Purpose: This study compared the effects of individualizing supramaximal interval rowing interventions using anaerobic power reserve (APR [high-intensity interval training (HIIT) prescribed according to individual APR (HIIT_APR)]) and power associated with maximal oxygen uptake (${\mathrm{W}\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ [HIIT prescribed based on the individual ${\mathrm{W}\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ (HIIT_W)]) on the homogeneity of physiological and performance adaptations. Methods: Twenty-four well-trained rowers (age 24.8 [4.3] y, stature 182.5 [3] cm, body mass 86.1 [4.3]) were randomized into interventions consisting of 4 × 30-second intervals at 130%APR (${\mathrm{W}\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ + 0.3 × maximal sprint power) with weekly progression by increasing the number of repetitions per set (5, 6, 7, 8, 9, and 10, from first to sixth session) and the same sets and repetitions with the intensity described as 130% ${\mathrm{W}\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$. The work-to-recovery ratio was 1:1 for repetitions and 3 minutes between sets. Responses of aerobic fitness indices, power output, cardiac hemodynamics, locomotor abilities, and time-trial performance were examined. Results: Both HIIT_APR and HIIT_W interventions significantly improved ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$, lactate threshold, cardiac hemodynamics, and 2000-m performance, with no between-groups difference in changes over time. However, HIIT_APR resulted in a lower interindividual variability in adaptations in ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ and related physiological parameters, but this is not the case for athletic performance, which can depend on a multitude of factors beyond physiological parameters. Conclusions: Results demonstrated that expressing supramaximal interval intensity as a proportion of APR facilitates imposing the same degrees of homeostatic stress and leads to more homogeneous physiological adaptations in maximal variables when compared to prescribing a supramaximal HIIT intervention using ${\mathrm{W}\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$. However, lower interindividual variability would be seen in submaximal variables if HIIT interventions were prescribed using ${\mathrm{W}\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$.