The R-R intervals recorded by the portable heart rate (HR) monitor (with a sampling rate of 1000 Hz) were downloaded to the Polar Precision Performance program (v. 3.0, Polar Electro, Finland). The software enabled the visualization of the HR and the extraction of a cardiac period (R-R interval) file in the “txt” format. Using digital filtering complemented with manual filtering for the elimination of premature ectopic beats and artifacts, at least 256 R–R intervals were used for the data analysis. Only series with more than 95% sinus rhythm were included in the study (10 ,11 (link)). The heart rate variability (HRV) was analyzed at the following four time points after exercise: seated rest with spontaneous breathing, 0-5 min, 5-10 min and 10-15 min in the standing position. We evaluated the linear and non-linear indices of the HRV. To calculate the indices, we used the HRV Analysis software (Kubios HRV v.1.1 for Windows, Biomedical Signal Analysis Group, Department of Applied Physics, University of Kuopio, Finland)(12 (link)).