This study investigated the neural timing control characteristics of countermovement jumps between elite athletes and nonathletes using muscle synergy theory. Twenty male participants (high-level group [HLG, N = 10] and untrained group [UG, N = 10]) performed the countermovement jump while surface electromyography from eight lower limb muscles and three-dimensional force plate data were recorded. Nonnegative matrix factorization extracted three muscle synergy modules, and bootstrap resampling with bias-corrected 95% confidence intervals (CIs) analyzed temporal parameters. Results demonstrated: (a) HLG achieved significantly greater jump height (95% CI: [-0.139, -0.026]); (b) HLG exhibited delayed activation onset (95% CI: [-0.227, -0.015]), peak timing (95% CI: [-0.300, -0.028]), and offset (95% CI: [-0.216, -0.014]) in Synergy module 1, delayed onset (95% CI: [-0.225, -0.054]) and offset (95% CI: [-0.224, -0.072]) in Synergy module 2, and delayed offset in Synergy module 3 (95% CI: [-0.197, -0.017]); and (c) HLG showed narrower full width at half maximum in Synergy module 1 (95% CI: [0.009, 0.094]), with no group differences in amplitude parameters. These findings suggest that, compared with UG, HLG exhibit delayed synergy activation timing during the countermovement jump. This temporal pattern may be associated with more effective use of the eccentric phase and more coordinated interjoint timing during propulsion.

Muscular fatigue often induces compensatory adjustments-such as increased motor unit recruitment and synchronization-that can elevate kinematic variability. By contrast, mental fatigue alters top-down neural control, modulates corticospinal excitability, and changes prefrontal-motor cortical activity, indirectly influencing muscle activation patterns. These central and peripheral distinctions suggest that mental and muscular fatigue may differently affect movement variability and synergy organization, yet it remains unclear how the structure of variability diverges between the two. The purpose of this study was to examine the effect of mental and muscular fatigue on movement variability during dart throwing using the uncontrolled manifold method. This method decomposes joint kinematic into two components: components of joint variability that either stabilize (parallel variance) or destabilize (orthogonal variance) performance variable. Participants were 28 young individuals (19 females and nine males) aged 25-35 without regular experience in throwing darts. All participants threw darts under three conditions: mental fatigue, muscular fatigue, and nonfatigue. Throwing kinematics data was collected with a motion capture system and quantified movement variability using the uncontrolled manifold approach. We hypothesized that the structure of movement variability would differ across the three conditions-mental fatigue, muscular fatigue, and nonfatigue. Repeated-measures multivariate analysis of variance was used to test these hypotheses. The results showed that the main effect of fatigue has a significant effect on parallel variance (p = .034, partial η2 = .31) but not on orthogonal variance (p = .289, partial η2 = .23) and synergy index (p = .864, partial η2 = .14) at different times of the throwing cycle. Increasing parallel variance is an effective strategy for helping to be more flexible in using degrees of freedom to perform a task. These results suggest that an increase in parallel variance may reflect an adaptive mechanism to maintain stability.

A core feature of joint action is task-sharing-the dynamic coordination of individual efforts to produce and stabilize a shared outcome. Yet, it remains unclear which features of task-sharing dynamics relate to stable performance. In this study, we address this gap by identifying behavioral markers that capture the organization and robustness of task-sharing in a joint force-production task. Thirty dyads performed a continuous force-production task in which each partner independently applied force to jointly match a target total force. Real-time visual feedback was provided on their combined output. The task was completed under low-force (10% maximum voluntary contraction) and high-force (30% maximum voluntary contraction) conditions to manipulate difficulty. Trials revealed qualitatively distinct patterns of force contribution, including cases in which a single partner carried most of the output, patterns in which partners contributed with distinct temporal roles, and fully synergistic task-sharing in which both partners continuously shaped total force fluctuations. We used within-trial uncontrolled manifold (UCM) analysis to characterize the dominant, synergistic mode along two dimensions. The first is the degree of variation in task-sharing patterns that leaves performance unchanged (VUCM). The second is the degree of irregularity-computed as sample entropy-of these patterns (SampEnUCM). Dyads with lower VUCM and lower SampEnUCM demonstrated greater performance stability. VUCM and SampEnUCM thus serve as indices of robust task-sharing patterns, offering behavioral access to the control mechanisms that enable stable joint performance, particularly under more challenging conditions.

