The effects of altitude training on hormonal response in professional cyclists

Introduction The Alps offer numerous possibilities for athletes to prepare competitions at altitude training with the aims of further gains for near sea-level performances through physiological adaptations. Hematological adaptations (e.g., increase in hemoglobin mass (Hbmass)), improved oxygen delivery or peripheral adaptations at the muscle level have been thoroughly investigated in the past decades. While the impact of prolonged sojourns at altitude on hematological variations is increasingly well understood, research is very limited on the hormonal responses to altitude, and the underlying mechanisms underpinning putative anabolic and erythropoietic adaptations in elite endurance athletes. Methods 21 professional cyclists (25.4 ± 3.3 yrs, 69.8 ± 5.0 kg, maximal aerobic power 560 ± 34 W) underwent a 3-weeks altitude training camp at an altitude of 2050 m (inspired oxygen pressure 115 mmHg, Kühtai, Austria) while training between 500 and 2500 m of altitude (Live-High Train-Low (LHTL) approach). Total hemoglobin mass (Hbmass) and plasma volume (PV) were determined by CO-rebreathing at the start and end of the altitude sojourn. Additional blood samples were taken two weeks before, 72 h after and 10 days after the training camp to monitor i) steroidal hormones (testosterone), and ii) endocrine response (Insuline-like growth factor-1 (IGF-1)). Results At the end of the altitude training camp, Hbmass had increased in average by 3.7% (+40 g, p<0.001) while PV was decreased by 5.7% (-216 mL, p=0.002). During the 21 days at altitude, a significant increase was observed for testosterone (from 5.2 ± 2.6 to 8.3 ± 2.7 ng/mL, p<0.001)), and it was still elevated 48 h after returning to low altitude (6.8 ± 2.3 ng/mL) but decreased towards baseline after 10 days (6.59 ± 2.6, p= 0.01). IGF-1 was elevated 48 h after the altitude camp when compared to the initial baseline (273.5 ± 65.1 vs. 235.9 ± 51.6 µg/L, p=0.003). Discussion/Conclusion In summary, this study was the first to monitor hormonal markers over 7 weeks before, during, and after a 3-week altitude training camp in a large cohort of professional cyclists. The increase in both testosterone and IGF-1 during the time course of the altitude sojourn suggests an anabolic stimulus linked to training adaptations. Concomitantly, a positive erythropoietic effect was observed while a moderate decrease in PV reflected a thorough monitoring of fluid balance during the stay at altitude. The individual changes observed for IGF-1 at altitude should additionally be further considered in the context of the newly implemented endocrine passport monitoring this variable for anti-doping purposes. Overall, this study supports positive physiological adaptations in elite endurance athletes following a LHTL training camp planned according to the current state of the art knowledge collected in the past 60 years investigating hypoxic training strategies.