Living For Six Days At 2200 M Improves Prolonged Time-Trial Performance Of Sea-Level Residents Exposed To 4300 M.

Abstract

It is well established that the magnitude of the initial impairment in prolonged time-trial (TT) performance that occurs when sea-level residents (SLR) ascend rapidly to high altitude (e.g., 4300 m) is attenuated with acclimatization to the same elevation. Whether adaptations acquired from living temporarily at a moderate altitude ("staging") just prior to the high altitude exposure will also benefit TT performance is less certain. PURPOSE: To determine the effectiveness of staging at 2200 m on TT performance of SLR during subsequent exposure to 4300 m. METHODS: Ten healthy men (mean ± SE: 21 ± 1 yrs) were tested on a cycle ergometer during steady-state exercise (SSE) and then during a 720 kJ maximum effort TT at SL, and again beginning within 3 hrs of exposure to 4300 m (459 Torr) before (preSTG) and after (postSTG) staging for 6 d at 2200 m (601 Torr). SSE during preSTG and postSTG was performed for 20 min at low (73 ± 5 W) and moderate (116 ± 8 W) power outputs to assess adaptation. During the TT, the men freely adjusted power output. Arterial oxygen saturation (SaO2), heart rate (HR), and ratings of perceived exertion (RPE) were measured every 5 min during all exercise. RESULTS: At 4300m, from preSTG to postSTG, SaO2 increased during low SSE (75 ± 2 to 77 ± 1%) while HR (148 ± 5 to 140 ± 5 b/min) and RPE (12 ± 1 to 9 ± 1) decreased during moderate SSE (all P<0.01). TT duration increased (P<0.01) from 73 ± 6 min at SL to 111 ± 6 min at preSTG and to 92 ± 7 min at postSTG, and was 17 ± 6% (19 ± 6 min) faster postSTG than preSTG (P<0.01). Despite performing the TT at a higher power output postSTG than preSTG (120 ± 7 vs 100 ± 10 W, P<0.01), RPE was lower (13 ± 1 vs 16 ± 1, P<0.01) and SaO2 tended to be higher (76 ± 1 vs 74 ± 1%, P=0.15). TT performance of all 10 men improved preSTG to postSTG (range: 2 to 56 min) with the extent of each individual's improvement being directly related to their increase in SaO2 during SSE and the TT (R = 0.88, P<0.03). CONCLUSIONS: The impairment in prolonged TT performance of SLR rapidly exposed to 4300 m was attenuated after living for 6 days at a moderate altitude of 2200 m. The close association between improved TT performance and higher exercise SaO2 suggest the major contributing factor was increased ventilation. Funding provided by US Army Medical Research and Materiel Command ATO IV.MD.2006.01. Authors' views; not official U.S. Army or DoD policy.