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Introduction: The upper body Wingate Anaerobic Test (WAnT) is a 30-s maximal effort sprint against a set load (percentage of body mass). However, there is no consensus on the optimal load and no differential values for males and females, even when there are well-studied anatomical and physiological differences in muscle mass for the upper body. Our goal was to describe the effects of load, sex, and crank position on the kinetics, kinematics, and performance of the upper body WAnT., Methods: Eighteen participants (9 females) performed three WAnTs at 3%, 4%, and 5% of body mass. Arm crank forces, 2D kinematics, and performance variables were recorded during each WAnT., Results: Our results showed an increase of ~49% effective force, ~36% peak power, ~5° neck flexion, and ~30° shoulder flexion from 3% to 5% load ( P < 0.05). Mean power and anaerobic capacity decreased by 15%, with no changes in fatigue index ( P < 0.05). The positions of higher force efficiency were at 12 and 6 o'clock. The least force efficiency occurred at 3 o'clock ( P < 0.05). Sex differences showed that males produced 97% more effective force and 109% greater mean power than females, with 11.7% more force efficiency ( P < 0.001). Males had 16° more head/neck flexion than females, and females had greater elbow joint variability with 17° more wrist extension at higher loads. Males cycled ~32% faster at 3% versus 5% WAnT load with a 65% higher angular velocity than females. Grip strength, maximal voluntary isometric contraction, mass, and height positively correlated with peak and mean power ( P < 0.001)., Conclusions: In conclusion, load, sex, and crank position have a significant impact on performance of the WAnT. These factors should be considered when developing and implementing an upper body WAnT., (Copyright © 2024 by the American College of Sports Medicine.)

Exercise induced performance fatigue has been shown to impair many aspects of fine motor function in the distal upper limb. However, most fatiguing protocols do not reflect the conditions experienced with computer use. The purpose of this study was to determine how a prolonged, low-force mouse clicking fatigue protocol impacts performance fatigue of the distal upper limb for gamers and non-gamers. Participants completed a total of 1 h of mouse clicking at 5 clicks per second. Muscle fatigue and performance were intermittently assessed. RMS amplitude increased for the forearm flexors throughout the fatigue protocol. Accuracy decreased following the first bout of clicking and returned to baseline values after 40-min. EDC and ECU displayed the greatest muscle activity while aiming, producing 11.4% and 12.9% of MVC, respectively. These findings indicate that mouse clicking may not result in performance fatigue, however, high levels of extensor activity may explain common injuries among gamers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Arm-cycling is a versatile exercise modality with applications in both athletic enhancement and rehabilitation, yet the influence of forearm orientation remains understudied. Thus, this study aimed to investigate the impact of forearm position on upper-body arm-cycling Wingate tests. Fourteen adult males (27.3 ± 5.8 years) underwent bilateral assessments of handgrip strength in standing and seated positions, followed by pronated and supinated forward arm-cycling Wingate tests. Electromyography (EMG) was recorded from five upper-extremity muscles, including anterior deltoid, triceps brachii lateral head, biceps brachii, latissimus dorsi, and brachioradialis. Simultaneously, bilateral normal and propulsion forces were measured at the pedal-crank interface. Rate of perceived exertion (RPE), power output, and fatigue index were recorded post-test. The results showed that a pronated forearm position provided significantly (p < 0.05) higher normal and propulsion forces and triceps brachii muscle activation patterns during arm-cycling. No significant difference in RPE was observed between forearm positions (p = 0.17). A positive correlation was found between seated handgrip strength and peak power output during the Wingate test while pronated (dominant: p = 0.01, r = 0.55; non-dominant: p = 0.03, r = 0.49) and supinated (dominant: p = 0.03, r = 0.51; don-dominant: p = 0.04, r = 0.47). Fatigue changed the force and EMG profile during the Wingate test. In conclusion, this study enhances our understanding of forearm position's impact on upper-body Wingate tests. These findings have implications for optimizing training and performance strategies in individuals using arm-cycling for athletic enhancement and rehabilitation., (© Journal of Sports Science and Medicine.)

Background: Lower activation of higher threshold (type-II) motor units (MUs) has been suggested in children compared with adults. We examined child-adult differences in discrete MU activation of the flexor carpi radialis (FCR)., Methods: Fifteen boys (10.2 ± 1.4 years), and 17 men (25.0 ± 2.7 years) completed 2 laboratory sessions. Following a habituation session, maximal voluntary isometric wrist flexion torque (MVIC) was determined before completing trapezoidal isometric contractions at 70%MVIC. Surface electromyography was captured by Delsys Trigno Galileo sensors and decomposed into individual MU action potential trains. Recruitment threshold (RT), and MU firing rates (MUFR) were calculated., Results: MVIC was significantly greater in men (10.19 ± 1.92 Nm) than in boys (4.33 ± 1.47 Nm) (p < 0.05), but not statistically different after accounting for differences in body size. Mean MUFR was not different between boys (17.41 ± 7.83 pps) and men (17.47 ± 7.64 pps). However, the MUFR-RT slope was significantly (p < 0.05) steeper (more negative) in boys, reflecting a progressively greater decrease in MUFR with increasing RT. Additionally, boys recruited more of their MUs early in the ramped contraction., Conclusion: Compared with men, boys tended to recruit their MUs earlier and at a lower percentage of MVIC. This difference in MU recruitment may explain the greater decrease in MUFR with increasing RT in boys compared with men. Overall, these findings suggest an age-related difference in the neural strategy used to develop moderate-high torque in wrist flexors, where boys recruit more of their MUs earlier in the force gradation process, possibly resulting in a narrower recruitment range., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The ability of the median nerve (MN) to adapt in response to altered carpal tunnel conditions is important to mitigate compressive stress on the nerve. We assessed changes in MN deformation and position throughout the entire time course of hand force exertions. Fourteen right-handed participants ramped up force from 0% to 50% of maximal voluntary force (MVF) before ramping force back down in three different hand force exertion tasks (pulp pinch, chuck pinch, power grip). Pinch and grip forces were measured with a digital dynamometer, which were time synchronized with transverse carpal tunnel images obtained via ultrasound. Ultrasound images were extracted in 10% increments between 0% and 50% MVF while ramping force up (loading phase) and down (unloading phase). MN deformation and position relative to the flexor digitorum superficialis tendon of the long finger were assessed in concert. During loading, the nerve became more circular while displacing dorsally and ulnarly. These changes primarily occurred at the beginning of the hand force exertions while ramping force up from 0% to 20%, with very little change between 20% and 50% MVF. Interestingly, deformation and position changes during loading were not completely reversed during unloading while ramping force down. These findings indicate an initial reorganization of carpal tunnel structures. Mirrored changes in nerve deformation and position may also reflect strain-related characteristics of adjoining subsynovial connective tissue. Regardless, time-varying changes in nerve deformation and position appear to be an important accommodative mechanism in the healthy carpal tunnel in response to gripping and pinching tasks., (© 2023 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals LLC on behalf of Orthopaedic Research Society.)

