title: Heat acclimation improves exercise performance.
abstract: This study examined the impact of heat acclimation on improving exercise performance in cool and hot environments. Twelve trained cyclists performed tests of maximal aerobic power (VO2max), time-trial performance, and lactate threshold, in both cool [13°C, 30% relative humidity (RH)] and hot (38°C, 30% RH) environments before and after a 10-day heat acclimation (∼50% VO2max in 40°C) program. The hot and cool condition VO2max and lactate threshold tests were both preceded by either warm (41°C) water or thermoneutral (34°C) water immersion to induce hyperthermia (0.8-1.0°C) or sustain normothermia, respectively. Eight matched control subjects completed the same exercise tests in the same environments before and after 10 days of identical exercise in a cool (13°C) environment. Heat acclimation increased VO2max by 5% in cool (66.8 ± 2.1 vs. 70.2 ± 2.3 ml·kg(-1)·min(-1), P = 0.004) and by 8% in hot (55.1 ± 2.5 vs. 59.6 ± 2.0 ml·kg(-1)·min(-1), P = 0.007) conditions. Heat acclimation improved time-trial performance by 6% in cool (879.8 ± 48.5 vs. 934.7 ± 50.9 kJ, P = 0.005) and by 8% in hot (718.7 ± 42.3 vs. 776.2 ± 50.9 kJ, P = 0.014) conditions. Heat acclimation increased power output at lactate threshold by 5% in cool (3.88 ± 0.82 vs. 4.09 ± 0.76 W/kg, P = 0.002) and by 5% in hot (3.45 ± 0.80 vs. 3.60 ± 0.79 W/kg, P < 0.001) conditions. Heat acclimation increased plasma volume (6.5 ± 1.5%) and maximal cardiac output in cool and hot conditions (9.1 ± 3.4% and 4.5 ± 4.6%, respectively). The control group had no changes in VO2max, time-trial performance, lactate threshold, or any physiological parameters. These data demonstrate that heat acclimation improves aerobic exercise performance in temperate-cool conditions and provide the scientific basis for employing heat acclimation to augment physical training programs.
authors: Dept. of Human Physiology, Univ. of Oregon, Eugene, OR 97403-1240, USA.
authors: Santiago
authors: S
authors: Lorenzo
authors: John R
authors: JR
authors: Halliwill
authors: Michael N
authors: MN
authors: Sawka
authors: Christopher T
authors: CT
authors: Minson
mesh_terms: D000064:Acclimatization; D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D015308:Anaerobic Threshold; D001642:Bicycling; D002302:Cardiac Output; D003080:Cold Temperature; D015444:Exercise; D005260:Female; D006339:Heart Rate; D006358:Hot Temperature; D006801:Humans; D006979:Hyperthermia, Induced; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption; D010953:Plasma Volume; D013997:Time Factors; D055815:Young Adult
chemical_list: D019344:Lactic Acid