Sprint interval training (SIT) increases peak oxygen uptake (VO2peak) but the mechanistic basis is unclear. The Fick principle broadly attributes increases in VO2peak to changes in peak cardiac output (Qpeak) and/or peak arteriovenous oxygen difference (peak a-vO2diff). The main purpose of this thesis was to investigate the role of Qpeak, measured non-invasively using inert gas rebreathing (IGR), on SIT-induced changes in VO2peak. It also considered the time course of these responses and the influence of biological sex. The SIT protocol involved 3 x 20-s “all out” sprints performed within a 10-min session of low-intensity cycling. Study 1 measured Qpeak after 2, 6, and 12 weeks of SIT and found it was increased after 12 weeks and associated with the change in VO2peak. Peak a-vO2diff, estimated based on the Fick equation (peak a-vO2diff = VO2peak/Qpeak), was also increased after SIT and associated with the change in VO2peak. Study 2 found that a novel constant-load protocol elicited Qpeak values that were non-inferior to an established step protocol, within a margin of 0.5 L/min. Both protocols elicited VO2 values at Qpeak that were similar to VO2peak. The constant load protocol had similar day-to-day repeatability as the VO2peak test (typical error = 6.6 and 6.4%, respectively). Study 3 investigated an exploratory finding from Study 1 that suggested Qpeak was increased in male but not female participants. The design was similar, but Study 3 employed suggested best practices for making sex-based comparisons. Contrary to our hypothesis, Qpeak was unchanged after 12 weeks of SIT and there was no sex-based difference. Like Study 1, peak a-vO2diff was increased and correlated with VO2peak. This thesis advances knowledge regarding the influence of SIT on Qpeak determined non-invasively and highlights the need for more mechanistic work to comprehensively assess the basis for the increase in VO2peak. / Thesis / Candidate in Philosophy / Sprint interval training (SIT) is a form of exercise that involves brief bursts of near-maximal to “all out” efforts separated by short recovery periods. The method improves cardiorespiratory fitness — an important health marker that is quantified as the highest amount of oxygen used by the body during strenuous exercise (VO2peak) — but the mechanisms are not well understood. This thesis examined the effect of SIT on peak cardiac output (Qpeak), which is the highest rate of blood pumped by the heart each minute, and the relationship to changes in VO2peak. Qpeak was measured non-invasively by having participants breathe an inert gas mixture. Two separate 12-week training studies confirmed that SIT increased VO2peak but yielded conflicting results regarding the role of Qpeak. The findings also suggest that the capacity of skeletal muscles to extract oxygen is increased after SIT. Biological sex does not appear to influence SIT-induced changes in Qpeak or VO2peak.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/28942 |
| Date | January 2023 |
| Creators | Bostad, William |
| Contributors | Gibala, Martin, Kinesiology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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