The effect of a task-specific training on upper limb performance and kinematics while performing a reaching task in a fatigued state

Frédérique Dupuis; Félix Prud’Homme; Arielle Tougas; Alexandre Campeau-Lecours; Catherine Mercier; Jean-Sébastien Roy

doi:10.1371/journal.pone.0297283

. 2024 Jan 22;19(1):e0297283. doi: 10.1371/journal.pone.0297283

The effect of a task-specific training on upper limb performance and kinematics while performing a reaching task in a fatigued state

Frédérique Dupuis ^1,², Félix Prud’Homme ^1,², Arielle Tougas ^1,², Alexandre Campeau-Lecours ^1,^2,³, Catherine Mercier ^1,², Jean-Sébastien Roy ^1,^2,^*

Editor: Aliah Faisal Shaheen⁴

PMCID: PMC10802943 PMID: 38252643

Abstract

Background

Fatigue impacts motor performance and upper limb kinematics. It is of interest to study whether it is possible to minimize the potentially detrimental effects of fatigue with prevention programs.

Objective

To determine the effect of task-specific training on upper limb kinematics and motor performance when reaching in a fatigued state.

Methods

Thirty healthy participants were recruited (Training group n = 15; Control group n = 15). Both groups took part in two evaluation sessions (Day 1 and Day 5) during which they performed a reaching task (as quickly and accurately as possible) in two conditions (rested and fatigued). During the reaching task, joint kinematics and motor performance (accuracy and speed) were evaluated. The Training group participated in three task-specific training sessions between Day 1 and Day 5; they trained once a day, for three days. The Control group did not perform any training. A three-way non-parametric ANOVA for repeated measures (Nonparametric Analysis of Longitudinal Data; NparLD) was used to assess the impact of the training (Condition [within subject]: rested, fatigued; Day [within subject]: Day 1 vs. Day 5 and Group [between subjects]: Training vs. Control).

Results

After the training period, the Training group significantly improved their reaching speed compared to the Control group (Day x Group p < .01; Time effect: Training group = p < .01, Control group p = .20). No between-group difference was observed with respect to accuracy. The Training group showed a reduction in contralateral trunk rotation and lateral trunk flexion in Day 2 under the fatigue condition (Group x Day p < .04; Time effect: Training group = p < .01, Control group = p < .59).

Conclusion

After the 3-day training, participants demonstrated improved speed and reduced reliance on trunk compensations to complete the task under fatigue conditions. Task-specific training could help minimizing some effects of fatigue.

Introduction

In recent years, there has been a growing interest in understanding the phenomenon of fatigue. Fatigue is a common experience in everyday activities and work, with potential consequences such as decreased performance, and reduced productivity [1–3]. It is recognized as a symptom that affects both physical and cognitive functions, leading to alterations in muscle function and the central nervous system’s ability to plan voluntary movement, and ultimately resulting in changes in movement control [4, 5]. These changes in movement control can increase the risk of injuries by impacting the mechanical loads on musculoskeletal structures, such as tendons, muscles, and cartilage [6]. The shoulder joint, being the most mobile joint of the body, is particularly vulnerable to fatigues, as its stability highly depends on neuromuscular control [4, 7].

Fatigue has been extensively studied as a symptom [4]; however, it remains crucial to identify strategies for preventing its detrimental consequences, especially for individuals exposed to repetitive tasks. If these detrimental consequences are associated with changes in motor control, one potential approach could involve implementing prevention interventions. In these adaptations to fatigue, evidence suggests involvement of various levels of the motor system, spanning from the spinal cord to the motor cortex [6, 8]. Optimizing motor control during tasks that pose a high risk of injury, such as those involving elevated arm positions, could prove to be a promising preventive measure [9]. This could be achieved through motor training interventions that promote motor learning, entailing repeated practice of context-specific motor tasks [8]. Motor training has been primarily used in sport-injury prevention programs to enhance performance and reduce injury rates [8, 10, 11]. Additionally, motor training has shown effectiveness in improving muscle recruitment patterns, even in tasks outside the context of sport-injury prevention [12–14]. It is believed to improve movement planning, strengthen internal representation, and reinforce feedforward control [12–14].

Based on these underlying mechanisms of motor training, we hypothesize that task-specific motor training could mitigate the adverse effects of fatigue (i.e., upper limb kinematic alterations and decreased performance) [10, 11, 15, 16]. However, to the best of our knowledge, no study has yet investigated this potential preventive strategy. Therefore, the primary objective of our study is to explore the impact of task-specific training on upper limb kinematics and motor performance during a reaching task performed in an elevated position under a state of fatigue. The choice of an elevated position reaching task is based on the understanding that it poses a heightened risk of shoulder injury with repeated execution [17].

Methods

Healthy participants were recruited between May 16^th and June 30^th, 2022, and randomly assigned to either the Training group or the Control group. Participants were aged between 18 and 30 years old, did not have any self-reported shoulder or neck pain/disability, and had no history of upper limb/spine fracture, surgery, or shoulder dislocation. The Sectorial Rehabilitation and Social Integration Research Ethics Committee of the CIUSSS-CN approved this study (2017–527) and written informed consent were obtained from every participant.

Both groups participated in two evaluation sessions, with a 5-day interval between them (i.e., Day 1 and Day 5). During these sessions, they performed the same reaching task under two conditions (rested and fatigued). Both evaluation sessions were conducted at the same time of the day, and all participants first performed the task in the rested condition, and then in the fatigued condition, after completing a shoulder fatigue protocol (Fig 1). During the reaching task, data on surface electromyographic (sEMG) activity, joint kinematics and motor performance were collected.

