Comparison Of Muscle Activity Research Articles

ELECTROMYOGRAPHIC ANALYSIS OF MULTIFIDUS MUSCLE ACTIVITY DURING THREE EXERCISES

https://youtu.be/V-jzFHp4z3Y INTRODUCTION The multifidus muscle is integral to spinal stability and posture control. To enhance rehabilitation and training programs, it is essential to understand the patterns of its activation across various exercises. The purpose of this study was to analyze the electromyographic (EMG) activity of the multifidus muscle during three specific exercises: deadlifts, bird-dogs, and single-leg balance exercises, to determine which exercise most effectively activates this muscle. METHODS Twenty adults (men: 9; women: 11; age: 24.7 + 2.1 yr; height: 167.9 + 10.8 cm; weight: 73.9 + 15.8 kg (mean+SD)) participated in the study. Surface EMG electrodes were placed bilaterally at the L4-L5 level after skin preparation. Deadlifts (5 reps at 50% body weight), bird-dog held for 10 sec on each side while holding a 2.27 kg weight in the outstretched hand, and single-leg stance held for 10 sec on each foot were performed under supervision in a randomized order. EMG data (max amplitude) were recorded with each session lasting ~15 minutes. Data were analyzed to compare muscle activation patterns across exercises. RESULTS EMG activity showed significant (p<0.05) differences across exercises with deadlifts inducing the highest mean muscle activation (0.949 + 0.623 mV), followed by bird-dog right (0.370 + 0.173 mV) and bird-dog left (0.352 + 0.161 mV). The single-leg balance exercises elicited the lowest mean muscle activations, both for the right (0.124 + 0.049 mV) and left sides (0.134 + 0.068 mV). There were no bilateral differences for any of the exercises. CONCLUSIONS The multifidus muscle showed varying levels of activation across different exercises, with the highest activation during deadlifts and the lowest during single-leg balance tasks. The deadlifts elicited a significantly stronger muscle response compared to balance exercises, suggesting that weight-bearing exercises might be more effective for multifidus muscle activation. The findings suggest that rehabilitation programs that include deadlifts could potentially offer greater benefits for improving core stability and reducing back pain.

KINETIC CHAIN MODIFIES MUSCLE ACTIVATION IN ADULTS WITH SHOULDER PAIN: A RANDOMIZED CROSS-OVER TRIAL.

A kinetic chain approach to shoulder rehabilitation is recommended. This study aimed to compare muscle activity between the isolated external rotation exercise and an exercise incorporating a kinetic chain approach in adults with shoulder pain. It also sought to identify muscle activation differences with the same tasks between asymptomatic adults and those experiencing shoulder pain. This is a randomized crossover trial. Twenty-four adults participated, 12 with shoulder pain and 12 without. Both groups performed isolated external rotation and kinetic chain exercises, with the sequence randomly allocated. Shoulder and scapular muscles were measured using surface electromyography. Mixed-effects models were used for the main statistical analysis. Significant changes in muscle activation levels were observed with the kinetic chain strategy compared to isolated resistance exercise. In the exercise factor, a significant decrease of 8.9% was observed in the maximum activation of the infraspinatus muscle with kinetic chain implementation. Conversely, the latissimus dorsi muscle showed a significant increase of 16.5% in maximal activation with kinetic chain compared to external rotation exercise. Implementing the kinetic chain approach led to significant changes in muscle activation. It offers potential benefits for shoulder rehabilitation, making it an alternative to isolated external rotation exercises.