Background: Understanding differential strength capability between sexes is critical in ergonomics and task design. Variations in study designs and outcome measures generates challenges in establishing workplace guidelines for strength requirements to minimize upper extremity risk for workers. The purpose of this systematic review was to collate and summarize sex differences in strength at the shoulder across movement directions and contraction types., Methods: A total of 3,294 articles were screened from four databases (Embase, Medline, SCOPUS, and Web of Science). Eligibility criteria included observational studies, direct measurement of muscular joint, and healthy adult participants (18-65 years old). Strength outcome measures were normalized to percentages of male outputs to allow comparisons across articles., Results: A total of 63 studies were included within the final review. Majority of articles observed increased strength in males; the gap between male-female strength was greater in flexion and internal/external rotation, with females generating ~30% of male strength; scaption strength ratios were most consistent of the movement groups, with females generating 55-62% of male strength., Conclusion: Sex strength differences should be considered as an important factor for workplace task design as women are more at risk for occupational-related injuries than men in equivalent strength requirements. Differences in strength were not synonymous across motions; females demonstrated increased disparity relative to male strength in horizontal flexion/extension, forward flexion and internal/external rotation. Some movements had an extremely limited pool of available studies for examination which identified critical research gaps within the literature. Collating and quantifying strength differences is critical for effective workstation design with a range of users to mitigate potential overexertion risk and musculoskeletal injury., Competing Interests: Michael W. R. Holmes is an Academic Editor for PeerJ., (© 2024 Kritzer et al.)

The robotics discipline is exploring precise and versatile solutions for upper-limb rehabilitation in Multiple Sclerosis (MS). People with MS can greatly benefit from robotic systems to help combat the complexities of this disease, which can impair the ability to perform activities of daily living (ADLs). In order to present the potential and the limitations of smart mechatronic devices in the mentioned clinical domain, this review is structured to propose a concise SWOT (Strengths, Weaknesses, Opportunities, and Threats) Analysis of robotic rehabilitation in MS. Through the SWOT Analysis, a method mostly adopted in business management, this paper addresses both internal and external factors that can promote or hinder the adoption of upper-limb rehabilitation robots in MS. Subsequently, it discusses how the synergy with another category of interaction technologies - the systems underlying virtual and augmented environments - may empower Strengths, overcome Weaknesses, expand Opportunities, and handle Threats in rehabilitation robotics for MS. The impactful adaptability of these digital settings (extensively used in rehabilitation for MS, even to approach ADL-like tasks in safe simulated contexts) is the main reason for presenting this approach to face the critical issues of the aforementioned SWOT Analysis. This methodological proposal aims at paving the way for devising further synergistic strategies based on the integration of medical robotic devices with other promising technologies to help upper-limb functional recovery in MS., Competing Interests: GA and JZ were employed by ReWing s r l. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Albanese, Bucchieri, Podda, Tacchino, Buccelli, De Momi, Laffranchi, Mannella, Holmes, Zenzeri, De Michieli, Brichetto and Barresi.)

Sex differences in strength have been attributed to differences in body anthropometrics and composition; these factors are often ignored when generating workplace guidelines. These differences directly impact the upper extremity, leaving female workers exposed to injury risk. The wide range of tools and techniques for measuring upper extremity strength presents a challenge to ergonomists and work task designers; collating outcomes to provide a clear outlook of differences between males and females is essential and the purpose of this work. Four online databases were searched (PROSPERO ID: CRD42022339023) with a focus on articles assessing sex differences in wrist strength. A total of 2,378 articles were screened for relevancy; 25 full-text articles were included in this systematic review. Articles examined movement pairs (ulnar/radial deviation, pronation/supination, and flexion/extension), as well as contraction types (isometric and isokinetic) to observe sex differences in wrist strength. Across all articles, females produced ∼60-65% of male flexion/extension strength, ∼55-60% pronation/supination strength, and ∼60-70% ulnar/radial deviation strength. Overall, females presented lower strength-producing abilities than males, but when considering strength relative to body mass, male-female differences were less pronounced and occasionally females surpassed male strength metrics; typically, this occurred during flexion/extension, particularly in isokinetic contractions. This review has identified a scarcity of articles examining ulnar/radial deviation, pronation/supination, as well as isokinetic contractions; these are needed to supplement workplace exposure guidelines., Competing Interests: Michael W.R. Holmes is an Academic Editor for PeerJ., (©2023 Napper et al.)

The aim of this study was to compare the muscle activity of the gluteus medius (GMe), gluteus maximus (GMa), biceps femoris (BF), vastus lateralis (VL), vastus medialis (VM) and erector spinae (ES) as well as medial knee displacement (MKD) while using varying stiffness resistance bands (red: 1.68 kg; black: 3.31 kg; gold: 6.44 kg) during a barbell back squat (BBS) among males and females. A total of 23 (females: 11) resistance trained people were recruited for this study. Muscle activity was measured using electromyography, and motion capture cameras tracked lower-limb kinematics and MKD. Three resistance bands were placed at the distal end of the femur while performing a BBS at their 85% repetition maximum (RM). Parametric and non-parametric statistical analyses were conducted with the alpha level of 0.05. The gold resistance band resulted in a smaller knee-width-index value (i.e., greater MKD) compared to other bands (p < 0.01). Males exhibited less MKD compared to females during the BBS for each resistance band (p = 0.04). Males produced greater VL activity when using the black and gold resistance bands during the BBS (p = 0.03). When using a gold resistance band, the GMe muscle activation was higher compared to other resistance bands (p < 0.01). VM muscle activity was reduced when using a gold resistance band compared to no band condition (p < 0.01). BF (p = 0.39) and ES (p = 0.88) muscle activity did not change when using different resistance bands. As a result, females may be at a biomechanical disadvantage when using resistance bands compared to males while performing the BBS hindering them from optimal performance., Competing Interests: The authors declare no conflict of interest., (Copyright: © Academy of Physical Education in Katowice.)

Background: COVID-19 caused a transition to work-from-home conditions, closures of recreation facilities and cancelation of social events., Objective: This study sought to characterize and quantify the impact COVID-19 related shutdowns had on perceptions of health and wellbeing, musculoskeletal discomfort, and physical characteristics of workstation set-up in full time workers who transitioned to working from home., Methods: 297 participants from 8 countries completed a retrospective pre/post survey design that assessed outcomes prior to COVID-19 shutdowns and when each participant was experiencing peak pandemic-related restrictions. There were 3 categories including, health and wellbeing, musculoskeletal discomfort, and workplace ergonomics., Results: General discomfort on a scale from 1 to 100 increased from 31.4 pre to 39.9 during COVID-19. Notable areas increasing in severity of discomfort from pre to during included the neck (41.8 to 47.7), upper back (36.3 to 41.3) and right wrist (38.7 to 43.5). The percentage of the population experiencing discomfort increased from pre to during in the low back (41.5% to 55.2%), upper back (28.7% to 40.9%), neck (45.5% to 60.9%) and right wrist (16.1% to 23.7%)., Conclusion: There were three distinct groups for physical activity one group including, one maintaining and one that decreased, which did not have an impact on perceived general discomfort. There was a significant decrease in usage of a desk and adjustable chair and an increase in laptop use. Working from home in some capacity will likely be a more common occurrence which will require further ergonomic assessments and considerations to keep a healthy workforce.

