Replication Data for PONE-D-21-19666 article

Changes in heart rate and heart rate variabilty (HRV) were investigated in young (starting their first racing season) and adult (with 1-3 years of race experience) racehorses before and after a 12-week conventional training. HRV was measured at rest over 1 h between 9:00 and 10:00 AM on the usual rest day of the horses. The smallest worthwhile change (SWC) rate was calculated for all HRV parameters. Young horses had significantly higher heart rate compared to adults (P<0.001) which may be the result of training experience between groups. There were no gender- or training-related differences inheart rate. The root-mean-square of successive differences (rMSSD) in the consecutive inter-beat-intervals obtained after the 12-week training period was lower compared to pre-season rMSSD (P<0.001) indicating decreased vagal tone for the post-season recordings. The rMSSD was not influenced by breed, age or gender. In adult horses, there was a significant decrease in the high frequency (HF) component of HRV (P=0.030) as the result of the 12-week training. These results may reflect saturation of high-frequency oscillations of inter-beat intervals rather than the reduction in parasympathetic influence on the heart. The HF did not differ significantly between the two measurements in young horses; however, 16.6% of the animals showed a decrease in HF below SWC (P=0.012). This supports the likelihood of parasympathetic saturation. Although no significant decrease in heart rate was found for the post-season, 30.0% of adult and 58.3% of young horses still showed a decrease in heart rate below the SWC. Also by individual examination, it was also visible that despite significant post-season decrease in rMSSD, 1 (4.6%) adult and 2 (6.7%) young horses reached SWC increase in rMMSD. In the case of these horses, the possibility of maladaptation should be considered.The present results suggest that heart rate and vagal tone-related HRV might be useful to assess physiological adaptation to training in racehorses. Detailed analysis of HRV parameters based on SWC highlights the importance of fitness evaluation at individuallevel. However, a more frequent recording would be necessary to provide relevant results in the field of equine sport science.