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.

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.

This study investigated the effects of textured insoles on postural control in adults with autism spectrum disorder (ASD), examining how enhanced somatosensory feedback influences sensorimotor integration under varying sensory conditions. Twenty-one adults with ASD (Mage = 28.4 ± 4.2years) participated in a within-subjects design study with a 2 × 2 × 2 factorial design (surface: firm/foam, vision: eyes open/closed, and insole: with/without). Postural control was assessed using the Gaitview AFA-50 pressure platform system. Center of pressure parameters, including envelope area, root mean square, and total path length were analyzed to evaluate spatial and temporal aspects of postural control performance. The results showed that textured insoles significantly reduced postural sway parameters, indicating improved postural control, most significantly in conditions where sensorimotor integration was challenging (eyes closed on foam surface). Envelope area was reduced by 45.2% (p < .01), root mean square by 38.2% (p < .001), and total path length by 31.1% (p < .001), indicating improved postural control. Astrong interaction between surface type and insole condition was found particularly for root mean square (ηp2 = .685, p < .001), suggesting that the effects of somatosensory enhancement are greater when proprioceptive information is limited. Our results suggest that textured insoles reduce postural sway in adults with ASD, indicating improved postural control by enhancing plantar somatosensory feedback. This sensory augmentation may compensate for sensory integration difficulties commonly observed in ASD by strengthening one sensory channel, potentially facilitating more effective multisensory integration for postural control.

We develop a dynamics-based model of discrete movement for lateral manual interception capable of generating movements with realistic kinematics. For the present purposes, we focus on the situation of to-be-intercepted targets moving at constant speed along rectilinear trajectories oriented orthogonally with respect to the interception axis. The proposed phenomenological model is designed to capture the time evolution of empirically observed hand movements along the interception axis under different conditions of target arrival location and target speed-induced time pressure. Pattern formation dynamics combine a Duffing stiffness function, allowing for creating a fixed-point attractor at the perceived location of the target arrival on the interception axis, with a hybrid Rayleigh plus Van der Pol damping function. After parametrizing the model for required movement direction (left/right), amplitude, and duration, it adequately reproduces the (variations in) empirically observed kinematics with a single set of four coefficients for all conditions considered. The model is also demonstrated to inherently incorporate speed-accuracy trade-off characteristics.

The great toe contributes to healthy gait and balance but may be impacted by exposure to cold. The purpose of this study was to examine the effects of 60min of cold-water immersion on great toe flexor force and single-limb balance. Forty-four healthy adults participated in one of two experiments. All participants placed one foot in water that was maintained at 10°C and the other foot in water maintained at body temperature (37°C) for 60 min. Both feet were submerged to a depth just above the malleolus. For the first experiment (n = 25), maximum voluntary great toe flexion force and control of submaximal force were measured while standing using a custom designed apparatus both before and immediately following immersion. For the second experiment (n = 19), postural sway was assessed before and after immersion while standing on an unstable surface with a single limb and eyes open. Cold-water immersion resulted in a significant decrease in maximal flexor force of the great toe (332.6 ± 111.5N vs. 235.1 ± 108.2N, p < .001, Cohen's d = -0.89), but it did not impact the amount of error measured during control of submaximal flexor force (13.5 ± 4.4N vs. 14.4 ± 5.6N, p = .368). Further, exposure to cold resulted in significant increases to center of pressure rambling in the mediolateral direction (4.0 ± 0.9mm vs. 4.8 ± 1.0mm, p < .001, Cohen's d = 0.79) and trembling (3.2 ± 0.9mm vs. 3.9 ± 1.4mm, p = .002, Cohen's d = -0.63) and range of motion (49.6 ± 15.3mm vs. 61.8 ± 21.9mm, p = .007, Cohen's d = -0.62) in the anteroposterior direction. Cold-water immersion can impact force at the great toe and may adversely affect balance.

Movement disorders, such as stroke and amyotrophic lateral sclerosis, result in loss of upper limb function and, hence, severe impairments of bimanual coordination. Although motor imagery is increasingly used to enhance neurorehabilitation, cognitive and neurophysiological parameters that inform effective strategies remain elusive. The aim of the present study is to elucidate the neural dynamics that underlie learning during real and imagined movement using both unimanual and bimanual coordination patterns. The post movement beta rebound (PMBR) has been implicated as a biomarker of motor control and therefore was the focus of this study. Healthy adults (n = 21) learned a visuomotor tracking task in a single session using either one or both hands while brainwaves were captured using electroencephalography. Postmovement beta rebound was evident in the sensorimotor cortex for both unimanual and bimanual conditions. Task-related power of the beta band demonstrated that actual unimanual movement requires greater contralateral activity compared with both actual bimanual movement and imagined movement of either condition. Notably, the PMBR was evident even in imagined movement, although to a lesser extent than real movement. Neurophysiological results support a functional role for beta band in movement. Results of these data may inform neurorehabilitation strategies for patients recovering from movement disorders of the upper limbs.

The aim of the present study was to compare the differences in joint coordination patterns and variability in the lower extremity between the first and second landing phases of the drop jump. Eighteen resistance-trained men (age: 22.8 ± 1.8years) performed drop jumps from a height of 0.40m. An eight-camera motion capture system was utilized to record kinematic trajectories. Modified vector coding technique and circular statistics were used to determine the coordination pattern and variability of the following joint couples during the first and second landings: hip frontal-knee frontal (HfKf), hip sagittal-knee frontal (HsKf), hip sagittal-knee sagittal (HsKs), knee frontal-ankle frontal (KfAf), knee sagittal-ankle frontal (KsAf), and knee sagittal-ankle sagittal (KsAs). Statistical differences in the distribution frequencies of coupling angles and variability between the dominant and nondominant limbs across the two landing phases were compared using two-way repeated analysis of variance and Wilcoxon rank-sum tests. During the second landing phase, the proportion of HsKs, KfAf, and KsAs showing in-phase coordination was reduced but the proportion of KfAf and KsAs showing proximal joint (knee) coordination was increased (p < .05). Significant differences in bilateral asymmetry were observed only for the HfKf and KfAf patients (p < .05). HsKs, KfAf, and KsAf varied considerably during the second landing phase (p < .05). Joint coordination patterns during the second landing phase of the drop jump differed considerably from those during the first landing phase, thereby increasing the risk of knee and ankle injuries.

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.

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.

We review a body of literature related to the drawing and recognition of geometrical two-dimensional linear drawings including letters. Handwritten letters are viewed not as two-dimensional geometrical objects but as one-dimensional trajectories of the tip of the implement. Handwritten letters are viewed as composed of a small set of kinematic primitives. Recognition of objects is mediated by processes of their creation (actual or imagined)-the imitation principle, a particular example of action-perception coupling. The concept of spatial directional field guiding the trajectories is introduced and linked to neuronal population vectors. Further, we link the kinematic description to the theory of control with spatial referent coordinates. This framework allows interpreting a number of experimental observations and clinical cases of agnosia. It also allows formulating predictions for new experimental studies of writing.