Background: Lateral elbow tendinopathy is associated with changes to forearm muscle activity and wrist posture during gripping. Multidirectional elastic tape is thought to exert a deloading effect on underlying musculotendinous structures, which could potentially alter muscle activity or wrist posture., Methods: This single-blinded randomised crossover trial compared the immediate effects of tensioned multidirectional elastic tape, untensioned control tape, and no tape, in individuals with lateral elbow tendinopathy. Muscle activity of extensor carpi radialis longus and brevis, extensor carpi ulnaris, and extensor digitorum and wrist extension angle were recorded during a submaximal gripping task. Muscle activity was normalised to the maximum amplitude recorded during maximal grip. Change scores were calculated (post-condition minus baseline). Repeated-measure analyses of variance were used to examine between-condition differences., Findings: 27 participants (16 males, mean age (SD): 48.6 (11.9) years) underwent all conditions. Extensor digitorum muscle activity was reduced during the multidirectional elastic tape, compared to control tape and no tape (MD -5.6% [95%CI: -9.9 to -1.3], MD -5.8% [95%CI: -10.2 to -1.4], respectively). Extensor carpi ulnaris muscle activity was reduced during the multidirectional elastic tape, compared to the control tape (mean difference [MD] -3.2% [95%CI: -5.3 to -1.1]), but increased during the control tape, compared to the no tape (MD 2.9% [95%CI: 0.8 to 5.0]). No differences were observed in extensor carpi radialis brevis or longus muscle activity, or extension wrist angle between conditions., Interpretation: A decreased in extensor carpi ulnaris and extensor digitorum muscle activity during multidirectional elastic tape may be evidence of a deloading effect during submaximal gripping., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Caitlin Hill reports financial support was provided by Sports Medicine Australia. Crystal Kean reports equipment, drugs, or supplies was provided by Strapit Medical & Sports Supplies Pty. Ltd., (Copyright © 2022. Published by Elsevier Ltd.)

This study sought to compare and validate baseball pitching mechanics, including joint angles and spatiotemporal parameters, from a single camera markerless motion capture solution with a 3D optical marker-based system. Ten healthy pitchers threw 2-3 maximum effort fastballs while concurrently using marker-based optical capture and pitchAI TM (markerless) motion capture. Time-series measures were compared using R -squared (r 2 ), and root mean square error (RMSE). Discrete kinematic measures at foot plant, maximal shoulder external rotation, and ball release, plus four spatiotemporal parameters were evaluated using descriptive statistics, Bland-Altman analyses, Pearson's correlation coefficients, p-values, r 2 , and RMSE. For time-series angles, r 2 ranged from 0.69 (glove arm shoulder external rotation) to 0.98 (trunk and pelvis rotation), and RMSE ranged from 4.37° (trunk lateral tilt) to 20.78° (glove arm shoulder external rotation). Bias for individual joint angle and spatiotemporal parameters ranged from -11.31 (glove arm shoulder horizontal abduction; MER) to 12.01 (ball visible). RMSE was 3.62 m/s for arm speed, 5.75% height for stride length and 21.75 ms for the ball visible metric. pitchAI TM can be recommended as a markerless alternative to marker-based motion capture for quantifying pitching kinematics. A database of pitchAI TM ranges should be established for comparison between systems.

Fatigue is a temporary condition that arises as a result of intense and/or prolonged use of muscles and can affect skilled human performance. Therefore, the quantitative analysis of these effects is a topic of crucial interest in both ergonomics and clinical settings. This study introduced a novel protocol, based on robotic techniques, to quantitatively assess the effects of fatigue on the human wrist joint. A wrist manipulandum was used for two concurrent purposes: (1) implementing the fatigue task and (2) assessing the functional changes both before and at four time points after the end of the fatigue task. Fourteen participants completed the experimental protocol, which included the fatigue task and assessment sessions over 2 days. Specifically, the assessments performed are related to the following indicators: (1) isometric forces, (2) biomechanical properties of the wrist, (3) position sense, and (4) stretch reflexes of the muscles involved. The proposed fatigue task was a short-term, submaximal and dynamic wrist flexion/extension task designed with a torque opposing wrist flexion. A novel task termination criterion was employed and based on a percentage decrease in the mean frequency of muscles measured using surface electromyography. The muscle fatigue analysis demonstrated a change in mean frequency for both the wrist flexors and extensors, however, only the isometric flexion force decreased 4 min after the end of the task. At the same time point, wrist position sense was significantly improved and stiffness was the lowest. Viscosity presented different behaviors depending on the direction evaluated. At the end of the experiment (about 12 min after the end of the fatigue task), wrist position sense recovered to pre-fatigue values, while biomechanical properties did not return to their pre-fatigue values. Due to the wide variety of fatigue tasks proposed in the literature, it has been difficult to define a complete framework that presents the dynamic of fatigue-related changes in different components associated with wrist function. This work enables us to discuss the possible causes and the mutual relationship of the changes detected after the same task., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Albanese, Falzarano, Holmes, Morasso and Zenzeri.)

The purpose of this work was to investigate forearm muscle activity and wrist angular displacement during radial and ulnar wrist perturbations across various isometric hand grip demands. Surface electromyography (EMG) was recorded from eight muscles of the upper extremity. A robotic device delivered perturbations to the hand in the radial and ulnar directions across four pre-perturbation grip magnitudes. Angular displacement and time to peak displacement following perturbations were evaluated. Muscle activity was evaluated pre- and post-perturbation. Results showed an inverse relationship between grip force and angular displacement ( p ≤ 0.001). Time to peak displacement decreased as grip force increased ( p ≤ 0.001). There was an increase in muscle activity with higher grip forces across all muscles both pre-and post-perturbation ( p ≤ 0.001) and a greater average muscle activity in ulnar as compared to radial deviation ( p = 0.02). This work contributes to the wrist joint stiffness literature by relating wrist angular displacement to grip demands during novel radial/ulnar perturbations and provides insight into neuromuscular control strategies., Competing Interests: Michael W.R. Holmes is an Academic Editor for PeerJ., (© 2022 Mannella et al.)

Muscular weakness and loss of motor function are common symptoms of multiple sclerosis. Robotic rehabilitation can improve sensorimotor function and motor control in this population. However, many studies using robotics for rehabilitation have overlooked changes in muscular strength, despite research demonstrating its utility in combating functional impairments. The purpose of this scoping review was to critically examine changes in muscular strength following robotic rehabilitation interventions for individuals with multiple sclerosis. A literature search of five databases was conducted and search terms included a combination of three primary terms: robotic rehabilitation/training, muscular strength, and multiple sclerosis. Thirty one articles were found, and following inclusion criteria, 5 remained for further investigation. Although muscular strength was not the primary targeted outcome of the training for any of the included articles, increases in muscular strength were present in most of the studies suggesting that robotic therapy with a resistive load can be an effective alternative to resistance training for increasing muscular strength. Outcome measures of isometric knee-extensor force (kg) (right: p < 0.05, left: p < 0.05), isometric knee flexion and extension torque (Nm) ( p < 0.05), ankle dorsiflexion and plantarflexion torque (Nm) (all p < 0.05) and handgrip force (kg) ( p < 0.05) all improved following a robotic training intervention. These adaptations occurred with sustained low resistive loads of hand grip or during gait training. This scoping review concludes that, despite a lack of studies focusing on strength, there is evidence robotics is a useful modality to improve muscular strength in combination with motor control and neuromotor improvements. A call for more studies to document changes in strength during robotic rehabilitation protocols is warranted., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Mannella, Cudlip and Holmes.)

