Exercise modality influences oxygen pulse flattening during incremental cardiopulmonary exercise testing in healthy adults

Purpose To compare oxygen pulse (O₂P) responses during cardiopulmonary exercise testing (CPET) in healthy adults using two ergometers, Treadmill and Cycle ergometer, and to determine the prevalence of O₂P flattening and the modality-specific characteristics of O₂P curve dynamics. Methods Thirty-four healthy adults (29.4 ± 6.9 years; 35% female) completed two maximal CPETs on both Cycle and Treadmill, in a random order within three weeks. O₂P flattening, defined as the absence of a further increase in O₂P despite increasing workload, was assessed visually and confirmed quantitatively. Results Twelve participants (35%) demonstrated O₂P flattening or decline, nine (27%) exclusively during Treadmill testing. A significant group × modality interaction was observed for peak O₂P ( p < 0.05), with lower values in participants with flattening than in those showing a continuous rise. (Cycle: 9.9 ± 3.2 vs. 13.6 ± 2.7 ml/min/beat; Treadmill: 11.8 ± 3.7 vs. 16.6 ± 3.7 ml/min/beat). In addition, an O 2 P of ≤ 12.8 ml/beat on the Cycle increased the likelihood of flattening during maximal Treadmill exercise by 7.5 times (OR 7.5, p = 0.03). Conclusion O₂P flattening was more frequently observed during treadmill exercise, indicating that O₂P trajectories are exercise modality dependent. In individuals with low peak O₂P during cycle ergometry, additional assessment using treadmill CPET may offer complementary information.