Comparison of Shifts in Skeletal Muscle Plasticity Parameters in Horses in Three Different Muscles, in Answer to 8 Weeks of Harness Training.
Authors: de Meeûs d'Argenteuil Constance, Boshuizen Berit, Vidal Moreno de Vega Carmen, Leybaert Luc, de Maré Lorie, Goethals Klara, De Spiegelaere Ward, Oosterlinck Maarten, Delesalle Cathérine
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Eight weeks of standardised harness training induces differential muscular adaptations across functionally distinct muscle groups, with the vastus lateralis demonstrating the most pronounced remodelling in a cohort of twelve Standardbred mares. Whilst all three muscles examined (pectoralis, vastus lateralis, and semitendinosus) showed significant baseline fibre type composition differences—notably the semitendinosus harbouring a more anaerobic phenotype with elevated type IIX fibres—training consistently triggered reductions in fibre cross-sectional area accompanied by meaningful increases in capillary density, particularly in the vastus lateralis. Critically, mitochondrial density remained unchanged despite these structural adaptations, suggesting that training-induced muscle plasticity prioritises optimising fuel delivery and fibre size rather than oxidative capacity per se. The coordinated decrease in muscle fibre diameter coupled with enhanced vascularisation appears to facilitate more efficient substrate uptake and processing, potentially supporting rapid utilisation of emerging fuel candidates including branched-chain amino acids and microbiome-derived metabolites. These findings underscore the importance of muscle-specific assessment protocols and highlight that standard training responses cannot be assumed uniform across postural and locomotor muscles, with practical implications for designing targeted conditioning programmes and interpreting metabolomic changes in exercising horses.
Read the full abstract on PubMed
Practical Takeaways
- •Different muscles respond distinctly to training; postural and locomotor muscles show different adaptation patterns, so training programs should account for these differential responses
- •Muscle fiber shrinkage with enhanced blood supply suggests the body is optimizing fuel delivery efficiency during harness training—monitor conditioning progression accordingly
- •Baseline muscle composition varies significantly between muscles, implying that standard training protocols may need individualization based on muscle-specific physiology
Key Findings
- •Vastus lateralis showed the most pronounced training-induced plasticity with significant post-training decrease in fiber cross-sectional area accompanied by increased capillary supply
- •Semitendinosus muscle displayed baseline anaerobic profile with higher type IIX fibers and showed selective type IIAX fiber atrophy post-training
- •No shifts in mitochondrial density were detected despite capillary supply increases, suggesting optimization toward smaller fiber structures for rapid fuel delivery
- •Significant differences in baseline muscle profiles existed between the three muscles studied (pectoralis, vastus lateralis, semitendinosus)