Critical load estimation in young swimming rats using hyperbolic and linear models

Abstract

We analysed the viability of critical load (CL) and anaerobic swimming capacity (ASC) estimation by different mathematical models and the effects of varying the number/intensity of predictive trials on these parameters in young swimming rats. After familiarised to swimming, 9 male animals had time to exhaustion (TEX) accessed in efforts against 9, 11, 13 and 15% of their body mass (bm). CL and ASC were calculated by the hyperbolic load vs. TEX (Hyp) as well as linear load vs. 1/TEX (Lin1) and load·TEX vs. TEX (Lin2) models. Moreover, parameters derived from the 11 possible combinations of 2, 3 or 4 efforts using the Lin1 regression were compared. The Lin1 model resulted in a lower R2 compared to Lin2 and Hyp methods (0.968±0.010 vs. 0.995±0.004 and 0.988±0.013; P<0.05), but no significant differences were found between models regarding CL (7.8±1.2, 7.9±1.1 and 7.8±1.0% bm) or ASC (526±129, 521±104 and 534±117% bm?s). Except for the atypical CL (1.4 ± 4.2% bm) and ASC (1079 ± 383% bm⋅s) from trials against 13 and 15% bm, varying the number/intensity of predictive bouts had no significant effects on parameter estimates. The observed viability and robustness of CL and ASC estimation by different mathematical models in young swimming Wistar rats suggest the load-time relationship as an interesting tool to investigate the physiological mechanisms underlying exercise tolerance in laboratory rodents.