Heat suit training increases hemoglobin mass in elite cross-country skiers

Purpose The primary purpose was to test the effect of heat suit training on hemoglobin mass (Hb(mass)) in elite cross-country (XC) skiers. Methods Twenty-five male XC-skiers were divided into a group that added 5 x 50 min weekly heat suit training sessions to their regular training (HEAT; n = 13, 23 +/- 5 years, 73.9 +/- 5.2 kg, 180 +/- 6 cm, 76.8 +/- 4.6 ml center dot min(-1)center dot kg(-1)) or to a control group matched for training volume and intensity distribution (CON; n = 12, 23 +/- 4 years, 78.4 +/- 5.8 kg, 184 +/- 4 cm, 75.2 +/- 3.4 ml center dot min(-1)center dot kg(-1)) during the five-week intervention period. Hb(mass), endurance performance and factors determining endurance performance were assessed before and after the intervention. Results HEAT led to 30 g greater Hb(mass) (95% CI: [8.5, 51.7], p = 0.009) and 157 ml greater red blood cell volume ([29, 285], p = 0.018) post-intervention, compared to CON when adjusted for baseline values. In contrast, no group differences were observed for changes in work economy, running velocity, and fractional utilization of maximal oxygen uptake (V?O-2max) at 4 mmol center dot L-1 blood lactate, V?O-2max or 15-min running distance performance trial during the intervention. Conclusion HEAT induced a larger increase in Hb(mass) and red blood cell volume after five weeks with five weekly heat suit training sessions than CON, but with no detectable group differences on physiological determinants of endurance performance or actual endurance performance in elite CX skiers.