Efficiency of FNS leg cycle ergometry

The efficiency of electrically induced leg cycle ergometry performed by spinal-cord-injured (SCI) subjects was compared to voluntary leg cycle ergometry performed by able-bodied (AB) subjects at power output (PO) levels of 6-42 W. Twenty SCI (nine quadriplegics and 11 paraplegics) and twenty AB subjects exercised on a leg cycle ergometer. SCI subjects received functional neuromuscular stimulation (FNS) of paralyzed leg musculature, while AB subjects pedaled voluntarily. Subjects performed a discontinuous, progressive intensity exercise test with 6-W (for SCI) or 12-W (for AB) PO increments between stages. Each exercise bout was 5 min in duration and was followed by a 5-min rest period. Steady-rate oxygen uptake (VO₂) and respiratory exchange ratio (RER) values were determined by open-circuit spirometry during the final minute of each stage. Gross, net, work, and data efficiencies were calculated for each PO. These efficiencies ranged from 2 to 14% for FNS cycling by SCI subjects and from 4 to 34% during voluntary cycling by AB subjects. At most POs, efficiencies for FNS cycling were significantly lower (by approximately one-half) than those for voluntary cycling. Despite the apparent energy-wastefulness or inefficiency of FNS leg cycle ergometry, the relatively high metabolic rates elicited by the exercise may be advantageous to SCI individuals seeking aerobic (cardiopulmonary) training effects