Arm Muscle Activity Research Articles

Upper arm muscle activity is influenced by both forearm posture and wrist exertion direction during isometric wrist flexion and extension

The purpose of this study was to determine how wrist exertion direction and forearm posture independently influence upper arm muscle activity during isometric wrist contractions. Surface electromyography was recorded from three muscles of the upper-limb: biceps brachii, triceps brachii, and brachioradialis. Participants were seated with their forearm supported in one of three postures (supinated/neutral/pronated) with an adjustable force transducer that could be placed either above, below, or to the right/left of the participant’s hand. Participants performed randomized trials of isometric wrist flexion or extension at five relative intensities: 20, 40, 60, 80, or 100% of maximal force. Trials lasted 4.5 s and both wrist force and electromyography data were assessed. In general, the elbow flexors were more active during wrist flexion, while the triceps were more active in wrist extension, but this pattern reversed in certain forearm postures and wrist exertion directions. Both forearm posture and wrist exertion direction resulted in unique effects on upper arm muscle activity. These findings suggest that muscle activity of the upper arm muscles is influenced independently by both posture and force direction, which should be carefully considered by both motor control specialists and ergonomists.

Acute effects of blood flow restriction on EMG activity of arm muscles during karate tsuki strike in young men

BackgroundThe positive effect of Blood Flow Restriction (BFR) on muscular performance have been documented in previous researches. However, its effect on agonist-antagonist cocontraction during fist movement has not been considered from a biomechanical perspective. The purpose of this research was to investigate the acute effect of BFR on EMG activity of arm muscles during karate tsuki strike in young men. Methods20 professional young, male karatekas voluntarily participated in this research. Biceps and triceps muscular activity and their cocontraction in the right arm (with BFR) and the left arm (control) were captured and compared using an EMG device during tsuki strike until exhaustion. ResultsThe results of independent t-test showed that biceps and triceps EMG activity in the BFR arm were significantly higher than the control arm (24.45% and 27.78% for biceps and triceps, respectively). Moreover, muscular cocontraction in BFR arm was significantly less than control arm (32.05%). ConclusionThe results indicate that acute arm BFR can increase arm muscle EMG activity during tsuki strike until exhaustion, which indirectly it is a sign for activation of type II motor units. However, BFR decreased agonist-antagonist cocontraction, which may increase the risk for injury during elbow extension in throw fist.

Arm muscle synergies enhance hand posture prediction in combination with forearm muscle synergies

Objective. We analyze and interpret arm and forearm muscle activity in relation with the kinematics of hand pre-shaping during reaching and grasping from the perspective of human synergistic motor control. Approach. Ten subjects performed six tasks involving reaching, grasping and object manipulation. We recorded electromyographic (EMG) signals from arm and forearm muscles with a mix of bipolar electrodes and high-density grids of electrodes. Motion capture was concurrently recorded to estimate hand kinematics. Muscle synergies were extracted separately for arm and forearm muscles, and postural synergies were extracted from hand joint angles. We assessed whether activation coefficients of postural synergies positively correlate with and can be regressed from activation coefficients of muscle synergies. Each type of synergies was clustered across subjects. Main results. We found consistency of the identified synergies across subjects, and we functionally evaluated synergy clusters computed across subjects to identify synergies representative of all subjects. We found a positive correlation between pairs of activation coefficients of muscle and postural synergies with important functional implications. We demonstrated a significant positive contribution in the combination between arm and forearm muscle synergies in estimating hand postural synergies with respect to estimation based on muscle synergies of only one body segment, either arm or forearm (p < 0.01). We found that dimensionality reduction of multi-muscle EMG root mean square (RMS) signals did not significantly affect hand posture estimation, as demonstrated by comparable results with regression of hand angles from EMG RMS signals. Significance. We demonstrated that hand posture prediction improves by combining activity of arm and forearm muscles and we evaluate, for the first time, correlation and regression between activation coefficients of arm muscle and hand postural synergies. Our findings can be beneficial for myoelectric control of hand prosthesis and upper-limb exoskeletons, and for biomarker evaluation during neurorehabilitation.