Objective: The purpose of this study was to examine the effects of submaximal isometric neck muscle fatigue and manual therapy on wrist joint position sense (JPS) within healthy individuals and individuals with subclinical neck pain (SCNP)., Methods: Twelve healthy participants and 12 participants with SCNP were recruited. Each group completed 2 sessions, with 48 hours between sessions. On day 1, both groups performed 2 wrist JPS tests using a robotic device. The tests were separated by a submaximal isometric fatigue protocol for the cervical extensor muscles (CEM). On day 2, both groups performed a wrist JPS test, followed by a cervical treatment consisting of manual therapy (SCNP) or neck rest (20 minutes, control group) and another wrist JPS test. Joint position sense was measured as the participant's ability to recreate a previously presented wrist angle. Each wrist JPS test included 12 targets, 6 into wrist flexion and 6 into wrist extension. Kinematic data from the robot established absolute, variability, and constant error., Results: Absolute error significantly decreased (P = .01) from baseline to post-fatigue in the SCNP group (baseline = 4.48 ± 1.58°; post-fatigue = 3.90 ± 1.45°) and increased in the control group (baseline = 3.12 ± 0.98°; post-fatigue = 3.81 ± 0.90°). The single session of manual cervical treatment significantly decreased absolute error in participants with SCNP (P = .004)., Conclusion: This study demonstrated that neck pain or fatigue can lead to altered afferent input to the central nervous system and can affect wrist JPS. Our findings demonstrate that acute wrist proprioception may be improved in individuals with SCNP by a single cervical manual therapy session., (Copyright © 2022. Published by Elsevier Inc.)

Elastic resistance exercise is a popular mode of strength training that has demonstrated positive effects on whole-body strength and performance. The purpose of this work was to identify the efficacy of elastic resistance training on improving upper limb strength and performance measures for the shoulder. Seven online databases were searched with a focus on longitudinal studies assessing shoulder elastic training strength interventions. In total, 1367 studies were initially screened for relevancy; 24 full-text articles were included for review. Exercise interventions ranged from 4-12 weeks, assessing pre-/post-strength and performance measures inclusive of isometric and isokinetic strength, 1RM strength, force-velocity tests, and throwing-velocity tests. Significant increases in various isometric strength measures (IR:11-13%, ER:11-42%, FL: 14-36%, EXT: 4-17%, ABD: 8-16%), 1RM strength (~24% in bench press), force-velocities, throwing- and serve-velocities (12%) were all observed. Elastic resistance training elicited positive effects for both strength and performance parameters regardless of intervention duration. Similar significant increases were observed in isometric strength and 1RM strength across durations. Isokinetic strength increases were variable and dependent on the joint velocity conditions. Quantifying the dosage of appropriate exercise prescription for optimal strength and performance gains is inconclusive with this study due to the heterogeneity of the intervention protocols.

Muscle fatigue is represented as a reduction in force production capability; however, fatigue does not necessarily result in performance impairments. As the distal upper limb serves as the end effector when interacting or manipulating objects, it is important to understand how muscle fatigue may impact motor functionality. The aim of this study was to systematically review the literature to identify how various aspects of motor performance of the distal upper limb are impaired following muscle fatigue. Four databases were searched using 23 search terms describing the distal upper limb, muscle fatigue, and various performance metrics. A total of 4561 articles were screened with a total of 28 articles extracted and critically appraised. Evidence extracted indicates that muscle fatigue results in unique impairments based on the type of motor performance being evaluated. Furthermore, much data suggests that muscle fatigue does not result in consistent, predictable performance impairments, particularly while performing submaximal tasks. Additionally, magnitude of fatigue does not directly correlate with reductions in performance outcomes at the hand and wrist. Fatiguing protocols used highlighted the importance of fatigue specificity. When fatiguing and performance tasks are similar, performance impairment is likely to be observed. The numerous muscles found in the hand and wrist, often considered redundant, play a critical role in maintaining task performance in the presence of muscle fatigue. The presence of motor abundance (e.g. multiple muscles with similar function) is shown to reduce the impairment in multiple performance metrics by compensating for reduced function of fatigued muscles. Continued exploration into various fatiguing protocols (i.e. maximal or submaximal) will provide greater insights into performance impairments in the distal upper limb., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The aim of this study was to characterise wrist extensor and flexor muscle activity during combinations of moderate-to-high handgrip and wrist forces that are similar to actions and intensities used in many workplace settings. Surface electromyography was recorded from three wrist flexors and three wrist extensors while participants performed simultaneous handgrip forces and wrist forces ranging in intensities from 15% to 60% of maximum. While the wrist flexors were highly task-dependent, in that their activity significantly changed between conditions, wrist extensor activity was consistently high throughout the experiment. Wrist joint co-contraction was also significantly higher when the wrist extensors were functioning as the antagonists. These findings suggest that the wrist extensors likely demonstrate consistently higher muscleactivity during most tasks of the hand and wrist, which is likely a leading mechanism behind why they develop chronic overuse injuries more frequently than the wrist flexors. Practitioner Summary: This study was conducted to identify forearm muscle activity patterns that might help explain why the wrist extensors develop overuse injuries more frequently than the flexors. Results demonstrated that the wrist extensors are consistently, highly active during combined handgrip and wrist forces and exhibit no periods of low muscle activity. Abbreviations: BB: biceps brachii; ECR: extensor carpi radialis; ECU: extensor carpi ulnaris; ED: extensor digitorum; EMG: electromyography; ES: effect size; FCR: flexor carpi radialis; FCU: flexor carpi ulnaris; FDS: flexor digitorum superficialis; MVC: maximal voluntary contraction; MVE: maximal voluntary excitation; SD: standard deviation; SE: standard error; TB: triceps brachii.

Objective: The purpose of this study was to quantify the differences in upper limb muscle activity and kinematics when performing shoulder elastic resistance exercises with no cue, slouched posture, and corrected posture., Design: Fifteen healthy participants completed four shoulder elastic resistance exercises (unilateral flexion, bilateral flexion, external rotation, and external rotation with towel) across three simulated body postures (no cue, corrected posture, and slouched posture). Surface electromyography was measured on 16 upper limb muscles and kinematics were collected. Two-way repeated-measures analyses of variance examined differences in muscle activation and kinematics across postures and exercises., Results: Interactions between exercise and posture were found for most muscles. Muscle activity interactions existed in 14 of the 16 muscles examined, with 8 muscles having the greatest activity in the unilateral flexion, slouched condition (P < 0.0001). The slouched posture generated activity up to 88.4 ± 5.1 %MVC in the cervical extensors. Completing flexion or external rotation exercises with a slouched posture led to increased glenohumeral range of motion (P < 0.0001), but these differences were less than 5 degrees between the greatest and smallest ranges of motion (85.8 vs. 81.0 degrees)., Conclusion: Posture influenced muscle activation and kinematics, with slouched postures increasing muscle activity and range of motion. There was little to no difference between the no cue and corrected cue conditions, suggesting that perhaps a clinician's time may be better spent focusing on avoiding slouched postures rather than ensuring mastering technique., Competing Interests: Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

The purpose of this study was to evaluate anthropometry and forearm muscle activity as predictors of maximal isometric wrist torque. Thirteen anthropometric measures, forearm electromyography from flexor carpi radialis (FCR) and extensor carpi radialis (ECR), and maximal isometric wrist flexion/extension torque were obtained from 25 male participants. Pearson correlation coefficients assessed relationships between peak isometric torque and: (1) anthropometrics, (2) FCR and ECR activation, (3) FCR/ECR antagonist/agonist coactivation ratios. Based on significant correlations, linear regression equations were developed (SPSS v.25; p < 0.05). Hand thickness, forearm circumference and ECR activation or hand thickness, elbow circumference, FCR activation and body weight were most highly correlated with extension or flexion torque, respectively. Hand thickness, forearm circumference, and ECR activation (R 2  = 54.5%; p = 0.001) and hand thickness, elbow circumference, FCR activation (R 2  = 68.3%; p < 0.001) explained similar variance in torque regressions as did the addition of body weight to extension (R 2  = 58.0%; p = 0.001) and flexion (R 2  = 69.9%; p < 0.001) torque regression equations, respectively. Circumference measurements, a pseudo for muscle size, and activation amplitude influenced wrist force output more than limb length or coactivation., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this study, we implemented a protocol for the robotic assessment of the effects of forearm muscle fatigue on wrist dynamics. The potential of robotic devices lies in the possibility to control and measure a wide variety of kinematic and physiological variables, both in repeated sessions over time and during real-time assessments. The implemented fatigue task is tailored to the robotically assessed single-subject maximal force and based on a real-time evaluation of muscle activity. The protocol resulted to be repeatable across sessions evaluated on the same subject and a preliminary step toward a better understanding of which features should be monitored to design a robust and strongly controlled dynamic fatiguing task.

