High-intensity interval exercise in the cold regulates acute and postprandial metabolism.

High-intensity interval exercise (HIIE) has been shown to be more effective than moderate-intensity exercise for increasing acute lipid oxidation and lowering blood lipids during exercise and postprandially. Exercise in cold environments is also known to enhance lipid oxidation; however, the immediate and long-term effects of HIIE exercise in cold are unknown. The purpose of this study was to examine the effects cold stress during HIIE on acute exercise metabolism and postprandial metabolism. Eleven recreationally active individuals (age: 23 ± 3 yr, weight: 80 ± 9.7 kg, V̇O2peak: 39.2 ± 5.73 mL·kg-1·min-1) performed evening HIIE sessions (10 × 60 s cycling, 90% V̇O2peak interspersed with 90 s active recovery, 30% V̇O2peak) in thermoneutral (HIIE-TN, control; 21°C) and cold environment (HIIE-CO; 0°C), following a balanced crossover design. The following morning, participants consumed a high-fat meal. Indirect calorimetry was used to assess substrate oxidation, and venous blood samples were obtained to assess changes in noncellular metabolites. During acute exercise, lipid oxidation was higher in HIIE-CO (P = 0.002) without differences in V̇O2 and energy expenditure (P ≥ 0.162) between conditions. Postprandial V̇O2, lipid and CHO oxidation, plasma insulin, and triglyceride concentrations were not different between conditions (P > 0.05). Postprandial blood LDL-C levels were higher in HIIE-CO 2 h after the meal (P = 0.003). Postprandial glucose area under curve was 49% higher in HIIE-CO versus HIIE-TN (P = 0.034). Under matched energy expenditure conditions, HIIE demonstrated higher lipid oxidation rates during exercise in the cold; but only marginally influenced postprandial lipid metabolism the following morning. In conclusion, HIIE in the cold seemed to be less favorable for postprandial lipid and glycemic responses.NEW & NOTEWORTHY This is the first known study to investigate the effects of cold ambient temperatures on acute metabolism during high-intensity interval exercise, as well as postprandial metabolism the next day. We observed that high-intensity interval exercise in a cold environment does change acute metabolism compared to a thermoneutral environment; however, the addition of a cold stimulus was less favorable for postprandial metabolic responses the following day.