Assessing mouse, trackball, touchscreen and leap motion in ship vibration conditions: A comparison of task performance, upper limb muscle activity and perceived fatigue and usability

A variety of interaction devices are increasingly used for human-computer interaction (HCI) tasks in ship vibration conditions, but have seldom been well assessed. This study aimed to examine task performance, upper limb muscle activity, and perceived fatigue and device usability for four typical interaction devices (i.e., mouse, trackball, touchscreen, and Leap Motion) under simulated ship vibration conditions. A two-factor within-subjects design was employed in this study, where participants performed basic HCI tasks with the four interaction devices under three conditions (i.e., static condition, and low and high vibration conditions). The results showed that vibration condition significantly reduced task performance, especially for Leap Motion. Differences in task performance, upper arm and shoulder muscle activities, perceived fatigue and device usability were found among interaction devices. Mouse and touchscreen achieved the best task performance, compared with trackball and Leap Motion, while both touchscreen and Leap Motion achieved larger upper limb muscle activities, compared with trackball and mouse. Relevance to industryThe findings provide important implications for the use and configuration of interaction devices, and for the development of prevention interventions for risks of musculoskeletal disorders in using interaction devices under ship vibration conditions.

Can single-use versus standard duodenoscope improve ergonomics in ERCP? A comparative, simulation-based pilot study.

Background and study aims Musculoskeletal disorders (MSDs) and injuries (MSIs) are frequent in gastrointestinal endoscopy. The aim of this study was to assess potential ergonomic advantages of a lighter single-use duodenoscope compared with a standard reusable one for endoscopists performing endoscopic retrograde cholangiopancreatography (ERCP). Methods Three experienced endoscopists performed an ergonomic, preclinical, comparative protocol-guided simulation study of a single-use and a standard reusable duodenoscope using an anatomic bench model. Surface EMG signals from left forearm and arm muscles were recorded. A commercial inertial sensor-based motion capture system was applied to record body posture as well. Results A significant lowering of root mean square amplitude and amplitude distribution of biceps brachii signal (ranging from 13% to 42%) was recorded in all the participants when using a single-use duodenoscope compared with a reusable one. An overall reduction of muscle activation amplitude and duration was also associated with the single-use duodenoscope for forearm muscles, with different behaviors among subjects. Participants spent most of the time in wrist extension (> 80%) and ulnar deviation (> 65%). A consistent pattern of functional range of motion employed for completing all procedures was observed. Conclusions Our study showed that a lighter scope has a promising effect in reducing upper arm muscle activity during ERCP with potential benefit on musculoskeletal health in the ERCP setting.

Arm Muscle Activation Performance Analysis Using Machine Learning Algorithm in the Assembly System

Arm Muscle Activation Performance Analysis Using Machine Learning Algorithm in the Assembly System

Changes in Electromyographic Activity of the Dominant Arm Muscles during Forehand Stroke Phases in Wheelchair Tennis.

The aim of this study was to determine the muscle activations of the dominant arm during the forehand stroke of wheelchair tennis. Five players participated in the present study (age: 32.6 ± 9.9 years; body mass: 63.8 ± 3.12 kg; height: 164.4 ± 1.7 cm). The electrical muscle activity of six dominant arm muscles was recorded using an sEMG system. A significant effect of the muscle's activity was observed, and it was shown that the muscle activation was significantly higher in the execution phase compared to the preparation phase in the anterior deltoid and biceps brachii (34.98 ± 10.23% and 29.13 ± 8.27%, p < 0.001); the posterior deltoid, triceps brachii, flexor carpi radialis, and extensor carpi radialis were higher in the follow-through phase than in the execution phase (16.43 ± 11.72%, 16.96 ± 12.19%, 36.23 ± 21.47% and 19.13 ± 12.55%, p < 0.01). In conclusion, it was determined that the muscle activations of the dominant arm muscles demonstrate variances throughout the phases of the forehand stroke. Furthermore, the application of electromyographic analysis to the primary arm muscles has been beneficial in understanding the muscular activity of the shoulder, elbow, and wrist throughout the various phases of the forehand stroke in wheelchair tennis.

