A study to examine whether fluctuations in daily training load lead to changes in heart rate variability in elite rugby union players

This study investigated whether fluctuations in daily training load would lead to changes in heart rate variability (HRV) within elite rugby union players. Sixteen professional rugby union players (age 27 ± 2 years; height 187.8 ± 6.6 cm; weight 102.7 ± 11.0 kg) recorded their resting HRV and wellness scores daily for 28 days. Session rating of perceived exertion (sRPE) was quantified for all training sessions. One principal component was extracted from the wellness measures, explaining 52% of the variance of all the wellness measures and two principal components were extracted for the training load measures, explaining 71% and 21% of the variance of all the training load measures. Three variables (fatigue, daily load and 3-day load exponentially weighted moving average (EWMA)) were selected to run in a linear mixed model. Changes in daily load (effect size correlations; ES = 0.00; ± 0.01), 3-day EWMA (ES = 0.01; ± 0.01) and fatigue (ES = 1.53; ± 0.65) were found to have an almost certainly trivial change in HRV. In conclusion, this study questions the usefulness of HRV as a monitoring tool for rugby union players as changes in daily training load were not associated with changes in HRV.