Modeling the expenditure and reconstitution of distance above critical speed during two swimming interval training sessions

In swimming, the speed-time relationship provides the critical speed (CS) and the maximum distance that can be performed above CS (D '). During intermittent severe intensity exercise, a complete D ' depletion coincides with task failure, while a sub-CS intensity is required for D ' reconstitution. Therefore, determining the balance D ' remaining at any time during intermittent exercise (D'BAL) could improve training prescription. This study aimed to 1) test the D'BAL model for swimming; 2) determine an equation to estimate the time constant of the reconstitution of D' (-rD '); and 3) verify if-rD ' is constant during two interval training sessions with the same work intensity and duration and recovery intensity, but different recovery duration. Thirteen swimmers determined CS and D ' and performed two high-intensity interval sessions at a constant speed, with repetitions fixed at 50 m. The duration of passive recovery was based on the work/relief ratio of 2:1 (T2:1) and 4:1 (T4:1). There was a high variability between sessions for-rD' (coefficient of variation of 306%). When-rD ' determined for T2:1 was applied in T4:1 and vice versa, the D'BAL model was inconsistent to predict the time to exhaustion (coefficient of variation of 29 and 28%). No linear or nonlinear relationships were found between-rD ' and CS, possibly due to the high within-subject variability of-rD'. These findings suggest that-rD ' is not constant during two high intensity interval sessions with the same recovery intensity. Therefore, the current D'BAL model was inconsistent to track D ' responses for swimming sessions tested herein.