Author(s): TAKEI, N., MURAKI, R., GIRARD, O., HATTA, H., TAKAHASHI, Y., Institution: THE UNIVERSITY OF TOKYO, Country: JAPAN, Abstract-ID: 797

INTRODUCTION:
Repeated sprint training in hypoxia (RSH) is used to enhance repeated-sprint ability, yet athletes may show heterogeneous adaptations. This study investigated (1) whether inter-individual variability exists in training effects of RSH intervention, and (2) which training parameters (SpO₂, training load, mechanical work) are associated with that variability.
METHODS:
Sixteen male highly-trained sprint runners completed a 2-week RSH intervention in normobaric hypoxia (FiO₂ = 0.15): 6 sessions (3/week), each comprising 2 sets of 5 × 10-s all-out cycling sprints (30-s recovery; 5-min between sets). Repeated sprint performance was assessed pre/post in normoxia (FiO₂ = 0.21) using 10 × 10-s all-out cycling sprints with 30-s recovery. Mean power output (MPO), sprint decrement score (Sdec), SpO₂, blood lactate concentration, TRIMP, and mechanical load was assessed. Inter-individual variability was estimated using test–retest data to account for random noise, and responder proportion was derived relative to the smallest worthwhile change.
RESULTS:
MPO increased by +3.8% after the intervention (P = 0.001), and Sdec improved (P = 0.047), while heart rate and blood lactate did not meaningfully change. Inter-individual variability existed with 81.3% classified as responders (~20% non-responders). Average SpO₂ during training correlated with relative total work (r = 0.435, P = 0.008), and relative total work strongly correlated with %MPO improvement (r = 0.833, P < 0.001). TRIMP showed no significant association with SpO₂, relative total work, or performance improvement.
CONCLUSION:
Despite a clear group-mean improvement following RSH intervention, inter-individual variability exists, with a notable proportion of non-responders (~20%). Variability in arterial oxygen desaturation (SpO₂) appears to influence the mechanical work achieved during hypoxic training, which in turn is strongly linked to performance gains. Monitoring SpO₂ together with mechanical output (work performed) may help individualize RSH prescription to maximize training benefits.