Human Movement Science最新文献

The ability to coordinate actions between the limbs is important for many operationally relevant tasks associated with space exploration. A future milestone in space exploration is sending humans to Mars. Therefore, an experiment was designed to examine the influence of inherent and incidental constraints on the stability characteristics associated with the bimanual control of force in simulated Martian gravity. A head-up tilt (HUT)/head-down tilt (HDT) paradigm was used to simulate gravity on Mars (22.3° HUT). Right limb dominant participants (N = 11) were required to rhythmically coordinate patterns of isometric forces in 1:1 in-phase and 1:2 multifrequency patterns by exerting force with their right and left limbs. Lissajous displays were provided to guide task performance. Participants performed 14 twenty-second practice trials at 90° HUT (Earth). Following a 30-min rest period, participants performed 2 test trials for each coordination pattern in both Earth and Mars conditions. Performance during the test trials were compared. Results indicated very effective temporal performance of the goal coordination tasks in both gravity conditions. However, results indicated differences associated with the production of force between Earth and Mars. In general, participants produced less force in simulated Martian gravity than in the Earth condition. In addition, force production was more harmonic in Martian gravity than Earth gravity for both limbs, indicating that less force distortions (adjustments, hesitations, and/or perturbations) occurred in the Mars condition than in the Earth condition. The force coherence analysis indicated significantly higher coherence in the 1:1 task than in the 1:2 task for all force frequency bands, with the highest level of coherence in the 1–4 Hz frequency band for both gravity conditions. High coherence in the 1–4 Hz frequency band is associated with a common neural drive that activates the two arms simultaneously and is consistent with the requirements of the two tasks. The results also support the notion that neural crosstalk stabilizes the performance of the 1:1 in-phase task. In addition, significantly higher coherence in the 8–12 Hz frequency bands were observed for the Earth condition than the Mars condition. Force coherence in the 8–12 Hz bands is associated with the processing of sensorimotor information, suggesting that participants were better at integrating visual, proprioceptive, and/or tactile feedback in Earth than for the Mars condition. Overall, the results indicate less neural interference in Martian gravity; however, participants appear to be more effective at using the Lissajous displays to guide performance under Earth's gravity.

The jump smash is badminton's most aggressive technical manoeuvre, which is often the key to winning a match. This paper aims to explore the neuromuscular control strategies of advanced and beginner players when jumping smash in different ways. Collecting sEMG and kinematic data from 18 subjects with different motor experiences when jumping smash. Nonnegative Matrix Factorization and K-Means clustering were used to extract muscle synergies and exclude irrelevant combined synergies. Uncontrolled manifold analysis was then used to explore the association between synergies and shoulder stability. In addition, motor output at the spinal cord level was assessed by mapping sEMG to each spinal cord segment. The study found that advanced subjects could respond to different jump smash styles by adjusting the coordinated activation strategies of the upper-limb and postural muscles. Long-term training can induce a rapid decrease in the degree of co-variation of the synergies before contact with a shuttlecock to better cope with an upcoming collision. It is recommended that beginners should focus more on training the coordination of upper-limb muscles and postural muscles.

Bradykinesia, or slow movement, is a defining symptom of Parkinson's disease (PD), but the underlying neuromechanical deficits that lead to this slowness remain unclear. People with PD often have impaired rates of motor output accompanied by disruptions in neuromuscular excitation, causing abnormal, segmented, force-time curves. Previous investigations using single-joint models indicate that agonist electromyogram (EMG) silent periods cause motor segmentation. It is unknown whether motor segmentation is evident in more anatomically complex and ecologically important tasks, such as handgrip tasks. Aim 1 was to determine how handgrip rates of force change compare between people with PD and healthy young and older adults. Aim 2 was to determine whether motor segmentation is present in handgrip force and EMG measures in people with PD. Subjects performed rapid isometric handgrip pulses to 20–60% of their maximal voluntary contraction force while EMG was collected from the grip flexors and extensors. Dependent variables included the time to 90% peak force, the peak rate of force development, the duration above 90% of peak force, the number of segments in the force-time curve, the number of EMG bursts, time to relaxation from 90% of peak force, and the peak rate of force relaxation. People with PD had longer durations and lower rates of force change than young and older adults. Six of 22 people with PD had motor segmentation. People with PD had more EMG bursts compared to healthy adults and the number of EMG bursts covaried with the number of segments. Thus, control of rapid movement in Parkinson's disease can be studied using isometric handgrip. People with PD have impaired rate control compared to healthy adults and motor segmentation can be studied in handgrip.

