Control of bipedal posture following localised muscle fatigue of the plantar-flexors and finger-flexors

The Use of the Anchor System Reduces Postural Sway During Upright Standing Irrespective of Plantar Flexors Muscle Fatigue in Young and Older Adults

Our purpose was to verify the effects of the use of the anchors on postural control after the fatigue of the plantar flexor muscles in young and older adults. They stood barefoot, with their eyes closed in four conditions combining the use of the anchors and the fatigue. When using the anchors, participants held one cable in each hand and kept the cable taut without removing the loads (125 g) from the ground. The fatigue protocol consisted of performing a single series of bilateral plantar flexion movements. The fatigue protocol increased postural sway in both groups. Both groups reduced postural sway with the anchors, but this effect was independent of fatigue. We conclude that the anchors contributed to the reduction of postural sway in young and older adults, but they were unable to compensate for the disturbing effect in postural control created by fatigue of the plantar flexor muscles.

Leg skin stimulation can be a strategy to improve postural control in the elderly

Previous studies suggested that skin stimulation by using medical tape glued to the skin over the Achilles tendon can improve postural control in young adults. Such strategy can be valuable if helping to improve postural control in the elderly. Here, we tested the effects of skin stimulation on the postural control of elderly while standing barefoot. Twenty-two voluntary elderly had postural control assessed under different conditions of skin stimulation. Center of pressure was monitored while they stood quietly barefoot on a force plate during standing with and without medical tape glued to the skin over the Achilles tendon. There were effects of skin stimulation for anteroposterior amplitude of center of pressure displacement, mediolateral amplitude of center of pressure displacement, and area of the ellipse for 95% of center of pressure data (P<.05). These results are promising considering that skin stimulation by using medical tape is feasible even for low incoming subjects and possible to self manage for improvements in postural control.

Sensory Substitution for Balance Control Using a Vestibular-to-Tactile Device

Postural control is essential for most activities of daily living. The impairment of this function can be extremely disabling. This work was stimulated by the testimony of a bilateral partial foot amputee who describes his difficulty in maintaining balance while washing his hair in the shower. We postulated that if the postural control system could not rely on accurate and reliable somatosensory inputs from the foot and ankle, as is probably the case following bilateral foot amputation due to the loss of the foot afferents and efferents, the weight of visual and vestibular cues would increase. We therefore assessed if a vestibular-to-tactile sensory substitution device could compensate for this impairment. Two separate experiments were conducted. Experiment 1: The effect of a vestibular-to-tongue tactile biofeedback balance system on the postural stability of this amputee was tested (on a force platform) and compared with a non-amputated, matched control group. The results showed that use of the biofeedback reduced centre of foot (CoP) displacement in all subjects but more spectacularly in the amputee. Experiment 2: The effect of the biofeedback was tested in 16 young healthy adults following a protocol of ankle muscle fatigue (known to alter ankle neuromuscular function and to perturb the control of bipedal posture). The results showed a significant decrease in CoP displacement compared with the control, non-biofeedback condition and a significantly greater effect of the biofeedback in the fatigue than the non-fatigue condition. Taken together, the results of these two studies suggest that an individual with double partial foot amputation was able to improve his balance control thanks to the use of a vestibular-to-tongue tactile biofeedback balance system and that young healthy individuals were able to take advantage of it to reduce the postural destabilisation induced by plantar-flexor muscle fatigue. Further studies are however necessary to confirm this in larger numbers of impaired persons as well as to assess the effectiveness in dynamic situations.

Physiological load and posture control thresholds

The aim of the study was to evaluate the influence of the physiological load on postural control. Special attention was directed toward the identifying the intensity level in which the major deterioration in balance abilities occurs. Thirty subjects randomly divided into two groups performed multistage all-out exertion protocol on cycle-ergometer with measurements of ventilatory-metabolic and subjective parameters of exertion. Each stage lasted three minutes and was followed with three minute breaks during which the subjects underwent the static (keeping the cursor in the center of the screen) and the dynamic balance testing (following the cursor clockwise or counter clock wise by body movements) on balance platform. In a control group, the protocol encompassed only balance testing procedures followed by 3 min rest. After the completion of the testing procedures, the five intensity zones were determined according to the ventilatory-metabolic parameters. The significant differences in both static and dynamic balance tests were found between the test stages in exercising group. The post hoc analyses revealed the significant negative effect of exercise on the static balance with three visible "balance thresholds". The first threshold was at the rest to work transition, the second at the anaerobic threshold and the third at the maximal exertion level. The dynamic balance was also negatively affected with exercise, however no "balance thresholds" were clearly identified. No significant changes in neither static nor dynamic balance abilities were observed in the control group so the changes in the experimental group could have been attributed to the exercise intensity.