Effects of Altitude Descent: Hemodilution in Young Cyclists

To investigate the effects of descent from moderate altitude combined with exposure to high ambient temperatures on plasma volume, a repeated measures design was used in young male cyclists (n = 10). The cyclists (age 18.2 ±1.2 years, VO2max 62.0 ±4.1 ml/kg/min), who lived at an altitude of 2600 m, trained at a lower altitude (450 m) for seven days. Hematological variables were measured prior to descent, at low altitude, and one day after returning to 2600m. Hemoglobin mass was measured before descent and used for indirect calculation of plasma volume (PV). Hb decreased from 17.1 ±0.7g/dl to 15.9 ±0.6 by day 1 and to 15.4 ±0.3g/dl by day 5 (both p < 0.001), then increased to 16.5 ±0.7g/dl the day after returning to the initial altitude. PV increased from 2946 ±463 ml by 12.9 ±6.6% on day 1, reached a maximum of 16.2 ±9.7% on day 5 (both p < 0.01), and decreased again to +7.4 ±9.5% after returning to altitude. The change from moderate to low altitude leads to a rapid increase in PV, which can be expected to affect performance by reducing oxygen transport capacity and increasing maximal cardiac output. Additionally, the athlete’s biological passport may be affected erroneously.