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Effects of Mental Fatigue on Strength Endurance: A Systematic Review and Meta-Analysis

Carlos Alix-Fages, Jozo Grgic, Pablo Jiménez-Martínez, Eneko Baz-Valle, and Carlos Balsalobre-Fernández

The purpose of the present systematic review and meta-analysis was to explore the effects of mental fatigue on upper and lower body strength endurance. Searches for studies were performed in the PubMed/MEDLINE and Web of Science databases. We included studies that compared the effects of a demanding cognitive task (set to induce mental fatigue) with a control condition on strength endurance in dynamic resistance exercise (i.e., expressed as the number of performed repetitions at a given load). The data reported in the included studies were pooled in a random-effects meta-analysis of standardized mean differences. Seven studies were included in the review. We found that mental fatigue significantly reduced the number of performed repetitions for upper body exercises (standardized mean difference: −0.41; 95% confidence interval [−0.70, −0.12]; p = .006; I 2 = 0%). Mental fatigue also significantly reduced the number of performed repetitions in the analysis for lower body exercises (standardized mean difference: −0.39; 95% confidence interval [−0.75, −0.04]; p = .03; I 2 = 0%). Our results showed that performing a demanding cognitive task—which induces mental fatigue—impairs strength endurance performance. Collectively, our findings suggest that exposure to cognitive tasks that may induce mental fatigue should be minimized before strength endurance-based resistance exercise sessions.

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Principal Component Analysis can Be Used to Discriminate Between Elite and Sub-Elite Kicking Performance

Michal Vagner, Daniel J. Cleather, Petr Kubový, Vladimír Hojka, and Petr Stastny

Contemporary descriptions of motor control suggest that variability in movement can be indicative of skilled or unskilled performance. Here we used principal component analysis to study the kicking performance of elite and sub-elite soldiers who were highly familiar with the skill in order to compare the variability in the first and second principal components. The subjects kicked a force plate under a range of loaded conditions, and their movement was recorded using optical motion capture. The first principal component explained >92% of the variability across all kinematic variables when analyzed separately for each condition, and both groups and explained more of the variation in the movement of the elite group. There was more variation in the loading coefficient of the first principal component for the sub-elite group. In contrast, for the second principal component, there was more variation in the loading coefficient for the elite group, and the relative magnitude of the variation was greater than for the first principal component for both groups. These results suggest that the first principal component represented the most fundamental movement pattern, and there was less variation in this mode for the elite group. In addition, more of the variability was explained by the hip than the knee angle entered when both variables were entered into the same PCA, which suggests that the movement is driven by the hip.

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Decay of Short-Term Motor Memory Regarding Force Reproduction

Koichi Hiraoka, Masaya Ishimoto, Mai Kishigami, Ryota Sakaya, Asahi Sumimoto, and Kazuki Yoshikawa

This study investigated the process that contributes to the decay of short-term motor memory regarding force reproduction. Participants performed tonic flexion of the right index finger with the target force feedback (criterion phase) and reproduced this force level without feedback 3, 10, 30, or 60 s after the end of the criterion phase (recall phase). The constant error for force reproduction was significantly greater than zero, indicating that information about the somatosensation and/or motor command in the criterion phase is positively biased. Constant and absolute errors were not influenced by the retention interval, indicating that neither bias nor error represents the decay of short-term motor memory over time. Variable error, defined as SD of bias (force in the recall phase minus that in the criterion phase), increased as the retention interval increased. This indicates that the decay of short-term motor memory is represented by the increase in inconsistency of memory bias among the trials. The correlation coefficient of the force between the criterion and recall phases with 3-s retention interval was greater than that with longer intervals. This is explained by the view that the contribution of the information of the practiced force to the force reproduction process is great within 3 s after the end of the practice, but the additional contribution of the noise information becomes greater after this time, causing lesser relative contribution of the information of the practiced force to the force reproduction process.

