Thomas Rupp

Transcranial magnetic stimulation (TMS) is a widely-used investigative technique in motor cortical evaluation. Recently, there has been a surge in TMS studies evaluating lower-limb fatigue. TMS intensity of 120-130% resting motor threshold (RMT) and 120% active motor threshold (AMT) and TMS intensity determined using stimulus–response curves during muscular contraction have been used in these studies. With the expansion of fatigue research in locomotion, the quadriceps femoris is increasingly of interest. It is important to select a stimulus intensity appropriate to evaluate the variables, including voluntary activation, being measured in this functionally important muscle group. This study assessed whether selected quadriceps TMS stimulus intensity determined by frequently employed methods is similar between methods and muscles.

This study aimed to compare changes in skeletal muscle, prefrontal (PFC), and motor (MC) cortex hemodynamics during prolonged (i.e., 4-h) fatiguing whole-body exercise using multichannel near-infrared spectroscopy (NIRS). Ten subjects completed three successive 80-min cycling bouts at 45 % of their maximal power output. After the 4-h cycling, maximal voluntary contraction force of the leg was decreased by ~25 %. Muscle exhibited reproductive deoxygenation patterns during each of the three bouts, whereas intra-bout cerebral hemodynamics were different throughout the protocol. Results demonstrate that specific responses to fatiguing exercise are found between tissues but also between cortical sites involved in cycling, as shown by concomitant PFC hyperoxygenation and MC deoxygenation in the first 80 min of exercise. Further insights are needed to understand the consequences of these changes regarding the integrative control of motor output while fatigue develops over several hours.