Oxygen Uptake Kinetics In Heavy Intensity Exercise And Endurance Performance In Swimmers

Abstract

Although a faster VO2 kinetics have been associated to a lower O2 deficit and a greater fatigue tolerance, it is not known if changes in this parameter will influence endurance performance in swimming. PURPOSE: To verify if the VO2 kinetics parameters determined at heavy intensity swimming exercise are related to middle distance swimming performance. METHODS: Fifteen Portuguese male swimmers (20.5 ± 3.0 yr.; 77.7 ±11.9 kg; 1.80 ± 0.07m) performed on two separate days: 1) 5 × 200 m with 30 s rest and 5-10% velocity increment in between for determination of maximal oxygen uptake (VO2max) and ventilatory threshold (VT). The last repetition was performed at maximal velocity. VO2max was recorded as the highest 30 s average and VT was established by the V-slope method; 2) two 6-min constant velocity exercise bouts at D25% [= VT+0.25 × (VO2max - VT)] with at least 24 hr rest. All the tests were performed in front crawl with breath by breath analysis (K4b2, Cosmed, Italy) using a swimming snorkel (Aquatrainer). Endurance performance was recorded as the time performed in an official 400 metres freestyle competition within a 1 month from the other tests (T400).The breath-by-breath data of the two 6-min exercises were 1-s interpolated, time-aligned and averaged. The parameters of the VO2 kinetics (td1, t1, A1, td2, t2, A2; i.e. time delay, time constant and amplitude of the primary phase and slow component, respectively) were modelled with two exponential functions. The modelling incorporated an individual "snorkel delay" corresponding to the difference between the onset of exercise and the time when the following breaths summed a tidal volume superior to the outlet tube volume. RESULTS: T400 (250.9 ± 12.2 s) presented a significant correlation with t1 (15.8 ± 4.6 s; r = 0.60; p = 0.02). None of the other VO2 kinetics parameters presented significant correlations with T400 (td1: 11.3 ± 3.1 s, r = 0.39; A1: 37.4 ± 5.1 ml.min-1kg-1, r = -0.31; td2: 166 ± 55 s, r = 0.02; t2: 63.2 ± 67.1 s, r = -0.31; A2: 5.9 ± 3.1 ml.min-1kg-1, r = 0.01. T400 showed also a significant correlation with VO2max (4226 ± 729.2 ml.min-1, r = -0.74, p = 0.01). CONCLUSIONS: Shorter time constant for the primary phase of the VO2 response seems to be related to higher middle distance performance in aerobic swimming events, contrarily to the slow component amplitude.