Improved Maximal Oxygen Uptake Following High-intensity Interval Training Relates To An Increase In Blood Volume

Abstract

Improved maximal oxygen uptake following high-intensity interval training relates to an increase in blood volume High-intensity interval training (HIT) is an effective training mode for improving maximal oxygen uptake (VO2max). As past research has focused on peripheral adaptations to HIT, little is known about central factors governing cardiac output and thus VO2max. PURPOSE: The aim of this study was to test the hypothesis that HIT-induced improvements in VO2max are accompanied by increases in blood volume (BV) and cardiac stroke volume. Further, we investigated if inter-individual differences in the increase in in VO2max could be attributed to changes in BV. METHODS: Twenty subjects (10 females, 10 males) participated in a 6-week long training intervention consisting of 3 HIT sessions per week. Each session comprised of three 30 s all-out sprints against a breaking force equivalent to 7.5% of body weight. The sprints were separated by 2 min rest. VO2max, peak exercise cardiac output and BV (measured with carbon monoxide rebreathing) was assessed before (PRE) and after (POST) the intervention. RESULTS: VO2max increased by 9% (44.9±7.9 to 48.7±7.8 mL/min/kg) from PRE to POST (P < 0.05) and the increase in BV was 5% (5.4±0.8 to 5.7±0.9 L, P < 0.05) with a corresponding increase in peak exercise stroke volume. Accounting for inter-individual variance, approximately 60% of the change in VO2max could be attributed to changes in BV. CONCLUSION: This is the first study to show that improvements in VO2max with HIT are associated with increased blood volume. This suggest that a large part of HIT-induced improvements in VO2max are mediated by increased oxygen delivery, which at least in part is due to increased blood volume.