Endocrine and androgenic response to altitude training in professional cyclists

This study investigated endocrine and steroidal blood markers in 31 male elite cyclists monitored over 7 weeks, including a 3 week altitude training camp either at 2050 m (n = 19) or 3000 m (n = 12). Serum samples were analysed for steroidal [e.g. testosterone (T)] and endocrine [i.e. insulin-like growth factor-1 (IGF-1) and N-terminal propeptide type III procollagen (P-III-NP)] variables. Total haemoglobin mass (Hbmass) and plasma volume (PV) were measured by CO-rebreathing. After 21 days at altitude, T increased at 2050 m (from 5.2 ± 2.6 to 8.3 ± 2.7 ng mL^-1, P < 0.001) but not at 3000 m. IGF-1 was elevated (by 16%, P = 0.003, and 11%, P = 0.01 at 2050 and 3000 m, respectively) only after returning to near sea-level. P-III-NP decreased by 20% (P = 0.01) at 2050 m but increased by 25% (P < 0.001) at 3000 m. After altitude, Hbmass increased by 3.7% (+40 g, P < 0.001) at 2050 m, and by 3.5% (+34 g, P < 0.001) at 3000 m. Conversely, PV had decreased by 5.7% (-216 mL, P = 0.002) at 2050 m, and by 12.2% (-460 mL, P < 0.001) at 3000 m. In both groups pooled, Hbmass correlated with both T levels (r = 0.38, P = 0.003) and IGF-1 values (r = -0.25, P = 0.04). In conclusion, a higher hypoxic dose at 3000 m (vs. 2050 m) did not result in a larger relative increase in Hbmass. Steroidal and endocrine variations were observed during the altitude sojourn with differences depending on the altitude level. The amplitude of haematological and training adaptations may be linked to changes in T and IGF-1 after 3 weeks at 2050 m. KEY POINTS: Altitude training camps are widely used by athletes to increase their haemoglobin mass towards enhanced sea-level performance, while haematological responses are very individual, depending on the hypoxic dose (how high and for how long); steroidal and endocrine responses during altitude training camps have not been investigated to date. This study investigated endocrine and steroidal blood markers in 31 male elite cyclists before, during and after 21 days at 2050 or 3000 m. Steroidal and endocrine variations were observed during the altitude camps with differences depending on the altitude level. The amplitude of haematological and training adaptations may be linked to changes in testosterone and insulin-like growth factor-1 after 3 weeks at 2050 m, but further research is required to infer causal relationships.