Biophysical analyses of various interval training sets at critical swimming velocity.

Background: Critical swimming velocity (CV) is widely used as an index for setting intensity in endurance training (IT). This study aimed to examine the effects of varying repetitive swimming distances on physiological and stroke parameters during IT at CV.

Methods: Eleven male national-level collegiate swimmers participated in all-out 200 and 400 m front crawl swims to determine the CV. The participants then completed three interval training sets at CV: 5×400 m (400-m IT), 10×200 m (200-m IT), and 20×100 m (100-m IT) interval swims at the CV with rest periods of 60, 30, and 15 s, respectively.

Results: The mean calculated CV value was 1.44±0.07 m/s. Posttest blood lactate concentration was significantly lower during the 100-m IT (3.4±1.9 mmol/L, P<0.05) versus the 400-m IT (6.4±2.6 mmol/L) and 200-m IT (5.3±3.2 mmol/L). Across all tests, heart rate (HR) and rating of perceived exertion (RPE) were significantly higher with longer repetitive swimming distances, while stroke length (SL) was lowest in the 400-m IT (P<0.05). The increases in HR and RPE, as well as the decrease in SL, were statistically significant throughout all training sets (P<0.05).

Conclusions: The findings indicate that longer repetitive swimming distances at CV elicit higher the metabolic, perceptual, and mechanical stimuli. These changes suggest that IT at CV is an effective training condition for enhancing endurance performance.