The effects of skin cold stimulation on quadriceps muscle activity during walking in older adults.

Purpose: Given that walking speed declines with ageing and decreasing walking speed restricts activities of daily living (ADL), it is important for the old to maintain walking speed in order to prevent affecting ADL. Although skin cold stimulation (SCS) facilitates instantaneous muscle activity, which occurs during walking, the effects of SCS on muscle activity during walking remain unclear. Thus, the present study aimed to investigate the effect of SCS during walking in older adults.Methods: Seventeen community-dwelling healthy older adults (73 ± 6 years old) participated in this study. Walking speed at a comfortable pace and the electromyographic (EMG) activity of the vastus lateralis (VL) and biceps femoris (BF) were measured. SCS, which maintains the skin temperature at 25 °C, was applied to the front of the thigh during the procedures. Walking speed, root mean square EMG (rmsEMG) and mean power frequency (MPF) were compared under SCS and control conditions.Results: SCS significantly increased the walking speed (p < 0.01) and the rmsEMG of the vastus lateralis (p = 0.032). No change in the rmsEMG of the BF was observed, and SCS had no effect on MPF of both the VL and BF. Furthermore, a significant relationship was observed between these changes (r = 0.619, p = 0.042).Conclusion: SCS increased the EMG activity of the VL while increasing walking speed. Our results suggest that SCS is an effective strategy that can be included in daily life in order to improve walking ability of older adults.

EFFECTS OF THE TURNING POINTS OF DECREASING SKIN TEMPERATURE ON THE THRESHOLD FORCE OF MOTOR UNITS DURING SLOW RAMP CONTRACTION / 体力科学

The present study examined the recruitment threshold of motor units (MUs) and the cold reflex activation of the cutaneous receptors at the first turning point (TP1) and the second turning point (TP2) of decreasing skin temperature. The skin temperatures of the biceps brachii were continuously reduced using a cooling chamber fixed at -10°C. TP1 and TP2 appeared at 25.5±0.5°C and 18.5±2.21°C, respectively. The data were collected at±1°C of TP1 and TP2 (TP1-B, TP1-A, TP2-B and TP2-A) . The MUs was collected during a slow ramp contraction for 3 sec to 20% maximal voluntary contraction (20%MVC) at the each measure points (TE) . The rates of decrease in skin temperature were 1.242±0.349°C min at slope-1 (TP1-B), 0.627±0.284°C rain at slope-2 (TP1-A and TP2-B), and 0.201±0.045°C/min at slope-3 (TP2-A) . The difference of the threshold force value (ΔTF= TE-control value) of LT-MUs were positive value, on the other hand, ΔF of HT-MUs were negative value at TP1-B, TP1-A, TP2-B and TP2-A. The changes of ΔTF of LT-MUs were a little at TP1-B, TP1-A, TP2-B, and increased markedly more at TP2-A than at TP1-B (p<0.05) . On the other hand, the ΔTF of HT-MUs decreased significantly more at TP1-B than at TP1-A and TP2-B (p<0.05), however, it did not significantly differ at TP2-A. These results suggested that the threshold force of HT-MUs depend on skin temperature and LT-MUs depend on decrease speed of skin temperature.