Polar precision performance program

RR intervals were recorded through the portable RS800CX monitor with a sampling rate of 1 kHz. The RR intervals were then transferred to the Polar Precision Performance program (v.3.0, Polar Electro, Finland). The Polar transmitter detects heart beats in the left ventricular muscle and transmit the signal to the computer through a wireless technology. The software allowed the visualization and the removal of RR interval file in “txt” format.
We performed HRV analysis based on directives from the Task Force guidelines [6 (link)]. Specific details of HRV analysis have been previously documented [23 (link), 24 (link)].
HRV was analyzed in the time (RMSSD: root-mean square of differences between adjacent normal RR intervals, SDNN: standard deviation of all normal RR intervals) and frequency domain (LF: low frequency band ranging from 0.04 to 0.15, HF: high frequency band ranging from 0.15 to 0.4) in absolute units. HRV analysis also included approximate entropy (ApEn) and the Poincaré plot (SD1: standard deviation of the instantaneous variability of the beat-to-beat heart rate, SD2: standard deviation of long-term continuous RR interval variability) [6 (link)].
We employed the Kubios^® HRV v. 2.0 software to compute these indices [25 (link)].

After the initial evaluation, the heart monitor strap was placed on each subject’s thorax over the distal third of the sternum. Besides, the HR receiver (Polar RS800CX monitor, Polar Electro OY, Kempele, Finland) was placed on the wrist.
The R-R intervals recorded by the portable HR monitor (with a sampling rate of 1000 Hz) were downloaded to the Polar Precision Performance program (v. 3.0, Polar lectro, Finland). The software enabled the visualization of HR and the extraction of a cardiac period (R-R interval) file in “txt” format. Following digital filtering complemented with manual filtering for the elimination of premature ectopic beats and artifacts, at least 256 R–R intervals were used for data analysis. Only the series with more than 95% sinus rhythm were included in the study (10 (link), 11 (link)).

We recorded RR intervals through the RS800CX HR monitor, which had a sampling rate of 1 kHz. The RR intervals were transferred to the Polar Precision Performance program (v.3.0, Polar Electro, Finland). The Polar HR monitor distinguishes all heart beats in the left ventricular cardiac muscle and records the data, transferring the signal to the computer through a wireless infrared methodology. The Polar ProTrainer software allows the visualization and the removal of the RR interval file in “txt” format.
Specifics of the HRV analysis have been supplied previously^{16 (link),17 (link)} and were in accordance with the directives from the Task Force^{13 (link)}.
To study the parasympathetic regulation of HR we inspected the high frequency band of spectral analysis (HF: 0.15 Hz to 0.4 Hz) in absolute units in the frequency domain, RMSSD (root-mean square of differences between adjacent normal RR intervals) in the time domain and the SD1 Poincaré plot (standard deviation of the instantaneous variability of the beat-to-beat heart rate). We applied the Kubios^® HRV v. 2.0 software to compute these indices¹⁸ .