Maximal Lactate Steady State is Altered in the Heat

The aim of this study was to compare the maximal lactate steady state (MLSS) and ventilatory threshold (VT) under different environments (TEMP: 22 degrees C; and HOT: 40 degrees C; 50% RH). 8 male subjects (age 23.9 +/- 2.4 years, body mass 75.9 +/- 7.3 kg and VO(2max) 47.8 +/- 4.9 mL.kg(-1).min(-1)) performed a series of tests to determine the peak workload (W(peak)), VT and MLSS on a cycle ergometer. W(peak) was higher in the TEMP as compared to the HOT condition (225 +/- 9 W vs. 195 +/- 8 W, respectively; p < 0.05). The workload at MLSS was higher at 22 degrees C (180 +/- 11 W) than 40 degrees C (148 +/- 11 W; p < 0.05), as well as VT at 22 degrees C (156 +/- 9 W) was higher than 40 degrees C (128 +/- 6 W). Likewise, the blood lactate concentration at MLSS was higher at 22 degrees C (5.60 +/- 0.26 mM) than 40 degrees C (4.22 +/- 0.48 mM; p < 0.05). The mean of heart rate (HR) was not statistically different between TEMP (168 +/- 3 bpm) and HOT (173 +/- 3 bpm) at MLSS, despite being different at trials between the 25(th) and the 30(th) min of exercise. The HR at VT was significantly higher in HOT (153 +/- 4 bpm) as compared to the TEMP (145 +/- 2 bpm). Our results suggest that environmental conditions may influence the determination of MLSS and VT. Moreover, VT was appropriate for estimation of the workload at MLSS in the HOT.