Perceptual acuity ability in endurance runners: How cardiorespiratory fitness, not biological sex, shapes interoceptive awareness

This study examined sex differences in perceptual acuity ability, quantified via the just-noticeable difference approach (JND), through V ˙ O 2 kinetics expressed relative to individual V ˙ O 2max , their relationship to time perception, rating of perceived exertion (RPE), speed, and heart rate (HR) in recreational runners. Sixty-four runners (Females: n = 30, V ˙ O 2max = 48.0 ± 5.2 ml·kg −1 ·min −1 ; Males: n = 34, V ˙ O 2max = 57.0 ± 5.6 ml·kg −1 ·min −1 ) completed a maximal estimation trial and four 5-min JND bouts at 70% V ˙ O 2max , designed to quantify the V ˙ O 2 difference during the final 30 s between each JND bout and the preceding standard stimulus at intensities perceived as just above (JND-A) and just below (JND-B) the reference exertion. V ˙ O 2 -time trajectories were modeled with generalized additive models; secondary outcomes were assessed via repeated-measures ANOVA. No sex differences emerged in total JND magnitude (Females: 6.83 ± 3.69% V ˙ O 2max ; Males: 6.23 ± 2.82% V ˙ O 2max ; d = 0.182) or time perception (η 2 p = 0.009). Females exhibited higher V ˙ O 2 (+3.54% V ˙ O 2max ) and distinct V ˙ O 2 -time trajectories. Independent of sex, JND-A elicited a greater magnitude of change than JND-B: higher relative <mml:math xml