Although the trunk segment shows well-coordinated movements in concert with the arms and legs during bipedal walking, little is understood about the neural mechanisms controlling the trunk muscles in response to sudden tactile sensations in the foot during walking. This study examined the cutaneous reflexes (CR) to shed light on the neural mechanisms underlying the regulation of the trunk muscles during walking and standing. Eleven healthy men participated in the study. Electromyographic (EMG) activities were recorded in the trapezius (TRAP), erector spinae (ES), and rectus abdominis (RA) muscles. To elicit CR, non-noxious electrical stimulation of the sural nerve at the ipsilateral lateral malleolus was applied during treadmill walking and tonic contraction of the test muscles during standing. During walking, cutaneous nerve stimulation in the foot gave rise to facilitatory CR in all the muscles, and the amplitude of the CR was strongly modulated in a phase-dependent manner. The amplitude of the background EMG and the amplitude of the CR showed a highly significant correlation in all the muscle tested during standing. However, this was true only in the ES during walking. In the RA, the inhibitory CR during standing changed to a facilitatory one during walking. In addition, reflex ratios were significantly larger during walking than standing. These findings suggest that common neural mechanisms in limb muscles could function in the TRAP and RA, however, in the ES disparate neural mechanisms play a crucial role in modulating cutaneous reflexes during walking and standing.

We investigated the effect of anodal transcranial direct current stimulation (anodal tDCS) on the performance of full-effort box stepping exercises in athletes and non-athletes. Twenty-one subjects (athletes: five men and six women, non-athletes: four men and six women) participated in this study. tDCS was applied through two electrodes placed on the vertex (anode) and the forehead (cathode). A 2-mA anodal stimulation was applied for 15 minutes, while sham stimulation was applied on different days with similar electrodes. Participants were asked to apply a maximal effort while stepping up and down a 10-cm tall box for 20 s following termination of the tDCS. The 20 s box stepping was repeated three times with 15 s of rest. The number of total steps was significantly increased following anodal tDCS compared to sham tDCS. The degree of increase in performance was more prominent in non-athletes than in athletes. In non-athletes, a differential pattern of fatigue in performance between stimulus conditions was observed. In contrast, this significant performance modulation between stimulus conditions was not detected in athletes. Our findings of improved stepping performance following anodal tDCS depended on the training level of the subject group; this implies modulation of descending command from CNS to active muscles by tDCS. It is suggested that the degree of neural modulation for controlling complex and full-effort leg movements due to tDCS is higher in non-athletes than in athletes.