The Method but Not the Protocol Affects Lactate-Threshold Determination in Competitive Swimmers

Abstract

Purpose: The study validated variables corresponding to lactate threshold (LT) in swimming. Speed (sLT), blood lactate concentration (BLLT), oxygen uptake (VO2LT), and heart rate (HRLT) corresponding to LT were calculated by 2 different incremental protocols and validated in comparison with maximal lactate steady state (MLSS). Methods: Ten competitive swimmers performed a 7 × 200-m front-crawl incremental “step test” with 2 protocols: (1) with 30-second rests between repetitions (short-rest incremental protocols) and (2) on a 5-minute cycle (swim + rest time, long-rest incremental protocols). Five methods were used for the assessment of sLT and corresponding BLLT, VO2LT, and HRLT: intersection of 2 lines, Dmax, modified Dmax, visual inspection, and intersection of combined linear and exponential regression lines. Subsequently, swimmers performed two to three 30-minute continuous efforts to identify speed (sMLSS) and physiological parameters corresponding to MLSS. Results: Both protocols resulted in similar sLT and corresponding physiological variables (P > .05). Bland–Altman plots showed agreement between protocols (sLT, bias: −0.017 [0.002] m·s−1; BLLT, bias: 0.0 [0.5] mmol·L−1; VO2LT, bias: −0.1 [2.2] mL·kg−1·min−1; HRLT. bias: −2 [8] beats·min−1). However, sLT calculated by modified Dmax using short rest was higher compared with speed at MLSS (1.346 [0.076] vs 1.300 [0.101] m·s−1; P < .05). Conclusions: Calculated sLT, BLLT, VO2LT, and HRLT using all other methods in short-rest and long-rest incremental protocols were no different compared with MLSS (P > .05). Both 7 × 200-m protocols are valid for determination of sLT and corresponding physiological parameters, but the modified Dmax method may overestimate sLT.