Reaching task

The reaching task was performed in a virtual reality environment using Unreal Engine (Epic games international, Unreal Engine, Switzerland). Participants wore HTC VIVE goggles (HTC corporation, VIVEPORT, Taoyuan City, Taoyuan County, Taiwan) that exposed them to the virtual environment. The task consisted of reaching five different targets (i.e., 5cm red radius ball) located around the participants in the virtual environment. They performed the task in a sitting position, the trunk free to move, and only their feet were fixed on the ground. The participants were asked to move naturally. Using a goniometer, the five targets were positioned prior to the experiment as follow: Target 1 = 90° of humeral elevation in the frontal plane (abduction), with 90° of humeral external rotation and elbow flexed at 90°; Target 2 = 90° of humeral elevation in the frontal plane (abduction) with the elbow extended; Target 3 = 120° of humeral elevation in the plane of the scapula (scaption) with the elbow extended; Target 4 = 120° of humeral elevation in the sagittal plane (flexion) with the elbow extended; and Target 5 = 140° of humeral elevation in the sagittal plane (flexion) with the elbow extended (S1 Fig). To complete the task, they had to reach each target 5 times in a random order, for a total of 25 targets reached (average 60 seconds). Every reaching movement started from the same initial position (i.e., starting position). To standardize this starting position, an additional target (5cm radius ball) was positioned in front of the participant, at 90° of humeral elevation (in the sagittal plane, elbow extended). Participants were required to return to this target between each reaching movement to initiate the release of the subsequent target.

The instruction given to the participants were to reach the targets as quickly, but also as accurately as possible using the most direct way through the targets. The participants held a controller in their dominant hand; it appeared to the participants as a virtual hand. In this virtual hand, they could see a 2cm radius ball on the palm. Participants were asked to place the 2cm radius ball directly through the 5cm radius target to succeed the reaching movement.

The participants’ perceived level of fatigue was assessed using the Borg Rating of Perceived Exertion Scale [18] both before and after each trial (10 points scale, 0 = no exertion and 10 = total exertion). One practice trial was performed before the beginning of the experiment.

Fatigue protocol

On both evaluation sessions, all participants performed a fatigue protocol before their second trial. The fatigue protocol used in this study has previously been validated and detailed by Ebaugh et al [19]. It consisted of three different tasks completed with the dominant arm: 1) manipulating screws on a wooden board for 2 minutes with the shoulders at 45° of flexion; 2) 20 repetitions of arm elevations in the sagittal plane holding a dumbbell; and 3) 20 repetitions of arm elevations in the scapular plane holding the same a dumbbell. The dumbbell used were 0.9 kg for women and 1.8 kg for men. The participants rated their perceived level of exertion every 30 seconds using the Borg Rating of Perceived Exertion Scale [18]. The three tasks of the fatigue protocol were repeated until the participant reached a perceived level of exertion of at least 8/10. This protocol was chosen as it has been shown to lead to decreased motor performance and kinematics alterations during reaching, as indicated by a previous study [20]. Therefore, it enables the evaluation of the potential effects of the task-specific training on these adaptations.

Task specific training

While the Control group only participated in the two evaluation sessions (Day 1 and Day 5), the Training group took part in three training sessions between Day 1 and Day 5 (training once a day during Day 2, 3, and 4). There is significant variability in the literature regarding motor training parameters targeting motor learning, but they typically involve task-specific practice with conscious attention to performing the appropriate movement [8]. Accordingly, during the training sessions, participants in the Training group performed the same task executed during evaluation sessions (task-specific training) [17, 18], five times using only the dominant arm. Altogether, the Training group completed the task 15 times between the two evaluation sessions, totaling 375 reaching movements. During a typical training session, they were instructed to focus on their accuracy for one trial (the most accurate performance without considering speed), on their speed for one trial (the fastest performance without considering accuracy) and then practice the combination of speed and accuracy for three trials. A minimum of two minutes rest periods were provided between each trial to prevent fatigue, which could be extended until participants rated their perceived level of exertion at 0 out of 10. The objective of the training was to let participants find and practice their own perceived effective strategy and reinforce their motor system ability to perform the task.

Measurements and outcomes

Performance was assessed using Unreal Engine, enabling us to track participants’ hand in a three-dimensional space with the controller. Performance data were extracted using custom software written in MATLAB. Performance data included reaction time, time to reach the targets and accuracy [2]. The reaction time was calculated from the moment the randomly released target appeared in the virtual environment to the moment the participant left the starting position to initiate the reaching movement. The time to reach the targets was calculated from the moment the participant left the starting position and reached the target (i.e., successfully placed the 2cm radius ball in the 5cm radius target). Accuracy was defined by 3 different variables. First, the initial angle of endpoint deviation (iANG) represented the initial trajectory of the hand. This angle was calculated using the shortest line between the starting position and the reaching target, and the line corresponding to the initial peak of acceleration [20]. It reflected movement planning, where a larger angle represents a larger error in movement planning. Second, the final error (fERR), measured as the arc distance between the ideal arrival point into the target reached (i.e., the most direct way) and the actual arrival point, reflected reaching accuracy. Third, the area under the curve (area) was calculated to represent to total movement error while reaching. It was calculated as the difference between the ideal trajectory (i.e., most direct way) and the actual trajectory used by the participants in the 3-dimensional space. More precisely, it is the summation of the rectangular trapezoids perpendicular to the ideal trajectory line and the actual trajectory line [20]. The mean values of the 25 reaching movements were calculated for every trial for analysis.

The second variable of interest was upper limb and trunk kinematics. It included joint angles at the trunk, sternoclavicular joint, shoulder, and elbow. Joint angles were measured using six inertial measurements units (IMUs) (MVN, Xsens Technologies, Enschede, Netherlands), positioned in accordance with Xsens sensors configuration at the trunk, head, sternum, dominant scapula, and dominant arm (i.e., arm and forearm). The IMU data were acquired at a sampling rate of 100Hz with a custom Matlab IMU acquisition software. The latter requires a calibration sequence consisting of a static position (arms alongside the body) and dynamic movements (raising the arm, flexing the trunk). The IMUs data were imported into MATLAB R2018a (The Math Works Inc., Natick, MA, USA) and data fusion was performed with a custom algorithm to obtain joint angles [21]. To describe the reaching movement, initial angles and final angles during the movement were calculated. Initial angles represent the angles before the beginning of the reaching movement, while waiting at the starting position. It reflects initial posture. Final angles were calculated when the targets were reached. It reflects movement strategy to reach the targets. The movement of interest were flexion/extension, rotations and lateral flexions at the trunk, elevation/depression at the sternoclavicular joint, elevation, plane of elevation, and rotation at the shoulder, and flexion/extension at the elbow. Mean values of the twenty-five reaching movements were calculated and used for statistical analysis.

