While the benefits arising from the traditional live high - train low (LHTL) altitude training have been attributed to an improved erythropoietic response, other non-haematological (muscle efficiency) factors have also the potential to improve sport-specific fitness. Recently, repeated sprinting in hypoxia (RSH) has proved superior to similar training in normoxia (RSN) in enhancing high-intensity, intermittent performance. The usefulness of combining LHTL and RSH on team-sport related activities has not yet been investigated. Using a double-blinded design, the aim of this study was to test the hypothesis that in-season RSH combined with LHTL, namely "live-high, train-low and high" (LHTLH) provides superior physical performance benefits in team-sport players than the combination of LHTL and RSN or than live low-train low (LLTL). Twenty-three elite field hockey players slept in normobaric hypoxia for 14 days (14h.day-1; simulated altitude of 2500-3000 m or FIO2 ~15.1-14.5%) and, in addition to their usual training, completed 6 repeated running sprint sessions (4 sets of 5 x 5-s sprints, 25 s of passive rest between sprints, 5 min between sets) either in normobaric hypoxia (LHTLH; 3000 m or FiO2 ~14.5%, n=11) or in normoxia (LHTL; n=12) on synthetic grass inside a 45-m long, mobile inflatable simulated hypoxic equipment. The control group (LLTL, n=9) slept and train as usually at sea-level. Before (Pre-) and after (Post-) intervention, haemoglobin mass (Hbmass) was measured in duplicate by using the 2-min optimised carbon monoxide rebreathing method. Repeated sprint ability (8 x 20-m sprints, 20 s recovery; RSA) and specific aerobic fitness (Yo-Yo Intermittent Recovery level 2; YYIR2) were tested. The two hypoxic groups similarly increased their Hbmass (888±107 vs. 924±114 g and 931±131 vs. 965±137 g for LHTLH and LHTL, respectively; both P<0.001), whereas there was no change for the LLTL group (929±171 vs. 937±179 g). From Pre- to Post-, LHTLH and LHTL (+21 and +22%; both P<0.001) improved their performance on the YYIR2 test to the same extent, while no significant improvement (+4%) occurred in LLTL. During the RSA test, both best (-3.0%, P<0.001 and -1.6%, P<0.05) and cumulated sprint (-3.6%, P<0.001 and -1.9%, P<0.01) times were shortened for LHTLH and LHTL groups, with no changes in LLTL (+0.2% and -0.7%). The combination of a 2-wk in season LHTL altitude training intervention with six sessions of RSH or RSN enhanced blood-carrying capacity and specific aerobic fitness but LHTLH induced larger immediate improvements in repeated-sprint ability than LHTL or LLTL in a group of elite field hockey players. Whether RSH up-regulates muscle glycolytic and oxidative pathways more than RSN and induces delayed (2-wk-post camp) performance enhancements will be determined using our full data set.
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