Dataset for "Autonomic cardiac regulation in response to exercise and molecular hydrogen administration in well-trained athletes"

Brief summary The aim of this randomized, double-blind, placebo-controlled crossover trial is to evaluate the effect of hydrogen-rich water (HRW) consumption on resting heart rate and heart rate variability in national-level monofin swimmers. Participants Twelve national-level monofin swimmers (eight females and four males) participated in this trial. The study was approved by the Ethics Committee of the Faculty of Physical Culture at Palacký University Olomouc (reference 11/2023) in accordance with the Declaration of Helsinki. Participants provided written informed consent. Experimental protocol The protocol was registered on ClinicalTrials.gov (NCT05799911). All participants participated in two testing session and receive HRW and placebo in random order. Each session included two units in a 25-m indoor swimming pool and a 24-hour monitored recovery. The first unit took place in the morning between 9 and 11 AM and included three high-intensity interval sets, each consisting of 4 × 50 m sprints. The afternoon unit took place between 5 and 6 PM and included a continuous 400-m time trial swim. The washout period between testing sessions was 7 days. HRW and placebo administration The Aquastamina-R HRW with molecular hydrogen concentration 0.9 ppm and Aquastamina-Placebo water (Nutristamina, Ostrava, Czech Republic) were contained within a 420 ml plastic aluminum package. Participants took HRW or placebo three days before (3 packages per day) and during testing day (6 packages), 15 packages in total. Measured variables Anthropometric measurements were determined using a SOEHNLE 7307 scale (Leifheit, Nassau, Germany) and a BC-418 MA bioimpedance device (Tanita, Tokyo, Japan). To assess heart rate variability, the ECG signal was recorded during an orthoclinostatic maneuver: supine (60 s)–standing (300 s)–supine (300 s). The sampling frequency used by the diagnostic system for the ECG signal was set at 1000 Hz (DiANS PF8, DIMEA Group, Olomouc, Czech Republic). The ECG record was examined, and all premature ventricular contractions, missing beats, and any artefacts were manually filtered. A set of 300 artefact-free subsequent RR intervals was obtained from the standing and second supine phase. Time domain variables included: the square root of the mean of the squares of differences between adjacent RR intervals (RMSSD) and the standard deviation of all RR intervals (SDNN). A spectral analysis was performed using the Fast Fourier Transform with a sliding 256 points Hanning window. Frequency domain variables included: low-frequency power (LF) calculated in the band from 0.05 to 0.15 Hz and high-frequency power (HF) calculated in the band from 0.15 to 0.50 Hz.