Middle and Long Latency Cutaneous Reflexes During the Stance Phase of Gait in Individuals with and Without Chronic Ankle Instability

Background/objectives: Lower limb cutaneous reflex amplitudes can modulate across gait, which helps humans adjust rhythmic motor outputs to maintain balance in an ever-changing environment. Preliminary evidence suggests people who suffer from repetitive ankle sprains and residual feelings of giving way demonstrate altered cutaneous reflex patterns in the gastrocnemius. However, before cutaneous reflex assessment can be implemented as a clinical outcome measure, there is a need to substantiate these early findings by measuring reflex amplitudes across longer latency periods and exploring the variability of reflexes within each subject. Methods: Forty-eight subjects with and without chronic ankle instability (CAI) walked on a treadmill at 4 km/h while activity of the lateral gastrocnemius (LG) was measured via surface electromyography. Non-noxious stimulations were elicited randomly to the ipsilateral sural nerve at the mid-stance phase of gait, and reflex amplitudes were calculated offline by comparing muscle activity during unstimulated and stimulated gait cycles. Two primary outcome measures were compared between groups at the middle latency (MLR: 80–120 ms) and late latency (LLR: 120–150 ms) time windows: (1) average reflex amplitudes and (2) standard deviation of reflex amplitudes for each subject across 10 trials. Results: Both groups demonstrated an equal amount of LG inhibition at the MLR and LG facilitation at the LLR. However, subjects with CAI showed significantly higher variability in LLR amplitude across trials than healthy controls. Conclusions: Increased variability of cutaneous reflex amplitudes may relate to symptoms associated with CAI. These findings suggest that reflex variability following sural nerve stimulation could serve as an objective measure to track treatment progress in patients with CAI, offering clinicians a new tool for conducting rehabilitation assessments in a controlled environment.

The use of lifting straps during snatch alters muscle activation patterns

The snatch is prevalent in competitive and recreational lifting as well as strength training. Lifting straps (LS) are an accessory that wrap around the hand and the barbell, reducing the limitations of grip strength. However, this benefit has not been quantitatively supported for the snatch. The aim of this study was to compare muscle activation patterns between using LS and not using them at 80% of the snatch one-repetition maximum in a group of twelve sub-elite male weightlifters. It was hypothesized that LS would decrease forearm muscle activation and increase larger muscle group activation. Eight dominant-side muscles located in the lower limbs, back, shoulders, and upper limbs were measured via electromyography. A two-way analysis of variance (ANOVA), followed by a Tukey Pairwise comparison, revealed that LS significantly impacted (p = 0.039) muscle activation in the snatch. Specifically, latissimus dorsi activation increased the most (17.2 ± 55.7%), while biceps brachii activation decreased the most (−8.0 ± 37.0%). Comparing muscle activation across different phases of the lift showed that LS decreased forearm and bicep brachii activation by 16.0 ± 25.2% and 7.1 ± 35.7% respectively during the pull phase, and increased vastus lateralis, latissimus dorsi, and medial deltoid activation between the second part of the first pull and the catching position, with a corrected effect size exceeding 1.5. These results support the hypothesis that LS decrease forearm activation, which could reduce grip strength limitations and consequently, reduce problems associated with fatigue. Increases in vastus lateralis activation with the use of LS suggest a greater training stimulus during the snatch, which can help develop leg strength.

Comparison of Empirical and Reinforcement Learning (RL)-Based Control Based on Proximal Policy Optimization (PPO) for Walking Assistance: Does AI Always Win?

The use of wearable assistive devices is growing in both industrial and medical fields. Combining human expertise and artificial intelligence (AI), e.g., in human-in-the-loop-optimization, is gaining popularity for adapting assistance to individuals. Amidst prevailing assertions that AI could surpass human capabilities in customizing every facet of support for human needs, our study serves as an initial step towards such claims within the context of human walking assistance. We investigated the efficacy of the Biarticular Thigh Exosuit, a device designed to aid human locomotion by mimicking the action of the hamstrings and rectus femoris muscles using Serial Elastic Actuators. Two control strategies were tested: an empirical controller based on human gait knowledge and empirical data and a control optimized using Reinforcement Learning (RL) on a neuromuscular model. The performance results of these controllers were assessed by comparing muscle activation in two assisted and two unassisted walking modes. Results showed that both controllers reduced hamstring muscle activation and improved the preferred walking speed, with the empirical controller also decreasing gastrocnemius muscle activity. However, the RL-based controller increased muscle activity in the vastus and rectus femoris, indicating that RL-based enhancements may not always improve assistance without solid empirical support.

