Elicitability of muscle cramps in different leg and foot muscles.

Introduction. To explore the efficacy of muscle motor point stimulation in eliciting muscle cramps, eleven subjects underwent eight sessions of electrical stimulation of the following muscles bilaterally: abductor hallucis, flexor hallucis brevis, and both heads of the gastrocnemius muscles. Methods. Bursts of 150 square wave stimuli (duration: 152 us; current intensity: 30% supramaximal) were applied. The stimulation frequency was increased from 4 pulses per second (pps) at increments of 2 pps until a cramp was induced. Results. The number of cramps that could be elicited was smaller in flexor hallucis brevis than in abductor hallucis (16 vs 22 out of 22 trials each; p<0.05) and in the lateral gastrocnemius than in the medial gastrocnemius (5 vs 20 out of 22 trials each; p<0.0001). Conclusions. We show that leg and foot muscles have different cramp susceptibility, and the inter-muscle variability in the elicitability profile for electrically induced cramps supports the use of the proposed method for cramp research.