Physical fitness and mitochondrial respiratory capacity in horse skeletal muscle.
Authors: Votion Dominique-Marie, Gnaiger Erich, Lemieux Hélène, Mouithys-Mickalad Ange, Serteyn Didier
Journal: PloS one
Summary
# Editorial Summary Physical conditioning in horses produces measurable improvements in mitochondrial respiratory capacity, a finding with direct implications for training programmes and performance management. Researchers used high-resolution respirometry on permeabilized muscle fibres from the triceps brachii to assess oxidative phosphorylation (OXPHOS) capacity across horses of varying fitness levels, from overweight to competitive athletes. Mitochondrial respiratory capacity increased substantially with training: from 77 pmol O₂·s⁻¹·mg⁻¹ in overweight horses to 129 pmol O₂·s⁻¹·mg⁻¹ in competitive horses—a 68% improvement. Crucially, the research revealed that Complex I-linked respiratory capacity (the primary aerobic pathway using carbohydrate substrates) showed disproportionate gains with fitness, improving from a 38% flux control ratio in unfit horses to 46% in competitive animals, whilst Complex II capacity remained stable. For practitioners, these findings suggest that aerobic conditioning specifically enhances the mitochondrial machinery responsible for glucose and pyruvate metabolism, offering a cellular-level explanation for improved endurance capacity and recovery in trained horses, and highlighting the value of systematic fitness programmes in optimising metabolic efficiency.
Read the full abstract on PubMed
Practical Takeaways
- •Mitochondrial respiratory capacity is a measurable biomarker of physical fitness in horses, increasing substantially with training and competitive conditioning
- •Training appears to improve the efficiency of Complex I-linked energy production, suggesting optimization of aerobic metabolism at the cellular level with conditioning
- •Assessment of muscle mitochondrial function could potentially provide objective data on fitness gains beyond traditional performance metrics
Key Findings
- •OXPHOS capacity increased progressively from overweight horses (77 pmol O2·s−1·mg−1) to competitive horses (129 pmol O2·s−1·mg−1), correlating with fitness level
- •Complex I-linked respiratory capacity deficit relative to maximum OXPHOS was reduced with increased physical fitness (flux control ratio 0.38 to 0.46 from overweight to competitive horses)
- •Equine mitochondrial OXPHOS capacity was limited by the phosphorylation system to 85% of electron transfer capacity, independent of fitness level
- •Addition of pyruvate to substrate cocktail increased OXPHOS capacity in trained horses by approximately 15 pmol O2·s−1·mg−1