Can a first-order exponential decay model fit heart rate recovery after resistance exercise?

The time-constant of postexercise heart rate recovery (HRR) obtained by fitting heart rate decay curve by a first-order exponential fitting has being used to assess cardiac autonomic recovery after endurance exercise. The feasibility of this model was not tested after resistance exercise (RE). The aim of this study was to test the goodness of fit of the first-order exponential decay model to fit heart rate recovery (HRR) after RE. Ten healthy subjects participated in the study. The experimental sessions occurred in two separated days and consisted of performance of 1 set of 10 repetitions at 50% or 80% of the load achieved on the one-repetition maximum test [low-intensity (LI) and high-intensity (HI) sessions, respectively]. Heart rate (HR) was continuously registered before and during exercise and also for 10min of recovery. A monoexponential equation was used to fit the HRR curve during the postexercise period using different time windows (i.e. 30, 60, 90, ... 600s). For each time window, (i) HRR was calculated and (ii) variation of HR explained by the model (R-2 goodness of fit index) was assessed. The HRR showed stabilization from 360 and 420s on LI and HI, respectively. Acceptable R-2 values were observed from the 360s on LI (R-2>0.65) and at all tested time windows on HI (R-2>0.75). In conclusion, this study showed that using a minimum length of monitoring (similar to 420s) HRR after RE can be adequately modelled by a first-order exponential fitting.