An infant's musculoskeletal and motor development is largely affected by their environment. Understanding how different mechanical environments affect an infant's movements and muscle use is necessary to inform the juvenile products industry and reduce incidents involving inclined nursery products each year. The purpose of this study was to determine how the coordinated movements and corresponding muscle activation patterns are affected by different mechanical environments, specifically the back incline angle. Thirty-eight healthy infants (age: 6.5 ± 0.7 months; 23 M/15 F) were enrolled in this IRB-approved in-vivo biomechanics study. Surface electromyography sensors recorded muscle activity of the erector spinae, abdominal muscles, quadriceps, and hamstrings while infants rolled in five different mechanical environments: a flat surface and four device configurations representing a range of inclines infants are commonly exposed to. Coordinated movements were determined using video. In all configurations featuring an inclined seatback angle, infants experienced significantly higher erector spinae muscle activation and significantly lower abdominal muscle activation compared to the flat surface. Infants also exhibited a different coordinated movement featuring spinal extension and a pelvic thrust in the inclined device configurations that was not previously observed on the flat surface alone. Understanding how infants coordinate their movements and use their muscles during rolling in different inclined environments provides more insight into motor development and may inform the juvenile products industry. Many factors impact an infant's movements, therefore future work should explore how other environmental interactions influence an infant's movements and muscle activation, particularly for rolling.

Previous research has reported mixed findings regarding age-related changes in dynamic postural stability, quantified by margin of stability (MOS), during gait. However, age-related changes in MOS may be better elicited by tasks imposing greater challenges to the postural control system. Older adults' MOS during obstacle crossing, a destabilizing task, has previously been characterized, although studies comparing MOS during this task between younger and older adults remain sparse. This study investigated age-related changes in dynamic postural stability during quiet standing, gait, and obstacle crossing. Participants aged 20–30 (n = 20), 60–69 (n = 18), 70–79 (n = 15), and 80+ (n = 7; not analyzed statistically) years old performed these tasks while whole-body motion was tracked using motion capture. MOS in each direction was estimated throughout each trial, and integrals, transient ranges, and trial minima were extracted (as applicable). MOS time series were also ensemble averaged across age groups. No age-related differences were identified for quiet standing or gait. However, obstacle crossing metrics revealed greater stability (i.e., more positive MOS) and less instability (i.e., less negative MOS) in older adults, and reduced ranges during transients. These findings potentially arise from shorter step lengths, which may be the result of age-related physical declines; or may reflect a cautious strategy in older adults, which maximizes postural stability in the direction with the greatest consequences for foot-obstacle contact, as it changes throughout the task. This study supports the use of tasks imposing physical challenges and/or voluntary perturbations to study age-related changes in dynamic postural stability. Findings also contribute to our theoretical understanding of the time course of dynamic postural stability during functional tasks in relation to periods of transition in the base of support, and task-specific strategies adopted for obstacle crossing by older adults to maintain dynamic postural stability and mitigate fall risk.

Purpose

Considering the relationship between aging and neuromuscular control decline, early detection of age-related changes can ensure that timely interventions are implemented to attenuate or restore neuromuscular deficits. The dynamic motor control index (DMCI), a measure based on variance accounted for (VAF) by one muscle synergy (MS), is a metric used to assess age-related changes in neuromuscular control. The aim of the study was to investigate the use of one-synergy VAF, and consecutively DMCI, in assessing age-related changes in neuromuscular control over a range of exercises with varying difficulty.

Methods

Thirty-one subjects walked on a flat and inclined treadmill, as well as performed forward and lateral stepping up tasks. Motion and muscular activity were recorded, and muscle synergy analysis was conducted using one-synergy VAF, DMCI, and number of synergies.

Results

Difference between older and younger group was observed for one-synergy VAF, DMCI for forward stepping up task (one-synergy VAF difference of 2.45 (0.22, 4.68) and DMCI of 9.21 (0.81, 17.61), p = 0.033), but not for lateral stepping up or walking.

Conclusion

The use of VAF based metrics and specifically DMCI, rather than number of MS, in combination with stepping forward exercise can provide a low-cost and easy to implement approach for assessing neuromuscular control in clinical settings.

