Can motor imagery balance the acute fatigue induced by neuromuscular electrical stimulation?

Purpose The combination of motor imagery (MI) and neuromuscular electrical stimulation (NMES) can increase the corticospinal excitability suggesting that such association could be efficient in motor performance improvement. However, differential effect has been reported at spinal level after MI and NMES alone. The purpose of this study was to investigate the acute effect on motor performance and spinal excitability following MI, NMES and combining MI and NMES.Methods Ten participants were enrolled in three experimental sessions of MI, NMES and MI + NMES targeting plantar flexor muscles. Each session underwent 60 imagined, evoked (20% MVC) or imagined and evoked contractions simultaneously. Before, immediately after and 10 min after each session, maximal M-wave and H-reflex were evoked by electrical nerve stimulation applied at rest and during maximal voluntary contraction (MVC).Results The MVC decreased significantly between PRE-POST (- 12.14 +/- 6.12%) and PRE-POST 10 (- 8.1 +/- 6.35%) for NMES session, while this decrease was significant only between PRE-POST 10 (- 7.16 +/- 11.25%) for the MI + NMES session. No significant modulation of the MVC was observed after MI session. The ratio Hmax/Mmax was reduced immediately after NMES session only.Conclusion The combination of MI to NMES seems to delay the onset of neuromuscular fatigue compared to NMES alone. This delay onset of neuromuscular fatigue was associated with specific modulation of the spinal excitability. These results suggested that MI could compensate the neuromuscular fatigue induced acutely by NMES until 10 min after the combination of both modalities.