Dissociation between exercise intensity thresholds: mechanistic insights from supine exercise

Goulding, Richie P and Marwood, Simon and Lei, Tze-Huan and Okushima, Dai and Poole, David and Barstow, Thomas and Kondo, Narihiko and Koga, Shunsaku (2021) Dissociation between exercise intensity thresholds: mechanistic insights from supine exercise. American Journal of Physiology: Regulatory Integrative and Comparative Physiology, 321 (5). R712-R722. ISSN 1522-1490

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Abstract

This study tested the hypothesis that the respiratory compensation point (RCP) and breakpoint in deoxygenated [heme] [deoxy[heme]BP, assessed via near-infrared spectroscopy (NIRS)] during ramp incremental exercise would occur at the same metabolic rate in the upright (U) and supine (S) body positions. Eleven healthy men completed ramp incremental exercise tests in U and S. Gas exchange was measured breath-by-breath and time-resolved-NIRS was used to measure deoxy[heme] in the vastus lateralis (VL) and rectus femoris (RF). RCP (S: 2.56 ± 0.39, U: 2.86 ± 0.40 L·min-1, P = 0.02) differed from deoxy[heme]BP in the VL in U (3.10 ± 0.44 L·min-1, P = 0.002), but was not different in S in the VL (2.70 ± 0.50 L·min-1, P = 0.15). RCP was not different from the deoxy[heme]BP in the RF for either position (S: 2.34 ± 0.48 L·min-1, U: 2.76 ± 0.53 L·min-1, P > 0.05). However, the deoxy[heme]BP differed between muscles in both positions (P < 0.05), and changes in deoxy[heme]BP did not relate to ΔRCP between positions (VL: r = 0.55, P = 0.080, RF: r = 0.26, P = 0.44). The deoxy[heme]BP was consistently preceded by a breakpoint in total[heme], and was, in turn, itself preceded by a breakpoint in muscle surface electromyography (EMG). RCP and the deoxy[heme]BP can be dissociated across muscles and different body positions and, therefore, do not represent the same underlying physiological phenomenon. The deoxy[heme]BP may, however, be mechanistically related to breakpoints in total[heme] and muscle activity.

Item Type:	Article
Additional Information and Comments:	This is the author accepted manuscript version of an article that was accepted for publication in the American Journal of Physiology: Regulatory, Integrative and Comparative Physiology. The final, published version is available from: https://journals.physiology.org/doi/full/10.1152/ajpregu.00096.2021
Keywords:	deoxy- + total (hemoglobin + myoglobin); exercise intensity thresholds; respiratory compensation point; supine exercise; time-resolved near-infrared spectroscopy.
Faculty / Department:	Faculty of Human and Digital Sciences > School of Health and Sport Sciences
Depositing User:	Simon Marwood
Date Deposited:	21 Feb 2024 10:47
Last Modified:	21 Feb 2024 10:47
URI:	https://hira.hope.ac.uk/id/eprint/4147

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