The effect of normoxic or hypobaric hypoxic endurance training on the hypoxic ventilatory response

Cross-sectional studies in endurance athletes have demonstrated a diminished hypoxic ventilatory response (HVR) compared with mountaineers or sedentary controls. Conversely, short-term altitude acclimatization may increase the HVR. The longitudinal effect of training, either at sea level or altitude, on HVR has not been previously reported. We therefore studied 21 untrained men and women before and after 5 wk of cycle ergometer training at either sea level or 2,500 m. HVR was determined using the steady-state method (16). Minute ventilation (V_E) was measured with a Tissot spirometer during the last minute of 5 min breathing room air, 8% and 12% O₂, administered in random order. CO₂ was added at the mouth in an effort to maintain end-tidal CO₂ at baseline levels. Oxyhemoglobin saturation was measured directly from arterial blood with a hemoximeter (OSM 3). HVR was defined as the positive slope of the line relating V_E to O₂ saturation in l-min^-1%^-1. One group of subjects trained at sea level at 70% maximal oxygen uptake (VO_2max; N = 7). A second group trained at 2,500 m in a hypobaric chamber, at the same relative exercise intensity (i.e., 70% altitude VO_2max) or same absolute intensity (same power output) as group 1 (N = 14). Both groups trained on a bicycle ergometer for 45 min-d^-1, 5 d-wk^-1for 5 wk. In the sea level group, training sufficient to raise sea level VO_2max from 3.00 ± 0.27 to 3.41 ± 0.27 l-min^-1 (mean ± SE, P< 0.05) had no effect on HVR (0.36 ± 0.09 to 0.31 ± 0.06 l-min^-1%^-1, P = NS). In the altitude group however, a similar increase in sea level VO_2max (3.05 ± 0.19 to 3.42 ± 0.20 l-min^-1, P< 0.05) was accompanied by an increase in HVR from 0.29 ± 0.06 to 0.41 ± 0.08 l.min^-1.%^-1 (P < 0.05). We therefore conclude that 5 wk of endurance training at sea level has no effect on HVR. However, when training occurs at altitude, HVR is increased, possibly due to increased chemoreceptor sensitivity.