain in the control group increased significantly after smartphone use for 20 min and continually increased to 41.30 minutes (p < 0.05). Overall pain and neck pain in the intervention group was significantly lesser than control group after smartphone use for 41.30 minutes (p < 0.05). In the control group, EMG of CES at 41.30 minute was significantly higher than that of at 0 min (p < 0.05). There was no significant difference in EMG of UT between the two groups. Conclusion smartphone user in the interventional group reported less pain when compared to control group after Smartphone use for 41.30 minutes. Therefore, the user aged 18-25 years should have a rest combined with correct posture, eye rest and self-stretching to prevent neck pain during prolonged smartphone use.

Effects of arm and leg positions on lumbar multifidus muscle activity while on hands and knees or while standing

BackgroundThe lumbar multifidus (LMF) muscle, which is involved in the mechanical stability of the lumbar spine, reportedly undergoes atrophy in patients with low back pain. Preventing or mitigating low back pain requires strengthening the LMF muscle; however, methods for triggering selective and significant contraction of this muscle have not been fully studied. This study aims to clarify how, in the hands-and-knees or standing position, the position of the arm and leg on one side affects the activity of the lumbar erector spinae (LES) and LMF muscles.MethodsWe recruited nine adult men with no prior history of low back pain. Measurements were taken in four different postures under varying conditions (that is, one arm and one leg were lifted in either the hands-and-knees or standing position,) as follows: (1) shoulder joint flexion and hip joint extension in the hands-and-knees position; (2) 90° shoulder joint abduction and hip joint abduction in the hands-and-knees position; (3) shoulder joint flexion and hip joint extension in the standing position; and (4) 90° shoulder joint abduction and hip joint abduction in the standing position. The 90° shoulder joint abduction involved simultaneous horizontal abduction, while the hip joint abduction involved simultaneous extension. Muscle activity of the LES and LMF in each posture was measured using a surface electromyograph.ResultsMuscle activity of the LMF was significantly higher in 90° shoulder joint abduction and hip joint abduction than in shoulder joint flexion and hip joint extension in both the hands-and-knees and standing positions. The LES muscle showed no significant differences in activity between each posture.ConclusionsThe results suggest that unilateral 90° shoulder joint abduction and contralateral hip joint abduction in the hands-and-knees and standing positions may produce selective and significant contraction of the LMF muscle.

플랭크 운동 시 고관절 외전각도 차이가 코어근육 활성도에 미치는 효과

The purpose of this study was to investigate the effects of different hip abduction angles on core muscle activity during prone plank exercise. Fourteen healthy male subjects performed plank in four hip abduction angles(-10°, 0°, 15°, and 30°). Muscle activity of erector spinae, gluteus maximus, rectus abdominis, and external oblique was measured by using surface electromyography. Repeated measures ANOVA was used to analyze the results from each angle of muscle and the ratio of muscle activation. SPSS 21.0 was used for data analysis, and the significance level was set at p<.05. Compared to the core muscles in the hip abduction angle, rectus abdominis muscle and gluteus maximus muscle activity were greater than erector spinae in the -10° and 0°(p<.05). Also, gluteus maximus muscle activity was greater than erector spinae in the 15° and 30°(p<.05). During plank exercise, the muscle activities of erector spinae, gluteus maximus, rectus abdominis, and external oblique are not significantly affected by hip joint abduction angle changes. Our findings suggest that plank exercise by applying any hip abduction angles(-10°, 0°, 15°, and 30°) can be effectively activated the core muscle.

