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Volume 28 (2024): Issue 3 (Jul 2024)

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Entropy as a Window Into Behavioral Phase Transitions: Unveiling Contextual Dynamics in Affordance-Based Reaching

Dalton S. Cooper, Tarcisio S. Moreira, and Tehran J. Davis

Prior work has demonstrated the presence of hysteresis effects in the control of affordance-guided behavior, in that behavioral transitions around a critical action boundary vary with directions of change in said action boundary. To date, research on this topic has overlooked the influence of the global context on these phenomena. We employ an affordance-based reaching task, whereby participants were asked to move a target to a goal by passing through one of two apertures (size variable or size constant). It was found that the direction of change in the size of the variable aperture influenced the point of behavioral transitions, and this effect interacted with the location of a given goal. In addition, we considered fluctuations in the entropy of participants’ reach trajectories as a window into the nature of the behavioral phase transitions. Differences in the structure of entropy were found depending on the direction of change in the size variable aperture. These results are discussed in light of a dynamical systems approach, and recommendations for future work are made.

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The Amount and Pattern of Reciprocal Compensations Predict Performance Stability in a Visually Guided Finger Force Production Task

Valéria Andrade, Nicole S. Carver, Francis M. Grover, Scott Bonnette, and Paula L. Silva

Previous work suggests that synergistic activity among motor elements implicated in force production tasks underlies enhanced performance stability associated with visual feedback. A hallmark of synergistic activity is reciprocal compensation, that is, covariation in the states of motor elements that stabilizes critical performance variables. The present study examined if characteristics of reciprocal compensation are indicators of individuals’ capacity to respond adaptively to variations in the resolution of visual feedback about criterion performance. Twenty healthy adults (19.25 ± 1.25 years; 15 females and five males) pressed two sensors with their index fingers to produce a total target force equivalent to 20% of their maximal voluntary contraction under nine conditions that differed in the spatial resolution of real-time feedback about their performance. By combining within-trial uncontrolled manifold and sample entropy analyses, we quantified the amount and degree of irregularity (i.e., non-repetitiveness) of reciprocal compensations over time. We found a U-shaped relationship between performance stability and gain. Importantly, this relationship was moderated by the degree of irregularity of reciprocal compensation. Lower irregularity in reciprocal compensation patterns was related to individuals’ capacity to maintain (or minimize losses in) performance under changes in feedback resolution. Results invite future investigation into how interindividual variations in reciprocal compensation patterns relate to differences in control strategies supporting adaptive responses in complex, visually guided motor tasks.

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Specific Contribution of the Transversus Abdominis for Postural Control Against Perturbation Caused by Kinesthetic Illusion

Hiroshi Akuzawa, Tsuyoshi Morito, Tomoki Oshikawa, Yu Okubo, Simon Brumagne, and Koji Kaneoka

Functional independence of the transversus abdominis (TrA) from other trunk muscles for postural control is still unclear. This study aimed to clarify the specific function of the TrA to control standing posture by vibratory stimulation of the triceps surae. Fifteen men participated in this study. Muscle activity of the TrA, internal oblique, lumbar multifidus, gluteus maximus, rectus femoris, biceps femoris, gastrocnemius, and tibialis anterior was measured using fine-wire and surface electrodes. Participants were asked to maintain a quiet standing posture with and without vibration of the triceps surae, which induced a kinesthetic illusion and the concomitant backward sway of the body. The muscle activity of each muscle for 10 s was extracted with and without vibration. The muscle activity levels were compared between the conditions by a paired t-test or Wilcoxon signed-rank test. The activity of the TrA and rectus femoris was increased, whereas the internal oblique showed no change as a result of the induced kinesthetic illusion. In addition, the activity of the multifidus and biceps femoris was decreased. The TrA and rectus femoris could contribute to control the backward sway of the body. Furthermore, the TrA may have functional independence from the internal oblique during standing postural control. These results warrant further study in patients with low back pain.

