Objective: This study aimed at comparing different recovery-based methods to assess the highest exercise oxygen uptake value ( V ˙ O2peak) when swimming at low-moderate, heavy and severe intensities. Complementarily, the different recovery curve kinetics were analysed. Approach: Eighteen competitive swimmers performed a 5 × 200 m front crawl intermittent protocol (0.05 m · s−1 increments and 3 min intervals), with respiratory gas exchange being continuously measured breath-by-breath during and post-exercise using a portable gas analyser. The directly determined V ˙ O2peak ( V ˙ O2dir) was compared with the values obtained by linear and exponential backward extrapolations (of different intervals) and the recovery curve mathematical modelling. Main results: V ˙ O2dir rose with intensity increase: 41.96 ± 6.22, 46.36 ± 6.89 and 50.97 ± 7.28 ml · kg−1 min−1 for low-moderate, heavy and severe swims. Linear and exponential regressions applied to the first 20 s of recovery presented the V ˙ O2peak values closest to V ˙ O2dir at low-moderate (42.80 ± 5.54 vs 42.88 ± 5.58 ml kg−1 min−1), heavy (47.12 ± 4.91 vs 47.48 ± 5.09 ml kg−1 min−1) and severe intensity domains (51.24 ± 6.89 vs 53.60 ± 8.54 ml kg−1 · min−1, respectively; r = 0.5–0.8, p < 0.05). The mono-exponential function was the best fit at low-moderate and heavy intensities, while the bi-exponential function better characterized the severe exercise domain (with a slow component amplitude, time delay and time constant of 6.2 ± 2.3 ml kg−1 min−1, 116.6 ± 24.3 and 39.9 ± 15.2 s, respectively). Significance: The backward extrapolation of the first 20 s of recovery is the best method to assess the V ˙ O2peak for a large spectrum of swimming intensities. Complementarily, intensity increases imply different recovery curve kinetics, particularly a mono-exponential behaviour for low-moderate and heavy exertions and a bi-exponential dynamics for severe paces.

The anaerobic threshold (AnT) seems to be not only a physiologic boundary but also a transition after which swimmers technique changes, modifying their biomechanical behaviour. We expanded the AnT concept to a biophysical construct in the four conventional swimming techniques. Seventy-two elite swimmers performed a 5×200 m incremental protocol in their preferred swimming technique (with a 0.05 m·s−1 increase and a 30 s interval between steps). A capillary blood samples were collected from the fingertip and stroke rate (SR) and length (SL) determined for the assessment of [La], SR and SL vs. velocity inflexion points (using the interception of a pair of linear and exponential regression curves). The [La] values at the AnT were 3.3±1.0, 3.9±1.1, 2.9±1 .34 and 4.5±1.4 mmol·l−1 (mean±SD) for front crawl, backstroke, breaststroke and butterfly, and its corresponding velocity correlated highly with those at SR and SL inflection points (r=0.91–0.99, p<0.001). The agreement analyses confirmed that AnT represents a biophysical boundary in the four competitive swimming techniques and can be determined individually using [La] and/or SR/SL. Blood lactate increase speed can help characterise swimmers’ anaerobic behaviour after AnT and between competitive swimming techniques.

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