Neuromuscular mechanisms underlying changes in force production during an attentional focus task

Wiseman, Shawn (2019) Neuromuscular mechanisms underlying changes in force production during an attentional focus task. Masters thesis, Memorial University of Newfoundland.

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Abstract

The objective of this thesis was to examine changes in maximal voluntary force output of the elbow flexors with attentional focus feedback cues and possible underlying physiological mechanisms for these changes. Eleven recreationally active males participated in two randomized experimental sessions (Day 1: n=11, Day 2: n=10); 1) Stimulation session where corticospinal excitability was measured and 2) No stimulation session where only electromyography and elbow flexor force was measured. In both sessions, four randomized blocks of three maximal voluntary contractions (MVC) were performed. Each block consisted of either externally or internally attentional focus cues given before each MVC. During the stimulation session transcranial magnetic, transmastoid and Erb’s point stimulations were used to induce motor evoked potentials (MEPs), cervicomedullary MEP (CMEPs) and maximal muscle action potential (Mmax). All MEPs and CMEPs were normalized to Mmax. Results showed participants could produce greater MVC force without stimulation and given an external focus cue before the MVC compared to an internal cue. Muscle co-activation data (expressed as % triceps/biceps rmsEMG) during the no stimulation session was greater with internally cued compared to externally cued contractions. There was no difference in corticospinal excitability shown between external and internal focus cues in the stimulation session. In conclusion, maximal voluntary force production of the elbow flexors was greater when an external focus feedback cue was provided. This appeared to be due to less coactivation of the triceps and biceps brachii. Secondly, stimulating the corticospinal pathway seemed to have some confounding effect on attentional focus. The distressing stimulations distracted participants from attentional focus cued feedback or stimulating the corticospinal pathway may have disrupted areas of the cortex responsible for attention and focus.

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