Comparison of muscle activity in school students while carrying backpacks and trolley bags.

Trolley bags have gained popularity among students, but there is limited research comparing them to backpack-style school bags. This study aimed to compare how carrying a backpack versus a trolley bag affects the activity of trunk and lower limb muscles in secondary school students. Electromyographic activity was measured in 25 students (13.4±1.1 years) as they walked on level ground and up/down stairs while carrying both types of bags. The activity of the gastrocnemius, tibialis anterior, semitendinosus, rectus femoris, lumbar erector spinae, and rectus abdominis muscles was assessed on both the dominant and non-dominant sides. The study found significantly reduced muscle activation in most of the targeted muscles when walking on level ground with the trolley bag and when going up/down stairs with the backpack. Lifting a trolley bag depends on the slope of the walking surface and is more efficient on level ground, while carrying a backpack is more efficient when going up and down stairs. Since it is not practical to switch bags when encountering stairs in schools, a bag with a mixed model design incorporating features of both trolley and backpack may be more beneficial and practical for students to use. Students, parents, and teachers should be aware of the injury risks associated with carrying different types of bags.

Comparison of muscle activation during quadrupedal movement training and traditional bodyweight exercises

Quadrupedal movement training (QMT) is a unique form of bodyweight training shown to improve flexibility, FMS scores, and proprioception, however, little is known about its muscle activation characteristics. Therefore, the purpose of this study was to compare surface EMG (sEMG) activity of muscles of the trunk, upper, and lower extremity during QMT movements and common traditional bodyweight exercises (TRA). Twenty (males n = 9) participants (age: 27.5 ± 10.8 yrs, height: 169.0 ± 7.0 cm, mass: 66.6 ± 10.9 kg) were prepped and fitted with sEMG electrodes on their right-side bicep brachii, medial deltoid, triceps brachii, pectoralis major, latissimus dorsi, rectus abdominus, rectus femoris and bicep femoris. Following completion of maximal voluntary isometric contraction (MVIC) tests for normalization, participants performed 4 repetitions of 8 QMT exercises (from the Animal Flow™ system) and 3 TRA exercises (pushup, squat and forearm plank) in random order. The pooled peak muscle activations of all QMT exercises resulted in moderate (21–40% MVIC) to very high (>60% MVIC) peak muscle activation levels for each muscle group with significantly higher (p > 0.05) muscle activation for the biceps (47.72 ± 21.41%), deltoid (66.58 ± 11.39%), and latissimus dorsi (62.81 ± 18.14%) than the pushup (23.31 ± 16.95, 45.63 ± 18.59, 29.17 ± 20.58% respectively) and significantly higher activation of the bicep femoris (41.89 ± 13.83%) than the squat (17.79 ± 11.12%). TRA (pushup) showed significantly higher activation of the triceps and pectoralis. There were no differences in rectus femoris or rectus abdominus. Muscle activation levels during QMT are comparable to or higher than common traditional bodyweight exercises and therefore may be an appealing strategy for training multiple muscle groups simultaneously.

Comparison of muscle response in patients treated with rigid and flexible fixed functional appliances.

