Progressive Muscle Fatigue Induces Loss in Muscle Force and Persistent Activation of Frontal Cortex as Measured by Multi-Channel fNIRT

The effect of fatiguing skeletal muscle exercise on brain, and in particular on ipsi- and ontralateral frontal cortex (FC) has not been fully clarified. The aim of this study was to investigate by functional near-infrared topography (fNIRT) the FC oxygenation response to a prolonged fatiguing rhythmic handgrip exercise performed at the maximal voluntary contraction separately with right or left hand. fNIRT is a not harmful and non-invasive optical technique allowing the simultaneous acquisition of oxygenated and deoxygenated hemoglobin concentration ([O2Hb], [HHb]) changes on the scalp. By using a 8-channel fNIRT (NIRO-200 with multi-fiber adapter, Hamamatsu Photonics) we demonstrated a significant [O 2Hb] increase, accompanied by a smaller and delayed significant [HHb] decrease, in all measurements points of both hemispheres. A significant hemisphere x task execution modality interaction was revealed only for [O2Hb] increase of the right FC during the right handgrip exercise (p= 0.008). A significant hemisphere x task execution modality interaction was found only for [HHb] decrease of the left FC during the left handgrip exercise (p<0.001). These results provide further evidence that FC plays a role in maintaining strength of the forearm muscles and ensuring a correct execution of motor tasks which require a fine motor control and coordination.