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The goal of this study was to investigate the control strategy employed by gymnasts in maintaining a hand balance. It was hypothesized that a “wrist strategy” was used in which perturbations in the sagittal plane were corrected using variations in wrist flexor torque with synergistic shoulder and hip torques acting to preserve a fixed body configuration. A theoretical model of wrist strategy indicated that control could be effected using wrist torque that was a linear function of mass center displacement and velocity. Four male gymnasts executed hand balances and 2-dimensional inverse dynamics was used to determine net joint torque time histories at the wrist, shoulder, and hip joints in the sagittal plane. Wrist torque was regressed against mass center position and velocity values at progressively earlier times. It was found that all gymnasts used the wrist strategy, with time delays ranging from 160 to 240 ms. The net joint torques at the shoulder and hip joints were regressed against the torques required to maintain a fixed configuration. This fixed configuration strategy accounted for 86% of the variance in the shoulder torque and 86% of the variance in the hip torque although the actual torques exceeded the predicted torques by 7% and 30%, respectively. The estimated time delays are consistent with the use of long latency reflexes, whereas the role of vestibular and visual information in maintaining a hand balance is less certain.

The present study quantified reaching movements in 17 patients with vascular hemiplegia at various stages of recovery and 6 control subjects. The task involved grasping a light cone placed at one of seven positions on a baseboard. 3D analysis of movement was performed. Quantification of the reaching movement in hemiparetic patients showed abnormal features that could be related either directly to the motor impairment or to two kinds of adaptation to the impairment: acquisition of a new motor coordination or acquisition of a new strategy. Two movement strategies were identified in hemiparetic patients. Patients with a predominantly proximal impairment slid their hands toward the target, thus making maximal use of the properties of the environment. Patients with a predominantly distal impairment made a downward grasping movement, which probably used the passive properties of the hand-object contact to ensure grasping. These features contribute to fulfillment of the goal and are thus consistent with the acquisition of adaptive behavior by the hemiparetic patients.

The purpose of this study was to simulate the control of an external force using different strategies of muscle coordination and to compare the predicted patterns of muscle forces with those of electromyographic activity reported in the literature for the same task. We simulated a motor task in which a person sitting on a chair exerts an external force by pushing on the ground (or pulling a strap) in five different directions with two different force magnitudes. The results of this study suggest that during the control of an external force in pushing directions, more force is allocated to muscles with long moment arms and a large physiological cross-sectional area, and the number of simultaneously active muscles is increased. This strategy of muscle coordination corresponds to the strategy of minimizing muscle fatigue, and it is characterized by features of muscle coordination that agree with those reported in experimental studies of walking, running, jumping, and cycling.

The hypothesis that persons with Down syndrome are likely to trade mechanical efficacy of motor patterns for safety was tested in a study of postural adjustments associated with fast voluntary movements. Control subjects and subjects with Down syndrome performed bilateral shoulder flexion and extension movements “as fast as possible” while standing on a force platform. Anticipatory changes in the background activity of postural muscles were seen in both groups of subjects. Subjects with Down syndrome demonstrated simultaneous EMG bursts in postural “agonist-antagonist” pairs. Subjects with Down syndrome also demonstrated patterns of deviations in the major postural joints, suggesting that they were using a different strategy which may be a correlate of “clumsiness.” It was concluded that practice in conditions of changing components of a motor task is the most promising way to encourage the central nervous system of persons with Down syndrome to search for alternative strategies and improve these individuals' ability to solve everyday motor problems.

To assess the postural strategies developed over the first 2 months following surgery by ACL patients during rehabilitation and highlight the sensory-motor impairment recovery, 21 patients were measured at three timeframes. Three two-legged standing conditions were assessed: with the eyes open, with the eyes closed either wearing or not wearing a knee orthosis. The results indicate that the weight-bearing asymmetry, initially observed (i.e., 56–44% of body-weight), disappeared progressively during rehabilitation (51–49%). The comparison of the plantar center-of-pressure displacements under both sound and operated legs demonstrated noticeable differences that also tended to decrease but without reaching a matched behavior during the last measures. These effects were seen in both eyes open and eyes closed conditions with the greatest effects in the latter condition. Wearing a knee orthosis inferred no particular changes in the postural control behaviors. These data could be used as benchmarks for highlighting the effects on undisturbed postural control of various surgery techniques and/or rehabilitation protocols.

A simultaneous turn and step motion is a vital component of many complex movements and may provide insight into age related balance and stability deficits during a weight transfer task. In this study, nine young adults and ten healthy, community dwelling older adults performed a simultaneous “turn and step” task from a quiet standing position under two self-selected speeds, self-paced and as quickly and efficiently as possible. Whole-body center of mass was estimated to investigate stability, segmental coordination, and variability. Older adults performed the task with greater variability, however they were unable to alter stability nor segmental coordination across the self-selected speeds; absence of this modulation portrays a trade-off between stability and manoeuvrability. An increase in variability with no observed directional differences suggests that the simultaneous turn and step task may be a sensitive discriminatory motor task helpful in elucidating the adoption of altered control strategies used by elderly populations.