Effects of lying posture and task type on muscle fatigue, visual fatigue, and discomfort while using a smartphone on the bed.

Neck-shoulder and arm musculoskeletal disorders in smartphone use have attracted increasing attention. This study aimed to examine the effect of different lying postures and task types by comparing the electrooculography (EOG) responses, perceived discomfort, and the activity of neck-shoulder and arm muscles while using a smartphone on the bed. Twenty participants were recruited to perform 30-min tasks (texting/ watching video) while holding the smartphone in three different lying postures (half-lying/lying/side-lying). Subjective discomfort, muscular activities including the abductor pollicis brevis (APB), upper trapezius (UT), and extensor carpi radialis (ECR), and EOG signals were simultaneously monitored. The results showed that the perceived discomfort of measured body parts increased significantly over time in all postures. Watching video significantly increases muscle activities of APB and UT and decreases blink frequency and blink duration. Compared to lying or half-lying, the side-lying posture has the highest blink frequency, blink duration, and muscle activities in ECR and UT. The findings of this study indicate that side-lying posture should be avoided while using a smartphone on the bed. It provides an understanding of the association between the postures of using smartphones on the bed and fatigue, which can help prevent muscle and visual fatigue in smartphone use.

Alterations in the preferred direction of individual arm muscle activation after stroke.

Stroke survivors have challenges appropriately coordinating the multiple muscles, resulting in a deficit in motor control. Therefore, comprehending the mechanism underlying abnormal intermuscular coordination becomes crucial in developing effective rehabilitation strategies. Quantitative analyses have been employed at pairwise or multi-dimensional levels to understand the underlying mechanism of abnormal intermuscular coordination and its relationship to motor impairment. However, how alterations in individual muscle activation contribute to abnormal intermuscular coordination, motor impairment, and motor performance remains unclear. Thus, we investigated the alterations in the preferred direction of individual muscles after stroke and their relationship with stroke-induced changes in intermuscular coordination, clinical motor impairment, and qualities of motor performance during isometric force generation in the upper extremity. Twenty-four stroke survivors and six age-matched controls were recruited and performed isometric force target matches while recording electromyographic signals from eight upper limb muscles. We determined the preferred activation direction of each muscle, evaluated abnormal intermuscular coordination through a muscle synergy analysis, assessed motor impairment using upper extremity Fugl-Meyer Assessment scores, and examined motor performance characteristics defined by force trajectory features. The post-stroke alterations in the preferred direction of the brachioradialis, anterior, middle, and posterior deltoid were correlated with the motor impairment level and attributed to the changes in muscle synergy characteristics. Only alterations in the preferred direction of the brachioradialis and posterior deltoid activation in forward-backward and upward-downward axes were associated with the qualities of isometric force generation, respectively. These findings imply that alterations in the preferred direction of individual muscle activation contribute to various aspects of motor deficit following stroke. This insight may serve as a foundation for the development of innovative stroke neurorehabilitation approaches that take into account specific attributes of individual muscle activation, including their preferred activation direction.

