Effects of supine and inverted seated positions on neuromuscular and cardiovascular parameters

Casey, Erica Jocelyn Paul (2014) Effects of supine and inverted seated positions on neuromuscular and cardiovascular parameters. Masters thesis, Memorial University of Newfoundland.

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Abstract

Purpose: The inverted and supine body positions are not common postures humans adopt. During unusual situations (e.g. overturned helicopters, motor vehicle accidents, gymnastics) when body position is altered, neuromuscular and cardiovascular (CV) responses can change. To optimally manage these situations, it is necessary to examine the changes in muscle force output, activation and CV parameters. In previous research, impairments during posture change were believed to be secondary to inhibition of sympathetic nervous system activity in recreational subjects. The purpose of this research was to evaluate the neuromuscular and CV changes in supine and inverted body positions on a group of aerobically trained athletes before and following physical fatigue. Methods: Twelve male athletes completed three trials in the upright, supine and inverted seated positions. At baseline (upright), leg extension (LE) and elbow flexion (EF) evoked contractile properties and MVCs were performed. The participant was then positioned for 150s in each posture, followed by a 30s MVC (MVC30). During each trial, stroke volume (SV), cardiac output (Q), heart rate (HR), time and frequency domain HR variability measures and mean arterial blood pressure (MAP) measurements were recorded. As well, force-fatigue and EMG relationships were evaluated. Results: An ANOVA showed no statistical differences in EF MVC force, but a tendency (p=0.12) for LE MVC decline across positions with moderate effect size. EF evoked resting twitch (p=0.1) had a decline in force that was not significant from upright to inverted and no change from upright to supine. Potentiated peak twitch (p=0.06) force displayed a tendency towards an increase from upright to supine and decline in force from upright to inverted postures (p=0.1). LE evoked resting twitch had a non-significant (p=0.1) but large magnitude increase in force across the three positions and there was a significant increase in potentiated twitch force (p=0.03). Force-fatigue, electromyography-fatigue relationships and HR variability during MVC30 fatigue across positions were not affected. HR and Q were significantly (p<0.01) lower with inversion following both LE and EF fatigue. Conclusions: The lack of significant postural changes in resting force and CV measures may demonstrate that highly trained individuals may adapt better to the supine and inverted positions.

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