Hematological, skeletal muscle fiber, and exercise performance adaptations to heat training in elite female and male cyclists

Heat exercise training may increase exercise performance in athletes. The underlying mechanisms remain partly unresolved, and it is unknown if female and male athletes may experience comparable gains. The aims were to investigate whether heat training ( HEAT) increases hemoglobin mass (Hb(mass)), skeletal muscle fiber characteristics, and thermoneutral exercise performance in elite female and male endurance athletes. Female (n = 20; <(V)over dot>O-2max = 58.2 +/- 6.7 mL. min(-1).kg(-1)) and male (n = 27; <(V)over dot>O-2max = 76.4 +/- 7.8 mL. min(-1).kg(-1)) cyclists were studied before and after 5 wk of randomized control or HEAT consisting of five weekly sessions each of 50 min duration, which were included in their normal training regimes. Overall, the observed relative responses to HEAT were largely similar in female and male study participants. HEAT increased (P < 0.05) Hbmass in females from 650 +/- 77 to 675 +/- 76 g (4.0 +/- 1.6%) and from 1,008 +/- 155 to 1,041 +/- 147 g ( 3.5 +/- 2.3%) in males. In contrast, skeletal muscle citrate synthase activity, fiber type distribution, and capillary density remained unchanged with HEAT. Lactate threshold, <(V)over dot>O-2max, and mean power output during 15-min all-out testing were all enhanced (P < 0.05) following HEAT in female and male study participants. In conclusion, 5 wk of HEAT increases Hb(mass) in female and male elite cyclists and improves exercise performance in a thermoneutral environment. Based on this, heat training may be recommended to elite female and male athletes aiming to perform in a thermoneutral environment. NEW & NOTEWORTHY We demonstrate in elite female and male cyclists that heat exercise training (5 x 50 min sessions/wk for 5 wk) facilities Hb(mass) and other hematological parameters more than control exercise training, whereas skeletal muscle properties remain unaltered. Collectively, this coincided with improvements in lactate threshold, <(V)over dot>O-2max, and 15-min all-out cycling performance.