Core Temperature And Blood Lactate Kinetics After Graded Exercise Testing In The Heat

Abstract

Utility of a verification trial to confirm maximal oxygen intake (VO2max) in the heat is unclear and initial studies are needed to explore recovery duration between the initial graded exercise test (GXT) and the verification trial to ensure verification trial fidelity. PURPOSE: To compare the recovery kinetics of gastrointestinal temperature (Tgi) and blood lactate (BLa) after a GXT in the heat between trained and untrained cyclists. METHODS: Trained (n=10; age: 22.6±2.2 y; body fat: 15.4±5.8%) and untrained (n=11; age: 23.4±2.9 y, body fat: 21.1±5.8%) male cyclists volunteered. Tgi, BLa (finger prick), expired gases, and power output (watts; W) were continuously measured during the GXT in a heated chamber (39°C, 31%RH). After the GXT, subjects exited the chamber and rested in a temperate room (22°C, 40%RH) until Tgi returned to pre-GXT values (defined as “recovery”) at which point BLa was re-assessed. Separate independent t-tests assessed differences in W, VO2max, and recovery duration between groups. Separate 2 by 3 (training status [trained vs. untrained] time [pre-GXT, post-GXT, recovery]) repeated measures ANOVAs evaluated changes in Tgi and BLa with Tukey post hoc tests (alpha = 0.05). RESULTS: As expected, the trained cyclists GXT was longer (709±81 vs. 610±98 s; p=0.02) and achieved greater peak power output (278±32 vs. 238±32 W; p=0.009) and VO2max (57.2±7.7 vs. 40.5±5.5 mL/kg/min; p<0.001) than untrained. Recovery time was longer for trained subjects (50±5.4 vs. 43.5±10.2 min; p=0.10) but this difference did not reach significance. Pre-GXT and recovery Tgi was higher in untrained (37.5±0.3 and 37.4±0.2°C) versus trained (37.1±0.2 and 37.2±0.2°C; p<0.01) with both groups achieving similar post-GXT values (untrained: 37.8±0.2; trained: 37.7±0.2°C; p=0.37). BLa at recovery (trained: 6.2±0.7; untrained 7.0±2.4 mmol/L) was lower than Post-GXT (trained: 12.8±1.9; untrained 13.3±2.9 mmol/L) but remained higher than Pre-GXT (trained: 2.3±0.3; untrained 3.3±1.5 mmol/L) in both groups (p<0.001) with no group main effects (p≥0.08). CONCLUSIONS: The thermoregulatory system managed the GXT-induced thermal load faster than the metabolic system cleared BLa. If verification trials in the heat are employed, extended recovery durations appear necessary regardless of training status.