Physiological and skeletal muscle responses to high-intensity interval exercise in Thoroughbred horses.
Authors: Mukai Kazutaka, Ohmura Hajime, Takahashi Yuji, Ebisuda Yusaku, Yoneda Koki, Miyata Hirofumi
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: High-Intensity Interval Training and Equine Muscle Adaptation Researchers compared three treadmill exercise protocols in eight trained Thoroughbreds—moderate-intensity continuous exercise at 70% VO₂max, high-intensity interval training (HIIT) comprising six 30-second efforts at 100% VO₂max, and sprint interval training (SIT) with six 15-second efforts at 120% VO₂max—to determine which provoked greater physiological stress and muscle adaptation. Although all three protocols covered equal distances, HIIT and SIT induced significantly greater arterial hypoxemia, lactic acidosis and plasma lactate accumulation than continuous work, with notably lower blood oxygen saturation and arterial pH values. Muscle glycogen depletion occurred acutely following both interval protocols but not continuous exercise, whilst HIIT uniquely triggered AMPK phosphorylation—a key metabolic sensor—immediately post-exercise; both HIIT and SIT upregulated mitochondrial biogenesis and angiogenic gene expression (PGC-1α and VEGF mRNA) at the 4-hour recovery point. For practitioners designing conditioning programmes, these findings suggest interval-based training elicits substantially greater metabolic stimulus and adaptive signalling within muscle tissue compared to steady-state work of equivalent duration, supporting their use for building aerobic capacity and mitochondrial density, though the greater physiological demands warrant careful management in horses prone to exercise-induced pulmonary haemorrhage or those with respiratory limitations.
Read the full abstract on PubMed
Practical Takeaways
- •High-intensity interval training produces more pronounced metabolic stress and muscle adaptation signals than continuous moderate-intensity work, suggesting it may drive fitness gains more efficiently in Thoroughbred training programs
- •HIIT activates AMPK signaling pathways that support mitochondrial adaptation, providing a physiological rationale for incorporating interval work into conditioning protocols
- •Both HIIT and SIT cause greater arterial hypoxemia and acidosis—monitor recovery carefully and ensure adequate rest between high-intensity sessions to avoid overtraining
Key Findings
- •HIIT and SIT induced significantly higher heart rate and plasma lactate concentration compared to MICT despite equal run distance
- •Muscle glycogen was significantly depleted in HIIT and SIT but not MICT immediately after exercise
- •HIIT uniquely activated AMPK signaling (p=0.014), a key metabolic regulator
- •Both HIIT and SIT upregulated mitochondrial biogenesis and angiogenesis markers (PGC-1α and VEGF mRNA) at 4 hours post-exercise, while MICT did not