Frontal cortex activation during electrical muscle stimulation as revealed by functional near-infrared spectroscopy

This study compared electrical muscle stimulation (EMS) and voluntary (VOL) contractions of the elbow flexors for changes in frontal cortex (FC) oxygenated hemoglobin (∆O2Hb) and deoxygenated Hb (∆HHb) determined by functional near-infrared spectroscopy (fNIRS). Nine healthy men underwent an EMS session with one arm and 24 h later performed VOL exercise with the other arm. For the EMS session, ∆O2Hb increased (P < 0.05) during the exercise performed at 30% of the maximal voluntary contraction (MVC), and thereafter progressively increased (P < 0.05) with increasing the current amplitude, and both variables were correlated (r = 0.68, P < 0.001). In the VOL session, ∆O2Hb did not change from baseline during 30% MVC contractions; however, ∆O2Hb progressively increased (P < 0.05) during 100% MVC contractions, and ∆O2Hb was greater (P < 0.05) during 100% MVC than 30% MVC. ∆O2Hb was greater (P < 0.05) for EMS than VOL at 30% MVC, but no difference in ∆O2Hb was evident between EMS and VOL at the respective maximum intensity. In conclusion, intensity-related increases in FC activation during EMS can be determined using fNIRS.