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Influence of Motor Imagery Modality on First-Serve Performance in Tennis Players

Dominique Laurent, Robbin Carien, and Nicolas Robin

Motor imagery (MI) is frequently used in tennis players. This pilot study aimed to assess whether the MI modality and preference of skilled tennis players could influence their service performance when using MI before serving first balls. Twenty expert players (M age = 18.6 years) completed the movement imagery questionnaire (third version) to assess their MI modality scores (internal visual, external visual, and kinesthetic) and their MI preference. Participants completed 4 experimental counterbalanced sessions spread over 4 weeks, each including the completion of 20 first-serve balls in match condition. The sessions included a control condition (i.e., only physical practice trials) and three MI conditions during which the players had to mentally imagine themselves performing a serve according to one of the imagery modalities, either internal visual, external visual, or kinesthetic, before serving. The percentage of success, the speed of the service balls (measured by a tablet with SWING VISION and a radar gun), and an efficiency score were recorded and then evaluated by experts and served as performance indicators and dependent variables. The results of this study showed that players benefited from MI before serving and that almost a third of the participants achieved a higher percentage of success and efficiency scores when using their preferred MI modality. These results lead us, in an applied way, to suggest to skilled tennis players to determine their MI preference and to have recourse to the mental simulation of a successful serve before serving the first balls in match condition.

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A Study of the Effects of Motor Experience on Neuromuscular Control Strategies During Sprint Starts

Zhengye Pan, Lushuai Liu, Yuan Sun, and Yunchao Ma

Much of the current research on sprint start has attempted to analyze the biomechanical characteristics of elite athletes to provide guidance on the training of sprint technique, with less attention paid to the effects of motor experience gained from long-term training on neuromuscular control characteristics. The present study attempted to investigate the effect of motor experience on the modular organization of the neuromuscular system during starting, based on he clarification of the characteristics of muscle synergies during starting. It was found that exercise experience did not promote an increase in the number of synergies but rather a more focused timing of the activation of each synergy, allowing athletes to quickly complete the postural transition from crouching to running during the starting.

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Response of Knee Joint Biomechanics to Landing Under Internal and External Focus of Attention in Female Volleyball Players

Lukáš Slovák, David Zahradník, William M. Land, Javad Sarvestan, Joseph Hamill, and Reza Abdollahipour

The aim of this study was to examine the effect of attentional focus instructions on the biomechanical variables associated with the risk of anterior cruciate ligament injury of the knee joint during a drop landing task using a time series analysis. Ten female volleyball players (age: 20.4 ± 0.8 years, height: 169.7 ± 7.1 cm, mass: 57.6 ± 3.1 kg, experience: 6.3 ± 0.8 years) performed landings from a 50 cm height under three different attentional focus conditions: (1) external focus (focus on landing as soft as possible), (2) internal focus (focus on bending your knees when you land), and (3) control (no-focus instruction). Statistical parameter mapping in the sagittal plane during the crucial first 30% of landing time showed a significant effect of attentional focus instructions. Despite the similarity in landing performance across foci instructions, adopting an external focus instruction promoted reduced vertical ground reaction force and lower sagittal flexion moment during the first 30% of execution time compared to internal focus, suggesting reduced knee loading. Therefore, adopting an external focus of attention was suggested to reduce most biomechanical risk variables in the sagittal plane associated with anterior cruciate ligament injuries, compared to internal focus and control condition. No significant differences were found in the frontal and horizontal planes between the conditions during this crucial interval.

