Participants were requested not to eat, drink or smoke for
4 h before the measurements and during the measurement they were asked to refrain from talking, falling asleep, making exaggerated body movements, and/or intentionally altering their respiration. Before HRV measurement, participants rested in a prone position at room temperature (25 C) for 20 min. HRV was assessed before and immedi- ately after the treatment/control period. Analysis was based on a 10 min period of ECG signal acquisition, followed by computerized Fourier analysis of the ECG waves, using the BIOPAC system. Participants were carefully monitored using the BIOPAC Respiratory Transducer SS5LB to ensure there were no significant respiratory pattern changes during the ECG measurement. HRV was then calculated manually using the power spectral analysis method (frequency domain method). The parameters used were set as follows: total power frequency (TPF) (0.00e0.40 Hz), low frequency (LF) power (0.04e0.15 Hz), high frequency (HF) power (0.15e0.40 Hz). The low frequency to high frequency ratio (LF/HF ratio) was calculated based on the outcome of the power spectral analysis. HF power was the main parameter of interest in this study.