Cardiac Cost During Submaximal Exercise as a Practical Monitoring Tool in French Standardbred Trotters: Short-Term Reproducibility of Non-Invasive Field-Derived Indicators.

Overview

• This study evaluated the short-term reproducibility of cardiac cost (heart rate relative to speed) and related cardiovascular indicators in French Standardbred trotters during submaximal exercise.
• The goal was to determine if these non-invasive, field-measured parameters could reliably monitor racehorses’ cardiac function under routine training conditions.

Background and Purpose

• Racehorses require regular cardiovascular monitoring to assess fitness and performance, ideally with indicators that are both practical to measure during training and reproducible across sessions.
• “Cardiac cost” (CC), defined as the ratio of heart rate to speed (beats per meter), is a promising candidate because it integrates cardiovascular response relative to exercise intensity.
• The study aimed to test the short-term reproducibility of CC and related indicators (such as heart rate recovery and speed at defined heart rate thresholds) measured non-invasively during submaximal exercise sessions in French Standardbred trotters.

Methods

• Data were collected from 60 French Standardbred trotter horses, comprising 483 total training sessions.
• For reproducibility analysis, the researchers grouped sessions into “follow-up blocks” when horses had three or more consecutive sessions less than 7 days apart, resulting in 36 blocks with 126 sessions involving 18 horses.
• Each session included:
• A warm-up period
• Two 2000-meter work blocks at increasing intensity (B1 and B2)
• Recovery periods
• Heart rate and speed data were recorded using the Polar Team Pro system, a non-invasive telemetry method.

Indicators Evaluated

• Cardiac Cost (CC): Ratio of heart rate (beats per minute) to speed (meters per second), specifically measured during work blocks (CC B1 and CC B2).
• Heart Rate Recovery (HRR): The decrease in heart rate after exercise during recovery periods following B1 and B2.
• Speed at defined heart rates: V150, V180, and V200 correspond to the speed at which horses reach 150, 180, and 200 beats per minute respectively.
• Recovery speed: speed during the recovery phase after exercise blocks.

Key Findings

• Short-term reproducibility was considered moderate for the following indicators:
  • Cardiac cost during the first work block (CC B1): Intraclass correlation coefficient (ICC) of 0.67, indicating moderate reliability.
  • Heart rate recovery after the first (HRR after B1) and second work blocks (HRR after B2): ICC around 0.60-0.66.
  • Speed at 150 bpm (V150): ICC about 0.59.
• Poor reproducibility was found for:
  • Cardiac cost during the second work block (CC B2)
  • Speed at 180 bpm (V180)
  • Recovery speed
• Adjusting for ambient temperature did not affect the reproducibility of CC B1 and HRR, suggesting that these indicators are robust to environmental variations.
• The wider dataset showed an increase in V200 speed with horse age, which aligns with prior studies indicating improved performance or fitness with age/training.
• Minimal detectable changes (smallest changes that indicate true variation rather than measurement error) were calculated as:
  • 0.04 beats per meter for CC B1
  • 26 beats per minute for HRR after B1

Interpretation and Practical Implications

• CC during the first work block (CC B1), heart rate recovery (HRR), and speed at 150 bpm (V150) may serve as practical, moderately reproducible markers for short-term cardiovascular monitoring of racehorses during training.
• These metrics can assist trainers and veterinarians in detecting meaningful changes in cardiac function or fitness without invasive methods.
• The lower reproducibility of CC in the second block and other indicators highlights the importance of focusing on early exercise phases or specific variables that show stable performance.
• Environmental factors like temperature do not significantly confound CC B1 and HRR measures, supporting their validity in field conditions.
• The study was limited by a “single-yard design,” meaning data came from a single training facility, which may restrict generalizability; results should be confirmed in broader settings.

Conclusion

• This study provides evidence supporting the use of cardiac cost during early submaximal exercise and heart rate recovery as reliable, non-invasive indicators to monitor cardiovascular function in Standardbred trotters.
• These tools have potential applications for everyday training monitoring, allowing more informed decisions about horse fitness and health.
• Further research extending to different training environments and larger populations would strengthen the applicability of these findings.