Purpose: The time course of physiological exercise responses after acute ascent to moderate altitude was investigated.
Methods: Fifteen young male subjects (16.5 +/- 0.8 yr) completed one familiarization and then two further sea level sessions to determine sea level values (SL). Subjects were then tested 6 h (ALT1), 18 h (ALT2), and 47 h (ALT3) after arrival at 1700 m. Subjects completed a 5-min submaximal cycle test, shuttle run test, and 45-s repeated push-up test. Hemoglobin (Hb) and hematocrit (Hct) were measured.
Results: Cycle test heart rate (HR) was higher at ALT1 than SL (182 +/- 15 vs 177 +/- 16 b.min(-1), P < 0.01) but had returned to 177 +/- 13 and 176 +/- 12 b.min(-1) at ALT2 and ALT3, respectively. At ALT1, only five subjects completed the full 5 min. Postexercise plasma lactate was not different. Shuttle test HR was higher at ALT1 than SL (191 +/- 8 vs 185 +/- 14 b.min(-1), P = 0.01) but had returned to 185 +/- 10 and 183 +/- 16 b.min(-1) at ALT2 and ALT3. Shuttle run time (SRT) was 37% shorter at ALT1 than SL (251 +/- 134 vs 401 +/- 115 s, P < 0.001) and remained impaired at ALT2 and ALT3 (330 +/- 124 and 344 +/- 115 s, both P < 0.001 vs SL). There was a significant relationship between magnitude of increased HR and reduction in SRT between SL and ALT1 (r = 0.52, P < 0.05). Push-up HR, Hb, and Hct were not affected by altitude.
Conclusions: These findings indicate that detrimental effects of acute ascent to 1700 m on exercise performance are greater after 6 h than after 18 or 47 h. Performance was not entirely restored to SL values even after 47 h, despite restoration of easily measured physiological parameters. The results suggest travel to moderate altitude should occur as early as is practical before competition.