Purpose: We assessed whether plasma lactate accumulation increased and the lactate threshold (LT) declined when the skin temperature was lowered by whole body skin surface cooling before exercise in cool, but not temperate, conditions, and whether the lowered LT was associated with sympathetic activation or lowered plasma volume (PV) by cold-induced diuresis.
Methods: Ten healthy subjects performed a graded maximal cycling exercise after pre-conditioning under three different conditions for 60 min. Ambient temperature (using an artificial climatic chamber) and water temperature in a water-perfusion suit controlled at 25 and 34 °C in temperate-neutral (Temp-Neut); 25 and 10 °C in temperate-cool (Temp-Cool); and at 10 and 10 °C in cool-cool (Cool-Cool) conditions, respectively. Esophageal (Tes) and skin temperatures were measured; plasma lactate ([Lac]p) and noradrenaline concentrations ([Norad]p), and relative change in PV (%ΔPV) were determined before and after pre-conditioning and during exercise, and LT was determined.
Results: After pre-conditioning, Tes was not different among trials, whereas the mean skin temperature was lower in Cool-Cool and Temp-Cool than in Temp-Neut (P < 0.001). During exercise, [Lac]p and [Norad]p were higher (P = 0.009 and P < 0.001, respectively) and LT was lower (P = 0.013) in Cool-Cool than in the other trials. The %ΔPV was not different among trials. LT was correlated with [Norad]p during exercise (R = 0.50, P = 0.005).
Conclusions: Whole body skin surface cooling before exercise increases lactate accumulation and decreases LT with sympathetic activation when exercise is performed in a cool, but not in a temperate, environment.
Keywords: Lactate concentration; Plasma volume; Precooling; Skin temperature; Sympathetic nerve activity.