Objective: To determine the efficacy of using modulated middle frequency alternating current (MFAC) muscle stimulation for functional electric stimulation-propelled cycling by people with spinal cord injury (SCI) compared with the conventional method of using standard low-frequency rectangular pulses (LFRP).
Design: Repeated-measures.
Setting: Laboratory setting.
Participants: Eleven otherwise healthy volunteer subjects with SCI (8 with American Spinal Injury Association [ASIA] grade A, 3 with ASIA grade B).
Interventions: To evaluate cycling-relevant differences between LFRP and modulated MFAC stimulation, we exposed participants to isometric measurements and cycling experiments performed during both 20 Hz LFRP and 4 KHz modulated with 50 Hz MFAC.
Main outcome measures: We recorded maximal isometric torque, maximal dynamic work during 20 minutes of ergometer cycling, and perceived discomfort for each of the 2 stimulation patterns.
Results: Both the isometric torque (P<.02) and work generated (P<.001) during MFAC stimulation were significantly lower than during standard LFRP stimulation. Four participants reported discomfort and 1 of them also developed skin burns during MFAC stimulation.
Conclusions: Our findings suggest that in SCI subjects, stimulated cycling with low frequency is generally more effective than cycling with modulated MFAC in terms of torque, work, and pain sensation.