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

Abstract

Purpose

The study compared the kinetic responses of heart rate (HR), pulmonary ($\dot V$O₂pulm) and muscular oxygen uptake ($\dot V$O₂musc) 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 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). $\dot V$O₂pulm was measured breath-by-breath and HR beat-to-beat. $\dot V$O₂musc 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 (τ) for HR (τHR), $\dot V$O₂pulm (τ $\dot V$O₂pulm) and $\dot V$O₂musc (τ $\dot V$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 exercises (56.1 ± 7.4 mL min⁻¹ kg⁻¹; p < 0.001). Significant differences were observed for τ $\dot V$O₂musc (UpBody: 41.1 ± 11.3 s vs LoBody: 29.5 ± 5.2 s; p < 0.05), but not for τ $\dot V$O₂pulm (49.1 ± 17.1 s vs 39.6 ± 11.2 s; p > 0.05) and τHR (29.1 ± 15.6 s vs 25.6 ± 8.0 s; p > 0.05).

Conclusions

Meaningful dissociations between $\dot V$O₂pulm and $\dot V$O₂musc kinetics exist for both UpBody and LoBody exercise during rapid work rate changes. Therefore, isolated $\dot V$O₂pulm kinetic estimations without the consideration of the circulatory distortions may not allow a reliable assessment of $\dot V$O₂musc kinetics.