External power output changes during prolonged cycling with electrical stimulation

Abstract

This study analysed external power output and physiologic responses in 5 individuals with paraplegia during 40 minutes of electrical stimulation leg cycle exercise. Cycling was performed on a motor-driven isokinetic ergometer that enabled precise determinations of power output. Electrical stimulation was increased to 120-140 mA within the first 5 minutes and remained constant thereafter. Power output increased to 10.7 +/- 3.0 W after 2 minutes, dropped to 5.3 +/- 1.8 W after 6 minutes and subsequently recovered to 8.2 +/- 2.2 and 6.1 +/- 2.3 W after 19.5 and 40 minutes, respectively. Oxygen consumption increased to 0.47 +/- 0.09 l/min after 6 minutes and declined during the second half of the exercise bout. Gross mechanical efficiency after 19.5 minutes was elevated compared with the value after 6 minutes. Heart rate was significantly increased at the end of the trial. The time-dependent variability of power output and physiological responses question the concept of steady state for this form of exercise.

Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost

“…Theisen et al [12], for example, have shown that efficiency can vary considerably during prolonged, constant-stimulation FES-cycling exercise. In a study with 5 SCI subjects they demonstrated that the net efficiency progressively increased up to a maximum of almost 9% after 40 min.…”

Development of an Isokinetic Functional Electrical Stimulation Cycle Ergometer

“…In a parallel investigation to the development of the iFES-LCE system, Theisen and coworkers (19) observed that cycling with the iFES-LCE at 50 rev/ min invoked a significant cardiorespiratory stimulus, including exercise-induced increases of heart rate and oxygen uptake. Further experimental research is required to compare the magnitude of the cardiorespiratory response induced by the iFES-LCE with that produced by presently available commercial FES-LCE systems.…”

Energetics of paraplegic cycling: a new theoretical framework and efficiency characterisation for untrained subjects

“…This, together with the weakness of paralysed muscle, results in low power output (Glaser et al 1989;Raymond et al 2002;Theisen et al 2002). It has been argued (Glaser et al 1989) that the low efficiency of stimulated cycling is of little consequence in the context of stationary ergometry since a key objective is to elicit metabolic and cardiopulmonary responses, while the external energy output is not harnessed to do useful external work.…”