Methods modulate: protocol choice shapes apparent sex differences in the determination of exercise intensity

Exercise intensity is often prescribed as a percentage of a "maximum" reference point. Both the choice of reference and the protocol to obtain it may bias apparent female-male differences in relative intensity. The objective of this study is to examine whether female-male differences in relative intensity expressed relative to a maximum reference [V̇o_2max or peak power output (PPO)] differ depending on the protocol used to determine it (ramp vs. step). Fifty trained cyclists (30 males, 20 females, 31 ± 8 yr old, V̇o_2max 3,866 ± 840 mL/min) completed a ramp-incremental and a 3-min step test on a cycle ergometer. Thresholds were determined in the step test from fixed and individualized blood lactate concentrations and from ventilation. Relative intensity was expressed in relation to PPO and V̇o_2max derived from each protocol. Linear mixed-effects models with participant as random intercept tested the fixed effects of Sex, Protocol, and their interaction. Agreement between ramp- and step-derived V̇o_2max values was evaluated using Bland-Altman analysis. For V̇o₂-based relative intensity, only protocol effects were small but significant (all P < 0.01). For Power, Sex had a significant influence in the models with males displaying higher relative intensities in all lactate-based thresholds (all P ≤ 0.02). Sex × Protocol interactions emerged for the onset of 2 mmol/L blood lactate (BLa₂) and Onset of minimum+ 0.5 mmol/l blood lactate (BLa_min+0.5) (both P < 0.05), indicating that using step or ramp protocols as reference can alter the magnitude or direction of female-male differences. Apparent sex differences in relative intensity depend on how "maximum" is defined and obtained. The same relative intensity does not ensure equivalent physiological strain across sexes.NEW & NOTEWORTHY Method matters when comparing men and women in exercise physiology. In trained cyclists, we show that apparent female-male differences in exercise intensity at lactate and ventilatory thresholds depend on how "maximum" is defined (V̇o_2max vs. peak power output) and the protocol used (ramp vs. step). Some sex effects appeared only under specific methodological choices, highlighting that differences often attributed to biology may, in fact, be artifacts of test design.