Effects of the site and extent of plantar cutaneous stimulation on dynamic balance and muscle activity while walking.

BACKGROUND: Previous studies have demonstrated that stimulating the cutaneous plantar sensory receptors of the foot through textured insoles improves human balance and walking. This study investigated the effect of medial and lateral zoned textured insoles using tibialis anterior/peroneus longus surface electromyographic activity and Centre-of-Pressure as indicators of postural stability while walking. METHODS: 15 asymptomatic subjects were tested using a within-subject randomised repeated measures design. The effect of lateral and medial zoned insoles of varying heights (control, 2, 4 and 6mm) on stability while walking under normal and impaired visual conditions was assessed. RESULTS: Impaired vision resulted in an increase in foot CoP variability while walking (p<0.05). The laterally zoned insole was associated with a significant (repeated measures ANOVA p<0.05) increase in the rate of medial-lateral CoP change. CONCLUSION: These findings suggest that the site of stimulation of the plantar foot cutaneous receptors may increase postural instability during walking. This should be considered in the design of insoles that aim to improve balance and reduce falls risk. The importance of vision in balance control has been highlighted and using impaired vision may serve as a way of trialling clinical products in the healthy population.

Effect of experimentally reduced distal sensation on postural response to hip abductor/ankle evertor muscle vibration.

This study assessed whether postural responses induced by vibratory perturbations of the hip abductors and ankle evertors, were modified when distal tactile sensation was experimentally reduced through cooling. Sixteen healthy subjects were investigated pre and post cooling. Subjects stood with their eyes closed with a stance width of 4 cm. A 2s vibratory stimulus was applied to the left or right hip abductor or ankle evertor muscle. The order of the site and side of the stimulation was randomised. The postural response to hip abductor and ankle evertor vibration was recorded using 3D motion analysis (Codamotion, Leicestershire). Medio-lateral centre of pressure motion was simultaneously recorded during quiet standing via a force plate (Kistler, UK). Pre-cooling people responded to unilateral ankle vibration with an ipsilateral translation and tilt of the pelvis, and an ipsilateral tilt of the trunk. People responded to unilateral hip vibration with a contralateral translation and tilt of the pelvis, and an ipsilateral tilt of the trunk. Following an experimental reduction in distal tactile sensation there was a significant reduction in the amplitude of pelvic tilt in response to ankle vibration (F(6.2)=P<0.05) and a significant increase in amplitude of pelvic tilt in response to hip vibration (F(5.2)=P<0.05). This suggests that the sensitivity to artificial stimulation of hip proprioception increases with distal cooling, possibly indicating a change in the gain/weighting placed upon sensory information from the hips.

Interactions between tidal turbine wakes: experimental study of a group of three-bladed rotors.

It is well known that a wake will develop downstream of a tidal stream turbine owing to extraction of axial momentum across the rotor plane. To select a suitable layout for an array of horizontal axis tidal stream turbines, it is important to understand the extent and structure of the wakes of each turbine. Studies of wind turbines and isolated tidal stream turbines have shown that the velocity reduction in the wake of a single device is a function of the rotor operating state (specifically thrust), and that the rate of recovery of wake velocity is dependent on mixing between the wake and the surrounding flow. For an unbounded flow, the velocity of the surrounding flow is similar to that of the incident flow. However, the velocity of the surrounding flow will be increased by the presence of bounding surfaces formed by the bed and free surface, and by the wake of adjacent devices. This paper presents the results of an experimental study investigating the influence of such bounding surfaces on the structure of the wake of tidal stream turbines.