In this study, we designed a robot-based method to compute a mechanical impedance model that could extract the viscoelastic properties of the wrist joint. Thirteen subjects participated in the experiment, testing both dominant and nondominant hands. Specifically, the robotic device delivered position-controlled disturbances in the flexion-extension degree of freedom of the wrist. The external perturbations were characterized by small amplitudes and fast velocities, causing rotation at the wrist joint. The viscoelastic characteristics of the mechanical impedance of the joint were evaluated from the wrist kinematics and corresponding torques. Since the protocol used position inputs to determine changes in mean wrist torque, a detailed analysis of wrist joint dynamics could be made. The scientific question was whether and how these mechanical features changed with various grip demands and perturbation velocities. Nine experimental conditions were tested for each hand, given by the combination of three velocity perturbations (fast, medium, and slow) and three hand grip conditions [self-selected grip, medium and high grip force, as percentage of the maximum voluntary contraction (MVC)]. Throughout the experiments, electromyographic signals of the extensor carpi radialis (ECR) and the flexor carpi radialis (FCR) were recorded. The novelty of this work included a custom-made soft grip sensor, wrapped around the robotic handle, to accurately quantify the grip force exerted by the subjects during experimentation. Damping parameters were in the range of measurements from prior studies and consistent among the different experimental conditions. Stiffness was independent of both direction and velocity of perturbations and increased with increasing grip demand. Both damping and stiffness were not different between the dominant and nondominant hands. These results are crucial to improving our knowledge of the mechanical characteristics of the wrist, and how grip demands influence these properties. This study is the foundation for future work on how mechanical characteristics of the wrist are affected in pathological conditions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Falzarano, Holmes, Masia, Morasso and Zenzeri.)

A deep investigation of proprioceptive processes is necessary to understand the relationship between sensory afferent inputs and motor outcomes. In this work, we investigate whether and how perception of wrist position is influenced by the direction along which the movement occurs. Most previous studies have tested Joint Position Sense (JPS) through 1 degree of freedom (DoF) wrist movements, such as flexion/extension (FE) or radial/ulnar deviation (RUD). However, the wrist joint has 3-DoF and many activities of daily living produce combined movements, requiring at least 2-DoF wrist coordination. For this reason, in this study, target positions involved movement directions that combined wrist flexion or extension with radial or ulnar deviation. The chosen task was a robot-aided Joint Position Matching (JPM), in which blindfolded participants actively reproduced a previously passively assumed target joint configuration. The JPM performance of 20 healthy participants was quantified through measures of accuracy and precision, in terms of both perceived target direction and distance along each direction of movement. Twelve different directions of movement were selected and both hands tested. The left and right hand led to comparable results, both target extents and directions were differently perceived according to the target direction on the FE/RUD space. Moreover, during 2-DoF combined movements, subjects' perception of directions was impaired when compared to 1-DoF target movements. In summary, our results showed that human perception of wrist position on the FE/RUD space is symmetric between hands but not isotropic among movement directions., Competing Interests: FM was employed by company MathWorks. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Albanese, Holmes, Marini, Morasso and Zenzeri.)

This study examined the influence of the Theraband TM CLX gold band on lower-limb muscle activity and kinematics during an overhead barbell squat. Participants performed two sets (band and no-band) of 12 repetitions of overhead barbell squats at 25% bodyweight. Three-dimensional kinematics were measured using motion capture with rigid bodies placed bilaterally on the foot, shank, thigh and thorax. Electromyography was collected from seven, bilateral muscles of the lower-limb and was unchanged for all muscles between conditions. Medial knee collapse was calculated using a knee-width index (KWI) ratio of the distance between the lateral epicondyles of the femur and the lateral malleoli. Average KWI was smaller during the band condition for the concentric (No band: 0.99 ± 0.05, Band: 0.97 ± 0.06, p  < 0.05) and eccentric phases (No band: 1.00 ± 0.06, Band: 0.97 ± 0.05, p  < 0.05). KWI was significantly smaller with the use of the Theraband TM CLX. As the gold band is the strongest of the CLX offerings, any benefit of increased proprioception may have been lost due to the high resistance of the band. Further research examining the dose-response of elastic band resistance to knee alignment may be needed to inform proper exercise prescription.

New Findings: What is the central question of this study? How do temperature manipulations affect motor unit (MU) properties during submaximal contractions to the same relative percentage of maximal force? What is the main finding and its importance? MU recruitment patterns are affected by temperature manipulations at the forearm. However, the relationship between MU potential amplitude and recruitment threshold indicates no change to the order or recruitment. Additionally, the MU potential amplitude and firing rate relationship was affected by temperature, suggesting that smaller MUs are more affected by temperature changes than larger MUs., Abstract: Temperature impacts muscle contractile properties, such that experiments with workloads based on thermoneutral values will produce different relative intensities if maximal force changes due to muscle temperature. We investigated how temperature affected motor unit (MU) properties with contractions performed at the same normalized percentage of maximal force. Twenty participants (10 females) completed evoked, maximal, and trapezoidal voluntary contractions during thermoneutral-, hot-, and cold-temperature conditions. Forearm temperature was established using 25 min of neutral (∼32°C), hot (∼44°C) or cold (∼13°C) water circulated through a tube-lined sleeve. Flexor carpi radialis MU properties were assessed with contractions at 30% and 60% MVC relative to each temperature using surface electromyography decomposition. Changes to contractile properties and electromechanical delay from the evoked twitch suggest that muscle contractility was changed from the thermal manipulations (effect size (d) ≥ 0.42, P < 0.05). Maximal force was not different between neutral and hot conditions (d = 0.16, P > 0.05) but decreased in the cold (d ≥ 0.34, P < 0.05). For both contraction intensities, MU potential (MUP) amplitude was larger and duration was longer in the cold compared to neutral and hot conditions (d ≥ 1.24, P < 0.05). Cumulative probability density for the number of MUs recruited revealed differences in MU recruitment patterns among temperature conditions. The relationship between MU recruitment threshold and firing rate or MUP amplitude was not different among temperature conditions (P > 0.05); however, the relationship between MUP amplitude and firing rate was (P < 0.05). Local temperature manipulations appear to affect MU recruitment patterns, which may act as compensatory mechanisms to the changes in muscle viscosity and contractile properties due to local temperature changes., (© 2020 The Authors. Experimental Physiology © 2020 The Physiological Society.)

