Cardiovascular Responses and Energy Expenditure During a Standardized Training Programme in Three-Year-Old Czech Warmblood Stallions

Background: Early training represents an important period in the development of young sport horses, yet field-based information on cardiovascular responses and estimated energy expenditure across different exercise modalities remains limited. Objectives: This study aimed to characterize heart rate (HR) responses and estimate energy expenditure in three-year-old Czech Warmblood stallions during an 18-week standardized training programme, with emphasis on exercise modality and temporal variation. Hypothesis: We hypothesized that HR responses and estimated energy expenditure would differ among exercise modalities and vary throughout the training period. Methods: Fourteen three-year-old Czech Warmblood stallions were monitored over 18 weeks, comprising 1003 training sessions across six exercise modalities. Session mean, peak, and minimum HR were recorded, and energy expenditure was estimated using HR-based equations and National Research Council (NRC) recommendations. Linear mixed-effects models assessed associations with exercise modality and monitoring week, accounting for repeated observations within horses. Results: Exercise modality was associated with mean HR (χ2 = 284.64, p < 0.001) and peak HR (χ2 = 122.08, p < 0.001), but not minimum HR (p = 0.066). Monitoring week was associated with all three HR outcomes (p < 0.001), with significant modality × week interactions. Estimated energy expenditure per session differed among exercise modalities (p < 0.001), with the highest model-based values observed during free jumping and horse walker exercise and the lowest during lunging. NRC-based estimates of daily energy expenditure (113.87 ± 11.73 MJ/day) exceeded estimates obtained using the Coenen HR (100.33 ± 6.23 MJ/day) and Coenen O2 (95.78 ± 6.68 MJ/day) methods. Conclusion: Cardiovascular responses and estimated energy expenditure differed among exercise modalities, while temporal HR variation could not be attributed solely to cardiovascular adaptation. Assessment of training load should consider both exercise characteristics and session duration. HR monitoring provides complementary information under field conditions, but HR-derived energy estimates should not be regarded as independently validated measures of energy requirements.