Fig 1.
(a) NMES was applied on the right TA during ON period (5 s). During OFF period (19 s), TMS and peripheral nerve stimulation were applied; (b) Participants were instructed to match the ankle dorsiflexor force to a target when the panel changed to the ON signal (black screen). The yellow line represented the target. Visual force feedback was presented using a white line; and (c) Force-matching task consisted of right leg isometric ankle dorsiflexion during 1 s contractions. The green line represented the target. Visual force feedback was presented using a red line. Abbreviations: EMG, electromyography; NMES, neuromuscular electrical stimulation; TA, tibialis anterior; TMS, transcranial magnetic stimulation.
Fig 2.
Time course of the experimental protocol.
Participants performed three interventions: (i) NMES alone; (ii) NMES+VOL; and (iii) VOL alone. The assessments of MEP and Mmax were measured before starting the interventions (Pre), during the interventions in the NMES OFF periods (During1 (0–4 min), During2 (4–8 min), During3 (8–12 min), During4 (12–16 min)), as well as immediately (Post0), 10 min (Post10), 20 min (Post20), and 30 min (Post30) after the interventions. Abbreviations: FMT, force-matching task; MEP, motor evoked potential; MVC, maximum voluntary contraction; NMES, neuromuscular electrical stimulation; VOL, voluntary contractions.
Table 1.
Outcome variables at the Pre time point and results of the statistical comparison between the interventions.
Fig 3.
(a) MEPs in the TA recorded before starting the interventions (Pre), during the interventions (During1–4), and after the interventions (Post0–30) from a representative participant. Traces indicate average MEP responses; (b) Changes in the TA MEP/Mmax; (c) Changes in the soleus MEP. Circles represent each individual data and error bars represent 2 standard deviation. The red lines indicate mean for each time point. Abbreviations: MEP, motor evoked potential; TA, tibialis anterior.
Table 2.
Results of Dunnett’s test for the TA MEP/Mmax differences between Pre and other time points for each intervention.
Fig 4.
Circles represent each individual data and error bars represent 2 standard deviation. The red lines indicate mean for each time point. Legend: *p < .05 indicates significant differences between NMES and NMES+VOL. †p < .05 indicates significant differences between NMES and VOL. Abbreviations: NMES, neuromuscular electrical stimulation; VOL, voluntary contractions.
Fig 5.
Changes in the motor control of ankle dorsiflexion (a) error; and (b) reaction time during force-matching task. Circles represent each individual data and error bars represent 2 standard deviation. The red lines indicate mean for each time point. Abbreviations: NMES, neuromuscular electrical stimulation; VOL, voluntary contractions.