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. © 2012 Springer Science+Business Media, LLC.