Low-Frequency Rectangular Pulse Is Superior to Middle Frequency Alternating Current Stimulation in Cycling of People With Spinal Cord Injury

(A) LFRP and (B) MFAC waveforms.

Isometric and ergometer measurement setups. Because patients’ geometric sitting position and the stimulator setup were identical, a combined draft of isometric and ergometer experiments is presented. The crank angle was set by manually turning the torque transducer axle (TTA) by a lever and fixing it with a screw during isometric measurement. Resistance torque and crank angle provided by TTA and decoder (C), respectively, were collected. Electrode leads were connected at a given crank angle alternately to the LFRP and MFAC stimulator by a switch. During ergometric measurements pedaling was motor braked. Tangential forces provided by built-in sensors in the crank arm and crank angle were collected. Either LFRP or MFAC stimulation was used. Legend: 1, 2, 3: stimulation of the quad, hamstrings, and gluteus muscle groups, respectively.

Isometric torques of left quadriceps muscle (red) and the sum of all muscle torques together (blue) produced when subject 10 pedaled in positive drive direction with (A) MFAC and (B) LFRP stimulation. Torques were actually measured at 40% to 80% of maximal stimulation and subsequently extrapolated to 100% (arrows). Zero degrees refer to the backward-pointing left crank arm. The dashed line indicates mean maximal isometric torque.

Power course (upper graph) of (A) subject 10 and (B) subject 9 generated during 20 minutes of FES ergometry using LFRP (blue) and MFAC (red) stimulation. Twenty-minute pedaling work was defined as the area under the corresponding curves. Stimulation course (lower graph) is expressed in percentage of maximal stimulation.

Mean isometric torque of 10 study participants (left) and work generated during 20 minutes of FES ergometry (right) of all study participants (n=11), using 20Hz LFRP (black) and MFAC (gray) stimulation. NOTE. Bars and segments plotted represent group means ± SD. *P<.02; ^†P<.001 (Wilcoxon signed-rank test).