Metabolic Heat Production Modulates the Cardiovascular Drift-V̇O2max Relationship Independent of Aerobic Fitness in Women

• Published in: Medicine and science in sports and exercise 2024-08
• Main Authors: Stone, Tori, Burnash, Sarah G, Earley, Ryan L, Mulholland, Annie M, Yoder, Hillary A, MacDonald, Hayley V, Richardson, Mark T, Wingo, Jonathan E
• Format: Article
• Language: English
• ISSN: 0195-9131; 1530-0315; 1530-0315
• DOI: 10.1249/MSS.0000000000003543

The purpose of this study was to test the hypothesis that cardiovascular (CV) drift and associated decrements in maximal oxygen uptake (V̇O2max) are greater in high-fit compared to low-fit women during exercise at the same %V̇O2max, but comparable at the same rate of metabolic heat production. Six high-fit (HI) and 6 low-fit (LO) women cycled in 35 °C for 15 min or 45 min at the same relative intensity (60% V̇O2max; 15REL and 45REL) or fixed rate of heat production (500 W; 15FX and 45FX), immediately followed by a GXT to measure V̇O2max. The separate 15- and 45-min trials permitted measurements of V̇O2max over the same time interval as CV drift. During 45REL, higher heat production in HI (496 ± 51 W vs. 364 ± 44 W in LO) resulted in greater end-exercise core temperature (38.7 ± 0.4 °C vs. 38.2 ± 0.1 °C, P = 0.03); greater increases in HR [15 beats·min-1 (10%) vs. 10 beats·min-1 (6%), P = 0.03] and decreases in SV [11 mL·beat-1 (16%) vs. 5 mL·beat-1 (8%), P = 0.001]; and larger reductions in V̇O2max (16% vs. 5%, P = 0.04) compared to LO. During 45FX, temperature responses, CV drift and decreased V̇O2max were not different between groups (all P > 0.05), despite differences in %V̇O2max (60% vs. 75% for HI and LO, respectively). We conclude metabolic heat production modulates the CV drift-V̇O2max relationship, independent of fitness level. These results support previous findings showing the magnitude of CV drift is proportional to reductions in V̇O2max.