A comparison between motor point and transcranial magnetic stimulation for estimating voluntary activation prior to, during and following fatiguing elbow flexor contractions

The objective of this thesis was to compare changes in voluntary activation (VA) with two different stimulation techniques in non-fatigued and fatigued elbow flexors. Participants completed a single experimental session in which they preformed four sequences of three consecutive fatiguing contractions (fatigue block). Submaximal muscle contractions were performed in sets of four between fatigue blocks. The contractions began with a 100% effort followed by a 25%, 50% and 75% of MVC contraction in random order (VA block). All VA block contractions were sustained for 5 seconds. VA block was completed prior to the first fatigue block, post 5 and 10 minutes. Stimulations were delivered during the final of three successive fatiguing contractions in the fatigue block and during all VA block contractions. Transcranial magnetic stimulation (TMS), Erb’s point stimulation, and motor point stimulation were delivered to induce motor evoked potentials (MEP), maximal muscle compound action potential (Mmax), and potentiated twitch, respectively. VA decreased throughout the fatigue protocol with motor point stimulation and TMS but TMS was significantly underestimated because of lower estimated resting twitch forces than motor point stimulation. There was no change in triceps/biceps brachii electromyography, biceps/triceps motor evoked potential (MEP) amplitudes or bicep MEP amplitudes throughout the fatigue protocol. In conclusion motor point stimulation as opposed to TMS led to a higher estimation of VA in non-fatigued elbow flexors, therefore stimulation type has substantial effect on predictive equation validity when fatigue is incorporated. Additionally, as fatigue increased, potentiated twitch, EMG amplitude and force production progressively reduced