Effects of an inverted seated position on single and sustained isometric contractions and cardiovascular parameters of trained individuals

Previous research demonstrated higher maximal voluntary contraction (MVC) force with upright vs. inverted positions in untrained individuals. The purpose was to determine the effects of inversion on force, activation, and cardiovascular responses before and following fatigue in trained individuals. Twelve male athletes completed two trials: upright and inverted seated positions. At baseline (upright), either leg extension (LE) or elbow flexion (EF) evoked contractile properties and MVCs were performed. LE and EF contractions were randomly allocated and performed in separate sessions. The subject was then positioned for 150 s in each posture, followed by a 30 s 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. ANOVA showed no statistical differences in EF MVC force, but a tendency (p = .12) for LE MVC decline with inversion vs. upright. Evoked resting (p = .1) and potentiated peak twitch (p = .04) force were increased with inverted LE but tended to diminish with inverted EF (p = .06 and p = .1). Force-fatigue, electromyography-fatigue relationships and HR variability during MVC30 fatigue were not affected. HR and Q were significantly (p = .01) lower with inversion following both LE and EF fatigue. Compared to the significant inversion-induced changes associated with untrained individuals in previously published studies, the lack of postural changes in resting force and CV measures may demonstrate that highly trained individuals adapt better to inversion.