Ergonomic Evaluation of Different Working Posture and Handle Designs of Mason Trowel during Wall Plastering Work based on Shoulder and Arm Muscle Activity

Ergonomic Evaluation of Different Working Posture and Handle Designs of Mason Trowel during Wall Plastering Work based on Shoulder and Arm Muscle Activity

347 The tradeoff between kinematic and muscular control of reaching as a potential biomarker of motor performance in stroke

OBJECTIVES/GOALS: Nearly 3 million Americans live with arm impairment following stroke. While as many as 20% of patients fully recover, individual differences in recovery make one-size-fits-all rehabilitation approaches suboptimal. The goal of this study was to use our custom rehabilitation platform to identify neuromuscular biomarkers of arm control in stroke. METHODS/STUDY POPULATION: Chronic stroke survivors (N = 10) reached for targets in a virtual reality environment using both hands. They completed 162 reaches divided into 3 blocks. Following baseline, we used our custom exoskeletons to provide 50% arm weight assistance to the impaired limb and 50% arm weight resistance to the non-impaired limb. We removed the exoskeletons during the retention block. We used electromyography to approximate muscle activity in the anterior deltoids. Relative contribution (RC) was calculated as the displacement of the impaired arm divided by the sum of displacements for both arms. Muscle contribution (MC) was calculated as the root mean square of impaired arm muscle activity divided by the sum of activity for both deltoids, normalized to maximum voluntary contraction. RESULTS/ANTICIPATED RESULTS: During baseline, RC of the impaired limb was 43%; patients reached significantly less with their impaired arm compared to their non-impaired arm (p = 0.02). MC of the impaired deltoid was 56% and was similar between arms (p = 0.5). During loading, RC did not change relative to baseline (p = 0.87), but MC tended to decrease by 11% (p = 0.12). These results suggest a tradeoff between kinematic and muscular control of reaching. This new finding closely matches our previous work in 12 healthy controls, where we found a 2% increase in RC and a 11% decrease in MC. Importantly, 4/10 patients exhibited an inverse tradeoff (i.e., decrease in RC and/or increase in MC). We will analyze neuroimaging data to determine the role lesion size and location play in predicting an individual’s response to gravity compensation. DISCUSSION/SIGNIFICANCE: Our tradeoff analysis serves as a potential neuromuscular biomarker of stroke survivors’ responsiveness to gravity compensation. This forms the basis for personalized technologies for stroke rehabilitation. With further development, clinicians can use our platform to fine-tune compensation levels based on the individual needs of the patient.

Muscle strength, rate of torque development and neuromuscular activation of the upper arm muscles in children and adolescents with spina bifida

BackgroundThe use of locomotive devices requires sufficient levels of upper limb strength. Therefore, it is important to evaluate the maximal isometric torque, rate of torque development and neuromuscular activation in youth with spina bifida. The objective was to investigate these parameters in the elbow muscles of youth with spina bifida versus healthy age-matched peers. MethodsForty-eight participants (8–17 years) were recruited: Spina Bifida (n = 23) and non-affected Controls (n = 25). Maximal isometric elbow flexor/extensor contractions were performed to assess maximal muscle strength (peak torque) and rate of torque development, along with synchronized electromyography recording in the biceps and triceps brachii muscles. FindingsDuring elbow flexor contractions, Spina Bifida showed reduced rate of torque development in the early contraction phase (0–50 ms) along with lowered relative rate of torque development in the later rate of torque development phase (0–100/200/300 ms) compared to controls. Spina Bifida showed reduced rate of torque development for the elbow extensors in the later phase of rising muscle force (0–200/300 ms) compared to controls. Lower isometric peak torque and smaller triceps brachii electromyography amplitudes (0–200/300 ms) were observed during elbow extensor contractions in Ambulatory spina bifida participants vs. controls. InterpretationAlthough a majority of peak torque and rate of torque development parameters did not differ, significant impairments in maximal and rapid elbow muscle force characteristics were noted in Spina Bifida compared to non-affected Controls. Ambulatory and Non-ambulatory spina bifida participants demonstrated similar rate of torque development in their upper arm muscles.

Physiological Demands and Muscle Activity of Jockeys in Trial and Race Riding.

