Effect of altitude training on serum creatine kinase activity and serum cortisol concentration in triathletes

In this investigation we evaluated the effect of a 5-week training program at 1860 m on serum creatine kinase (CK) activity and serum cortisol concent ration in national-caliber triathletes for the purpose of monitoring the re sponse to training in a hypobaric hypoxic environment. Subjects included 16 junior-level female (n = 8) and male (n = 8) triathletes who were training for the International Triathlon Union (ITU) World Championships. After an initial acclimatization period, training intensity and/or volume were incre ased progressively during the 5-week altitude training camp. Resting venous blood samples were drawn at 0700 hours following a 12-h overnight fast and were analyzed for serum CK activity and serum cortisol concentration. Subj ects were evaluated before [7-10 days pre-altitude (SL 1)] and after [7-10 days post-altitude (SL 2)] the 5-week training camp at 1860 m. At altitude, subjects were evaluated within 24-36 h after arrival (ALT 1), 7 days after arrival (ALT 2), 18 days after arrival (ALT 3), and 24-36 h prior to leavi ng the altitude training camp (ALT 4). A repeated-measures analysis of vari ance was used to evaluate differences over time from SL 1 to SL 2. Compared to SL 1, serum CK activity increased approximately threefold (P < 0.05) wi thin the initial 24-36 h at altitude (ALT 1), and increased by an additiona l 70% (P < 0.05) after the Ist week of altitude training (ALT 2). Serum CK activity remained significantly elevated over the duration of the experimen tal period compared to pre-altitude baseline levels. Serum cortisol concent ration was increased (P < 0.05) at the end of the 5-week altitude training period (ALT 4) relative to SL 1, ALT 1 and ALT 3. These data suggest that: (1) the initial increase in serum CK activity observed in the first 24-36 h at altitude was due primarily to acute altitude exposure and was independe nt of increased training intensity and/or training volume, (2) the subseque nt increases in serum CK activity observed over the duration of the 5-week altitude camp were probably due to the combined effects of altitude exposur e and increased training load, and (3) the increase in serum cortisol conce ntration observed at the end of the altitude training camp reflects the add itive effect of 5 weeks of altitude exposure in combination with a progress ively increased training intensity and/or volume.