Single-effort isometric handgrip strength tests are widely used as a proxy of overall muscular strength. While using peak force (PF) is practical and meaningful, additional force-time characteristics could provide insight into muscle function. The purpose of this study was to assess test-retest reliability of force-time characteristics for maximal voluntary handgrip contractions (Analysis 1) and assess the influence of fatigability and time-of-day (Analysis 2). Nineteen participants completed Analysis 1 (23.5 ± 5.7 years, 168.7 ± 8.3 cm, 75.4 ± 14.0 kg) and 18 participants completed Analysis 2 (23.4 ± 5.9 years, 168.7 ± 10.4 cm, 77.6 ± 14.6 kg). For both analyses, participants completed three 4-s maximal voluntary handgrip contractions with 1-min rest periods. For Analysis 2, participants completed the maximal voluntary handgrip contractions before and after a fatiguing handgrip intervention at three separate times-of-day. Variables included PF, time to PF, time to 90% PF (TT90), area under the curve deficit (AUC Deficit), plateau force coefficient of variation, and plateau derivative root mean square. Using point estimates, all dependent variables demonstrated moderate-excellent relative reliability. A Time-of-day × Fatigability interaction was observed for TT90, AUC Deficit, and force coefficient of variation. Main effects of fatigability were observed for all variables, excluding plateau derivative root mean square. Time-of-day did not demonstrate an impact to any dependent variable. While task specific, an adequate warm-up may mitigate time-of-day impact to performance previously reported. TT90 and force maintenance variables, such as AUC Deficit, and force coefficient of variation, appear to be sensitive to the interaction between time-of-day and fatigability. Force maintenance variables may provide further insight beyond PF when examining maximal effort handgrip strength.

Artificially restricting the center of mass (COM) motion during quiet standing through multisegment constraints has previously been shown to alter center of pressure (COP) dynamics. Increases in COP motion during such mechanically restricted stances have been interpreted as potential markers of exploratory behavior, whereby the central nervous system may generate movements to gather sensory input that would otherwise be limited by the imposed constraints. However, past studies relied on a plank-based apparatus that places participants in a nonecological posture, potentially limiting interpretations. This study compared the effects of the plank-based setup and a more ecologically valid belt-based apparatus that restricts COM movement without fully constraining the body. The analysis focused on both traditional measures of COP (i.e., variability) and dynamic measures (i.e., regularity and frequency components). Participants performed standing trials with both apparatuses, with eyes open and closed. Results revealed distinct COP behaviors between the two systems: compared with the unrestricted condition, the restricted condition with the plank-based apparatus yielded higher COP variability and regularity, whereas the belt-based system yielded lower COP variability and increased irregularity. These effects were not strongly influenced by visual input. The persistent COP motion observed under both conditions suggests that COP displacement may serve functions beyond merely stabilizing the COM, possibly reflecting exploratory behaviors. Overall, our findings support the use of belt-based systems as a more ecological alternative for restricting the COM motion, allowing for the study of the role of the COP in sensorimotor regulation without the limitations of a multisegment constraint.

The objective of this study is to examine the relationship between the spin-related variables during real four-seam fastball pitching in baseball and the finger force production capability and its coordination in the laboratory test. Consequently, the sets of variables were derived from two distinct experiments: a field task and a laboratory task. The field task was designed to quantify the spin-related variables during actual pitching performance, and the laboratory task was designed to quantify the strength of the two fingers and the coordination-related variables of the index and middle fingers during the cyclic net finger force production task. The statistical test was implemented with the primary objective of ascertaining the significant correlation between the two metrics from the field and laboratory tests. The findings indicated a negative correlation between finger forces and spin-related variables (p < .05), suggesting that those who have greater finger force do not have a positive effect on spin-related variables. The strength of the synergy indices of moment stabilization was associated with a positive effect on spin-related variables (p < .05). The present experiment demonstrated that the stabilization of mechanical variables by the force production of the two fingers, that is, the net moment, indicates that the rotational effect of finger force production plays a critical role in determining the superior spin qualities of a fastball pitch in baseball.

