Do Surrogate Markers of Cardiorespiratory Fitness Predict Individual Changes in VO2peak? A Randomized Controlled Trial.

The purpose of the current study was to test the hypothesis that individual response classification for surrogate markers of cardiorespiratory fitness (CRF) will agree with response classification for VO_2peak. Surrogate markers of CRF were time to fatigue on treadmill test (TTF), time trial performance (3kTT), resting heart rate (RHR), submaximal heart rate (SubmaxHR), and submaximal ratings of perceived exertion (SubmaxRPE). Twenty-five participants were randomized into a high-intensity interval training (HIIT: n = 14) group or non-exercise control group (CTL: n = 11). Training consisted of four weeks of high-intensity interval training (HIIT) - 4x4 minute intervals at 90-95% HR_max 3 times per week. We observed poor agreement between response classification for VO_2peak and surrogate markers (agreement < 60% for all outcomes). Although surrogate markers and VO_2peak correlated at the pre- and post-intervention time points, change scores for VO_2peak were not correlated with changes in surrogate markers of CRF. Interestingly, a significant relationship (r ² = 0.36, p = 0.02) was observed when comparing improvements in estimated training performance (VO₂) and change in VO_2peak. Contrary to our hypothesis, we observed poor classification agreement and non-significant correlations for changes scores of VO_2peak and surrogate markers of CRF. Our results suggest that individuals concerned with their VO_2peak response seek direct measurements of VO₂.