Optimal time of arrival for performance at moderate altitude (1700 m)

Purpose: The time course of physiological exercise responses after acute as cent to moderate altitude was investigated. Methods: Fifteen young male sub jects (16.5 +/- 0.8 yr) completed one familiarization and then two further sea level sessions to determine sea level values (SL). Subjects were then t ested 6 h (ALT1), 18 h (ALT2), and 47 h (ALT3) after arrival at 1700 m. Sub jects completed a 5-min submaximal cycle test, shuttle run test, and 45-s r epeated push-up rest. Hemoglobin (Hb) and hematocrit (Hct) were measured. R esults: Cycle test heart rate (NR) was higher at ALT1 than SL (182 +/- 15 v s 177 +/- 16 b . min(-1), P < 0.01) bur had returned to 177 +/- 13 and 176 +/- 12 b .min(-1) at ALT2 and ALT3, respectively. At ALT1, only five subjec ts 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 . mi n(-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% shelter at ALT1 than SL (251 +/- 134 vs 401 +/- 115 s, P < 0.001) and remained impaired at ALT2 and ALT 3 (330 +/- 124 and 344 +/- 115 s, both P < 0.001 vs SL). There was a signif icant relationship between magnitude of increased HR and reduction in SRT b etween SL and ALT1 (r = 0.52, P < 0.05). Push-up HR, Hb, and Hct were not a ffected by altitude. Conclusions: These findings indicate that detrimental effects of acute ascent to 1700 m on exercise performance are greater after 5 h than after 18 or 47 h. Performance was not entirely restored to SL val ues even after 47 h, despite restoration of easily measured physiological p arameters. The results suggest travel to moderate altitude should occur as early as is practical before competition.