The purpose of this study was to examine the effect of repeated intermittent normobaric hypoxia on exercise performance and stress response. Twelve-male collegeate long distance runners and triathlets were divided into a normoxic (N, n=6) or a hypoxic group [two 7-night blocks of hypoxia, interspersed with 7-nights of normoxia (H, n=6)]. H group subjects stayed in a normobaric hypoxic room (15.4% O₂; 2500m) in a for 10-12h a day at night. During the experimental period, subjects were undergone the submaximal treadmill running and hematological tests. Submaximal running efficiency was measured at the intensities of 50% and 80% of VO₂max predetermined during baseline test. Also, resting erythrocyte parameters, white blood cell subsets and stress hormones were measured before (pre) and 1st, 3rd and 7th day at each series. Erythrocyte was stimulated by hypoxia. RBC, Hb and Hct were not significantly changed by hypoxia. After experimental period, exercise efficiency of H group was not significantly improved by repeated LHTL, but blood lactate concentration at both intensities was tendency to decrease from the pre-values in H group. WBC subsets and epinephrine and norepinephrine as stress hormone were increased by hypoxia. From these results, it was concluded that repeated intermittent normobaric hypoxia was stimulate the erythrocyte, but did not enough to improve to the exercise efficiency. Also, Stress responses as WBC subsets and stress hormone may be relate the improvement of submaximal exercise efficiency in athletes.

DESCENTE SPORTS SCIENCE Vol.29/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE