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Repeated-sprint training in hypoxia (RSH) was recently shown to improve repeated-sprint ability (RSA) in cycling. This phenomenon is likely to reflect fiber type-dependent, compensatory vasodilation, and therefore, our hypothesis was that RSH is even more beneficial for activities involving upper body muscles, such as double poling during cross-country skiing. In a double-blinded fashion, 17 competitive cross-country skiers performed six sessions of repeated sprints (each consisting of four sets of five 10-s sprints, with 20-s intervals of recovery) either in normoxia (RSN, 300 m; FiO2, 20.9%; n= 8) or normobaric hypoxia (RSH, 3000 m; FiO2, 13.8%; n= 9). Before (pre) and after (post) training, performance was evaluated with an RSA test (10-s all-out sprints-20-s recovery, until peak power output declined by 30%) and a simulated team sprint (team sprint, 3× 3-min all-out with 3-min rest) on a double-poling ergometer. Triceps brachii oxygenation was measured by near-infrared spectroscopy. From pretraining to posttraining, peak power output in the RSA was increased (P< 0.01) to the same extent (29%±13% vs 26%±18%, nonsignificant) in RSH and in RSN whereas the number of sprints performed was enhanced in RSH (10.9±5.2 vs 17.1±6.8, P< 0.01) but not in RSN (11.6 T 5.3 vs 11.7±4.3, nonsignificant). In addition, the amplitude in total hemoglobin variations during sprints throughout RSA rose more in RSH (P< 0.01). Similarly, the average power output during all team sprints improved by 11% T 9% in RSH and 15% T 7% in RSN. Our findings reveal greater improvement in the performance of repeated …