Acute exercise in a hot environment increases heat shock protein 70 and peroxisome proliferator-activated receptor γ coactivator 1α mRNA in Thoroughbred horse skeletal muscle.
Authors: Ebisuda Yusaku, Mukai Kazutaka, Takahashi Yuji, Yoshida Toshinobu, Kawano Aoto, Matsuhashi Tsubasa, Miyata Hirofumi, Kuwahara Masayoshi, Ohmura Hajime
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Whilst heat acclimatisation training is widely used to condition horses for performance in warm climates, the underlying muscular adaptations occurring after acute heat exposure remain poorly characterised. This study examined whether a single exercise bout in hot conditions (WBGT 29.5°C) triggered different molecular signalling responses compared to the same work performed in cool conditions (WBGT 12.5°C), with 15 trained Thoroughbreds completing a standardised treadmill protocol involving walk, trot, canter and high-intensity efforts. Muscle biopsies from the middle gluteal taken 4 hours post-exercise revealed that only the hot-environment group exhibited statistically significant increases in heat shock protein 70 (HSP-70; 2.4-fold), the mitochondrial biogenesis regulator PGC-1α (8.4-fold), hypoxia-inducible factor 1-alpha (HIF-1α; 2.2-fold), and pyruvate dehydrogenase kinase 4 (PDK4; 14.1-fold), despite equivalent cardiovascular demands and similar lactate accumulation between groups. These findings suggest that acute thermal stress activates cellular protective mechanisms and metabolic remodelling independently of exercise intensity alone, implying that horses exercised in warm conditions may trigger adaptive processes that could support longer-term heat tolerance—though whether single exposures translate into meaningful performance benefits or if repeated thermal challenges are necessary for practical acclimatisation remains to be established.
Read the full abstract on PubMed
Practical Takeaways
- •Training in heat appears to trigger stronger cellular protective and adaptive responses in skeletal muscle compared to cool conditions, potentially supporting the practice of heat acclimatization training in Thoroughbreds
- •These molecular changes suggest heat exposure stimulates mitochondrial biogenesis and metabolic efficiency, which may improve performance capacity in hot climates
- •Standard exercise metrics (heart rate, lactate) may not fully capture the physiological stress and adaptation occurring during heated exercise, suggesting additional monitoring during heat acclimation programs would be valuable
Key Findings
- •Exercise in hot conditions (WBGT 29.5°C) induced significantly greater HSP-70 mRNA expression (2.4-fold, p=0.045) compared to cool conditions (1.9-fold, p=0.207)
- •PGC-1α mRNA increased 8.4-fold in hot conditions (p=0.010) versus 3.8-fold in cool conditions (p=0.424), indicating enhanced mitochondrial biogenesis signaling
- •Hot environment exercise produced significantly greater increases in HIF-1α (2.2-fold, p=0.018) and PDK4 (14.1-fold, p=0.047) mRNA, suggesting enhanced oxygen sensing and fatty acid oxidation pathways
- •Peak heart rate and plasma lactate were similar between groups despite different thermal conditions, indicating acute heat stress triggers molecular adaptations independent of cardiovascular or metabolic strain markers