Muscles fatigue assessment

To monitor the presence of fatigue when performing the reaching task in the fatigued state, wireless sEMG sensors (Delsys Trigno, USA) were placed on the anterior and middle deltoids and on the upper trapezius of the dominant arm. These muscles were chosen because they are the main agonists in shoulder elevation [20]. The skin was cleaned using alcohol prior to electrode placement, and the sensors were positioned according to The Surface EMG for Noninvasive Assessment of Muscles (SENIAM) [22]. Muscle activity was recorded using Delsys EMGworks^® Acquisition software (sampling rate: 1925.93Hz). All sEMG signals were processed using custom software written in MATLAB R2013a (The MathWorks Inc., Natick, Massachusetts, United States). sEMG signals were digitally filtered off-line with a zero-lag 4^th order Butterworth Filter (band-pass 20–450Hz) [20]. The power spectrum density was computed from the squared Fast-Fourier Transform. Fatigue was characterized as a downward shift in the sEMG power spectrum (i.e., median power frequency [MDF]), associated with an increase in sEMG signal amplitude [23].

Statistical analyses

Characteristics of both groups were compared using independent t-tests and χ2. For all variables, including the MDF and the sEMG amplitude of each muscle, a Nonparametric Analysis of Longitudinal Data (NparLD) was conducted using a three-way non-parametric ANOVA for repeated measures (Condition [within subject]: rested, fatigued; Day [within subject]: Day 1 vs. Day 5 and Group [between subjects]: Training vs. Control) was used. NparLD analyses are particularly relevant for small samples and do not require normality of the data [24]. Non-parametric post-hoc analyses were conducted to detail the differences when a significant interaction was present. Statistical analyses were conducted out using R 4.1.0 [24]. The significance level was set at 0.05.

Results

Thirty participants were recruited and assigned to either the Training group (n = 15) or the Control group (n = 15). There was no statistically significant between-group difference (p>.05) for baseline characteristics (Table 1).

Table 1. Participants characteristics.

Characteristics	Training group (n = 15)	Control group (n = 15)
Age (years; mean +/- SD)	26.3±3.5	24.1±3.2
Sex (N female)	8	7
Dominance (N right-handed)	15	15
Weight (Kg; mean +/- SD)	69.5±9.6	66.3±12.7
Height (cm; mean +/- SD)	171.9±10.7	171.9±9.9

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Perceived level of exertion and fatigue protocol

Mean perceived level of exertion after completing the task during the rested condition at Day 1 was 2.5±1.0/10 for the Training group and 2.9±1.4/10 for the Control group. There was a significant decrease for both groups of the mean perceived level of exertion in the rested condition between Day 1 and Day 5 (Day effect p < .01). The mean ratings decreased to 1.9±1.1/10 and 2.1±1.9/10 for the Training and the Control group, respectively. The fatigue protocol was performed for a mean duration of 298 sec on Day 1 and of 320 sec on Day 5 and led to a mean perceived level of exertion of 8/10 on both days. There was no between-group difference for the fatigue protocol duration or level of exertion after the protocol. As expected, both groups significantly perceived the task more demanding after performing the fatigue protocol, during the fatigued condition, with a mean perceived level of exertion of 7.5±1.2/10 for the Training group and 7.9±1.1/10 for the Control group. However, the mean perceived level of exertion in fatigued condition did not change between days (p = .13), regardless of the group.

Muscles fatigue assessment

After the fatigue protocol, significant EMG signs of fatigue were identified among the agonist muscles (Condition effect p < .01) as characterized by a significant increase in Anterior deltoid, Middle deltoid and the Upper trapezius sEMG amplitude and a significant decrease of their MDF on both days during the fatigued condition. There was no difference between the days of assessment, or the groups, on muscle fatigue (Time effect and Day x Group interaction p>.43).

Motor performance

Performing the task in a fatigued state led to decreased motor performance. There was a significant increase of the iANG (Condition effect, p = .02), fERR (Condition effect, p < .01) and of the time to reach the targets (p < .01) in both groups while experiencing fatigue compared to baseline. We did not identify any Day x Group interaction (p>.44) for accuracy data (i.e., iANG and fERR), meaning that the task-specific training did not decrease the impact of fatigue on movement accuracy. However, there was a significant difference between the groups in the evolution of movement speed across days (Day x Group interaction p < .01). The Training group showed improvement of their speed in both conditions in Day 5 (rested and fatigued), compared to baseline (post-hoc analysis: Training group = Time effect [Condition 1 x Day] p < .01; [Condition 2 x Day] p < .01), while the Control group did not show such improvement between the days (post-hoc analysis Control group = Time effects [Condition 1 x Day/Condition 2 x Day]: p>.20).

Kinematics

As expected, fatigue impacted kinematics in both groups. During task performance under a fatigued state, both groups showed significant alterations in their initial posture (initial angles), characterized by increased trunk contralateral rotation and extension (Condition effect, p < .01). Participants also used increased shoulder external rotation (Condition effect, p < .01), decreased shoulder elevation combined with a plane of elevation more along the frontal than the sagittal plane (Condition effect, p < .01, Fig 2A) and an increased sternoclavicular elevation (Condition effect, p < .01, Fig 2B) compared to the rested condition. Final angles also reflected a change in the reaching strategy under the fatigued condition. Increased trunk contralateral final rotation (Condition effect, p < .01) and trunk lateral flexion (Condition effect, p = .03) were observed in both groups. Additionally, a higher shoulder external rotation final angle was seen under the fatigued condition, accompanied by an increased use of sternoclavicular elevation (Condition effect, p < .01) and elbow flexion (Condition effect, p = .03).