We evaluated the effects of muscle fatigue on hand-tracking performance in young adults. Differences were quantified between wrist flexion and extension fatigability, and between males and females. Participants were evaluated on their ability to trace a pattern using a 3-degrees-of-freedom robotic manipulandum before (baseline) and after (0, 1, 2, 4, 6, 8, and 10 mins) a submaximal-intensity fatigue protocol performed to exhaustion that isolated the wrist flexors or extensors on separate days. Tracking tasks were performed at all time points, while maximal voluntary contractions (MVCs) were performed at baseline, and 2, 6-, and 10-mins post-task termination. We evaluated movement smoothness (jerk ratio, JR), shape reproduction (figural error, FE), and target tracking accuracy (tracking error, TE). MVC force was significantly lower in females ( p < 0.05), lower than baseline for all timepoints after task termination ( p < 0.05), with no muscle group-dependent differences. JR did not return to baseline until 10-mins post-task termination (most affected), while FE returned at 4-mins post-task termination, and TE at 1-min post-task termination. Males tracked the target with significantly lower JR ( p < 0.05), less TE ( p < 0.05), and less FE ( p < 0.05) than females. No muscle group-dependent changes in hand-tracking performance were observed. Based on this work, hand tracking accuracy is similarly impaired following repetitive submaximal dynamic wrist flexion or extension. The differences between male and female fatigability was independent of the changes in our tracking metrics., (Copyright © 2020 Kumar, Forman, Forman, Mugnosso, Zenzeri, Button and Holmes.)

Current research suggests that the wrist extensor muscles function as the primary stabilizers of the wrist-joint complex. However, most investigations have utilized isometric study designs, with little consideration for wrist dynamics or changes in posture. The purpose of the present study was to assess forearm muscle activity during the execution of dynamic wrist flexion/extension in multiple forearm orientations (pronation/supination). In 12 young adult males, surface electromyography (EMG) was recorded from eight muscles of the dominant arm: flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), extensor digitorum (ED), biceps brachii (BB) and triceps brachii (TB). While grasping a handle, participants performed dynamic wrist flexion/extension using a three-degrees-of-freedom wrist manipulandum. The robotic device applied torque to the handle, in either a flexion or extension direction, and in one of three forearm postures (30° supinated/neutral/30° pronated). Results indicated that forearm posture had minimal influence on forearm muscle activity, but significantly altered the activity of the biceps and triceps brachii. Movement phase (concentric-eccentric) dictated muscle activity in every muscle. Interestingly, muscle activity in the eccentric phase was equal between the two applied handle torques, regardless of whether the muscle acted as the agonist or antagonist. Co-contraction ratios were higher in the flexion conditions (flexion: 2.28 ± 2.04, extension: 0.32 ± 0.27), suggesting significantly greater wrist extensor activity-likely a contribution to wrist joint stability. This highlights the vulnerability of the wrist extensor muscles to overuse injuries in settings requiring prolonged use of dynamic wrist exertions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Functioning as wrist stabilizers, the wrist extensor muscles exhibit higher levels of muscle activity than the flexors in most distal upper-limb tasks. However, this finding has been derived mostly from isometric or wrist flexion-extension protocols, with little consideration for wrist dynamics or radial-ulnar wrist deviations. The purpose of this study was to assess forearm muscle activity during the execution of dynamic wrist radial-ulnar deviation in various forearm orientations (pronation/supination). In 12 healthy university-aged males, surface electromyography (EMG) was recorded from eight muscles of the dominant arm: flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), extensor digitorum (ED), biceps brachii (BB) and triceps brachii (TB). While grasping a handle, participants performed dynamic radial-ulnar deviation using a three-degrees-of-freedom wrist manipulandum. The robotic device applied torque to the handle, in either a radial or ulnar direction, and in one of three forearm postures (30° supinated/neutral/30° pronated). Results indicated that forearm posture influenced the muscles acting upon the hand (FDS/ED), whereas movement phase (concentric-eccentric) and torque direction influenced nearly every muscle. The ECR demonstrated the greatest task-dependency of all forearm muscles, which is possibly reflective of forearm muscle lines of action. Co-contraction ratios were much higher in radial trials than ulnar (Radial: 1.20 ± 0.78, Ulnar: 0.28 ± 0.18, P < 0.05), suggesting greater FCU and ECU contribution to wrist joint stability in radial-ulnar movement. These findings highlight a greater complexity of wrist extensor function than has previously been reported in isometric work., Competing Interests: Declaration of Competing Interest The authors declare they have no conflicts of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The wrist extensors demonstrate an earlier fatigue onset than the wrist flexors. However, it is currently unclear whether fatigue induces unique changes in muscle activity or corticospinal excitability between these muscle groups. The purpose of this study was to examine how sustained isometric wrist extension/flexion maximal voluntary contractions (MVCs) influence muscle activity and corticospinal excitability of the forearm. Corticospinal excitability to three wrist flexors and three wrist extensors were measured using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation. Responses were elicited while participants exerted 10% of their maximal handgrip force, before and after a sustained wrist flexion or extension MVC (performed on separate sessions). Post-fatigue measures were collected up to 10-min post-fatigue. Immediately post-fatigue, extensor muscle activity was significantly greater following the wrist flexion fatigue session, although corticospinal excitability (normalized to muscle activity) was greater on the wrist extension day. Responses were largely unchanged in the wrist flexors. However, for the flexor carpi ulnaris, normalized MEP amplitudes were significantly larger following wrist extension fatigue. These findings demonstrate that sustained isometric flexion/extension MVCs result in a complex reorganization of forearm muscle recruitment strategies during hand-gripping. Based on these findings, previously observed corticospinal behaviour following fatigue may not apply when the fatiguing task and measurement task are different.

Background . The physical demands associated with patient handling activities have been well documented in healthcare. However, many activities contribute to the physical demands of caregivers. Our purpose was to evaluate upper extremity muscle activity and kinematics during intravenous (IV) pole interaction. Materials and methods . Muscle activity was measured from six muscles using surface electromyography and joint kinematics were measured using motion capture. Participants performed two IV pole tasks: loading an IV bag and a medical device onto the pole. Two poles were evaluated: a traditional IV pole and a redesigned pole with ergonomic considerations. Results . Cervical extensor activity was significantly greater for the bag task with the traditional pole (43.29 ± 5.10% maximal voluntary exertion) compared to the redesigned pole (28.55 ± 3.42% maximal voluntary exertion). Peak right shoulder flexion was reduced from 102.88° ± 32.42° with the traditional pole to 55.44° ± 19.59° with the redesigned pole. Conclusion . Interactions with a traditional pole are comparable to upper extremity muscle activity during manual patient handling transfers. The redesigned pole reduced shoulder flexion during bag attachment, leading to less time in an overhead posture. Caregivers frequently interact with IV poles and reducing the physical demands associated with pole use could aid in a reduction of musculoskeletal disorders.

Due to their stabilizing role, the wrist extensor muscles demonstrate an earlier onset of performance fatigability and may impair movement accuracy more than the wrist flexors. However, minimal fatigue research has been conducted at the wrist. Thus, the purpose of this study was to examine how sustained isometric contractions of the wrist extensors/flexors influence hand-tracking accuracy. While gripping the handle of a three-degrees-of-freedom wrist manipulandum, 12 male participants tracked a 2:3 Lissajous curve (±32° wrist flexion/extension; ±18° radial/ulnar deviation). A blue, circular target moved about the trajectory and participants tracked the target with a yellow circle (corresponding to the handle's position). Five baseline tracking trials were performed prior to the fatiguing task. Participants then exerted either maximal wrist extension or flexion force (performed on separate days) against a force transducer until they were unable to maintain 25% of their pre-fatigue maximal voluntary contraction (MVC). Participants then performed 7 tracking trials from immediately post-fatigue to 10 min after. Performance fatigability was assessed using various metrics to account for errors in position-tracking, error tendencies, and movement smoothness. While there were no differences in tracking error between flexion/extension sessions, tracking error significantly increased immediately post-fatigue (Baseline: 1.40 ± 0.54°, Post-fatigue: 2.02 ± 0.51°, P < 0.05). However, error rapidly recovered, with no differences in error from baseline after 1-min post-fatigue. These findings demonstrate that sustained isometric extension/flexion contractions similarly impair tracking accuracy of the hand. This work serves as an important step to future research into workplace health and preventing injuries of the distal upper-limb., (Copyright © 2020 Forman, Forman, Mugnosso, Zenzeri, Murphy and Holmes.)

