Effects of aerobic fitness on oxygen uptake kinetics in heavy intensity swimming

Abstract

This study aimed to characterise both the $\dot{V}{\text{O}}_{2}$ kinetics within constant heavy-intensity swimming exercise, and to assess the relationships between $\dot{V}{\text{O}}_{2}$ kinetics and other parameters of aerobic fitness, in well-trained swimmers. On separate days, 21 male swimmers completed: (1) an incremental swimming test to determine their maximal oxygen uptake $(\dot{V}{\text{O}}_{2\max } )$, first ventilatory threshold (VT), and the velocity associated with $\dot{V}{\text{O}}_{2\max }$ $(v\dot{V}{\text{O}}_{2\max } )$ and (2) two square-wave transitions from rest to heavy-intensity exercise, to determine their $\dot{V}{\text{O}}_{2}$ kinetics. All the tests involved breath-by-breath analysis of freestyle swimming using a swimming snorkel. $\dot{V}{\text{O}}_{2}$ kinetics was modelled with two exponential functions. The mean values for the incremental test were 56.0 ± 6.0 ml min⁻¹ kg⁻¹, 1.45 ± 0.08 m s⁻¹; and 42.1 ± 5.7 ml min⁻¹ kg⁻¹ for $\dot{V}{\text{O}}_{2\max }$, $v\dot{V}{\text{O}}_{2\max }$ and VT, respectively. For the square-wave transition, the time constant of the primary phase (τ_p) averaged 17.3 ± 5.4 s and the relevant slow component (A′_sc) averaged 4.8 ± 2.9 ml min⁻¹ kg⁻¹ [representing 8.9% of the end-exercise $\dot{V}{\text{O}}_{2}$ (%A′_sc)]. τ_p was correlated with $v\dot{V}{\text{O}}_{2\max }$ (r = −0.55, P = 0.01), but not with either $\dot{V}{\text{O}}_{{ 2 {\text{max}}}}$ (r = 0.05, ns) or VT (r = 0.14, ns). The %A′_sc did not correlate with either $\dot{V}{\text{O}}_{{ 2 {\text{max}}}}$ (r = −0.14, ns) or $v\dot{V}{\text{O}}_{2\max }$ (r = 0.06, ns), but was inversely related with VT (r = −0.61, P < 0.01). This study was the first to describe the $\dot{V}{\text{O}}_{2}$ kinetics in heavy-intensity swimming using specific swimming exercise and appropriate methods. As has been demonstrated in cycling, faster $\dot{V}{\text{O}}_{2}$ kinetics allow higher aerobic power outputs to be attained. The slow component seems to be reduced in swimmers with higher ventilatory thresholds.