Coupling between muscle activities and muscle torques during horizontal-planar arm movements with direction reversal.

In this study we investigated the hypothesis that the simple set of rules used to explain the modulation of muscle activities during single-joint movements could also be applied for reversal movements of the shoulder and elbow joints. The muscle torques of both joints were characterized by a triphasic impulse. The first impulse of each joint accelerated the limb to the target and was generated by an initial burst of the muscles activated first (primary mover). The second impulse decelerated the limb to the target, reversed movement direction and accelerated the limb back to the initial position, and was generated by an initial burst of the muscles activated second (secondary movers). A third impulse, in each joint, decelerated the limb to the initial position due to the generation of a second burst of the primary movers. The first burst of the primary mover decreased abruptly, and the latency between the activation of the primary and secondary movers varied in proportion with target distances for the elbow, but not for the shoulder muscles. All impulses and bursts increased with target distances and were well coupled. Therefore, as predicted, the bursts of muscle activities were modulated to generate the appropriate level of muscle torque.

Effect of light touch on postural sway in individuals with balance problems: a systematic review.

The aim of the present review was to examine the experimental, case-control studies that investigated the effect of light touch on postural sway in individuals with balance problems due to aging, brain lesion or other motor or sensory deficits. Articles published before the end of March of 2013 were searched in PubMed, Scielo and Lilacs databases using terms related to postural control and sensory information. Twelve studies that assessed the postural sway of individuals with balance problems during quiet standing with the light touch using a force plate were reviewed. Two reviewers rated all selected articles as having good quality. The effect of light touch on postural control was reported by all eligible studies regardless of the cause of the balance problem of the participants. Such effect was more evident when the applied vertical force was greater than 1N, but if individuals with poor balance took more advantage of the light touch than healthy ones it depended on the source of their balance problems and not the amount of the applied force. These findings suggested that the maintenance of the fingertip lightly touching an external surface could provide additional somatosensory information for individuals with poor balance and then it could be used as a strategy to improve the control of upright standing during intervention programs.

Individuals with post-stroke hemiparesis are able to use additional sensory information to reduce postural sway.

The present study aimed to investigate whether stroke survivals are able to use the additional somatosensory information provided by the light touch to reduce their postural sway during the upright stance. Eight individuals, naturally right-handed pre-stroke, and eight healthy age-matched adults stood as quiet as possible on a force plate during 35s. Participants performed two trials for each visual condition (eyes open and closed) and somatosensory condition (with and without the right or left index fingertip touching an instrumented rigid and fixed bar). When participants touched the bar, they were asked to apply less than 1N of vertical force. The postural sway was assessed by the center of pressure (COP) displacement area, mean amplitude and velocity. In addition, the mean and standard deviation of the force vertically applied on the bar during the trials with touch were assessed. The averaged values of COP area, amplitude and velocity were greater for stroke individuals compared to healthy adults during all visual and somatosensory conditions. For both groups, the values of all variables increased when participants stood with eyes closed and reduced when they touched the bar regardless of the side of the touch. Overall, the results suggested that, as healthy individuals, persons with post-stroke hemiparesis are able to use the additional somatosensory information provided by the light touch to reduce the postural sway.