Heart rate variability before and after 14 weeks of training in Thoroughbred horses and Standardbred trotters with different training experience.
Authors: Nyerges-Bohák Zsófia, Nagy Krisztina, Rózsa László, Póti Péter, Kovács Levente
Journal: PloS one
Summary
# Editorial Summary: Heart Rate Variability Responses to Training in Racehorses Researchers compared how untrained and detrained Thoroughbreds and Standardbred trotters adapted their cardiac autonomic nervous system function over 14 weeks of conventional racing preparation, measuring resting heart rate variability (HRV) before and after the training block. Untrained horses displayed significantly elevated resting heart rates compared to detrained horses, yet both groups showed reduced root-mean-square of successive differences (rMSSD)—a key marker of parasympathetic tone—following training, suggesting the cardiac nervous system reaches a saturation point rather than simply becoming more suppressed. Notably, detrained horses exhibited a significant drop in high-frequency HRV components, whilst individual responses varied considerably: approximately 5–7% of horses actually showed maladaptive increases in rMSSD despite group-level improvements, and nearly 60% of untrained animals demonstrated meaningful resting heart rate reductions below established significance thresholds. These findings indicate that conventional training progressively alters autonomic cardiac responses in ways comparable to human athletes, but importantly highlight marked individual variation that standard group analyses can obscure. For practitioners, this underscores the value of serial HRV monitoring at the individual horse level to detect maladaptation early, and suggests that a single post-training assessment may miss clinically relevant changes in cardiac autonomic status.
Read the full abstract on PubMed
Practical Takeaways
- •Heart rate variability (rMSSD and HF components) decreases with training in racehorses and may reflect normal parasympathetic saturation rather than overtraining; use smallest worthwhile change thresholds rather than group averages for individual fitness assessment
- •Untrained horses begin racing with higher baseline heart rates than experienced horses—expect this physiological difference and monitor individual HRV response trajectories rather than comparing across groups
- •Some horses (5-7%) show maladaptation patterns during training; frequent HRV monitoring at individual level can identify these horses early for training program adjustment before performance suffers
Key Findings
- •Untrained horses had significantly higher resting heart rate than detrained horses (P<0.001), with no changes after 14 weeks of training
- •Root-mean-square of successive differences (rMSSD) decreased significantly after 14 weeks of training (P<0.001) in both groups, suggesting parasympathetic saturation
- •Detrained horses showed significant decrease in high-frequency (HF) HRV component after training (P≤0.05), while untrained horses showed individual variability with 16.6% exhibiting clinically meaningful HF decreases
- •Individual variation in cardiac adaptation identified, with 4.6-6.7% of horses showing maladaptation responses despite group-level training effects