This study compared neuromuscular fatigue induced by an acute wide-pulse high-frequency session, either applied in an isometric condition (WPHF) or combined with muscle lengthening (WPHF+LEN). Fifteen participants completed two randomized sessions, which involved 30 stimulation trains (pulse duration: 1 ms; frequency: 100 Hz; duty cycle: 15s ON/15s OFF) applied to the posterior tibial nerve at low stimulation intensity (5-10% maximal voluntary contraction, MVC). In the WPHF session, the ankle joint was held at a reference angle (90°) while a 10° muscle lengthening was superimposed during the stimulation in the WPHF+LEN session. Before and after each session, MVC was measured along with neural (voluntary activation level, VAL) and muscular (potentiated twitch, Pt) changes. Torque-time integral (TTI) was recorded for each train and the total TTI (ƩTTI) was calculated. Results showed a comparable decrease in MVC torque after the two sessions (-7.8 ± 6.9% for WPHF and -9.4 ± 5.7% for WPHF+LEN, P < 0.001) associated with a significant reduction in Pt amplitude (P < 0.001) indicating muscular changes, while VAL remained unchanged. ƩTTI was not different between sessions (9600 Nm.s for WPHF, 9550 Nm.s for WPHF+LEN; P = 0.95). However, although TTI significantly decreased throughout the WPHF session, it was preserved during the WPHF+LEN session. These findings indicate a similar amount of neuromuscular fatigue after the two sessions, primarily attributed to muscular alterations. Nevertheless, the combination of WPHF stimulation with muscle lengthening appears advantageous for preserving torque production throughout the stimulation trains.
Pineau et al. (Fri,) studied this question.