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

The study compared the kinetic responses of heart rate (HR), pulmonary (O(2)pulm) and muscular oxygen uptake (O(2)musc) for upper (UpBody) and lower body (LoBody) exercise. Eleven healthy men (24 +/- A 2 years, 184 +/- A 8 cm, 79 +/- A 7 kg) performed pseudo-random binary sequence (PRBS) work rate (WR) changes on a semi-recumbent cycle ergometer (30 and 80 W) and an arm cranking exercise device (20 and 50 W); followed by stepwise increases in WR (UpBody: 20 W 5 min(-1); LoBody: 50 W 5 min(-1)). O(2)pulm was measured breath-by-breath and HR beat-to-beat. O(2)musc was estimated by the approach as reported by Hoffmann et al. (Eur J Appl Physiol 113:1745-1754, 2013), accounting for circulatory distortions. Time constants (tau) for HR (tau HR), O(2)pulm (tau O(2)pulm) and O(2)musc (tau O(2)musc) were estimated during the PRBS phases by time-series analysis. Peak oxygen uptake differed significantly between UpBody (37.8 +/- A 5.0 ml min(-1) kg(-1)) and LoBody exercises (56.1 +/- A 7.4 mL min(-1) kg(-1); p < 0.001). Significant differences were observed for tau O(2)musc (UpBody: 41.1 +/- A 11.3 s vs LoBody: 29.5 +/- A 5.2 s; p < 0.05), but not for tau O(2)pulm (49.1 +/- A 17.1 s vs 39.6 +/- A 11.2 s; p > 0.05) and tau HR (29.1 +/- A 15.6 s vs 25.6 +/- A 8.0 s; p > 0.05). Meaningful dissociations between O(2)pulm and O(2)musc kinetics exist for both UpBody and LoBody exercise during rapid work rate changes. Therefore, isolated O(2)pulm kinetic estimations without the consideration of the circulatory distortions may not allow a reliable assessment of O(2)musc kinetics.