A significant between-group difference was observed in the changes between Day 1 and 5 for trunk compensations (Group x Day interaction p < .04 (Fig 2C and 2D). Post-hoc analyses revealed that the Training group showed a reduction in contralateral trunk rotation (Condition 2 x Day: Time effect p < .01) and lateral trunk flexion (Condition 2 x Day: Time effect p < .01) between the days under fatigue. They were able to maintain a more upright trunk posture when fatigued after their training sessions (Day 5). The Control group’s trunk values remained unchanged between the days under the fatigued condition (Condition 2 x Day: time effect p>.59). There was also a significant Group x Day interaction (p = .02) for trunk contralateral rotation final angles, but post-hoc analyses revealed there was no significant Time effect for either the Training or the Control group (p>.76).

Discussion

This study aimed at exploring the effect of task specific training on upper limb adaptations to fatigue during a task involving elevated arm positions [20]. Investigating the potential preventive effects of motor training interventions, such as a task-specific training, represents an initial step toward understanding and offering preventive modalities for musculoskeletal injuries, especially those affecting the shoulder, which are highly prevalent and impose a significant burden worldwide [25]. Some people are frequently exposed to fatiguing tasks, whether in repetitive work or sports, and it is essential to comprehend how to mitigate the risks factors associated with the presence of fatigue.

The initial alterations observed in motor performance and kinematics under fatigue were similar to those noted in a previous study [20]. These adaptations included a decrease in movement accuracy and speed, along with an increased utilization of trunk and sternoclavicular movement. We also noticed reduced shoulder elevation and increased elbow flexion. The task-specific training resulted in improved performance for the Training group, as they exhibited faster reaching movements under fatigue without compromising accuracy. The training also had a significant impact on kinematics, particularly in reducing compensatory trunk movements. The trunk angles, such as initial rotation and lateral flexion angles, decreased following training, even when experiencing the same level of fatigue [EMG signs and perceived level]. These observed trunk adaptations under fatigue were defined as "compensations", assuming that the increase in trunk extension, contralateral flexion, and rotation aimed to achieve the targets with less shoulder elevation [20].

It appears that participants in the Training group relied less on trunk compensation to complete the task after the training period. It can be hypothesized that the kinematic changes observed after the task-specific training reflect an enhanced capacity of the participants to tolerate the physical symptoms of fatigue in main shoulder agonists (e.g., symptoms and signs of fatigue), thereby delaying the onset of trunk compensations. There are potential mechanisms that could explain this capacity, such as the acquisition of a higher motor variability after the training period [26–28]. This may include increased variability in movement patterns, muscle activation, and redistribution of neural drive among agonist muscles [26]. These adaptations have been observed in individuals with extensive experience in repetitive manual tasks [26], and are believed to result from motor learning, and aiming at maintaining performance during demanding tasks. Other known potential changes in the upper limb subsequent to motor training include enhanced muscle activation in association with improved performance, reduced variability in motor unit discharge, enhanced force steadiness, and improved muscle coordination [27, 28].

Current knowledges suggest there are various mechanisms that may explain the observed changes following task-specific training, primarily related to the development of more efficient motor control. All of these mechanisms might have helped in mitigating the effects of fatigue on the primary shoulder muscles, increasing endurance, and reducing reliance on trunk compensation [26]. While the objective of this exploratory study did not involve investigating underlying mechanisms, such as variability or EMG activity redistribution, it would be interesting for future research to delve into these mechanisms concerning the impact of motor learning and fatigue.

In this study, performance improvement after task-specific training was characterized by enhance speed without compromising accuracy. This improvement could be related to the kinematic changes observed following the training period. Upper limb accuracy (i.e., shoulder movement and hand deviation) depends on an accurate prediction of trunk kinematics and is affected by miscalculated disturbance at the trunk [29]. Assuming that the development of trunk compensations in the fatigued state acted as trunk disturbances, the ability to reduce these compensations after the training period might have helped participants in the training group to improve upper limb performance. It is somewhat surprising that accuracy did not improve after the training period. One possible explanation for that is that the considerable variability (SD in movement trajectory and accuracy) limited the ability to detect any changes in accuracy. This might be related to the high level of difficulty of the task.

Strengths and limitations

To our knowledge, this is the first study to explore the effect of a task-specific training on motor performance and kinematics while experiencing fatigue. Although it is well-known that fatigue has deleterious effects, such as decreased performance and the potential development of musculoskeletal injuries [4, 7], minimal effort has been made to date to understand how to prevent these effects. Task-specific training is already extensively used in rehabilitation settings for populations with disabilities, such as musculoskeletal injuries and neurological conditions, as they have been shown to be effective for reducing pain [9, 30], improving functional outcomes [9, 30], and even reducing perceived level of fatigue [31]. Exploring the preventive, rather than curative, potential effects of task-specific trainings is a unique contribution to the literature. However, as an exploratory study, we acknowledge the limitations inherent in the study design, and its measurements, which should be mentioned. As we did not identify any study that previously investigated the potential protective effect of a task-specific training on the impact of fatigue, the chosen parameters may not be optimal. It is usually recognized that a high number of repetitions are needed to induce changes in motor control among people with disabilities, with emphasis on conscious attention on the movement performed [9, 31]. Based on these evidence, we included many repetitions performed over a period of three days [32], with conscious focus on movement quality (accuracy) and efficacy (speed). This training exposure seems sufficient, since studies have shown that it is possible to induce motor control changes (i.e., selectively activate different muscle subdivisions to correct scapular posture) after just an hour of training [26]. However, there is not enough literature on this specific subject to confirm that parameters were optimized. It should also be considered that the subjects in this study were young and healthy. Given that factors such as age, gender and the presence of pain can influence motor learning and movement [26, 32], these findings may not apply to all populations. Looking to the research ahead, it will be interesting to investigate further the mechanisms underlying the changes following a task-specific training and performance in the presence of fatigue, and to determine if these changes can be maintained over time.

