Effects of displacements of center of gravity and center of pressure on standing postural responses to platform translations after cooling of soles and crural muscles

The purpose of this study was to examine whether the sole cutaneous sensory and sole muscle spindle afferent signals or crural muscle (tibialis anterior: TA, soleus: Sol) spindle afferent signals contribute to dynamic postural control by cooling of the sole and crus. The subjects were 12 healthy young adult males (age: 21.3 ± 2.9, height: 170.8 ± 6.2 cm, weight: 65.3 ± 6.0 kg). The platform backward and forward translations were executed before cooling condition (control), and under cutaneous temperature below 20 degree C after cooling (cutaneous sensory, muscle spindle and muscle strength were inactive) and cutaneous temperature over 20 degree C after cooling (cutaneous sensory and muscle spindle were inactive) conditions. After applying platform translations, the first maximum displacements (cm) and peak time of COG and COP (ms) were selected. Latencies of Sol and TA EMG activities (RT) were measured in each condition. Latencies of Sol and TA EMG activities were not affected by cooling. In the first maximum displacements, peak times of COG and COP in the cutaneous temperature over 20 degree C after sole cooling and platform backward translation condition were significantly delayed compared to the control, however, there was no significant delay for the forward translation condition. The results suggest that sole cutaneous and muscle spindle afferent signals contribute were to reflexive postural reaction in platform backward translation, than Sol spindle afferent signals and that sole cutaneous afferent signals are not much related to reflexive postural reaction in platform forward translation.