Exoskeletons are wearable devices that support or augment users' physical abilities. Previous studies indicate that they reduce the physical demands of repetitive tasks such as those involving heavy material handling, work performed with arms elevated, and the use of heavy tools. However, there have been concerns about exoskeletons hindering movement and reducing its precision. To this end, the current study investigated how proprioception enables people to point to targets in a blindfolded, repetitive pointing task, and their ability to recalibrate their pointing movement based on visual feedback during an intervening calibration phase, both with and without an arm-support exoskeleton. On each trial, participants were instructed to follow a 40 BPM metronome to point six times alternating between two target points placed either on a vertical or horizontal line. Within a trial, each pointing movement alternated between flexion and extension. Results indicate that participants' average pointing error increased by 4% when they wore an exoskeleton, compared to when they did not. The average pointing error was 12% lower when the target points were aligned vertically as compared to horizontally. It was also observed that the average pointing error was 14% lower during flexion as compared to extension movement. Surprisingly, accuracy did not improve in the post-test as compared to the pre-test phase, likely due to accuracy being high from the beginning. Participants' movement dynamics were analyzed using Recurrence Quantification Analysis. It was found that movements were less deterministic (1% reduction in percentage of determinism) and less stable (13.6% reduction in average diagonal line length on the recurrence plot) when they wore the exoskeleton as compared to when they did not. These results have implications on the design of arm-support exoskeletons and for facilitating their integration into the natural motor synergies in humans.

Perception of task goal influences motor performance and coordination. In bimanual actions, it is unclear how one's perception of task goals influences bimanual coordination and performance in individuals with unilateral stroke. We characterized inter-limb coordination differences in individuals with chronic right- and left-hemisphere damaged (RCVA: n = 24, LCVA: n = 24) stroke and age-matched neurotypical controls (n = 24) as they completed bimanual reaching tasks under distinct goal conditions. In the dual-goal condition, participants reached to move two virtual bricks (cursors) assigned to each hand toward independent targets. In the common-goal condition, they moved a central common virtual brick representing both hands to a single, central target. Spatial and temporal coordination (cross-correlation coefficients of hand velocity and their time-lag), the redundant axis deviations (the hand deviations in the axis orthogonal to the axis along the cursor-target direction), and the contribution ratio of the paretic hand were measured. Compared to the dual-goal condition, reaching actions to the common-goal demonstrated better spatial bimanual coordination in all three participant groups. Temporal coordination was better during common-goal than dual-goal actions only for the LCVA group. Additionally, and novel to this field, sex, as a biological variable, differently influenced movement time and redundant axis deviation in participants with stroke under the common-goal condition. Specifically, female stroke survivors showed larger movements in the redundant axes and, consequently, longer movement times, which was more prominent in the LCVA group. Our results indicate that perception of task goals influences bimanual coordination, with common goal improving spatial coordination in neurotypical individuals and individuals with unilateral stroke and providing additional advantage for temporal coordination in those with LCVA. Sex influences bimanual performance in stroke survivors and needs to be considered in future investigations.

Predictive simulation of human motion could provide insight into optimal techniques. In repetitive or long-duration tasks, these simulations must predict fatigue-induced adaptation. However, most studies minimize cost function terms related to actuator activations, assuming it minimizes fatigue. An additional modeling layer is needed to consider the previous use of muscles to reveal adaptive strategies to the decreased force production capability. Here, we propose interfacing Xia's three-compartment fatigue dynamics model with rigid-body dynamics. A stabilization invariant was added to Xia's model. We simulated the maximum repetition of dumbbell biceps curls as an optimal control problem (OCP) using direct multiple shooting. We explored three cost functions (minimizing torque, fatigue, or both) and two OCP formulations (full-horizon and sliding-horizon approaches). We adapted Xia's model by adding a stabilization invariant coefficients $S=\left(10,5\right)$ for direct multiple shooting. Sliding-horizon OCPs achieved 20 to 21 repetitions. The kinematic strategy slowly deviated from a plausible dumbbell lifting task to a swinging strategy as fatigue onset increasingly compromised the humerus to remain vertical. In full-horizon OCPs, the latter kinematic strategy was used over the whole motion, resulting in 32 repetitions. We showed that sliding-horizon OCPs revealed a reactive strategy to fatigue when only torque was included in the cost function, whereas an anticipatory strategy was revealed when the fatigue term was included in the cost function. Overall, the proposed approach has the potential to be a valuable tool in optimizing performance and helping reduce fatigue-related injuries in a variety of fields.