Physiological parameters and muscle activity of jockeys may affect their fall and injury risk, performance, and career longevity, as well as the performance and welfare of the horses they ride. Therefore, this study aimed to quantify the physiological demands, body displacement, and electromyographic (EMG) activity of twelve jockeys riding 52 trials and 16 professional races. The jockeys were instrumented with heart rate (HR) monitors, accelerometers, and integrated EMG clothing (recording eight muscle groups: quadriceps, hamstrings, gluteal, erector spinae/lower back, abdominal external obliques, abdominal, trapezial and pectoral) which recorded continuously whilst riding. During race day, jockeys rode an average of 5 ± 4 trials and 4 ± 2 races over 2−2.5 h. The trials represented lower intensity cardiovascular demand (~81% HRmax) and Training Impulse (TRIMP) scores (4.4 ± 1.8) than races at maximal intensity effort (~94% HRmax, 7.2 ± 1.8 TRIMP, p < 0.05). Jockey head displacement was similar in trials (5.4 ± 2.1 cm) and races (5.6 ± 2.2 cm, p > 0.05), with more vertical (6.7 ± 2.7 cm) and less medio/lateral (2.3 ± 0.7 cm) and fore/aft (3.7 ± 1.6 cm) displacement for jockeys riding in trials than races (5.5 ± 2.3, 2.8 ± 1.0, 5.6 ± 2.5 cm, p < 0.05). Jockeys in races adopted a lower crouched posture, with their centre of mass (COM) shifted anteriorly, using greater hamstring activation and less upper arm muscle activation than in trials. The differences in riding posture and physiological demands on jockeys riding in a race rather than a trial, highlight the requirement for an off-horse race-specific training programme to improve jockey fitness and performance. Greater jockey stability and coordination will have mutual benefits for both horse welfare and performance.

The effect of vibration on kinematics and muscle activation during cycling

ABSTRACT Vibration has the potential to compromise performance in cycling. This study aimed to investigate the effects of vibration on full-body kinematics and muscle activation time series. Nineteen male amateur cyclists (mass 74.9 ± 5.9 kg, body height 1.82 ± 0.05 m, Vo2max 57 ± 9 ml/kg/min, age 27 ± 7 years) cycled (216 ± 16 W) with (Vib) and without (NoVib) vibration. Full-body kinematics and muscle activation time series were analysed. Vibration did not affect lower extremity joint kinematics significantly. The pelvic rotated with vibration towards the posterior direction (NoVib: 22.2 ± 4.8°, Vib: 23.1 ± 4.7°, p = 0.016, d = 0.20), upper body lean (NoVib: 157.8 ± 3.0°, Vib: 158.9 ± 3.4°, p = 0.001, d = 0.35) and elbow flexion (NoVib: 27.0 ± 8.2°, Vib: 29.4 ± 9.0°, p = 0.010, d = 0.28) increased significantly with vibration. The activation of lower extremity muscles (soleus, gastrocnemius lat., tibialis ant., vastus med., rectus fem., biceps fem.) increased significantly during varying phases of the crank cycle due to vibration. Vibration increased arm and shoulder muscle (triceps brachii, deltoideus pars scapularis) activation significantly over almost the entire crank cycle. The co-contraction of knee and ankle flexors and extensors (vastus med. – gastrocnemius lat., vastus med. – biceps fem., soleus – tibialis ant.) increased significantly with vibration. In conclusion vibrations influence main tasks such as propulsion and upper body stabilization on the bicycle to a different extent. The effect of vibration on the task of propulsion is limited due to unchanged lower body kinematics and only phase-specific increases of muscular activation during the crank cycle. Additional demands on upper body stabilization are indicated by adjusted upper body kinematics and increased muscle activation of the arm and shoulder muscles during major parts of the cranking cycle.

Prediction of leg muscle activities from arm muscle activities in arm and leg cycling.