Comparison of flexion relaxation phenomenon between female yogis and matched non-athlete group

BackgroundTrunk flexion is a common exercise during daily activities. Flexion relaxation phenomenon (FRP) occurs during forward bending in which there is a sudden silence of erector spinae (ES) muscles. The pattern of forward bending differs in yoga practitioners. This learned pattern probably predisposes yogis to injuries. The hypothesis of this study was that FRP differs in yogis in comparison to non-yogis individuals.MethodsThis observational cross-sectional study was performed on 60 women assigned into yogis and non-athlete groups. Each participant was asked to bend forward and then return to the initial position. ES activity was recorded at L3 level, 4 cm from mid line during the trial. Trunk inclination and lumbar flexion angles were calculated at FRP onset and cessation moments.ResultsThe FRP occurred in 80% of yoga practitioners in comparison to 96.7% in the control group. Trunk inclination angle was significantly greater at FRP initiation in yogis compared to control group. Lumbar flexion angle was not different between the groups.ConclusionsIt is concluded that the altered pattern of forward bending observed in yogis may change patterns of ES muscles activity if it becomes part of a person's daily lifestyle which might predispose these muscles to fatigue and subsequent injuries; however, further studies are warranted for clarification.

Comparison among low intensity bridge exercises using suspension devices based on muscle activity and subjective difficulty.

Recent clinical studies have revealed the advantages of using suspension devices. Although the supine, lateral, and forward leaning bridge exercises are low-intensity exercises with suspension devices, there is a lack of studies directly comparing exercise progression by measuring muscular activity and subjective difficulty. To identify how the variations in the bridge exercise affects trunk muscle activity, the present study investigated changes in neuromuscular activation during low-intensity bridge exercises. We furthermore explored whether the height of the suspension point affects muscle activation and subjective difficulty. Nineteen asymptomatic male participants were included. Three bridge exercise positions, supine bridge (SB), lateral bridge (LB), forward leaning (FL), and two exercise angles (15 and 30 degrees) were administered, thereby comparing six bridge exercise conditions with suspension devices. Surface electromyography and subjective difficulty data were collected. The rectus abdominis activity was significantly higher with the LB and FL exercises compared with the SB exercise (p< 0.05). The erector spinae muscle activity was significantly higher with the SB and LB exercises, compared with the FL exercise (p< 0.05). The LB exercise significantly increased the internal oblique muscle activity, compared with other exercise variations (p< 0.05). The inclination angle of the exercise only affected the internal oblique muscle and subjective difficulty, which were significantly higher at 30 degrees compared with 15 degrees (p< 0.05). Relatively higher inclination angle was not effective in overall activation of the trunk muscles; however, different bridge-type exercises could selectively activate the trunk muscles. The LB and SB exercises could be good options for stimulating the internal oblique abdominis, and the erector spinae muscle, while the FL exercise could minimize the erector spinae activity and activate the abdominal muscles.

Effects of the ankle angle on the electromyographic activity of the trunk and lower extremities during isometric squat exercises

Background: Life in modern society has become convenient, but the lack of exercise due to a sedentary lifestyle has led to muscle weakness. The quadriceps femoris is essential for walking, standing, and using stairs in daily life. Muscle weakness can lead directly to impaired function. Squatting is the most representative exercise for effective muscle development and increasing the knee extensor strength. This study examined the effects of ankle angle during wall squats on the muscle activity of the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), rectus abdominis (RA), and erector spinae (ES) to determine which ankle angle can better strengthen the vastus medialis oblique as a method of rehabilitation training after a knee joint injury. Methods: All subjects (n = 20) performed the following three types of wall squats randomly: (1) GWS (General Wall Squat), (2) WSD 10° (Wall Squat with dorsiflexion 10°), and (3) WSP 10° (Wall Squat with plantarflexion 10°). Each subject completed all three kinds of wall squatting exercises three different times, and the muscle activity data of the VMO, VL, RF, BL, RA, and ES were recorded. Results: Compared to GWS exercise, the VMO and RF muscle activity increased significantly under WSP 10° exercise (p &lt; 0.05), whereas the VL, BF, RA, and ES activity did not increase significantly (p &gt; 0.05). No significant change between WSD 10° and WSP 10° was observed (p &gt; 0.05). Conclusions: WSP 10° can help increase the quadriceps muscle activity. Wall squat exercise with different ankle angles can be used for quadriceps muscle strengthening training for normal people and for recovery training for patellofemoral pain syndrome (PFPS) patients in the rehabilitation stage.