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Dominant and Nondominant Leg Kinematics During Kicking in Young Soccer Players: A Cross-Sectional Study

Francesco Frontani, Marco Prenassi, Viviana Paolini, Giovanni Formicola, Sara Marceglia, and Francesca Policastro

The goal of the study is to analyze the kinematics and provide an EMG analysis of the support limb during an instep kick in adolescent players. We set a video camera, two torque transducers on the knee, and EMG sensors. A sample of 16 adolescent soccer players between 10 and 12 years old performed kicks. The kinematics shows a p = .039 on frontal plane (dominant 15.4 ± 1.8, nondominant 18.8 ± 1.7); the EMG analysis shows a p = .04 on muscular activation timing for the vastus medialis. A difference between the legs on the frontal plane emerges. Moreover, a huge difference on sagittal plane between the adolescent pattern and adult pattern exists (15° in adolescent population, 40° in adult population). The result shows a greater activation of the vastus medialis in the nondominant leg; probably, in this immature pattern, the adolescents use this muscle more than necessary.

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Heating the Skin Over the Knee Improves Kinesthesia During Knee Extension

Meghan Lamers, Erika E. Howe, Geoffrey A. Power, and Leah R. Bent

To determine how heating affects dynamic joint position sense at the knee, participants (n = 11; F = 6) were seated in a HUMAC NORM dynamometer. The leg was passively moved through extension and flexion, and participants indicated when the 90° reference position was perceived, both at baseline (28.74 ± 2.43 °C) and heated (38.05 ± 0.16 °C) skin temperatures. Day 2 of testing reduced knee skin feedback with lidocaine. Directional error (actual leg angle–target angle) and absolute error (AE) were calculated. Heating reduced extension AE (baseline AE = 5.46 ± 2.39°, heat AE = 4.10 ± 1.97°), but not flexion. Lidocaine did not significantly affect flexion AE or extension AE. Overall, increased anterior knee-skin temperature improves dynamic joint position sense during passive knee extension, where baseline matching is poorer. Limited application of lidocaine to the anterior thigh, reducing some skin input, did not influence dynamic joint position sense, suggesting cutaneous receptors may play only a secondary role to spindle information during kinesthetic tasks. Importantly, cutaneous input from adjacent thigh regions cannot be ruled out as a contributor.

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Startling Acoustic Stimulation Has Task-Specific Effects on Intracortical Facilitation and Inhibition at Rest and During Visually Guided Isometric Elbow Flexion in Healthy Individuals

Yen-Ting Chen, Shengai Li, Yingchun Zhang, Ping Zhou, and Sheng Li

Startling acoustic stimulation (SAS) causes a transient effect on the primary motor cortex (M1) nonreflexively. It reduces the cortical excitability at rest, but not during voluntary contraction. However, the effect of SAS on intracortical activity is not clear. The purpose of this study was to investigate the SAS effect on short-interval intracortical inhibition and intracortical facilitation using transcranial magnetic stimulation (TMS). Eleven healthy individuals performed isometric elbow flexion at 10% of maximum voluntary contraction on the dominant side with a real-time visual target (i.e., M1 preactivation) or at rest. TMS was delivered to the M1 ipsilateral to elbow flexion without or with SAS delivered 90 ms prior to TMS. There were three TMS delivery conditions: (a) single pulse, (b) short-interval intracortical inhibition, and (c) intracortical facilitation. TMS-induced motor-evoked potential (MEP) was compared between predetermined TMS and SAS conditions at rest and during ipsilateral voluntary contraction. We confirmed that SAS decreased the MEP amplitude at rest, but not during M1 preactivation. SAS caused task-specific effects on intracortical excitability. Specifically, SAS increased intracortical facilitation at rest and during voluntary contraction. However, SAS decreased short-interval intracortical inhibition only during M1 preactivation. Collectively, our results suggest that SAS transiently influences the motor cortex excitability, possibly via its activation of higher centers, to achieve a visually guided goal-directed task.