Functional electrical stimulation (FES) driven leg cycling is usually controlled by previously established stimulation patterns. We investigated the potential utilization of a particular computational method for controlling electrical stimulation of lower limb muscles by real-time electromyography (EMG) signals of arm muscles during hybrid arm and leg cycling. In hybrid arm and leg cycling, arm cranking is performed voluntarily, while leg cycling is driven by FES. In this study, we investigate arm and leg cycling movements of able-bodied persons when both arm and leg cycling is performed voluntarily without FES. We present a neural network-based model in which the input of the neural network is given by a time series of upper limb muscle activities (EMG), and the output provides potential lower limb muscle activities. The particular neural network was a nonlinear autoregressive exogen (NARX) neural network. The measured EMG signals of the lower limb muscles were compared to the signals that were predicted by the neural network. The neural network was trained with data recorded from four participants. Our preliminary results show notable differences between the predicted and the experimentally measured lower limb muscle activities. The prediction was good only for 60% of the movement time. We conclude that-while including arm cycling in the movement-simpler control modalities or further consideration of applying machine-learning techniques has to be taken into account to improve voluntary upper limb-controlled FES assisted leg cycling.

Posture Estimation Using Surface Electromyography during Wheelchair Hand-Rim Operations.

This study examined competitive wheelchairs that facilitate sports participation. They can be moved straight ahead using only one arm. Our designed and developed competitive wheel-chairs have a dual hand-rim system. Their two hand-rims, attached to a drive wheel on one side, can be operated simultaneously for straight-ahead movement. Specifically, based on integrated electromyography (iEMG) data calculated from surface electromyography (sEMG), we examined the wheelchair loading characteristics, posture estimation, and effects on body posture during one-arm propulsion movement. The first experiment yielded insights into arm and shoulder-joint muscle activation from iEMG results obtained for two-hand propulsion and dual hand-rim system propulsion. Results suggest that muscle activation of one arm can produce equal propulsive force to that produced by two arms. The second experiment estimated the movement posture from iEMG during one-arm wheelchair propulsion. The external oblique abdominis is particularly important for one-arm wheelchair propulsion. The iEMG posture estimation validity was verified based on changes in the user body axis and seat pressure distribution. In conclusion, as confirmed by iEMG, which is useful to estimate posture during movement, one-arm wheelchair use requires different muscle activation sites and posture than when using two arms.

314 Exoskeletons increase paretic limb use in stroke survivors during a bimanual virtual reality reaching task

OBJECTIVES/GOALS: Almost 8 million Americans live with disability caused by stroke. However, recent advances in stroke rehabilitation are costly and lack resemblance to activities of daily living. The goal of this study was to develop a rehabilitation platform to increase stroke patients paretic limb use using inexpensive virtual reality and exoskeleton devices. METHODS/STUDY POPULATION: We conducted a feasibility study with 2 hemiplegic stroke participants. They reached for targets in a virtual reality environment using both hands. They completed 162 reaches divided into 3 blocks. Following baseline, we used an exoskeleton to provide 50% arm weight compensation to the paretic limb and used wrist weights to provide 50% arm weight resistance to the non-paretic limb. We removed the exoskeleton and wrist weights during the retention block. We used electromyography to approximate muscle activity in the biceps brachii. Relative contribution (RC) was calculated as the displacement of the paretic arm divided by the sum of displacements for both arms. Muscle contribution (MC) was calculated as the root mean square of paretic arm muscle activity divided by the sum of activity for both arms. RESULTS/ANTICIPATED RESULTS: During baseline, RC of the impaired limb was 44% and 48%, and MC of the impaired bicep was 43% and 35% in two mild to moderately impaired patients (Fugl-Meyer Upper Extremity scores of 43 and 37, respectively). During loading, RC increased by 5.6% and 1.1% and MC decreased by 8.3% and 11.8%. These data suggest hemiplegic stroke participants alter limb coordination when our device normalizes muscular output asymmetries between limbs. Importantly, these results closely match data from our previous work in 12 healthy controls, where we found a 2% increase in RC is significantly predicted by a 11% decrease in MC. By collecting more data on stroke patients, we will quantify this tradeoff between coordination and muscle activity modulation, allowing us to optimize the exoskeleton mechanics to maximize paretic limb use. DISCUSSION/SIGNIFICANCE: We demonstrate our platform is well tolerated by mild to moderately impaired stroke patients; this feasibility study forms the basis for low cost at-home technologies for stroke rehabilitation. With further development, clinicians can use our platform to fine-tune the level of limb constraint based on the individual needs of the patient.

