Does altitude level of a prior time-trial modify subsequent exercise performance in hypoxia and associated neuromuscular responses?

Abstract

We examined the influence of prior time-trials performed at different altitudes on subsequent exercise in moderate hypoxia and associated cardiometabolic and neuromuscular responses. In normobaric hypoxia (simulated altitude 2000 m; FiO2: 0.163), 10 healthy males performed (1) an incremental test to exhaustion (VO2max_2000) and (2) a test to exhaustion at 80% of the power output associated to VO2max_2000 for a reference time (947 ± 336 sec). Thereafter, two sessions were conducted in a randomized order: a cycle time-trial corresponding to the reference time (TT1) followed 22 min later (passive rest at 2000 m) by a 6-min cycle time-trial (TT2). TT1 was either performed at 2000 or 3500 m (FiO2: 0.135), while TT2 was always performed at 2000 m. As expected, during TT1, the mean power output (247 ± 42 vs. 227 ± 37 W; P < 0.001) was higher at 2000 than 3500 m. During TT2, the mean power output (256 ± 42 vs. 252 ± 36 W) did not differ between conditions. Before and after TT1, maximal isometric voluntary contraction torque in knee extensors (pooled conditions: −7.9 ± 8.4%; P < 0.01), voluntary activation (−4.1 ± 3.1%; P < 0.05), and indices of muscle contractility (peak twitch torque: −39.1 ± 11.9%; doublet torques at 100 Hz: −15.4 ± 8.9%; 10/100 Hz ratio: −25.8 ± 7.7%; all P < 0.001) were equally reduced at 2000 m or 3500 m. Irrespective of the altitude of TT1, neuromuscular function remained similarly depressed after TT1 both before and after TT2 at 2000 m. A prior time-trial performed at different altitude influenced to the same extent performance and associated cardiometabolic and neuromuscular responses during a subsequent exercise in moderate hypoxia.