Skeletal myosin heavy chain composition and carriage training

Area of Science:

• Equine exercise physiology
• Skeletal muscle biology
• Animal biomechanics

Background:

• Equine skeletal muscle comprises various myosin heavy chain (MHC) isoforms (MHC-I, MHC-IIA, MHC-IIX) and hybrid fiber types.
• Understanding how training impacts MHC composition is crucial for equine athletic performance and health.

Purpose of the Study:

• To investigate the effects of heavy carriage training on skeletal muscle myosin heavy chain (MHC) composition in horses.
• To determine if training influences fiber type distribution, oxidative capacity, and capillary supply in equine gluteus medius muscle.

Main Methods:

• Analysis of gluteus medius muscle biopsies from trained horses and controls using electrophoresis and immunohistochemistry.
• Assessment of fiber type areas, oxidative capacity, and capillary counts via histochemistry.
• Standardized exercise tests to individually adjust training intensity.

Main Results:

• Heavy carriage training led to a decrease in MHC-IIX and an increase in MHC-I.
• The percentage of type IIX and IIAX fibers decreased, while type I fibers increased.
• Oxidative capacity of muscle fibers increased, with no significant changes in fiber size or capillary density.

Conclusions:

• Carriage training induces a shift in equine skeletal muscle MHC composition, favoring slower isoforms (MHC-IIX → MHC-IIA → MHC-I).
• This adaptation suggests an increase in muscle fatigue resistance and a potential decrease in muscle shortening velocity.
• These findings provide insights into the physiological adaptations of equine skeletal muscle to endurance-based training.