Acute biochemical and physiological responses to swimming training series performed at intensities based on the 400-m front crawl speed

Purpose The objective of this study was to compare blood lactate concentration (LAC), heart rate (HR), rating of perceived exertion (RPE), tryptophan (TRP), prolactin (PRL), nonesterified fatty acids (NEFA), branched-chain amino acids (BCAAs) plasma concentrations, and TRP/BCAAs ratio along interval training swimming series at 90 and 95% of the mean speed 400-m front crawl (s400).