Conclusion

Task-specific training minimized some of the compensations associated with upper-limb reaching in a fatigue-state. Following the 3-day training, performance improved, and participants relied less on trunk compensation to complete the task under fatigue. Task-specific training could help minimize the deleterious effects of fatigue when performing repetitive tasks.

Supporting information

S1 Fig. Experimental setup.

Top left: positions of the targets relative to the participant (Target 1 = 90° of humeral abduction and 90° of external rotation, elbow flexed at 90°, Target 2 = 90° of shoulder abduction, elbow extended, Target 3 = 120° of shoulder scaption, elbow extended, Target 4 = 120° of shoulder flexion, elbow extended and Target 5 = 140° of shoulder flexion, elbow extended. Bottom left: vision of the participant in the virtual reality environment. Right: A left-handed participant in initial position.

(DOCX)

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Acknowledgments

The research team would like to thank Dr Jean Leblond for his help with statistical analyses.

Data Availability

Data cannot be shared publicly because of ethical restrictions. Data are available from the Lyne Martel, Ethics Committee (contact via lyne.martel2.ciussscn@ssss.gouv.qc.ca) for researchers who meet the criteria for access to confidential data.

Funding Statement

This study was funded by the Natural Sciences and Engineering Research Council of Canada (RGPIN-2023-04929). Frederique Dupuis is supported by a scholarship from the Canadian Institute of Health Research (CIHR). Jean-Sebastien Roy is supported by salary awards from Fonds de recherche Québec – Santé (FRQS) and Catherine Mercier holds the Canada Research Chair in Sensorimotor Rehabilitation and Pain and the University Laval Research Chair in Cerebral Palsy. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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PLoS One. doi: 10.1371/journal.pone.0297283.r001

Decision Letter 0

Aliah Faisal Shaheen

31 Oct 2023

PONE-D-23-24819The effect of a task-specific training on upper limb performance and kinematics while performing a reaching task in a fatigued statePLOS ONE

Dear Dr. Roy,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Specifically, the reviewers have noted that the rationale for conducting the study and this setup is not always aligned with the introduction and discussion. In addition, more clarity is needed in reporting - potentially met by adding more figures and tables that illustrate the setup and results as well as reviewing the language used.

Please submit your revised manuscript by Dec 15 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Aliah Faisal Shaheen

Academic Editor

PLOS ONE

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“This study was funded by the Natural Sciences and Engineering Research Council of Canada (RGPIN-2023-04929). Frederique Dupuis is supported by a scholarship from the Canadian Institute of Health Research (CIHR). JSR is supported by salary awards from Fonds de recherche Québec – Santé (FRQS) and CM holds the Canada Research Chair in Sensorimotor Rehabilitation and Pain and the University Laval Research Chair in Cerebral Palsy.”

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Reviewer #1: Partly

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: No

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Overall comments. The manuscript is interesting and novel. But it is not clear to me how that reaching task could represent athletic or daily movements. In the introduction, the authors discussed the importance of motor learning to improve the insurance of fatigue and to avoid consequent possible pathologies. But it is not clear to me the practical application of the specific testing, fatigue protocol, and training. It could be better argued in the discussion section, that is in fact too short. It contains a poor description of the obtained results, supported by few comparisons with other studies. Finally, in the manuscript there are some typos and unusual expressions that must be corrected. The authors should pay attention to the manuscript details.

Lines 82-106: I suggest changing the order of the Introduction. Lines 94-106 describe the general effect of fatigue on motor control and performance, and they could be placed before lines 82-91, that are more specific for the upper limbs. Lines 91-93 could be placed before the study aims.

Lines 83-87: The explicit reference to their previous work is unnecessary.

Lines 133-136: I strongly suggest reporting angles only according to the anatomical planes (sagittal, frontal, transversal), so Target 1 and Target 3 position should be expressed as the combination of flexion/extension, adduction/abduction, and rotation of the shoulder and elbow. In addition, I find necessary to provide a figure that shows (or represent) the subject and targets positioning.

Lines 145-147: I suggest providing a reference for Borg RPE Scale interpretation.

Lines 150-153: There is no description of the fatigue protocol. The reference to another paper could not be enough. I strongly suggest adding information about the fatigue protocol, to be exhaustive. In addition, how did the author assess the Borg RPE value? How many times did they asked it to the subjects? Which was the cadence of the evaluations? I found it difficult to understand without the description of the fatigue protocol.

Line 153: The explicit reference to their previous work is confounding, as it seems like they are referring to a previous section of the current manuscript.

Line 183-184: Did the authors measured the duration of training and testing session? How long was, on average, the rest period that subjects considered necessary to avoid fatigue?

Lines 191-192: How was the beginning of the movement computed? Was it defined as the displacement from a baseline? Was it computed by the custom software or obtained from IMUs or from an onset of EMG data?

Lines 194-196: This part is not clear to me. How did the authors measure the angles to assign the scores? I believe more details could help for understanding.

Lines 201-202: There is a lack of information. The reference to the previous study of the authors is not exhaustive.

Lines 204-220: I suggest listing all the measurement methods one after the other. Thus, the authors could place these lines right after Muscles fatigue assessment paragraph.

Lines 187-203: I suggest moving these lines after the measurement methods, before Task specific training.

Line 224: I suggest to explicit the meaning of the NparLD, the software or package the authors used for statistics.

Line 237: All the numbers should be expressed with the same number of digits. In this case: 2.5 ± 1.0.

Lines 256, 258, 263-265, 269-270, 274-275, 277, 285, 287: All the p-values reported appear with different number of digits. The authors should select the number of digits they want to display for p-values and be coherent for the entire manuscript.

Lines 267-268: It would be better to refer to Condition 2 as fatigued condition to improve readability.

Lines 272-273, 279: It is better to introduce the figures in a numeric order (Figure 1.1, Figure 1.2, and so on).