Sudden disturbances (perturbations) to the hand and wrist are commonplace in daily activities and workplaces when interacting with tools and the environment. It is important to understand how perturbations influence forearm musculature and task performance when identifying injury mechanisms. The purpose of this work was to evaluate changes in forearm muscle activity and co-contraction caused by wrist perturbations during a dynamic wrist tracking task. Surface electromyography was recorded from eight muscles of the upper-limb. Participants performed trials consisting of 17 repetitions of ±40° of wrist flexion/extension using a robotic device. During trials, participants received radial or ulnar perturbations that were delivered during flexion or extension, and with known or unknown timing. Co-contraction ratios for all muscle pairs showed significantly greater extensor activity across all experimental conditions. Of all antagonistic muscle pairs, the flexor carpi radialis (FCR)-extensor carpi radialis (ECR) muscle pair had the greatest change in co-contraction, producing 1602% greater co-contraction during flexion trials than during extensions trials. Expected perturbations produced greater anticipatory (immediately prior to the perturbation) muscle activity than unexpected, resulting in a 30% decrease in wrist displacement. While improving performance, this increase in anticipatory muscle activity may leave muscles susceptible to early-onset fatigue, which could lead to chronic overuse injuries in the workplace.

Altered afferent input from the neck due to fatigue alters upper limb proprioception and is likely to impact upper limb performance accuracy. This study examined the effect of cervical extensor muscle (CEM) fatigue on eye-hand tracking accuracy in healthy participants. Twenty-four healthy right-handed individuals were randomly assigned to either a control or CEM fatigue group. Each participant performed a tracking task which required shoulder rotation to move a circular object to a square target on a touchscreen computer. The task was performed with vision of the target and with the target hidden. A prone lying position, CEM fatigue protocol required participants to hold a 2 kg weight against gravity with their head in a neutral posture. The control intervention rested for 5 min, in a prone position, with the head supported in a neutral posture. Participants performed 3 trials with vision and 3 without at 5 different time points: (1) pre-intervention (fatigue or control), (2) immediately post-intervention, (3) 5 min, (4) 10 min, and (5) 20 min post-intervention. There were significant differences between the target with vision and the hidden condition for both groups between pre- and post-fatigue trials in angle of trajectory (p = 0.0001), and distance from release point to the target (p = 0.0001). Significant differences occurred in the hidden target condition for the fatigue group immediately post fatigue (p = 0.018) for distance from release to the target. Neck muscle fatigue reduced the accuracy of an upper limb tracking task to a hidden target, suggesting that altered afferent input from the neck due to fatigue may impair body schema and result in decreased upper limb performance accuracy., (Crown Copyright © 2019. Published by Elsevier Ltd. All rights reserved.)

Forearm rotation (supination/pronation) alters corticospinal excitability to the biceps brachii, but it is unclear whether corticospinal excitability is influenced by joint angle, muscle length, or both. Thus the purpose of this study was to separately examine elbow joint angle and muscle length on corticospinal excitability. Corticospinal excitability to the biceps and triceps brachii was measured using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation. Spinal excitability was measured using cervicomedullary motor evoked potentials (CMEPs) elicited via transmastoid electrical stimulation. Elbow angles were manipulated with a fixed biceps brachii muscle length (and vice versa) across five unique postures: 1 ) forearm neutral, elbow flexion 90°; 2 ) forearm supinated, elbow flexion 90°; 3 ) forearm pronated, elbow flexion 90°; 4 ) forearm supinated, elbow flexion 78°; and 5 ) forearm pronated, elbow flexion 113°. A musculoskeletal model determined biceps brachii muscle length for postures 1-3 , and elbow joint angles ( postures 4-5 ) were selected to maintain biceps length across forearm orientations. MEPs and CMEPs were elicited at rest and during an isometric contraction of 10% of maximal biceps muscle activity. At rest, MEP amplitudes to the biceps were largest during supination, which was independent of elbow joint angle. CMEP amplitudes were not different when the elbow was fixed at 90° but were largest in pronation when muscle length was controlled. During an isometric contraction, there were no significant differences across forearm postures for either MEP or CMEP amplitudes. These results highlight that elbow joint angle and biceps brachii muscle length can each independently influence spinal excitability. NEW & NOTEWORTHY Changes in upper limb posture can influence the responsiveness of the central nervous system to artificial stimulations. We established a novel approach integrating neurophysiology techniques with biomechanical modeling. Through this approach, the effects of elbow joint angle and biceps brachii muscle length on corticospinal and spinal excitability were assessed. We demonstrate that spinal excitability is uniquely influenced by joint angle and muscle length, and this highlights the importance of accounting for muscle length in neurophysiological studies.

Purpose: Force variability is affected by environmental temperature, but whether the changes are from altered muscle temperature or proprioception are unclear. We tested how forearm muscle warming and cooling affected a force tracking task., Methods: Twelve males and four females completed evoked, maximal, and isometric wrist flexion contractions (0-30% maximal) during thermoneutral-, warm-, and cold-muscle conditions. Forearm muscle temperature was manipulated using neutral (~ 33 °C), hot (~ 44 °C), or cold (~ 13 °C) water circulated through a tube-lined sleeve. Evoked and voluntary contractions were performed before and after thermal manipulations., Results: Thermal manipulations altered contractile properties as evident in the twitch half-relaxation time, rate of force development, and duration (all P < 0.05), suggesting that muscle temperature was successfully altered. Changes in surface electromyography of the flexor carpi radialis root-mean-square amplitude and mean power frequency between temperature conditions (all P < 0.05) also indicate muscle temperature changes. No changes to root-mean-square error or variance ratio of the force trace were observed with muscle temperature changes (both P > 0.05). Muscle temperature changes did not have a consistent effect on coefficient of variation during each plateau of the staircase contraction., Conclusions: Our results suggest that the ability to perform a multi-plateaued isometric force task is not affected by changes to forearm muscle temperature. As the thermal manipulation was limited to the forearm, changes to hand temperature would be minimal, thus, proprioception in the wrist and hand was preserved allowing performance to be maintained. Therefore, modest changes to forearm muscle temperature are not likely to affect force variability if proprioception is maintained.

