Effects of bed rest and the use of intermittent centrifugation to protect human balance and neuromotor reflexes

Intermittent artificial gravity (AG) treatments may reduce bone, muscle, and cardiovascular deconditioning during prolonged space flight; however, the effects of repeated centrifugation on central processing of vestibular information remain unknown. This study investigated the effects of one intermittent AG prescription on balance control and neuromotor reflex function in a ground-based study of subjects exposed to bed rest. Fifteen male volunteers were exposed to 21 days of 6° head-down-tilt (HDT) bed rest (BR) to simulate some of the effects of space flight. Eight were treated with daily 1 h AG exposures aboard a short radius centrifuge that provided 1-g footward loading at heart level. The other seven served as control subjects. Balance control was assessed using a computerized dynamic posturography (CDP) protocol modified by adding low frequency pitch-plane head movements. Neuromotor reflex function was assessed using tendon (MSR) and functional stretch reflex (FSR) data collected from the triceps surae muscle group. CDP performance was degraded by BR in both groups, but was unaffected by AG. BR also degraded MSR and FSR functions in both groups, but AG blunted the decrement in MSR. This AG prescription had little functionally relevant effect on balance control, but may have had some salutary effect on neuromotor reflexes.