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Validation of a Novel Reaction Time Test Specific for Military Personnel

Danica Janicijevic, Sergio Miras-Moreno, Alejandro Pérez-Castilla, Jesús Vera, Beatriz Redondo, Raimundo Jiménez, and Amador Garcia-Ramos

A military-specific reaction time (RT) test was developed to explore its reliability and sensitivity to discriminate between military personnel and sport science students. Fifteen male professional Spanish soldiers and 16 male sport science students completed two RT test modalities: military-specific and nonspecific RT tests. For each RT test modality, both the Simple (i.e., one stimulus, one response) and the Go, No-Go RT (i.e., true, and false stimuli, one response) were tested. The military-specific RT test consisted of a video presented through virtual reality glasses of a forest environment in which soldiers would appear from behind different bushes (stimuli) and the response consisted of pressing the button of a gun-shaped mouse (when they saw a soldier pointing a rifle at them). Both Simple and Go, No-Go RT reached acceptable reliability in both populations (coefficient of variation ≤ 9.64%). Military personnel presented a lower RT than sport science students during the military-specific RT test (p ≤ .001), while no differences were obtained during the nonspecific RT test. RT values were not significantly correlated between the military-specific and nonspecific RT tests (r ≤ .02). These findings collectively suggest that the novel military-specific RT test is an ecologically valid alternative to evaluate the information processing abilities of military personnel.

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Distraction From Smartphones Changed Pedestrians’ Walking Behaviors in Open Areas

Yue Luo, Nicolas Grimaldi, Haolan Zheng, Wayne C.W. Giang, and Boyi Hu

The prevalence of phone use has become a major concern for pedestrian safety. Using smartphones while walking reduces pedestrians’ ability to perceive the environment by increasing their cognitive, manual, and visual demands. The purpose of this study was to investigate the effect of common phone tasks (i.e., reading, tapping, gaming) on walking behaviors during outdoor walking. Nineteen young adults were instructed to complete four walking conditions (walking only, walking–reading, walking–tapping, and walking–gaming) along an open corridor. Results showed that all three phone tasks increased participants’ neck flexion (i.e., neck kyphosis) during walking. Meanwhile, the reading task showed a greater influence on the temporal aspect during the early phases of a gait cycle. The tapping task lowered the flexion angles of the middle and lower back (i.e., torso lordosis) and induced a longer terminal double support. And the gaming task resulted in a decrease in middle back flexion, a shorter stride length, and a longer terminal double support while walking. Findings from the study confirmed our hypothesis that phone tasks changed pedestrians’ physical responses to smartphone distraction while walking. To avoid potential risks caused by the observed posture and gait adaptations, safety precautions (e.g., roadside/electronic warning signals) might be imposed depending on the workload expected by different phone tasks.

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Patterns of Movement Performance and Consistency From Childhood to Old Age

Jessica Prebor, Brittany Samulski, Cortney Armitano-Lago, and Steven Morrison

It is widely accepted that the general process of aging can be reflected by changes in motor function. Typically, optimal performance of a given motor task is observed for healthy young adults with declines being observed for individuals at either end of the lifespan. This study was designed to examine differences in the average and variability (i.e., intraindividual variability) of chewing, simple reaction time, postural control, and walking responses. For this study, 15 healthy children, 15 young adults, and 15 older adults participated. Our results indicated the movement performance for the reaction time and postural sway followed a U shape with young adults having faster reaction times and decreased postural sway compared to the children and older adults. However, this pattern was not preserved across all motor tasks with no age differences emerging for (normalized) gait speed, while chewing rates followed a U-shaped curve with older adults and children chewing at faster rates. Taken together, these findings would indicate that the descriptive changes in motor function with aging are heavily influenced by the nature of the task being performed and are unlikely to follow a singular pattern.

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Adaptive Regulation in a Stable Performance Environment: Trial-To-Trial Consistency in Cue Sports Performance

Jing Wen Pan, Pui Wah Kong, and John Komar

This study aimed to investigate individual trial-to-trial performance in three tests to define adaptive regulation as a key feature of expertise in nine-ball. Thirty-one male players were assigned into the low-skilled (n = 11), intermediate (n = 10), or high-skilled groups (n = 10). The power control, cue alignment, and angle tests were selected to assess participants’ ability to control the power applied in shots, strike the ball straight, and understand the ball paths, respectively. Error distance and correction of error distance were identified for each shot using 2D video analysis. Results of one-way analysis of variance showed that the high-skilled group performed better in two out of the three tests than the other two groups (p = .010 for the cue alignment test; p = .002 for the angle test). However, the adaptation effect represented by the decreased error distances across trials was not observed. Pearson correlation revealed only a few significant correlations between the error distance and its correction within each participant in all tests (p < .05), and hence, the hypothesis that “low correction happened after small error and vice versa” is not supported.