Lines 292: The explicit reference to their previous work is confounding, as it seems like they are referring to a previous section of the current manuscript.

Lines 331-335: The first sentence sounds like a limitation of the study. In addition, which contribute was provided by the measurements of EMG in this protocol? What would have happened if EMG results were significant? Would it become a primary objective?

Lines 338-339: How is the upper limb accuracy affected by miscalculated disturbance at the trunk. An explanation could improve the understanding more than a reference.

Lines 359-360: How did the authors decide the number of tasks, trials, training days, repetitions in the training days, if there is no past literature on the same topic? Did they perform pilot studies?

Reviewer #2: PONE-D-23-24819 Review commends:

This study aimed to investigate the impact of task-specific training on upper extremity kinematics and motor performance under fatigue. Thirty healthy participants were divided into a Training group and Control group, both evaluated for reaching tasks under rested and fatigued conditions. The Training group, after three days of training, exhibited improved speed and reduced trunk compensation when fatigued, indicating that task-specific training can mitigate the effects of fatigue.

1. Additional figures and tables are needed to provide a clearer description of the experimental setup, procedure, and outcome measurements. This would enhance the comprehensibility of the study for the audience.

2. Line 322: Author reference that motor variability may result from motor learning that aimed at maintaining performance during a repetitive demanding task. Have you assessed the difference in the motor variability between Training group and Control group? Did they develop those variability during the 3-day training?

3. Did Training group consistently practice the same reaching movement during the 3-day training? It is noteworthy that there is no Day * Group interaction regarding accuracy, this is surprising, does author have any explanation for this observation?

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Reviewer #1: No

Reviewer #2: No

**********

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PLoS One. 2024 Jan 22;19(1):e0297283. doi: 10.1371/journal.pone.0297283.r002

Author response to Decision Letter 0

14 Nov 2023

• Thank you for your comments. They have contributed to improving the quality of the manuscript. In light of the constructive feedback received, we have made several changes in the introduction and the discussion. These changes aim to strengthen the argument for the relevance of this study in relation to the burden of musculoskeletal injury and the risks associated with fatigue. In the clean copy file, we have also made major revisions related to the language and sentence structure to further enhance the manuscript.

• Please find below the specific changes we made in response to each comment.

• Thank you for this suggestion. The introduction has been revised, with several changes made to the order and content. We believe this new version of the introduction is now more reader friendly.

Lines 83-87: The explicit reference to their previous work is unnecessary.

• We removed this sentence.

• We added a figure of the experimental design (Figure 1, Line 121), as well as a figure of the experimental setup (in supplementary file, Figure S1, Line 136).

Lines 145-147: I suggest providing a reference for Borg RPE Scale interpretation.

• The suggested changes have been made, with references added to lines 145 to 147, and lines 155 to 160. We also added precisions related to the use of the Borg Scale: The participants rated their perceived level of exertion every 30 seconds using the Borg Rating of Perceived Exertion Scale. The three tasks of the fatigue protocol were repeated until the participant reached a perceived level of exertion of at least 8/10, Line 155.

• We have included additional information to help readers comprehend the fatigue protocol performed and the methods used to evaluate the level of exertion. We added the following sentence, line 151-160: It consisted of three different tasks completed with the dominant arm: 1) manipulating screws on a wooden board for 2 minutes with the shoulders at 45° of flexion; 2) 20 repetitions of arm elevations in the sagittal plane holding a dumbbell; and 3) 20 repetitions of arm elevations in the scapular plane holding the same a dumbbell). The dumbbell used were 0.9 kg (2 pounds) for women and 1.8 kg (4 pounds) for men. Please see the revised version of the ‘’Fatigue protocol’’ section.

Line 153: The explicit reference to their previous work is confounding, as it seems like they are referring to a previous section of the current manuscript.

• We have rephrased this section to prevent any confusion. We used ‘’in a previous study’’ instead of ‘’we previously showed that…’’’.

Line 183-184: Did the authors measured the duration of training and testing session? How long was, on average, the rest period that subjects considered necessary to avoid fatigue?

• We acknowledge that the duration of both the training and testing sessions was not precisely monitored. Regarding the testing sessions, one trial consisted of 25 reaching movements, which, on average, took 60 seconds to complete. This information has been added to the ‘’Reaching task’’ section of the manuscript, line 135. However, the duration of the training session varied as the requirement for ‘’speed’’ was not consistent throughout. Consequently, it is not feasible to accurately determine the length of the training sessions. Our focus was more on the number of repetitions than on the length of the sessions. Still, we recognize the importance of reporting the total exposition to the task. In future studies, we will ensure to include this information.

• We also did not monitor the exact duration of the rest period for each participant between the trials. To prevent fatigue, we ensured that each participant had a minimum of 2 minutes of rest between trials. However, the actual duration of the rest period varied for each participant based on the time needed to return to a ‘’perceived level of exertion of 0/10’’. This was determined based on their self-reported perceived level of exertion, which was inquired every 30 seconds. We have included this information in the ‘’Task specific training’’ section, line 155-160.

• We realized that the confusion arose due to the lack of introduction regarding the standardization of the ‘’initial position’’. To clarify, the initial position consisted of a 5cm radius target that participant were required to reach between movements. This setup allowed us to monitor the position of the hand (with the controller as described) relative to that initial position. We have included this information in the ‘’Reaching task’’ section, line 135-144 on the clean copy.

• We used the data obtained from the controller to track the hand’s position relative to the initial position in the virtual environment, enabling us to determine when the participant initiated the reaching movement.

• The initiation of the movement was computed through a custom-written Matlab program, utilizing the data collected with Unreal Engine. This information is presented in ‘’Measurements and outcomes’’ section. We made few changes to clarify, line 178-181 of the clean copy: Performance was assessed using Unreal Engine, enabling us to track participants’ hand in a three-dimensional space with the controller. Performance data were extracted using custom software written in MATLAB.

Lines 194-196: This part is not clear to me. How did the authors measure the angles to assign the scores? I believe more details could help for understanding.

