Inter-individual variability in performance benefits from repeated sprint training in hypoxia and associated training parameters

This study examined whether inter-individual variability exists in repeated sprint training in hypoxia (RSH) and how peripheral oxygen saturation (SpO₂) affects physiological demands and mechanical output, and subsequent training outcomes. Sixteen highly-trained sprint runners completed six sessions of RSH consisting of two sets of 5 × 10-s all-out sprints (fraction of inspired oxygen: 0.15), with pre- and post-tests involving 10 × 10-s all-out sprints in normoxia. Average SpO₂, training impulse (TRIMP), and relative total work (relative TW; standardized by pre-test TW) during training sessions were calculated. After the intervention, MPO increased by +3.8% (<i>P</i> = 0.001) and sprint decrement score by +6.0% (<i>P</i> = 0.047). However, inter-individual variability in performance improvement observed and nearly 20% of participants did not obtain performance benefit. Average SpO₂ during training sessions correlated significantly with relative TW (<i>r</i> = 0.435, <i>P</i> = 0.008), indicating that participants with higher SpO₂ performed more work during training. Relative TW was strongly correlated with performance improvement (<i>r</i> = 0.833, <i>P</i> < 0.001), suggesting that those who produced more work during training experienced greater performance gains. TRIMP showed no significant correlation with SpO₂ or performance improvement. In summary, greater peripheral deoxygenation leads to lower mechanical work and consequently smaller performance improvement following RSH. The variability in peripheral deoxygenation and relative TW among highly-trained sprint runners may contribute to the heterogeneous training effects observed.