ELSEVIER 0268~0033(95)00030-5 Clinical Biomechanics Vol. 11, No. 1, pp. Sl-57, 1996 Copyright 0 1995 Elsevier Science Limited Printed in Great Britain. All rights resewed 0268~0033/96 $15.00 + 0.00 Pedal forces produced during neuromuscular electrical stimulation cycling in paraplegics P J Sinclair BPE MEd, G M Davis BPE PhD, R M Smith MSC MEd, B S Cheam BA~~SC, J R Sutton MD DSC Department of Biomedical Sciences, Faculty of Health Sciences, The University of Sydney, NSW, Australia Summary-This study investigated forces applied to the pedal of a cycle ergometer by paraplegic subjects undergoing neuromuscular electrical-stimulation-induced leg exercise. The patterns of force application were compared with those of able-bodied subjects cycling under voluntary muscle control in order to investigate the effectiveness of the muscle stimulation parameters. Results show that paraplegic subjects applied significantly larger peak forces than the able-bodied subjects because of the short duration of neuromuscular stimulation. Able-bodied subjects were able to achieve the same average workload by applying smaller forces over a greater percentage of each crank revolution. It is suggested that the large forces produced by paraplegjc subjects contribute to the low efficiency reported by previous studies, and that increasing the range of angles over which muscles are stimulated may provide a means to increase the efficiency of cycling for paraplegic individuals. Relevance-Cycling using neuromuscular electrical stimulation has been prescribed as an exercise regime for spinal-cord-injured individuals with proposed benefits such as augmented cardiovascular fitness, reversal of muscle wasting, increased blood flow in the legs, and reduced incidence of muscle spasms. The intensity and duration of such exercise is limited due to rapid fatigue of the leg muscles and this reduces the potential benefit to some patients. The purpose of the study was to improve our understanding of the mechanics of electrically-stimuated cycling and the loads exerted by paraplegic subjects during this activity. Key words: Electrical stimulation therapy, paraplegia, cycling, force, exercise, biomechanics, FES, FNS, NMES, electrical stimulation Clin. Biomech. Vol. 11, No. 1, 51-57, 1996 Introduction Spinal cord injury above the level of the tenth thoracic vertebra inhibits nerve impulses to the leg muscles but may not directly limit their ability to contract, provided the functional motor units remain intact’. Applying an alternating electrical current via percutaneous electrodes over the neuromuscular motor points elicits muscle contractions that can be used to pedal a cycle ergometer and provide an exercise stimulus. Cycling using computer-controlled neuromuscular electrical stimulation (NMES) has been proposed as a rehabilitation tool by several researchers from different countries2-‘. Some of the hypothesized benefits of Received: 29 October 1994; Accepted: 13 April 1995 Correspondence and reprint requests to: Peter Sinclair, Faculty of Health Sciences, The University of Sydney, East St Lidcombe, NSW, 2141, Australia NMES cycling include augmented cardiovascular fitness, reversal of muscle wasting, increased blood flow in the legs, and reduced incidence of muscle spasms’. Classically, only very low power outputs can be sustained by paraplegic subjects attempting NMES cycling and this has been attributed to several factors3,6*7. Weakness of the muscles coincident with atrophy of the unused lower limbs is the most obvious cause of low power outputs3. Also, long-term neuro- muscular denervation after spinal-cord injury has been shown to result in a marked reduction or complete loss of type I (aerobic) fibres, necessitating the use of anaerobic energy sources for NMES leg exercise829. A further factor in the low efficiency of NMES exercise is the timing and coordination of muscle actions required to produce external forces5. The stimulated muscle recruitment patterns during NMES cycling are crude compared to those inherent in