• We added the following sentence to offer additional details: This angle was calculated using the shortest line between the initial position and the reaching target, and the line corresponding to the initial peak of acceleration. Line 186-188.

Lines 201-202: There is a lack of information. The reference to the previous study of the authors is not exhaustive.

• We have included the following sentence to provide a more comprehensive explanation, avoiding a reference to the previous study: (…) is the summation of the rectangular trapezoids perpendicular to both the ideal trajectory line and the actual trajectory line. Line 194 to 196 of the clean copy. We hope this clarification is helpful.

Lines 204-220: I suggest listing all the measurement methods one after the other. Thus, the authors could place these lines right after Muscles fatigue assessment paragraph. Lines 187-203: I suggest moving these lines after the measurement methods, before Task specific training.

• We have made both modifications. Thank you.

Line 224: I suggest to explicit the meaning of the NparLD, the software or package the authors used for statistics.

• We have added the following sentence in the “Statistical analysis” section: (…) a Nonparametric Analysis of Longitudinal Data (NparLD) was conducted using a three-way non-parametric ANOVA for repeated measures (…).

• We have also included information about the software used for statistical analysis.

Line 237: All the numbers should be expressed with the same number of digits. In this case: 2.5 ± 1.0.

• Thank you, we have made the necessary corrections throughout the manuscript.

• Done.

Lines 267-268: It would be better to refer to Condition 2 as fatigued condition to improve readability.

• Done. We also made this change throughout the manuscript.

Lines 272-273, 279: It is better to introduce the figures in a numeric order (Figure 1.1, Figure 1.2, and so on).

• Done.

Lines 292: The explicit reference to their previous work is confounding, as it seems like they are referring to a previous section of the current manuscript.

• We replaced ‘’we previously showed’’ with ‘’a previous study showed’’.

• The objective of using EMG in this study was to confirm the presence of fatigue when performing the task in the fatigued state, as experimental sessions were conducted on two separate days. The aim was to ensure that the level of fatigue present in the main agonist muscles remained consistent across both days of investigation. We anticipated minimal changes in EMG fatigue indicators due to the nature of intervention and the criteria for terminating the fatigue protocol. Several factors may have influenced the presence of fatigue between the two days. Consequently, we considered it necessary to monitor the presence of fatigue through EMG sensors. In the event of any disparity between the two days, it would have been challenging to compare them directly, considering the uncertainty regarding the cause of the differences.

• Given this, if we had observed significant changes in the EMG, it would not have been the primary objective. This is due to the challenge of discerning whether these changes were a result of the training or other influencing factors.

• However, we believe that a few elements contributed to this confusion for the reader, prompting us to make some corrections:

o In the methods section, muscle fatigue assessment, we changed: ‘’To assess the presence of fatigue, wireless surface (…) for “To monitor the presence of fatigue when performing the reaching task in the fatigued state during the two evaluation sessions (i.e., days), wireless sEMG sensors (Delsys Trigno, USA) were placed on the anterior and middle deltoids and on the upper trapezius of the dominant arm. (…). Line 216 of the clean copy.

o In the muscle assessment results section, we changed this sentence ‘’There was no effect of the Task-specific training program on muscle fatigue (Day x Group interaction p>.43).’’ for the following: ‘’ There was no difference between the days of assessment, or the groups, on muscle fatigue (Time effect and Day x Group interaction p>.43).’’ Line 263-264

o We have revised the section of the discussion identified by the reviewer (line 331-335), as we acknowledge the potential confusion that could arise when discussing these mechanisms in relation to our EMG data. Please refer to the updated section for further details.

Lines 338-339: How is the upper limb accuracy affected by miscalculated disturbance at the trunk. An explanation could improve the understanding more than a reference.

• We have included the following information in the Discussion: Line 348-350 Upper limb accuracy (i.e., shoulder movement and hand deviation) depends on an accurate prediction of trunk kinematics and is affected by miscalculated disturbance at the trunk. Additionally, we have added the following sentence: ‘’These observed trunk adaptations under fatigue were defined as "compensations," assuming that the increase in trunk extension, contralateral flexion, and rotation aimed to achieve the targets with less shoulder elevation.’’ Line 320-322.

• We did not conduct a pilot study, but we pre-tested our protocol on members of our team. We selected the parameters based on motor control programs described in previous rehabilitation intervention studies, as they represent the available evidence. However, as you mentioned, these studies are not directly related to our topic but share similar aims. We have recognized this limitation in the “Limitations” section.

Reviewer #2: PONE-D-23-24819 Review commends:

• We added a figure of the experimental design (Figure 1, Line 121), as well as a figure of the experimental setup (in supplementary file, Figure S1, Line 136).

• No, we have not. To the best of our knowledge, this study was the first to evaluate the potential effects of such a prevention program on fatigue consequences. Hence, we initially did not include any measurement or analysis in the protocol to address this question. Our primary aim was to explore the potential impact on kinematics and motor performance, without delving into detailed mechanistic objectives. Nevertheless, based on these results, it would be interesting to design a study with appropriate measurements to further investigate this hypothesis. We added included elements in the discussion: While the objective of this exploratory study did not involve the investigation of underlying mechanisms, such as variability or EMG activity redistribution, it would be of interest for future research to delve into these mechanisms concerning the impact of motor learning and fatigue. Line 340-342 of the clean copy.

• Yes, they performed the same reaching movement. One potential explanation could be the high variability in accuracy within each reaching movement for individual participants. The considerable standard deviations might have limited our ability to detect a significant difference. This variability can be related to the task itself, as reaching in a virtual 3D environment can be challenging. We have added the following sentences at the end of this section in the discussion: ‘’ It is somewhat surprising that accuracy did not improve after the training period. One possible explanation for that is the considerable variability (SD in movement trajectory and accuracy) limited the ability to detect any changes in accuracy. This might be related to the high level of difficulty of the task. ‘’ Line 353-356

Attachment

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PLoS One. doi: 10.1371/journal.pone.0297283.r003

Decision Letter 1

Aliah Faisal Shaheen

5 Dec 2023

PONE-D-23-24819R1The effect of a task-specific training on upper limb performance and kinematics while performing a reaching task in a fatigued statePLOS ONE

Dear Dr. Roy,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please ensure that you address discrepancies between the versions submitted and make sure that the final version addresses all the comments (previous and new) suggested by the reviewers.