The present study was undertaken to evaluate and compare muscle activity after the treatment with rigid and flexible fixed functional appliance. The study was conducted on 14 skeletal Class II malocclusion patients in the age group of 13-17 years, divided into two groups comprising 7 patients in each group. Group I was treated with a rigid fixed functional appliance (MPA IV), and Group II was treated with a flexible fixed functional appliance (Churro Jumper). Masseter and anterior temporalis muscle activities were recorded using needle electromyography (EMG) at postural rest, saliva swallowing, and clenching during five intervals (T0 to T4) during fixed functional appliance treatment. Unpaired t-test, Mann-Whitney U, and Wilcoxon sign rank test were applied for statistical analysis, and a P value of <.05 was considered statistically significant. Group I (MPA IV) showed a significant increase in EMG activity during postural rest position (P = 0.003, P = 0.001), swallowing (P = 0.013, P = 0.005), and clenching (P = 0.001, P = 0.002) in masseter and anterior temporalis muscle, respectively. Group II (Churro jumper) also showed a significant increase in EMG activity during postural rest position (P = 0.000, P = 0.000), swallowing (P = 0.001, P = 0.000), and clenching (P = 0.001, P = 0.000) in masseter and anterior temporalis muscle, respectively. Both rigid (MPA IV) and flexible (Churro Jumper) fixed functional appliances caused a significant increase in EMG activity of masseter and anterior temporalis muscle during postural rest position, swallowing, and clenching in 6 months of the observation period, but the flexible appliance (Churro Jumper) showed more significant increase.

Comparing Muscle Activity and Onset Time of Cervical and Thoracoscapular Muscles during Shoulder Flexion and Abduction in Individuals with and without Forward Head Posture

Comparing Muscle Activity and Onset Time of Cervical and Thoracoscapular Muscles during Shoulder Flexion and Abduction in Individuals with and without Forward Head Posture

Rehabilitation strategies and magnetic resonance imaging techniques for shoulder injuries in sports

ObjectiveShoulder sleeve injuries are high-risk in men's tennis, with rehabilitation focusing on activating shoulder muscle groups to regain strength. Specific plans use electromyography and isokinetic instruments to compare muscle activity and torque pre- and post-rehabilitation. The goal is to explore training effects on rotator cuff injuries and assess routine MRI and MRI shoulder arthrography for diagnostic value in shoulder injuries. This aims to provide a reference for restoring shoulder function in male tennis players. MethodsTwenty college students (n = 20) with rotator cuff injuries from a university tennis program were selected as experimental subjects, matched based on gender and injury severity, and divided into experimental (n = 10) and control (n = 10) groups. A paired sample T-test assessed the impact of rehabilitation training on muscle recruitment and strength around the shoulder joint in the experimental group before and after training. This evaluated the influence of rehabilitation plans on shoulder muscle mobilization and strength. Another paired sample T-test compared indicators before and after the experiment, examining mechanisms underlying the effects of functional rehabilitation training on shoulder sleeve injuries in male tennis players. Results(1) Surface electromyography (EMG) results for internal/external rotation showed a significant increase in anterior, middle, and posterior deltoid EMG values (P < 0.05). Supraspinatus and infraspinatus muscles exhibited substantial increases (P < 0.01), while no significant change occurred in the teres minor muscle. (2) Adduction/abduction EMG tests at 60°/s, 90°/s, and 120°/s revealed significant increases (P < 0.01) in deltoid bundles and supraspinatus/infraspinatus muscles for both experimental and control groups. Teres minor muscle showed no significant change. (3) Isokinetic muscle strength tests indicated a significant peak torque increase (P < 0.01) during inward/outward rotation at 60°/s, 90°/s, and 120°/s for the experimental group compared to the control group. ConclusionA 10-week functional shoulder rehabilitation training program can enhance the strength, endurance, and neuromuscular recruitment of shoulder-related muscles in male tennis players with rotator cuff injuries. This approach, combined with the diagnostic capabilities of routine MRI and MRI shoulder arthrography, enables modifications in the body's ongoing adaptation to injuries. This, in turn, contributes to improved shoulder joint stability and effectively facilitates the functional recovery of the rotator cuff muscle group.

