Passive exercise system: effect on muscle activity, strength, and lean body mass.

There is little information concerning the effects of passive exercise training in healthy humans. This prompted an investigation to evaluate muscle activity and the associated changes in strength and lean body mass resulting from a passive exercise program. Twenty-eight healthy volunteers, aged 26 to 44 years, participated in this six-week study. Lean body mass changes were evaluated by tetrapolar bioelectric impedance measurements, strength changes by isokinetic strength evaluation, and muscle activity by surface EMG techniques. Reproducible muscle activity was recorded in all three muscles studied during two of three preselected exercises. This involuntary muscle activity was attributed to fusimotor and postural reflexes. No significant change (p greater than .05), however, occurred in muscle strength or lean body mass at the end of the six weeks. Lack of these physiologic changes in light of the documented muscle activity is attributed to insufficient training effect.