Getting a Handle on Sales: Shopping Carts Affect Purchasing by Activating Arm Muscles

This research demonstrates that the physical properties of shopping carts influence purchasing and spending. Prior research on ergonomics indicates that standard shopping carts, which are pushed via a horizontal handlebar, are likely to activate arm extensor muscles. Prior research on arm muscle activation, in turn, suggests that arm extensor activation may elicit less purchasing than arm flexor activation. The authors thus deduce that standard shopping carts may be suboptimal for stimulating purchases. The authors predicted that shopping carts with parallel handles (such as on a wheelbarrow or “walker”) would instead activate the flexor muscles and thus increase purchasing. An electromyography study revealed that both horizontal and vertical handles more strongly activate the extensor muscles of the upper arm (triceps), whereas parallel handles more strongly activate the flexor muscles (biceps). In a field experiment, parallel-handle shopping carts significantly and substantially increased sales across a broad range of categories, including both vice and virtue products. Finally, in a simulated shopping experiment, parallel handles increased purchasing and spending beyond both horizontal and vertical handles. These results were not attributable to the novelty of the shopping cart itself, participants’ mood, or purely ergonomic factors.

Arm muscle activity with no positive effect on ball speed during full effort pitching

The purpose of this study was to examine muscle activity that does not positively affect pitch velocity by comparing throwing arm muscle activity during full strength and force-regulated pitching. Subjects threw a baseball at 80% and 100% subjective intensity. Muscle activity of the biceps brachii (BB), triceps brachii (TB), flexor carpi ulnaris (FCU) and extensor carpi radialis (ECR) muscles was measured using a wireless EMG measurement system (Trigno wireless EMG system: Delsys Inc.) and compared between conditions. The co-contraction index (CCI) was also calculated during the comparison. Despite significant differences in velocity between the two conditions, there was no difference in throwing arm muscle activity or forearm co-contraction index from 190 ms before release to release. Upper arm co-contraction index was higher when throwing at full speed. Furthermore, we also analyzed whole-body muscle activity and found differences in lower extremity/trunk and nonthrowing arm muscle activity. The results of this study provide new insights into the motor control mechanisms that regulate pitch velocity in skilled pitchers.

Archery's signature: an electromyographic analysis of the upper limb.

Bow and arrow technology plays a significant role in the recent evolutionary history of modern humans, but limitations of preservation make it challenging to identify archaeological evidence of early archery. Since bone structure can change in response to muscle force, archers of the past can potentially be identified through analysis of upper arm bones. However, there is limited research on how archery impacts upper limb musculature. This study offers initial insights into how archery impacts humeral musculature and highlights the need for additional research focused on archery's direct impact on humeral morphology. Humeral morphology has been used to support behaviour reconstructions of archery in past populations. However, the lack of experimental research concerning the impacts that archery has on the upper limb weakens skeletal morphological approaches. The goal of this study was to determine how archery impacts the activation of upper limb musculature. More specifically, this study tested: (a) whether the relative muscle activations are similar between arms; and (b) what muscles were activated on the dominant (draw) arm compared with the non-dominant (bow) arm. Data on upper arm muscle activation were collected bilaterally for nine archers using surface electromyography (EMG). Results show similar levels of muscle activation bilaterally with different muscles being activated in each arm. There were significantly higher integrated EMG and peak muscle activations of the biceps brachii muscles in the draw arm compared with the bow arm. In contrast, the lateral deltoid and the triceps brachii muscles had significantly higher integrated EMG and peak muscle activations on the bow arm compared with the draw arm. This work offers initial insights into how archery impacts humeral musculature and highlights the need for additional research focused on archery's direct impact on humeral morphology.