Duration of electrically induced muscle cramp increased by increasing stimulation frequency

Electrically induced muscle cramps (EIMC) do not last long enough to study many cramp treatments. Increasing stimulation frequency lengthens cramp duration; it is unknown which frequency elicits the longest EIMC.

To determine which stimulation frequency elicits the longest EIMC and whether cramp duration and stimulation frequency are correlated.

Randomized, crossover.

Laboratory.

20 participants (12 male, 8 female; age 20.7 ± 0.6 y; height 174.9 ± 1.9 cm; mass 76.6 ± 2.2 kg) with a self-reported history of muscle cramps in their lower extremities within the 6 mo before the study.

The dominant leg's tibial nerve was percutaneously stimulated with 2-s-duration electrical stimuli trains starting at a frequency of 4 Hz. After 1 min of rest, stimulation frequency increased in 2-Hz increments until a cramp occurred in the flexor hallucis brevis. The stimulation frequency at which a cramp occurred was termed cramp threshold frequency (TF). Cramp duration was determined using strict clinical criteria (loss of hallux rigidity and return of hallux neutral). On the next 4 consecutive days, participants were stimulated at 5, 10, 15, or 20 Hz above TF, and cramp duration was reassessed.

Cramp TF and duration.

Cramp TF was 16.9 ± 5.1 Hz. Cramp duration was longer at 15 and 20 Hz above TF (77.9 ± 37.6 s and 69.5 ± 36.9 s, respectively) than at TF (40.8 ± 34.0 s; P < .05). Cramp duration and TF were highly correlated (r = .90).

Stimulating at 15 and 20 Hz above cramp TF produces the longest-lasting EIMC.