Examination of the relationship between masseter muscle activity during sleep and wakefulness measured by using a wearable electromyographic device

Purpose This study aimed to measure masseter muscle activity throughout the day in outpatients suspected of having awake bruxism (AB) and/or sleep bruxism (SB) and examine the relationship between AB and SB by comparing muscle activity during daytime wakefulness and nighttime sleep.Methods Fifty outpatients with suspected SB and/or AB participated in this study. A single-channel wearable electromyogram (EMG) device was used for EMG recording. The selected EMG bursts were divided into bursts during sleep (S-bursts) and bursts during awake state (A-bursts). The number of bursts per hour, average burst duration, and ratio of burst peak value to maximum voluntary contraction were calculated for both the S- and A-bursts. These values of the S- and A-bursts were then compared, and the correlations between them were analyzed. Additionally, the ratios of phasic and tonic bursts in the S- and A-bursts were compared.Results The number of bursts per hour was significantly higher for A-bursts than for S-bursts. No significant correlation was found between the numbers of S- and A-bursts. The ratio of phasic bursts was large and that of tonic bursts was small in both the S- and A-bursts. A comparison of the S- and A-bursts showed that the S-bursts had a significantly lower ratio of phasic bursts and higher ratio of tonic bursts than the A-bursts.Conclusions The number of masseteric EMG bursts during wakefulness did not show any association with that during sleep. It became clear that sustained muscle activity was not dominant in AB.

Muscle Activation During Squat on Different Surfaces

This study aimed to compare the vastus medialis and vastus lateralis muscle activations during squat exercises performed on different surfaces. Recreationally active 14 males (age: 20.43±1.28 years; height: 176.94±6.58 cm; body weight: 72.78±10.72 kg) participated in this study. A ground surface is used as a stable surface, a gymnastics mat and a Bosu ball are used as an unstable surface. Participants performed two sets of squats on three surfaces and ten repetitions of each set. Participants performed squat exercises with their body weight. Muscle activation measurements were made from the vastus medialis and vastus lateralis muscles during the squat movement on each surface. A one-way repeated-measures analysis of variances was used to statistically compare muscle activations between surfaces. As a result of statistical analysis, no significant differences were found in the vastus medialis and vastus lateralis muscle activations between surfaces (p&gt;0.05). In conclusion, it was determined that the vastus medialis and vastus lateralis muscle activation in the squat movement was not affected by the stability of the surfaces. Therefore, it can be suggested that the surfaces used in this study can be used interchangeably for vastus medialis (VM) and vastus lateralis (VL) muscle activation in the squat exercise.

EMG Analysis During Static Balance in Chronic Ankle Instability, Coper and Controls.

Patients with chronic ankle instability (CAI) consistently display postural control alterations, which may result from sensorimotor dysfunction. This study aimed to compare muscle activity in the lower extremity and postural control among individuals with CAI, copers and uninjured controls during a static balance test. A total of 57 physically active participants were categorized into three groups (CAI, copers and controls) and performed a single-leg balance test with two visual conditions: eyes open and eyes closed. Muscle activity in six lower extremity muscles and center of pressure (CoP) variables were recorded and analyzed. Patients with CAI exhibited greater muscle activity in the medial gastrocnemius and gluteus maximus compared to controls or copers, regardless of the visual condition. Copers displayed increased gluteus medius activity compared to controls. Additionally, all groups demonstrated increased muscle activity and CoP variables when visual feedback was disrupted. These findings suggest that patients with CAI may have less effective recruitment of motor units during static balance. On the other hand, greater muscle activity in the gluteus medius in copers may represent a coping mechanism to avoid further ankle injuries. Further research on muscle activity during dynamic postural control is warranted to explore sensorimotor alterations in patients with CAI.

Laptop use and muscle activity in adult females: Ground sitting has lower muscular demand than using a chair.

