Effect of β-blockade on measures and reproducibility of heart rate, oxygen uptake and work rate across repeated bouts of short-duration, RPE-regulated exercise.

Purpose: We examined the effect of β-blockade on measures and reproducibility of heart rate (HR), oxygen uptake ( $\dot{V}{O}_2$ ) and work rate (WR) across repeated bouts of short-duration, RPE-regulated exercise.

Methods: Participants completed an RPE-regulated, interval-based exercise session under control and β-blockade conditions with six 3-min bouts alternating between RPE 13 and RPE 15, separated by 2-min active recovery periods. Participants adjusted treadmill speed/grade to meet the target RPE. Linear mixed effects models assessed the effect β-blockade on exercise responses for each RPE, while intraclass correlation coefficients (ICC) and coefficients of variation (CV) evaluated reproducibility across bouts.

Results: β-Blockade significantly reduced HR (- 36.5 beat min^-1, p < 0.001), $\dot{V}{O}_2$ (- 4.2 mL kg^-1 min^-1, p < 0.001) and work rate (- 0.6 METs, p = 0.022) during exercise. Differences between conditions remained significant for %HR_peak (p < 0.001) but not % $\dot{V}$ O_2peak or %WR_peak (p > 0.05). Exercise responses were consistently higher at RPE 15 than RPE 13 (all p < 0.001). A significant interaction showed greater HR reduction at RPE 15 (45.5 beat min^-1) than RPE 13 (40.0 beat min^-1) under β-blockade (p = 0.041). ICC values indicated good to excellent reproducibility across bouts, with no significant difference between conditions. Variability across bouts was low (mean CV = 2-8%) and unaffected by β-blockade.

Conclusion: Our findings suggest that despite significant reductions in absolute responses, β-blockade does not affect relative measures of $\dot{V}$ O₂ or work rate. RPE-regulated exercise may facilitate highly reproducible exercise intensities, making it particularly valuable for populations where β-blocker use is prevalent.