Please submit your revised manuscript by Jan 19 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Aliah Faisal Shaheen

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

**********

6. Review Comments to the Author

Reviewer #1: Overall comments. The introduction has undergone significant enhancement. The study's objective has been explicitly articulated. The discussion is now more focused on the results and has been augmented with pertinent information. I would like to access the supplementary material of the article to view the explanatory images related to the exercises conducted in the study. Additionally, I have observed that the version of the manuscript with Track Changes does not precisely match the one without Track Changes. Some sentences in the text still require changes.

Lines 84-85: I suggest re-formulating this in a more scientific language.

Lines 86-88: I suggest adding a reference here.

Lines 88-90: The sentence is repetitive. You may remove “that reduce the occurrence of such changes in a fatigued state” (lines 89-90).

Lines 98-99: I suggest adding a reference here.

Lines 129-133: I do think it is necessary to express angles using joint anatomical planes, in this case referred to the shoulder or elbow, avoiding expression such as humeral abduction and rotation (Target 1), shoulder scaption (Target 3) by expressing them as combination of sagittal and frontal plane movements.

Line 133: Unfortunately, I cannot see the supplementary file.

Line 136-138: The description of the starting point should be improved. The sentence is not clear and fluent, more confusing than explanatory. The verb “to reach” is repetitive.

Lines 153: Is the closing parenthesis at the end of the sentence an error?

Lines 153-154: I think it is unnecessary to express dumbbell weight in pound, as measurement units must be expressed according to the International System of Units guidelines.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

**********

PLoS One. 2024 Jan 22;19(1):e0297283. doi: 10.1371/journal.pone.0297283.r004

Author response to Decision Letter 1

11 Dec 2023

Lines 84-85: I suggest re-formulating this in a more scientific language.

• Done

Lines 86-88: I suggest adding a reference here.

• Done, the reference added summarizes the current state of knowledge on fatigue.

Lines 88-90: The sentence is repetitive. You may remove “that reduce the occurrence of such changes in a fatigued state” (lines 89-90).

• Removed as suggested.

Lines 98-99: I suggest adding a reference here.

• References 12 to 14 should have been placed after this sentence; consequently, they were relocated accordingly.

• The planes of movement were added as suggested. However, we believe that some readers would prefer the anatomical angles, so we decided to keep this information within brackets.

Line 136-138: The description of the starting point should be improved. The sentence is not clear and fluent, more confusing than explanatory. The verb “to reach” is repetitive.

• We made some modifications to improve the description as follow:

• ‘’ To standardize this starting position, an additional target (5cm radius ball) was positioned in front of the participant, at 90° of humeral elevation (in the sagittal plane, elbow extended). Participants were required to return to this target between each reaching movement to initiate the release of the subsequent target.’’

Lines 153: Is the closing parenthesis at the end of the sentence an error?

• Yes, it is, thank you for noticing.

Lines 153-154: I think it is unnecessary to express dumbbell weight in pound, as measurement units must be expressed according to the International System of Units guidelines.

• We agree, we removed this additional information.

Attachment

Submitted filename: Response to reviewer-11dec2023.docx

Click here for additional data file.^{(259.8KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0297283.r005

Decision Letter 2

Aliah Faisal Shaheen

3 Jan 2024

The effect of a task-specific training on upper limb performance and kinematics while performing a reaching task in a fatigued state

PONE-D-23-24819R2

Dear Dr. Roy,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Aliah Faisal Shaheen

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

**********

6. Review Comments to the Author

Reviewer #1: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

**********

PLoS One. doi: 10.1371/journal.pone.0297283.r006

Acceptance letter

Aliah Faisal Shaheen

12 Jan 2024

PONE-D-23-24819R2

PLOS ONE

Dear Dr. Roy,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

* All references, tables, and figures are properly cited

* All relevant supporting information is included in the manuscript submission,

* There are no issues that prevent the paper from being properly typeset

If revisions are needed, the production department will contact you directly to resolve them. If no revisions are needed, you will receive an email when the publication date has been set. At this time, we do not offer pre-publication proofs to authors during production of the accepted work. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few weeks to review your paper and let you know the next and final steps.

Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

If we can help with anything else, please email us at customercare@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Aliah Faisal Shaheen

Academic Editor

PLOS ONE

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Fig. Experimental setup.

(DOCX)

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Attachment

Submitted filename: Response to reviewer.docx

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Attachment

Submitted filename: Response to reviewer-11dec2023.docx

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Data Availability Statement

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PERMALINK

The effect of a task-specific training on upper limb performance and kinematics while performing a reaching task in a fatigued state

Frédérique Dupuis

Félix Prud’Homme

Arielle Tougas

Alexandre Campeau-Lecours

Catherine Mercier

Jean-Sébastien Roy

Roles

Abstract

Background

Objective

Methods

Results

Conclusion

Introduction

Methods

Fig 1. Experimental design.

Reaching task

Fatigue protocol

Task specific training

Measurements and outcomes

Muscles fatigue assessment

Statistical analyses

Results

Table 1. Participants characteristics.

Perceived level of exertion and fatigue protocol

Muscles fatigue assessment

Motor performance

Kinematics

Fig 2. Joints initial angles.

Discussion

Strengths and limitations

Conclusion

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Aliah Faisal Shaheen

Roles

Author response to Decision Letter 0

Decision Letter 1

Aliah Faisal Shaheen

Roles

Author response to Decision Letter 1

Decision Letter 2

Aliah Faisal Shaheen

Roles

Acceptance letter

Aliah Faisal Shaheen

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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