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Acute and Acclimated Effects of Wearing Compression Garments on Balance Control in Community-Dwelling Older Adults

You-jou Hung, Frederick Couverette, Jeffrey Hamon, and Dustyn Willard

Falls are very serious health concerns among older adults. Providing additional cutaneous and proprioceptive feedback to older adults may enhance their balance control and therefore reduce the incidents of falls. This study aimed to investigate the acute and acclimated effect of wearing waist-to-above-ankle compression garments (CGs) on balance control in community-dwelling older adults. Thirty-one older adults participated in the study. The Timed Up and Go, Berg Balance Scale, and the Fall Risk Test of the Biodex Balance System were used in a random order to examine balance control in three testing sessions 1 week apart. Results indicated wearing CGs had a significant impact on the Timed Up and Go test (p < .001), Berg Balance Scale (p = .001), and the Fall Risk Test (p = .001). For the Timed Up and Go test, participants exhibited significant improvement in both the acute (8.68 vs. 7.91 s) and acclimated effect (7.91 vs. 7.41 s) of wearing CGs. For the Berg Balance Scale, participants showed significant improvement after wearing CGs for 1 week in comparison to the no CGs condition (55.77 vs. 55.39 points). For the Fall Risk Test, participants showed a significant improvement in the acute effect of wearing CGs in comparison to the no CGs condition (1.55° vs. 1.31°). This exploratory study showed that wearing waist-to-above-ankle CGs provided a positive impact on balance control in healthy community-dwelling older adults. It lays the foundation for future studies with a larger sample size to investigate the potential benefits of wearing CGs in individuals with balance control deficits and/or other comorbidities.

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Assessing Postural Control From Birth to Adulthood Among Individuals Born Preterm: A Systematic Review

Soraia Pereira, Augusta Silva, Rubim Santos, and Cláudia Costa Silva

Premature life exposure, meaning an immature central nervous system, presents a significant challenge for the development of postural control and, in turn, overall motor development. Preventing motor delay thus requires identifying, characterizing, and quantifying deficit in postural control as early as possible. In our study, we reviewed the procedures used in past studies to assess postural control among individuals born preterm, specifically the characterization of participants, the instruments and motor tasks involved, the types of data collected and analyzed, and the outcomes. To that end, we performed a literature search on PubMed, Wiley Online Library, Web of Science, and Scopus using Boolean logic and assessed the quality of the studies with a standardized assessment based on the Strengthening the Reporting of Observational Studies in Epidemiology guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. Of 35 potential studies, 24 were included; all evaluated infants born preterm, but six did not include a control group of full-term infants. Although the heterogeneity of measurements, variability of instruments, and divergence in motor tasks examined limit definitive conclusions based on quantitative synthesis and the generalization of the results, most studies revealed dysfunctional postural control among individuals born preterm.

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Influence of Pedal Interface During Pedaling With the Upper Versus Lower Limbs: A Pilot Analysis of Torque Performance and Muscle Synergies

Laurent Vigouroux, Théo Cartier, and Guillaume Rao

Pedaling is a physical exercise practiced with either the upper or the lower limbs. Muscle coordination during these exercises has been previously studied using electromyography and synergy analysis, and three to four synergies have been identified for the lower and upper limbs. The question of synergy adaptabilities has not been investigated during pedaling with the upper limbs, and the impact of various modalities is yet not known. This study investigates the effect of pedal type (either clipped/gripped or flat) on the torque performance and the synergy in both upper and lower limbs. Torques applied by six participants while pedaling at 30% of their maximal power have been recorded for both upper and lower limbs. Electromyographic data of 11 muscles on the upper limbs and 11 muscles on the lower limbs have been recorded and synergies extracted and compared between pedal types. Results showed that the torques were not modified by the pedal types for the lower limbs while a deep adaptation is observable for the upper limbs. Participants indeed used the additional holding possibility by pulling the pedals on top of the pushing action. Synergies were accordingly modified for upper limbs while they remain stable for the lower limbs. In both limbs, the synergies showed a good reproducibility even if larger variabilities were observed for the upper limbs. This pilot study highlights the adaptability of muscle synergies according to the condition of movement execution, especially observed for the upper limbs, and can bring some new insights for the rehabilitation exercises.