PURPOSE: To examine physiological and technical responses to repeated-sprint training in normobaric hypoxia at approximately 3,000 m (RSH, n = 11) or in normoxia (RSN, n = 11) compared to a control group (CON, n = 8) in well-trained tennis players. Participants were 28.8 +/- 5.9 years old without any previous experience of training in hypoxia. METHODS: In addition to maintaining their usual training (CON), both RSH and RSN groups completed five tennis specific repeated-shuttle sprint sessions (4 x 5 x approximately 8 s maximal sprints with approximately 22 s passive recovery and approximately 5 min rest between sets) over 12 days. Before (Pre), the week after (Post-1) and 3 weeks after Post-1 (Post-2), physical/technical performance during Test to Exhaustion Specific to Tennis (TEST), repeated-sprint ability (RSA) (8 x approximately 20 m shuttle runs-departing every 20 s) and heart rate variability (HRV) were assessed. RESULTS: From Pre to Post-1 and Post-2, RSH improved TEST time to exhaustion (+18.2 and +17.3%; both P < 0.001), while the "onset of blood lactate accumulation" at 4 mmol L(-1) occurred at later stages (+24.4 and +19.8%, both P < 0.01). At the same time points, ball accuracy at 100% V虈O(2m) (ax) increased in RSH only (+38.2%, P = 0.003 and +40.9%, P = 0.007). Markers of TEST performance did not change for both RSN and CON. Compared to Pre, RSA total time increased significantly at Post-1 and Post-2 (-1.9 and -2.5%, P < 0.05) in RSH only and this was accompanied by larger absolute Delta total hemoglobin (+82.5 and +137%, both P < 0.001). HRV did not change either supine or standing positions. CONCLUSION: Five repeated sprint training sessions in hypoxia using tennis specific shuttle runs improve physiological and technical responses to TEST, RSA, and accompanying muscle perfusion responses in well-trained tennis players.