A Lower-Back Exoskeleton With a Four-Bar Linkage Structure for Providing Extensor Moment and Lumbar Traction Force

Lower back pain and related injuries are prevalent and serious problems in various industries, and high compression force to the lumbosacral (L5/S1) region has been known as one of the key factors. Previous research on passive lower back exoskeletons focused on reducing lumbar muscle activation by providing an extensor moment. Additionally, lumbar traction forces can reduce the compression force, and is a common treatment method for lower back pain in clinics. In this paper, we propose a novel passive lower back exoskeleton that provides both extensor moment and lumbar traction force. The working principle of the exoskeleton, extending the coil springs during lumbar flexion, and its design criteria regarding the amount of each force element were provided. The kinematic model explained its operation, and the dynamic simulation estimated its performance and validated its satisfaction with the design criteria. The biomechanical model provided a brief insight into the expected exoskeleton's effect on the reduced lower back compression force. Ten subjects performed static holding and dynamic lifting tasks, and the generated force elements in two directions, parallel and perpendicular to the trunk, were evaluated using a force sensor and electromyography sensors, respectively. The experiment demonstrated a pulling force opposite to the direction of intradiscal pressure and reduced erector spinae activation. This implies the effect of wearing the exoskeleton to decrease the intervertebral pressure during static back bending or heavy lifting tasks.

New Strategies for Controlling Pelvic Transverse Rotation and Selective Activation of Hip Muscles during Prone Hip Extension with Knee Flexion

Background : Prone hip extension with knee flexion (PHEKF) is a commonly used exercise for strengthening the gluteal muscles. However, PHEKF exercise is associated with a risk of increased hamstring and erector spinae activities, lumbar rotation to compensate for gluteal muscle weakness. Therefore, PHEKEF with isometric hip 30 abduction was evaluated in this study using Thera-Band to reduce pelvic transverse rotation compensation and effectively strengthen gluteal muscle strength. Objectives : The purpose of this study was to investigate the activity of the gluteus maximus (GMax), gluteus medius (GMed), erector spinae (ES) and hamstring (HAM) muscles and pelvic transverse rotation during PHEKF in three conditions. Methods : Fifteen healthy women participated in the study. The pelvic transverse rotation was measured using a smart phone-based measurement tool. The surface electromyography was attached the GMax, GMed, ES and HAM muscles. Then, the maximum voluntary isometric contraction was measured. The PHEKF exercise was performed in three different conditions (PHEKF, PHEKF with 30º hip abduction, and PHEKF with 30º isometric hip abduction [IHA]) by randomly. A one-way repeated measures ANOVA was performed to determine the difference in pelvic transverse rotation angle and muscle activity between the condition. Results : The GMax and GMed amplitudes were highest in PHEKF with 30° IHA, followed by 30º and 0° hip abduction during PHEKF (GMax, p < 0.001; GMed, p < 0.001). HAM and ipsilateral ES amplitudes were not significantly different among the three conditions (ipsilateral ES, p = 0.268; HAM, p = 0.577). In the pelvic transverse rotation angle and contralateral ES, the PHEKF with 30° IHA showed significantly lower than PHEKE with 30° abduction (the pelvic transverse rotation angle, p < 0.05; contralateral ES, p < 0.05). Conclusions : The results of these studies can examine that the PHEK with 30º IHA was effective to control pelvic transverse rotation and increase the contribution of the selective muscles activities of GMax and GMed muscles.

