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 × 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·min(−1)·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·min(−1)·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 (V̇O(2max)) at 4 mmol·L(−1) blood lactate, V̇O(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.