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Home / Equine Research Bank / Vet Sci / Locomotory Profile, Heart Rate Variability, and Blood Parame...
Veterinary sciences2025; 12(11); 1028; doi: 10.3390/vetsci12111028

Locomotory Profile, Heart Rate Variability, and Blood Parameters Reveal Adaptive Responses in Endurance Horses Trained on Deep Sand.

Abstract: Training on deep sand is commonly employed in endurance horses, but its physiological adaptation remains poorly characterized. This study aimed to characterize locomotor adaptations during a 7 km controlled-speed canter on deep sand in eighteen endurance horses, to identify heart rate variability (HRV) components, and to investigate changes in hematological variables before and after exercise. Stride frequency (SF) and stride length (SL), HRV, and hematological profiles were recorded during exercise and recovery with a fitness tracker. Associations between maximum speed and locomotor parameters were assessed by linear regression, while Pearson's correlation assessed HRV relationships, also with physiological parameters. Hematological parameters were assessed with paired t-test before and after training. SL percentage change was the strongest predictor of speed (β = 0.677). HRV analysis revealed delayed parasympathetic reactivation; the parasympathetic recovery index (PNS REC) was correlated with mean RR interval on the ECG (r = 0.968) and heart rate (r = -0.964) during recovery. Post-exercise rectal temperature showed correlations with HRV recovery indices. Hematological evaluation revealed post-exercise increases in red blood cell count, hematocrit, hemoglobin, and corpuscular indices. SL plays a predominant role in achieving higher speeds on deep sand, while PNS REC emerges as a practical and accessible marker of autonomic recovery and fatigue. Horses with enhanced thermoregulation recover better. Hematological results confirm a physiological stress response that may optimize oxygen delivery. Integrating locomotor, cardiovascular, and hematological monitoring may improve management and welfare in endurance training.
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Publication Date: 2025-10-23 PubMed ID: 41295665PubMed Central: PMC12656824DOI: 10.3390/vetsci12111028Google Scholar: Lookup
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  • Journal Article

Summary

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Overview

  • This study investigates how training endurance horses on deep sand affects their movement patterns, heart rate variability, and blood parameters to understand physiological adaptations and recovery.

Study Objectives and Rationale

  • Training on deep sand is a common method used to condition endurance horses, yet the physiological adaptations to this specific substrate have not been well studied.
  • The study aimed to:
    • Characterize locomotor adaptations during a 7 km controlled-speed canter on deep sand.
    • Identify key components of heart rate variability (HRV) during exercise and recovery as markers of autonomic nervous system function.
    • Assess changes in hematological parameters induced by exercise on deep sand to evaluate physiological stress and recovery responses.

Methodology

  • Participants: Eighteen endurance horses trained and tested on deep sand.
  • Exercise: Horses performed a 7 kilometer controlled-speed canter on deep sand.
  • Data Collection:
    • Locomotion data: Stride frequency (SF) and stride length (SL) were tracked using fitness trackers during exercise.
    • Heart Rate Variability (HRV): Measured before, during, and after exercise to assess autonomic nervous system activity, specifically parasympathetic reactivation.
    • Hematological Parameters: Blood samples taken before and after exercise to measure red blood cell count, hematocrit, hemoglobin, and other corpuscular indices.
  • Statistical Analysis:
    • Linear regression evaluated the link between maximum speed and locomotor parameters (SF, SL).
    • Pearson’s correlation assessed relationships between HRV components and physiological parameters such as heart rate and rectal temperature.
    • Paired t-tests compared hematological values before and after exercise.

Key Findings

  • Locomotor Adaptations:
    • The percentage change in stride length (SL) was the strongest predictor of achieving higher speed on the deep sand (β = 0.677).
    • This suggests that horses adapt to the more resistant surface primarily by increasing their stride length rather than stride frequency.
  • Heart Rate Variability and Autonomic Recovery:
    • HRV analysis revealed a delay in parasympathetic reactivation during recovery after exercise.
    • The parasympathetic recovery index (PNS REC), a measure of vagal tone return, correlated strongly with mean RR interval (r = 0.968) and inversely with heart rate (r = -0.964) during recovery.
    • Higher post-exercise rectal temperatures correlated with HRV recovery indices, suggesting horses with better thermoregulation recover more effectively.
  • Hematological Changes:
    • Post-exercise blood analyses showed increased red blood cell count, hematocrit, hemoglobin, and corpuscular indices.
    • These changes reflect a typical physiological stress response which likely serves to optimize oxygen delivery during and after exertion.

Implications and Conclusions

  • Stride length adjustment is a key locomotor strategy for endurance horses to maintain speed on challenging substrates like deep sand.
  • Parasympathetic recovery index (PNS REC) is a practical and accessible measure to monitor autonomic recovery and fatigue in endurance horses post-exercise.
  • Efficient thermoregulation supports better recovery, indicating that managing body temperature is critical in training and conditioning.
  • The hematological changes confirm that exercise on deep sand induces a measurable physiological stress response, potentially enhancing oxygen transport to tissues.
  • Overall, integrating locomotor, cardiovascular, and hematological monitoring provides a comprehensive approach that can help optimize endurance training, improve horse welfare, and prevent overtraining or injury.

Cite This Article

APA
(2025). Locomotory Profile, Heart Rate Variability, and Blood Parameters Reveal Adaptive Responses in Endurance Horses Trained on Deep Sand. Vet Sci, 12(11), 1028. https://doi.org/10.3390/vetsci12111028

Publication

Veterinary sciences
ISSN: 2306-7381
NlmUniqueID: 101680127
Country: Switzerland
Language: English
Volume: 12
Issue: 11
PII: 1028

Researcher Affiliations

Grant Funding

  • Codice 2022Z39C97, CUP J53D23010670 006 / Founded by the European Union - Next Generation EU - Missione 4, Componente 2 - Investimento 1.1 - MUR-PRIN2022, ECOS (Equine resilience and welfare in Climate change and stressful scenarios using Omic technologies and innovative low cost Sensors - ECOS)

Conflict of Interest Statement

The authors declare no conflicts of interest.

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