Autonomic Response To Training Load Through Daily Control Of Heart Rate Variability In Professional Female Soccer Players

PURPOSE: The purpose of this study was to analyze whether the autonomic response of professional soccer players, measured by daily heart rate variability (HRV), is related to the player’s training load of the previous day and, therefore, could be used as a valid indicator in women's soccer. METHODS: Seventeen professional soccer players (m ± SD: 20.53 ± 3.26 years; 21.19 ± 1.28 BMI) from two teams in the Spanish Second Division participated in the study. Over a 6-week period, players were instructed to measure their daily HRV, as well as other self-reported indicators of fatigue, recovery and sleep quality, using the HRV4Training-app upon waking. Player’s training load was measured in arbitrary units (rate of perceived exertion (RPE) x minutes of effort). The phases of the menstrual cycle were monitored using a self-reported calendar. For the statistical analysis, a multilevel analysis was performed for the entire sample based on linear mixed models and a second multilevel analysis for the sample segmented by phase of the menstrual cycle. RESULTS: Player’s autonomic response, measured by HRV, was not associated with the training load of the previous day (p = 0.557), regardless of the phase of the menstrual cycle (menstrual phase p = 0.566; follicular phase p = 0.189; luteal phase p = 0.699). However, HRV was statistically significantly associated, with a low to moderate effect size, with other self-reported indicators of fatigue, recovery, and sleep quality (p < 0.001). Being altered some of these relationships according to the phase of the menstrual cycle. CONCLUSIONS: Overall, the findings suggested that HRV by itself cannot be used as a valid indicator of training load in women's soccer. However, HRV is related to important indicators in the adaptation to training load. Additionally, the results suggested that the phases of the menstrual cycle influence the relationship between HRV and these indicators. Specifically, this association seems to be consolidated in the luteal phase and be less consistent during the menstrual and follicular phases. More research is needed to objectively analyze the relationship between training load, fatigue, recovery, sleep quality and menstrual cycle with the player's autonomic response.