Effects of Isometric Hip Abduction using an Elastic-band on Muscle Activation in the Gluteus Maximus, Hamstring, and Erector Spinae during Forward Bending and Return Task

Background : Trunk bending requires coordination of the pelvis and hip joints and activation of the gluteal and lower extremity muscles. The gluteus maximus (GM) is an important muscle for trunk bending task and repeated trunk extension increases erector spinae (ES) muscle activity, and these extensors exhibit muscle activity opposite that of the gluteal muscles at a given lumbo-pelvic angle. Elastic band placed around the legs was found to increase GM muscle activity during exercise. Previous studies have compared GM, ES, and HS muscle activities during flexion movements. However, there is no study that applies elastic band during trunk forward bending and compared the activity of the GM, ES and HS muscles. Objectives : The purpose of this study was to investigate muscle activity in the gluteus maximus (GM), erector spinae (ES), and hamstring (HS), as well as hip joint angle during trunk forward bending in a hip abduction exercise using an elastic band. Methods Fourteen healthy women were recruited. Surface electromyographic activity was recorded from the GM, HS, and ES muscles, and hip joint angle was measured using Image J during trunk forward bending while performing a hip abduction exercise using an elastic band. Results : The hip joint angle during the forward bending movement increased significantly when an elastic band was used compared to when it was not. Muscle activity in the GM increased significantly, whereas that in the HS decreased significantly, with the elastic-band intervention. No significant change in ES muscle activity was observed with the band. Conclusions : During trunk forward bending with isometric hip abduction using an elastic band could be beneficial to promote hip joint movement and GM muscle relative to HS muscle activity.

Analysis of Muscle Activity Following the Application of Myofascial Release Techniques for Low-Back Pain-A Randomized-Controlled Trial.

Introduction. Lumbosacral dysfunctions and the resulting pain syndromes, such as low-back pain (LBP), are one of the most common musculoskeletal problems being faced by society around the world. So far, a contributory role of thoracolumbar fascia (TLF) dysfunction in some cases of LBP has been suggested. Research also confirms that muscle resting activity level in the TLF area is increased in people with LBP. Myofascial release (MFR) is a therapeutic option offered to patients with chronic low-back pain (CLBP). The therapy aims to improve flexibility and sliding between layers of soft tissue, and thus decrease muscle activity, reduce pain intensity, and improve functional performance. Objective. This study aims to assess changes in resting activity of selected muscles within the TLF in a group of patients with CLBP immediately after a single MFR treatment and one month after the intervention. Methods. A total of 113 patients with CLBP completed the study. Simple randomization was applied to assign subjects to study groups. The experimental group (n = 59) underwent a single session of MFR therapy. No therapeutic intervention was applied to the control group (n = 54). Surface electromyography was used to evaluate positive treatment effects in patients immediately after receiving the therapy (experimental group) and after one month (experimental and control group). Results. A statistically reliable decrease in the activity of erector spinae (ES) and multifidus muscles (MF) was observed after a single session of MFR therapy. Effects of the treatment were present immediately after receiving the therapy and one month after the intervention. Conclusions. A single MFR treatment in patients with CLBP immediately reduces the resting activity levels of ES and MF. Results of measurements carried out one month after the treatment confirm that the therapeutic effects were maintained.

Age-Related Differences in Corticospinal Excitability and Anticipatory Postural Adjustments of the Trunk.

Anticipatory postural adjustments (APAs) are a feedforward mechanism for the maintenance of postural stability and are delayed in old adults. We previously showed in young adults that APAs of the trunk induced by a fast shoulder movement were mediated, at least in part, by a cortical mechanism. However, it remains unclear the relationship between delayed APAs and motor cortical excitability in ageing. Using transcranial magnetic stimulation we examined motor evoked potentials (MEPs) of the erector spinae (ES) muscles in healthy young and old adults prior to a fast shoulder flexion task. A recognition reaction time (RRT) paradigm was used where participants responded to a visual stimulus by flexing their shoulders bilaterally as fast as possible. The activity of bilateral anterior deltoid (AD) and ES muscles was recorded using electromyography (EMG). The onset of AD and ES EMG was measured to represent RRT and APAs, respectively. We found increases in amplitudes of ES MEPs at 40 ms than 50 ms prior to the EMG onset of the AD in both groups. The amplitude of ES MEPs at 40 ms prior to the onset of AD EMG correlated with the onset of ES activity counterbalancing the perturbation induced by the shoulder task in the elderly participants only. Our findings suggest that timing of increasing corticospinal excitability prior to a self-paced perturbation becomes more relevant with ageing in modulating postural control of the trunk.

