Metabolic and Cardiorespiratory Differences in Incremental Upper and Lower-Body Exercise in Healthy Adults—A Cross-Over Trial

Background: Upper-body exercise is increasingly applied in athletic and exercise settings; however, acute physiological and perceptual differences compared to lower-body exercise remain insufficiently characterized. This study compared maximal performance parameters during incremental upper- and lower-body exercise in healthy adults. Methods: Seventeen moderately trained participants (eight females, nine males) completed randomized incremental tests on a hand crank ergometer (HCE) and a cycle ergometer (CE). Maximal fat oxidation (MFO), intensity at maximal fat oxidation (FATmax), peak oxygen uptake (VO2peak), maximal heart rate (HRpeak), peak power output (PPO), immediate post-exercise lactate (LApost), and differentiated ratings of perceived exertion (RPEbreathing and RPEmuscles) were assessed. Results: MFO was significantly lower during HCE compared with CE (0.26 vs. 0.55 g·min−1, p < 0.001), occurring at a lower FATmax (42.6% vs. 51.6% of VO2peak, p = 0.016). Furthermore, relative VO2peak (34.1 vs. 48.9 mL·kg−1·min−1, p < 0.001), HRpeak (178 vs. 189 beats·min−1, p < 0.001), and relative PPO (1.8 vs. 4.1 W·kg−1, p < 0.001) were substantially reduced during HCE. While RPEbreathing was higher during CE (19.1 vs. 17.6, p < 0.001), RPEmuscles (19.4 vs. 19.8, p = 0.111) and LApost (9.8 vs. 8.6 mmol·L−1, p = 0.060) did not differ significantly between modalities. No significant modality-by-sex interactions were observed for any outcome. Conclusions: These findings demonstrate pronounced modality-specific differences in metabolic, cardiorespiratory, and perceptual responses. Exercise modality should therefore be carefully considered when interpreting maximal exercise tests and prescribing training or rehabilitation programs.