Journal of Motor Behavior最新文献

Cutaneous feedback plays a large role in the reflexive activation of muscle activity (Ia stretch reflex) generating postural responses during planned gait termination. As the mechanisms to induce a cutaneous afferent volley have been limited to electrical stimulation, it remains unknown if mechanical stimuli can modulate stretch reflex (SR) excitability. The purpose of this study was to examine the effect of adding cutaneous inputs on modulating the SR during perturbed gait termination. Thirty young adults completed walking trials when a platform unexpectedly tilted 10 degrees anteriorly or posteriorly, inducing a tibialis anterior (TA) or medial gastrocnemius (MG) short-latency reflex. The SR latency, the peak SR amplitude, and the total SR amplitude of the agonist burst, were compared between the stretched muscle and cutaneous facilitation. Statistically significant interactions were observed between the stretched muscle and cutaneous facilitation on the SR peak and SR burst. More notably, texture resulted in a consistent expression on the TA SR magnitude, without a similar effect in MG. Despite confirming the ability of cutaneous afferent facilitation on modulating spinal interneuronal circuitry, participant variability in response to texture highlights the importance of focusing on individual participant results when studying the effects of cutaneous facilitation on modulating spinal motorneuron excitability.

The literature that investigated the influence of visual feedback properties on the magnitude and temporal structure of variability suggests that increases in the precision of visual information of the torque output (through manipulation of visual gain and its intermittency) lead the neuromuscular system to produce torque in a more steady and complex manner. However, less is known about the influence of the nature of visual feedback on torque variability. The present study aimed to investigate the effect of two different feedback natures, one from the angular position and the other from the torque produced, on the magnitude and temporal structure of torque variability during submaximal hold isometric tasks. Twenty healthy and young participants performed a knee extension isometric task, consisting in sustaining an applied resistance equivalent to 40% of their Maximal Voluntary Isometric Contraction for 30 s with visual feedback from angular position (H_angle) and with visual feedback from torque (H_torque). The magnitude of torque variability was calculated through the coefficient of variation. Sample Entropy was used to analyze the temporal structure of torque fluctuations, i.e., torque complexity. We observed no significant differences between conditions (H_angle vs H_torque) in both magnitude (p = 0.117) and the temporal structure of torque fluctuations (p = 0.940). Our results demonstrated that torque regulation seems not to be affected by the nature of the visual feedback during hold submaximal isometric tasks, suggesting a participation of sensorimotor system due to the nature of the task. Researchers should take this into account to take methodological decisions when using hold submaximal isometric tasks to investigate possible changes in motor control.

Light touch contact of the fingertip reduces postural sway. The light touch effect was confirmed in several postural orientations. However, the effect on postural control in the crouching posture remains unclear. This study investigated the effect of a light fingertip touch on the perturbation of the center of pressure in bipedal standing and crouching. Twenty-two healthy participants engaged in eight postural control tasks: standing/crouching (Posture) × eyes opened/eyes closed (Vision) × light touch/no touch (Touch). The total trajectory length and root-mean-square of the center of pressure in the anterior-posterior and medio-lateral directions were analyzed. Light touch reduced the sway of the center of pressure in both the standing and crouching postures, particularly in the anterior-posterior direction. Furthermore, the touch effect on the sway of the center of pressure varied between the standing and crouching postures. Consistent effects were observed in the anterior-posterior direction, but differing effects were observed in the medio-lateral direction. These results indicate that somatosensory input from the fingertip reduces postural sway in both directions in a crouched posture. Variations of the center of pressure disturbances in the medio-lateral direction could originate from differences in postural strategies involving the ankle and hip joints between bipedal standing and crouching positions.

Researchers have investigated the sensorimotor mechanisms that result in Fitts' law. One approach has been to analyse movement trajectories during Fitts' tasks to reveal the processes that occur during movement preparation and execution. We used trajectory analysis in the current study to investigate how limb-target control contributed to Fitts' law during the transition from ballistic movements to movements with online control. Twenty-five participants made discrete reaching movements in seven conditions with indexes of difficulty that ranged from one to seven. There were strong linear relationships between index of difficulty, effective index of difficulty and movement time. Trajectory analysis suggested that the easiest condition had movements that were mostly ballistic. There was enough time for visual-based online corrections, but the condition was probably too easy to require limb-target control. Trajectory analysis also suggested that there was an increased reliance on limb-target control as the index of difficulty increased. In conclusion, there was a strong linear relationship between effective index of difficulty and movement time even with conditions that ranged from mostly ballistic to a high degree of limb-target control. We suggest that there is a direct relationship between effective index of difficulty and degree of limb-target control.

Proprioceptive inputs have crucial roles in control of the posture. The aim of the present study was to assess the effect of interfering with these signals on postural stability by ice-induced anaesthesia and local calf muscle fatigue. Seventeen healthy young individuals participated in this study to stand quietly and on an unstable platform under normal, anaesthesia, and fatigue conditions. A force platform calculated excursions of centre of pressure. Stabilogram-diffusion analysis was utilised to evaluate how body controls the posture with and without proprioceptive inputs. Time intervals of using the sensory feedback is significantly increased by anaesthesia in quiet standing (430 ms, p = 0.034) to note more delayed use of sensory information in a closed-loop. Additionally, fatigue significantly increased the time intervals of using sensory feedback during standing on the unstable platform (290 ms, p = 0.016). Interestingly, sensory interventions had no effect on the stability of the open-loop control of posture (short-term control), but they significantly influenced the closed-loop control (long-term control) (p < 0.004). Specifically, fatigue led to increased instabilities when the body used sensory inputs during both quiet standing (p = 0.021) and standing on the unstable platform (p = 0.041). These findings highlight the importance of proprioception in balance control for healthy individuals. Interfering with proprioceptive inputs, either through anaesthesia or fatigue, resulted in instabilities during balance maintenance. Our study provides new insights into the mechanisms underlying postural control, emphasising the significance of proprioceptive inputs. Understanding how proprioception affects balance maintenance may have implications for rehabilitation strategies, injury prevention, and the development of interventions to improve postural stability.