Motor Responses of Lumbar Erector Spinae Induced by Electrical Vestibular Stimulation in Seated Participants.

Introduction: The study of motor responses induced by electrical vestibular stimulation (EVS) may help clarify the role of the vestibular system in postural control. Although back muscles have an important role in postural control, their EVS-induced motor responses were rarely studied. Moreover, the effects of EVS parameters, head position, and vision on EVS-induced back muscles responses remain little explored.Objectives: To explore the effects of EVS parameters, head position, and vision on lumbar erector spinae muscles EVS-induced responses.Design: Exploratory, cross-sectional study.Materials and Methods: Ten healthy participants were recruited. Three head positions (right, left and no head rotation), 4 intensities (2, 3, 4, 5 mA), and 4 EVS durations (5, 20, 100, 200 ms) were tested in sitting position with eyes open or closed. EVS usually induced a body sway toward the anode (placed on the right mastoid). EMG activity of the right lumbar erector spinae was recorded. Variables of interest were amplitude, occurrence, and latency of the EVS-induced modulation of the EMG activity.Results: The short-latency response was inhibitory and the medium-latency response was excitatory. Increased EVS current intensity augmented the occurrence and the amplitude of the short- and medium-latency responses (more inhibition and more excitation, respectively). EVS duration influenced the medium-latency response differently depending on the position of the head. Right head rotation produced larger responses amplitude and occurrence than left head rotation. Opposite head rotation (left vs. right) did not induce a reversal of the short- and medium-latency responses (i.e., the inhibition did not become an excitation), as typically reported in lower legs muscles. The eyes open condition did not modulate muscle responses.Conclusion: Modulation of EVS parameters (current intensity and duration of EVS) affects the amplitude and occurrence of the lumbar erector spinae responses. In contrast, vision did not influence the responses, suggesting its minimal contribution to vestibulomotor control in sitting. The lack of response reversal in sagittal plane may reflect the biomechanical role of lumbar erector spinae to fine-tune the lumbar lordosis during the induced body sway. This hypothesis remains to be further tested.

The effects of shoulder posture on neck and shoulder musculoskeletal loading and discomfort during smartphone usage

While using their smartphone, users tend to adopt awkward neck and shoulder postures for an extended duration. Such postures impose the risk of MSDs on those body parts. Numerous studies have been undertaken to examine neck posture; however, few studies have investigated shoulder postures. This study examined various shoulder postures during smartphone use and their effect on neck and shoulder kinematics, muscle loading, and neck/shoulder discomfort. Thirty-two asymptomatic young adult smartphone users randomly performed texting tasks for 3 min at four different shoulder flexion angles (15°, 30°, 45°, and 60°), while maintained a neck posture in the neutral position (0° neck flexion angle). Measures were taken of neck and shoulder muscle activity of the cervical erector spinae (CES), anterior deltoid (AD), upper trapezius (UT) and lower trapezius (LT), and kinematic data (angle, distance and gravitational moment). Results showed AD and LT muscle activity significantly increased when the shoulder flexion angle increased with an opposite effect on CES and UT. A recommended shoulder posture was identified as 30° flexion, as this yielded the best compromise between activation levels of the four muscles studied. This angle also induced the lowest neck/shoulder discomfort score. The findings suggest smartphone users hold their device at approximately 30° shoulder flexion angle with their neck in a neutral posture to reduce the risk of shoulder and neck musculoskeletal disorders when smartphone texting. Relevance to industrySmartphone use in the manufacturing and service industries is an integral part of work and useful means of communication tool. Awkward postures during extensive smartphone use impose an increased risk of both neck and shoulder musculoskeletal disorders. Shoulder flexion angles need consideration when making recommendations about safe work postures during smartphone use.