External mechanical efficiency across incremental VO2 max stages and ventilatory efficiency in well-trained and less-trained adults.

BACKGROUND/OBJECTIVE: External mechanical efficiency (EME%) and ventilatory efficiency (VEF) reflect endurance performance, yet comparisons between well-trained (WT) and less-trained (LT) runners during incremental exercise are limited. This study examined stage-specific changes in EME% and VEF during a graded treadmill test and evaluated whether individuals can self-select appropriate treadmill speeds for a VO2 max protocol. METHODS: Thirty-six runners (19 WT, 17 LT) completed a Modified Astrand VO2 max Treadmill protocol. EME% was calculated as vertical work rate relative to metabolic rate, and VEF as the lowest VE/VCO2 value from three consecutive 15-s intervals. A linear mixed-effects model assessed EME% across stages, and a two-way ANCOVA and ANOVA examined effects of sex and training status on VEF and test duration. RESULTS: EME% showed significant effects of stage and group, with a stage × group interaction (p < 0.05). WT runners demonstrated greater EME% than LT runners at higher stages (3-5; all p < 0.05). VEF differed by sex (males: 27.49 ± 4.09; females: 29.96 ± 2.92, p = 0.017) but not by training status (p = 0.48). Although self-selected starting intensities differed from recommended values (55% LT; 77.5% for WT), self-selected treadmill speeds produced group mean test durations consistent with the recommended 8-12 min duration, and all participants achieved valid VO2 peak values. CONCLUSION: The EME% advantage of trained runners is stage-dependent, emerging at higher exercise intensities. VEF appears influenced by sex rather than training status. Despite differing from previously recommended starting intensities, self-selected treadmill speeds produced valid VO2 peak tests across training groups.