The Separate And Combined Effects Of Acute Simulated Altitude And High Ambient Temperature On Cycling Time Trial Performance

Abstract

Simulated altitude and high ambient temperature independently compromise endurance performance, although there is limited evidence on the combined exposure to both stressors. In addition, the effect of corresponding underlying key mechanisms has yet to be quantified. PURPOSE: To investigate the separate and combined effects of acute simulated altitude and high ambient temperature on time trial (TT) performance, VO2max, the ventilatory threshold (VT) and gross efficiency (GE). METHODS: Ten trained male cyclists performed 4 maximal incremental exercise tests (GXT) and GE-tests, both at sea-level (0 m; 20.93% O2) and simulated altitude (2000 m; 16.3% O2) in high environmental temperature (36.00 ± 1.4°C, 42.58 ± 0.8% RH) and temperate conditions (16.00 ± 0.32°C, 40.20 ± 1.2% RH). The GXT included 3 min at 100 W, followed by 25 W·min-1 until volitional fatigue. GE was determined at 50% of the power attained at VO2max in relative conditions, prior to and following 4000m TT performances. RESULTS: Although average PO was significantly reduced during TT performance at simulated altitude (31 ± 18 W, p<.001, n2p=.795) and high ambient temperature (9 ± 16 W, p=.007, n2p=.570), no significant interaction was found (p=.137). At simulated altitude, VO2max (3.77 ± 2.1 ml·kg-1·min-1, p<.001, n2p=.925), VT (3.39 ± 2.9 ml·kg-1·min-1, p<.001, n2p=.795) and GE (0.72 ± 0.97%, p=.021, n2p=0.555) were significantly reduced compared to sea level. However, VO2max (3.33 ± 3.1 ml·kg-1·min-1, p=.005, n2p=.608) and VT (2.05 ± 3.1 ml·kg-1·min-1, p=.021, n2p=.462) were significantly increased at high ambient temperature, although no effect on GE (p=0.240) was found. CONCLUSION: The reduction in TT performance at acute simulated altitude is associated with a decline in VO2max, VT and GE, likely because a lower SpO2. VO2max and VT are significantly higher at acute high ambient temperature, likely because the metabolic cost of physiological heat stress increases relative exercise intensity at similar absolute PO. GE was unaffected by acute high ambient temperature, likely because heat exposure during the GE-test was too short to increase Tcore. VO2max, VT and GE were not compromised during combined exposure, which corresponds with the absence of a significant interaction effect in endurance performance.