The purpose of this study was to examine forearm muscle activity during simultaneous execution of dual motor tasks; hand-gripping and wrist forces. Surface electromyography was recorded from eight muscles of the upper-limb: flexor carpi radialis, flexor carpi ulnaris, flexor digitorum superficialis, extensor carpi radialis, extensor carpi ulnaris, extensor digitorum, biceps brachii and triceps brachii. Participants were seated with their forearm supported in a neutral position with an adjustable force transducer placed on either the palmar or dorsal side of the hand (for palmar/dorsal forces). Participants performed trials of simultaneous handgrip and wrist forces of various magnitudes, ranging in intensity from 0 to 40% of their maximal voluntary contraction. Trials lasted 5 s and force and electromyography data were assessed. The wrist flexors provided greatest contributions to tasks dominated by palmar forces but exhibited very low muscle activity in dorsal dominant tasks. Wrist extensors were active at moderate-to-high levels across nearly all conditions and demonstrated greater activity than the wrist flexors during handgrip-dominant tasks. These findings suggest that the wrist extensors provide the greatest contribution to wrist stiffness in complex motor tasks, and highlight the importance of investigating forearm muscle recruitment strategies under dual task parameters., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

This study examined sex differences in head kinematics and neck muscle activity during sudden head perturbations. Sixteen competitive ice hockey players participated. Three muscles were monitored bilaterally using surface electromyography: sternocleidomastoid, scalene, and splenius capitis. Head and thorax kinematics were measured. Head perturbations were induced by the release of a 1.5-kg weight attached to a wire wrapped around an adjustable pulley secured to the participant's head. Perturbations were delivered in 4 directions (flexion, extension, right lateral bend, and left lateral bend). Muscle onset times, muscle activity, and head kinematics were examined during 3 time periods (2 preperturbation and 1 postperturbation). Females had significantly greater head acceleration during left lateral bend (31.4%, P < .05) and flexion (37.9%, P = .01). Females had faster muscle onset times during flexion (females = 51 ± 11 ms; males = 61 ± 10 ms; P = .001) and slower onset times during left lateral bend and extension. Females had greater left/right sternocleidomastoid and scalene activity during extension (P = .01), with no difference in head acceleration. No consistent neuromuscular strategy could explain all directional sex differences. Females had greater muscle activity postperturbation during extension, suggesting a neuromuscular response to counter sudden acceleration, possibly explaining the lack of head acceleration differences.

The cerebellum processes pain inputs and is important for motor learning. Yet, how the cerebellum interacts with the motor cortex in individuals with recurrent pain is not clear. Functional connectivity between the cerebellum and motor cortex can be measured by a twin coil transcranial magnetic stimulation technique in which stimulation is applied to the cerebellum prior to stimulation over the motor cortex, which inhibits motor evoked potentials (MEPs) produced by motor cortex stimulation alone, called cerebellar inhibition (CBI). Healthy individuals without pain have been shown to demonstrate reduced CBI following motor acquisition. We hypothesized that CBI would not reduce to the same extent in those with mild-recurrent neck pain following the same motor acquisition task. We further hypothesized that a common treatment for neck pain (spinal manipulation) would restore reduced CBI following motor acquisition. Motor acquisition involved typing an eight-letter sequence of the letters Z,P,D,F with the right index finger. Twenty-seven neck pain participants received spinal manipulation (14 participants, 18-27 years) or sham control (13 participants, 19-24 years). Twelve healthy controls (20-27 years) also participated. Participants had CBI measured; they completed manipulation or sham control followed by motor acquisition; and then had CBI re-measured. Following motor acquisition, neck pain sham controls remained inhibited (58 ± 33% of test MEP) vs. healthy controls who disinhibited (98 ± 49% of test MEP, P<0.001), while the spinal manipulation group facilitated (146 ± 95% of test MEP, P<0.001). Greater inhibition in neck pain sham vs. healthy control groups suggests that neck pain may change cerebellar-motor cortex interaction. The change to facilitation suggests that spinal manipulation may reverse inhibitory effects of neck pain.

Background: Medial knee collapse can signal an underlying movement issue that, if uncorrected, can lead to a variety of knee injuries. Placing a band around the distal thigh may act as a proprioceptive aid to minimize medial collapse of the knee during squats; however, little is known about EMG and biomechanics in trained and untrained individuals during the squat with an elastic band added., Hypothesis/purpose: To investigate the effects of the TheraBand® Band Loop on kinematics and muscle activity of the lower extremity during a standard barbell back squat at different intensities in both trained and untrained individuals., Study Design: Cross-sectional, repeated measures., Methods: Sixteen healthy, male, university aged-participants were split into two groups of eight, consisting of a trained and untrained group. Participants performed both a 3-repetition maximum (3-RM) and a bodyweight load squat for repetitions to failure. Lower extremity kinematics and surface electromyography of four muscles were measured bilaterally over two sessions, an unaided squat and a band session (band loop placed around distal thighs). Medial knee collapse, measured as a knee width index, and maximum muscle activity were calculated., Results: During the 3-RM, squat weight was unaffected by band loop intervention (p = 0.486) and the trained group lifted more weight than the untrained group (p<0.007). The trained group had a greater squat depth for both squat conditions, regardless of the band (p = 0.0043). Knee width index was not affected by the band during the eccentric phase of bodyweight squats in the trained (band: 0.76 ± 0.08, no band: 0.73 ± 0.08) or untrained group (band: 0.77 ± 0.70, no band: 0.75 ± 0.13) (p = 0.670). During the concentric phase, knee width index was significantly lower for 3-RM squats, regardless of group., Conclusion: Despite minimal changes in kinematics for the untrained group, increased muscle activity with the band loop may suggest that a training aid may, over time, lead to an increase in barbell squat strength by increasing activation of agonist muscles more than traditional, un-banded squats. Greater maximal muscle activity in most muscles during band loop sessions may provide enhanced knee stability via increased activation of stabilizing muscles., Level of Evidence: 3.

This pilot study compared a Nintendo Wii intervention to single-joint resistance training for the upper limb in children ages 7 to 12 with spastic hemiplegic cerebral palsy (CP). Children were randomized to Wii training (n= 3), or resistance training (n= 3) and trained at home for 6 weeks. Pre, post and 4-week follow-up measures were collected. Outcome measures were the Melbourne Assessment (MA2), and ABILHAND-Kids, and grip strength. Compliance, motivation and feasibility of each intervention was explored using daily logbook responses and questionnaires. Descriptive statistics were used. Three children improved in the MA2, two of which were in the Wii training group. Improvements in the ABILHAND-Kids were minimal for all participants. Grip strength improvements were observed in 3 participants, two of which were in the resistance training group. The Wii training group reported higher compliance and more consistently positive responses to motivation and feasibility questions. Therefore, Wii training may be an effective home-based rehabilitation strategy, and is worth exploring in a larger trial. Implications of Wii training in the context of motivation theory are discussed.

Objective: Mental rotation of objects and the frame of reference of those objects are critical for executing correct and skillful movements and are important for object recognition, spatial navigation, and movement planning. The purpose of this longitudinal study was to compare the mental rotation ability of those with subclinical neck pain (SCNP) to healthy controls at baseline and after 4 weeks., Methods: Twenty-six volunteers (13 SCNP and 12 healthy controls) were recruited from a university student population. Subclinical neck pain participants had scores of mild to moderate on the Chronic Pain Grade Scale, and controls had minimal or no pain. For the mental rotation task, participants were presented with an object (letter "R") on a computer screen presented randomly in either normal or backwards parity at various orientations (0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°). Participants indicated the object's parity by pressing "N" for normal or "B" for backwards. Each orientation for normal and backward parities was presented 5 times, and the average response time for all letter presentations was calculated for each participant, at baseline and 4 weeks later., Results: Both groups had overall improved response times from baseline to 4 weeks. Healthy participants had significantly improved response times compared to SCNP, both at baseline (P < .05) and 4 weeks (P < .05)., Conclusions: Healthy participants performed better than the SCNP group at both time points. Subclinical neck pain may impair the ability to perform a complex mental rotation task involving cerebellar connections, possibly due to altered body schema., (Copyright © 2016 National University of Health Sciences. Published by Elsevier Inc. All rights reserved.)