Numerous devices are being developed to assist visually impaired and blind individuals in performing everyday tasks such as reaching out to grasp objects. Considering that the size, weight, and cost of assistive devices significantly impact their acceptance, it would be useful to know how effective various types of guiding information can be. As an initial exploration of this issue, we conducted four studies in which participants with normal vision were visually guided toward targets. They were guided by information about the direction to the target, and either about the distance to the target or about the time required to reach the target. We compared participants' performance when provided with different amounts of each of these kinds of information. We found that restricting information about the distance from the target or the time it would take to reach the target to only a few possible values does not affect performance substantially. Restricting information about the direction to the target to only a few possible values appears to be more detrimental, but the disadvantage of having few possible directions can be mitigated by combining values in multiple directions. These findings can help optimize haptic presentations in assistive technology.

The aim of this study was to compare the kinematics of reaching tasks at different speeds between children with neonatal brachial plexus palsy (NBPP) and unaffected controls. This cross-sectional study included thirteen children with NBPP (10 ± 2 years old, of which six had upper Erb's palsy and seven had extended Erb's palsy) matched for age and sex with thirteen unaffected controls. Kinematic data were acquired using a Motion Monitor unit with a 3D motion tracking electromagnetic system (Liberty, Polhemus). Scapular, upper limb, and head were recorded during forward reaching tasks (hand on overhead ball and hand to head) and a backward reaching task (hand on the back pocket). The study revealed reduced shoulder flexion and extension in children with NBPP during hand on ball and on the back pocket tasks compared to unaffected controls. Limited elbow flexion was also observed in children with NBPP during the hand on ball and hand on the head tasks. During the hand to head task, children with NBPP presented increased head flexion compared to unaffected controls. Scapular kinematics analysis showed increased posterior tilt in children with NBPP during forward reaching (the hand on ball and hand to head tasks). In the backward reaching task (hand on the back pocket), the NBPP group exhibited reduced scapular external rotation compared to unaffected controls. These findings indicate distinct kinematics in the scapula, shoulder, elbow, and head during reaching tasks for children with NBPP compared to controls. Furthermore, different execution speeds did not alter the kinematic differences between the groups.

This study aimed to compare the effects of electroacupuncture on traditional acupoints and muscle belly of different target muscles against upper limb dysfunction in stroke patients with hemiplegia. A total of thirty-nine stroke patients with subacute hemiplegia were randomly divided into the control group (n = 19) and observation group (n = 20). The control group was treated with physical therapy and normal electroacupuncture, while the observation group was treated with physical therapy and ultrasound-guided electroacupuncture on the muscle belly. After three weeks' intervention, the scores of Barthel Index, Fugl-Meyer assessment and Action Research Arm Test were compared between the two groups. Before the intervention, there were no significant differences in the scores of Barthel Index, Fugl-Meyer assessment and Action Research Arm Test between these two groups. After three weeks' intervention, there was significant increase in the scores of Barthel Index, Fugl-Meyer assessment, and Action Research Arm Test between the observation and control groups. Electroacupuncture on muscle belly under ultrasound guidance could significantly improve the performance of activities of daily living, motor function and the upper limb function in patients with subacute hemiplegia after stroke, and its effect was superior to electroacupuncture on the acupoints.

This review verified the extent, variety, quality and main findings of studies that have tested the neurophysiological and clinical effects of muscle tendon vibration (VIB) in individuals with sensorimotor impairments. The search was conducted on PubMed, CINAHL, and SportDiscuss up to April 2024. Studies were selected if they included humans with neurological impairments, applied VIB and used at least one measure of corticospinal excitability using transcranial magnetic stimulation (TMS). Two investigators assessed the studies' quality using critical appraisal checklists and extracted relevant data. The 10 articles included were diverse in populations and methods, generally rated as 'average' to 'good' quality. All studies reported an increased corticospinal excitability in the vibrated muscle, but the effects of VIB on non-vibrated muscles remain unclear. Positive clinical changes in response to VIB were reported in a few studies, such as a decreased spasticity and improved sensorimotor function. These changes were sometimes correlated with corticospinal effects, suggesting a link between VIB-induced plasticity and clinical improvements. Despite the limited and heterogeneous literature, this review supports the facilitatory influence of VIB on motor outputs controlling vibrated muscles, even with altered sensorimotor functions. It highlights knowledge gaps and suggests future research directions on VIB mechanisms and clinical implications.

Individuals post-stroke commonly demonstrate alterations in motor behavior with regard to both task performance and the motor strategies used in pursuit of task goals. We evaluated whether constraining postural sway (motor strategy) during practice would affect upper-limb precision aiming performance (task performance) and postural control adaptations. Adults with stroke stood on a force plate while immersed in a virtual scene displaying an anterior target. Participants aimed to position a virtual laser pointer (via handheld device) in the target. Participants then completed practice trials involving aiming at a lateral target. For this practice session, participants were randomized to either (a) a "constraint" group wherein they received physical constraint to limit postural sway, or (b) a "no-constraint" group. Task performance and postural control were assessed before and after practice, and transfer to another upper-limb task was evaluated. After practice, both groups improved paretic upper-limb performance. For the target task, the no-constraint group showed task-sensitive changes in postural control. The constraint group showed no changes in postural control. At transfer, the constraint group increased postural sway. Constraining postural sway after stroke should be carefully considered with the recognition that postural sway arises from exploratory movements involved in the discovery of adaptable motor solutions.