METABOLIC AND HORMONAL RESPONSES TO INTERVAL TRAINING AT SEA LEVEL AND MODERATE ALTITUDE

Abstract

Lactate (LA) measurements are widely used to control training intensity in endurance sports. With regard to an altered LA accumulation pattern at altitude, we questioned whether extensive interval training performed with similar LA values at seal level (SL) and moderate altitude (ALT), yields a comparable metabolic and hormonal stress response. 12 runners (mean ± SEM: 26.6 ± 2.0 yrs, 176.1 ± 2.4 cm, 62.4 ± 2.1 kg, VO2max 64.6 ± 2.0 ml·kg−1), experienced in endurance training, performed an interval training session (IT, 10 ± 1000m, 2 min rest) on the track at SL (350m) with a running velocity corresponding to 112% of the individual anaerobic threshold (IAT). One day later, the athletes moved to ALT (1800 m). After acclimatization (7 days), IT was repeated with a lower velocity (107% IAT) to realize similar LA values compared to SL. LA and heart rate were measured during IT. Blood samples were drawn at rest, 0, 0.3, 3 and 24 h after IT for determination of plasma glucose (Glu), free fatty acids (FA), cortisol (CO), human growth hormone (GH) and insulin-like growth factor-I (IGF-I). LA was similar at SL and ALT (5.4 ± 0.4/5.3 ± 0.3 mmol·l−1) and intraindividual differences (SL/ALT) did not exceed 0.5 mmol·l−1. The rise of Glu after IT was more pronounced at ALT (p < .05), while no differences were found for the increases of FA, CO and GH. A decrease of IGF-I 24 h after IT occurred only at SL (−10.1 ± 3.7, ALT: −1.7 ± 2.9%, p < .05). Conclusions: IT performed with similar LA at SL and ALT, yields comparable increases of FA, CO and GH in athletes, acclimatized to ALT. The behaviour of Glu seems to reflect a higher rate of carbohydrate oxidation during IT at ALT. However, this does not seem to suppress hepatic IGF-I production as shown by unchanged post-exercise IGF-I levels at ALT.