With progressing technology in the portable computing field, laptops are now integral for work, home and social settings. Different working postures adopted by laptop users impose different loads on the relevant muscles, which can be associated with musculoskeletal discomfort in the various body regions. Some Arabic and Asian cultures adopted postures are not well investigated, particularly for the 20-30 years age-group. This study compared muscle activity in the cervical spine, arm, and wrist among different laptop workstation setups. In this cross-sectional study, 23 healthy female university students (age = 24.2±2.28 years, range 20-26 years) performed a standardized 10 minute typing task in four different laptop workstation setups: DESK, SOFA, GROUND sitting with back support, and laptop table (LAP-Tab). Differences between electromyography (EMG) muscle activity recorded in the trapezius (TR), cervical extensors (CE), deltoid (DEL), and wrist extensors (WE) were determined using one-way repeated ANOVA measures with a post-hoc Bonferroni test. Significantly higher muscle activity was observed respectively in the workstations of DESK > LAP-Tab > SOFA > GROUND. Significant differences were found between WE muscle activity and the three other muscle groups (p < 0.001). There was a significant interaction between workstations and muscle activity (F(9,264) = 3.81, p < 0.001, = 0.11), where the WE and DEL muscles showed respectively higher and lower muscle activity in all setups. Muscles showed variable activity in different workstations such that the GROUND workstation provided the minimum load, while the DESK workstation showed the maximum load on the measured muscle groups. These findings require further investigation in different cultural and gender specific groups.

Comparison of Muscle Activity around the Trunk and Hip according to Weight and Phase during Kettlebell Swing

Comparison of Muscle Activity around the Trunk and Hip according to Weight and Phase during Kettlebell Swing

Muscle activation patterns during active external rotation after reverse total shoulder arthroplasty: an electrophysiological study of the teres minor and associated musculature

Preoperative teres minor insufficiency has been identified as a risk factor for poor restoration of external rotation (ER) after reverse total shoulder arthroplasty (RTSA). However, there has been little investigation regarding muscle activation patterns generating ER. This prospective study sought to determine the timing and activation levels of the shoulder girdle musculature during ER in well-functioning RTSAs with an intact teres minor using a lateralized design. Patients who underwent RTSA ≥1 year previously with functional ER, an American Shoulder and Elbow Surgeons (ASES) score >70, superior rotator cuff deficiency, and an intact teres minor were identified. Electrophysiological and kinematic analyses were performed during ER in the modified neutral position (arm at side with 90° of elbow flexion) and in abduction (AB) (shoulder abducted 90° with 90° of elbow flexion). Dynamometer-recorded torque and position were pattern matched to electromyography during ER. The root-mean-square and integrated electromyography (in microvolts × milliseconds with standard deviation [SD]), as well as median frequency (MF) (in hertz with SD), were calculated to determine muscle recruitment. Pair-wise t test analysis compared muscle activation (P<.05 indicated significance). After an a priori power analysis, 16 patients were recruited. The average ASES score, visual analog scale pain score, and ASES subscore for ER in AB ("comb hair") were 87.7, 0.5, and 2.75 of 3, respectively. In AB, muscle activation began with the upper trapezius, middle trapezius, and latissimus dorsi, followed by the anterior deltoid activating to neutral. With ER beyond neutral, the teres major (9.6 μV × ms; SD, 9.2 μV × ms) initiated ER, followed by the teres minor (14.1 μV × ms; SD, 18.2 μV × ms) and posterior deltoid (11.1 μV × ms; SD, 9.3 μV × ms). MF analysis indicated equal contributions of the teres major (1.1 Hz; SD, 0.5 Hz), teres minor (1.2 Hz; SD, 0.4 Hz), and posterior deltoid (1.1 Hz; SD, 0.4 Hz) in ER beyond neutral. In the modified neutral position, the upper trapezius and middle trapezius were not recruited to the same level as in AB. For ER beyond neutral, the teres major (9.5 μV × ms [SD, 9 μV × ms]; MF, 1.1 Hz [SD, 0.5 Hz]), teres minor (11.4 μV × ms [SD, 15.1 μV × ms]; MF, 1.1 Hz [SD, 0.5 Hz]), and posterior deltoid (8.5 μV × ms [SD, 8 μV × ms]; MF, 1.2 Hz [SD, 0.3 Hz]) were activated in similar sequence and intensity as AB. No differences in muscle activation duration or intensity were noted among the teres major, teres minor, and posterior deltoid (P>.05). Active ER after RTSA is complex and is not governed by a single muscle-tendon unit. This study establishes a sequence, duration, and intensity of muscle activation for ER in well-functioning RTSAs. In both tested positions, the teres major, teres minor, and posterior deltoid function equally and sequentially to power ER.

