Fatigue in mammalian skeletal muscle stimulated under computer control

Functional electrical stimulation (FES) is used to provide paralyzed human subjects with postural support and a limited range of movements. Problems e ncountered with FES include jerky movements from tension oscillations durin g stimulation and rapid muscle fatigue. In this paper, we report experiment s on anesthetized cats that test a new, computer-controlled method of stimu lation of the muscle nerve supply, distributed across several inputs, which reduces these problems. After 5 min of continuous, distributed stimulation of the medial gastrocnemius muscle at 6 pulses per second (pps) across 6 c hannels, tension fell to 55.9 +/- 3.9% (SE) of its original value. In compa rison, after 5 min of synchronous stimulation of one muscle portion at 36 p ps, tension fell to 11 +/- 3.7%. At higher stimulation rates, 10 pps per ch annel (distributed) and 60 pps (synchronous), the differences in fatigue we re even greater. Similar results were obtained when an intermittent, rather than a continuous, stimulation protocol was used. These findings indicate that distributed stimulation has important advantages over other methods fo r applications such as FES.