Despite the main clinical criteria for Autism Spectrum Disorder (ASD) diagnosis being the dysfunction of socio-communicative interaction abilities and the presence of restricted interests and repetitive behaviors, sensory-motor dysfunctions are also frequently observed in this population. Moreover, among sensory-motor issues, both postural control and visual processing may be impaired. The main aim of this scoping review is to synthesize the evidence on the relationship between visual behavior and postural control dysfunctions in children and adolescents with ASD. This scoping review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocol, Extension for Scoping Reviews guidelines, and was registered a priori on the Open Science Framework. PubMed, CINAHL, Embase, PsycINFO, Scopus, and Web of Science databases were consulted. Primary studies with any study design were included. No time, geographical, or study setting limitations or language restrictions were applied. A total of 646 articles were found in the initial search, but only 14 studies met the full inclusion criteria. Findings highlighted that studies on the relationship between vision and posture in ASD children and adolescents are scarce, and their results are contrasting because of the significant heterogeneity in the methods. This scoping review carried out a relevant survey of the literature considering the relationship between vision and posture in ASD. Nonetheless, the characteristics of the included sample and the methodology used in the analyzed studies were highly variable. Thus, rigorous study methods with population-specific objective outcome measures are needed to draw generalizable conclusions.

Fatigue experienced by individuals with multiple sclerosis (MS) during activities of daily living affects their balance and increases the risk of falls. The aim was to assess the effect of fatigue induced by a functional task on balance control in individuals with MS. The study involved 10 individuals with MS and 10 gender-matched healthy volunteers who performed a functional sit-to-stand task using a standardized chair and metronome until they reported an inability to continue. Motor Control and Sensory Organization tests were implemented using Dynamic Posturography three times: before, immediately after fatigue, and after a 30-min rest period. The Motor Control Test revealed that individuals with MS, compared to healthy controls, showed significantly longer latencies during small, medium, and large amplitudes of backward perturbation. Longer latencies were observed in the MS group after fatigue, specifically during small and large amplitudes of forward perturbations. The Sensory Organization Test discovered that following fatigue, the MS group demonstrated significantly lower equilibrium scores compared with healthy controls in the following conditions: eyes closed (p < .001), sway-referenced visual surround (p = .02), and sway-referenced support surface (p = .03). Functional fatigue induced by sit-to-stand tasks significantly impacted outcomes of both the Motor Control and Sensory Organization tests of balance control in individuals with MS. These findings lay the groundwork for future investigations into the role of fatigue in balance control in individuals with MS.

Different attentional focus strategies are commonly employed in sports training, with the external focus of attention (EF) strategy shown to enhance performance in the standing long jump. However, the underlying muscular dynamics responsible for this improvement remain unclear. In this study, we utilized a Latin square design to recruit 12 healthy male participants, each undergoing standing long jump testing under EF, internal focus (IF), and control conditions. During the take-off phase, we synchronously recorded kinematic and dynamic data. Inverse dynamics calculations were performed on the dynamic and kinematic data. Compared with IF and control, the EF condition exhibited longer jump distances, lower projection angles, and higher peak horizontal take-off velocities and impulses alongside increased center of mass displacement during the eccentric phase and decreased center of mass displacement during the concentric phase (p < .05). The peak muscle force and rate of muscle force development of the vastus lateralis, vastus medialis, vastus intermedius, and gluteus maximus during the take-off phase were also higher in the EF group (p < .05). These results indicate that the EF strategy optimizes standing long jump mechanics by enhancing the efficiency of eccentric muscle contractions, thereby increasing stored elastic potential energy in the muscles. Consequently, this leads to greater muscle force and rate of muscle force development during the concentric phase, ultimately resulting in increased jump distances.