Twitch potentiation induced by two different modalities of neuromuscular electrical stimulation: Implications for motor unit recruitment



Introduction: We tested the hypothesis that twitch potentiation would be greater following conventional (CONV) neuromuscular electrical stimulation (50-µs pulse width and 25-Hz frequency) compared with wide-pulse high-frequency (WPHF) neuromuscular electrical stimulation (1-ms, 100-Hz) and voluntary (VOL) contractions, because of specificities in motor unit recruitment (random in CONV vs. random and orderly in WPHF vs. orderly in VOL). Methods: A single twitch was evoked by means of tibial nerve stimulation before and 2 s after CONV, WPHF, and VOL conditioning contractions of the plantar flexors (intensity: 10% maximal voluntary contraction; duration: 10 s) in 13 young healthy subjects. Results: Peak twitch increased (P < 0.05) after CONV (+4.5 ± 4.0%) and WPHF (+3.3 ± 5.9%), with no difference between the 2 modalities, whereas no changes were observed after VOL (+0.8 ± 2.6%). Conclusions: Our results demonstrate that presumed differences in motor unit recruitment between WPHF and CONV do not seem to influence twitch potentiation results. Muscle Nerve 51: 412–418, 2015