Oxygen uptake and heart rate kinetics during dynamic upper and lower body exercise: an investigation by time‑series analysis

Purpose: The study compared the kinetic responses of heart rate (HR), pulmonary (V'O₂pulm) and muscular oxygen uptake (V'O₂musc) kinetics for upper (UpBody) and lower body (LoBody) exercise. Methods: Eleven healthy men (24 ± 2 years; 184 ± 8 cm; 79 ± 7 kg) performed pseudo-random binary sequence (PRBS) work rate (WR) changes with a semi-recumbent cycle ergometer (30 and 80 W) and an arm cranking exercise device (20 and 50 W); followed by step-wise increases in WR (UpBody: 20 W · 5 min^-1; LoBody: 50 W · 5 min^-1).V'O₂pulm was measured breath-by-breath and HR beat-to-beat. V'O₂musc was estimated by the approach of Hoffmann et al. (2013), accounting for circulatory distortions. Time constants (τ) for HR (τHR), V'O₂pulm (τV'O₂pulm) and V'O₂musc (τV'O₂musc) were estimated during the PRBS phases by time-series analysis.Results: Peak oxygen uptake differed significantly between UpBody (37.8 ± 5.0 mL · min^-1 · kg^-1) and LoBody exercise (56.1 ± 7.4 mL · min^-1 · kg^-1; p<0.001). Significant differences were observed for τV'O₂musc (UpBody: 41.1 ± 11.3s vs. LoBody: 29.5 ± 5.2 s; p<0.05), but not for τV'O₂pulm (49.1 ± 17.1s vs. 39.6 ± 11.2 s; p>0.05) and τHR (29.1 ± 15.6s vs. 25.6 ± 8.0 s; p>0.05). Conclusions: Meaningful dissociations between V'O₂pulm and V'O₂musc kinetics exist for both UpBody and LoBody exercise during rapid work rate changes. Therefore, isolated V'O₂pulm kinetic estimations without the consideration of the circulatory distortions may not allow a reliable assessment of V'O₂musc kinetics.