Functional electrical stimulation-propelled cycling for paraplegics – Measurement of the patient's force and endurance

The ergometer training of paraplegics with functional electrical stimulation (FES) can induce cardiovascular adaptation processes that allow them to cover useful distances during FES cycling, but only if a minimum amount of mechanical output power is generated. As a rule this cannot be achieved in the case of untrained patients.

By concentrating on the work physiological aspect of FES-cycling, this study offers a novel approach to comprehension and measurement of the small powers and endurances observed in paraplegics. We also propose definitions for the driving capability and effort of individual patients with respect to a specific type of cycle.

Material and Methods: Eight completely paraplegic patients participated in the study (seven untrained and one exceptionally well trained). The isometrical torque profiles of the six stimulated muscle groups were determined with a torque measuring sensor (ATI, Garner, USA), and dynamic power was measured on an ergometer (Motomed-Viva2, Betzenweiler, Germany). Cadence, drag, and covered distance were recorded for each patient during outdoor cycling (FES-tricycle, OVG, Munich, Germany).

Results: Graphic representation of the observed cycling situations with respect to the endurance limit showed that FES cycling of the seven untrained (“weak„) patients took place in the fatigue region, whereas cycling of the trained („strong“) patient No. 8 was localized in the steady-state region. While still in the fatigue region, the cycling situations of four weak patients (Nos. 1,2,4 and 6) were situated near the borderline to the steady state region. The proposed measures „cycling capability“ and „individual effort“ of the patient in a certain cycling situation correlated well with the covered distance (correlation coefficients: 0.92 and 0.79, respectively).

Discussion and conclusion: The work physiological approach revealed that the excessive fatigue observed in the untrained paraplegic cyclist can be attributed to the fact that he or she works in the fatigue mode rather than in the steady-state mode. Training under load can bring the performance of some of the paraplegic cyclists (Nos. 1,2,4,6) into the region of steady-state work. The progress of the cyclist can be monitored by the performance measure „cycling capability“.

Key words FES cycling, paraplegic, power