Influence of leg muscle vibration on human walking

We studied the effect of vibratory stimulation of different leg muscles [bi lateral quadriceps (Q), hamstring (HS) muscles, triceps surae (TS), and tib ialis anterior (TA)] in seven normal subjects during 1) quiet standing, 2) stepping in place movements, and 3) walking on the treadmill. The experimen ts were performed in a dimly illuminated room, and the subjects were given the instruction not to resist the applied perturbation. In one condition th e velocity of the treadmill was controlled by a feedback from the subject's current position. In normal standing, TA vibration elicited a prominent fo rward body tilt, whereas HS and TS vibration elicited backward trunk or who le body inclination, respectively. Q vibration had little effect. During st epping in place, continuous HS vibration produced an involuntary forward st epping at about 0.3 m s(-1) without modifying the stepping frequency. When the subjects (with eyes closed) kept a hand contact with an external still object, they did not move forward but perceived an illusory forward leg fle xion relative to the trunk. Q, TS, and TA vibration did not cause any syste matic body translation nor illusory changes in body configuration. In tread mill locomotion, HS vibration produced an involuntary steplike increase of walking speed (by 0.1-0.6 m s(-1)). Continuous vibration elicited larger sp eed increments than phasic stimulation during swing or stance phase. For ph asic stimulation, HS vibration tended to be more effective when applied dur ing swing than during stance phase. Q, TA, and TS vibration had little if a ny effect. Vibration of thigh muscles altered the walking speed depending o n the direction of progression. During backward locomotion, the walking spe ed tended to decrease after HS vibration, whereas it significantly increase d after Q vibration. Thus the influence of leg muscle vibration on stepping in place and locomotion differed significantly from that on normal posture . We suggest that the proprioceptive input from thigh muscles may convey in formation about the velocity of the foot movement relative to the trunk.