Heart rate variability and overtraining in soccer players: A systematic review.

This systematic review aims to determine if there is a correlation between heart rate variability (HRV) indices and overtraining symptoms (OTS) in soccer players. Conforming to PRISMA guidelines, a search was conducted in February 2024 on Web of Science, PubMed, EMBASE, CINAHL, and SCOPUS. Studies published in English investigating the relationship between HRV parameters and OTS in adult soccer players (>18 years) were included. Accepted study designs were randomized controlled trials, controlled clinical trials, longitudinal studies, prospective studies, cross-sectional studies, and retrospective studies. Methodological quality was assessed using the Joanna Briggs Institute (JBI) checklist. The search identified 2041 articles, with 19 included postscreening. Most studies examined the correlation between HRV and OTS using linear indices. The average JBI checklist score was 6.3, indicating fair methodological quality. Thirteen studies showed a relationship between linear HRV parameters and OTS, linked to performance/clinical tests, training load, adaptation, fatigue, recovery, or hormonal markers. Thirteen correlations involved HRV frequency domain parameters, and 28 involved HRV time domain characteristics. HRV indexes were linked to OTS markers such as physical performance and psychological aspects in soccer players. Standardization in research methodologies, addressing confounding factors, and exploring additional indexes are crucial in the future.