Neuromotor variability partially explains different endurance capacities of expert pianists

During fatiguing piano tasks, muscle fatigue develops differently between expert pianists. Differences in neuromotor strategies employed could explain a slower rate of fatigue development. The objective was to compare muscle activation and kinematic variabilities between ShortDuration (i.e., pianists with less endurance) and LongDuration groups. Results from 49 pianists showed that EMG activation variability of most shoulder and upper limbs muscles was greater for the ShortDuration group with time during two piano fatiguing tasks, namely Digital and Chord tasks. Segment acceleration variability, assessed using inertial measurement units, was also greater with time for the ShortDuration group at the right arm during the Digital task, and at the thorax and head during the Chord task. Finally, thorax lateroflexion variability increased with time for the LongDuration group (but not the ShortDuration group) during the Digital task. During the Chord task, wrist flexion variability was higher for the LongDuration group compared to the ShortDuration group. These results showed a direct effect of time on the pianists’ acceleration variability and EMG activation variability. In contrast, a protective effect of fatigue development could be attributed to kinematic variability. Results also suggest a higher risk of injury among pianists in the ShortDuration group.

Comparison of Muscle Activity and Muscle Thickness According to Knee Flexion Angle during Supine Bridge Exercises using the Abdominal Drawing-in Maneuver on an Unstable Surface

Comparison of Muscle Activity and Muscle Thickness According to Knee Flexion Angle during Supine Bridge Exercises using the Abdominal Drawing-in Maneuver on an Unstable Surface

Comparison of Muscle Activity and Muscle Thickness According to Knee Flexion Angle during Supine Bridge Exercises using the Abdominal Drawing-in Maneuver on an Unstable Surface.

This study evaluated changes in deep trunk muscle thickness and lower extremity muscle activities during bridge exercises with the abdominal drawing-in maneuver. Bridge exercises were conducted on an unstable surface at different knee flexion angles (60º, 90º and 120º), with the aim of identifying more effective angles for bridge exercises. This study included 21 healthy adults, aged 20-27 years. Biceps femoris (BF), rectus abdominis, and rectus femoris activity was measured using surface electromyography. The thicknesses of the transverse abdominis (TrA), external oblique (EO) and internal oblique (IO) muscles were measured. BF (p = 0.000, partial η2 = 0.670) activity increased considerably as the knee flexion angle decreased. TrA (p = 0.000, partial η2 = 0.883) and IO (p = 0.000, partial η2 = 0.892) thickness significantly increased, while EO (p = 0.000, partial η2 = 0.893) thickness decreased as the knee flexion angle decreased. When performing bridge exercises using the abdominal drawing-in maneuver on an unstable surface, the knee flexion angles should be at 120º and 60º to increase trunk stability and lower extremity muscle activity, respectively.

Ergonomic Analysis of a Novel Shelf Stocking Cart

This study investigated the potential for an ergonomic intervention, specifically a prototype height-adjustable stocking cart to reduce the physical demands experienced when stocking shelves. This study compared muscle activity, kinematics, and subjective preferences when participants used the prototype cart versus a traditional, manual stocking method. Nine males and three females participated in this study. A traditional stocking method was compared to the prototype cart method for two types of dry grocery products as they were moved to three different destination shelf heights. EMG data, kinematic data, and subjective feedback generally favored the cart prototype over the traditional method. Bilaterally, anterior deltoid muscle activity was reduced for the cart condition when transferring products to the lower and higher shelves; trapezius activity was reduced for only the higher shelf; right side erector spinae activity was reduced for the lower shelf. The cart primarily benefited the anterior deltoid and trapezius descendens through reduced shoulder flexion. There were interaction effects of cart and shelf height on shoulder and spine kinematics. Questionnaire data showed that participants favored using the prototype. Study results support the continued development of the prototype cart toward a commercially available ergonomic aid for shelf stockers.