Energy metabolism in relation to skeletal muscle fibre properties during treadmill exercise.

The study examines the correlation between the type of skeletal muscle fibers in horses, energy metabolism during exercise, and the consumption of specific energy substrates like glycogen and triglycerides. It suggests that horses with a higher proportion of Type IIB fibers have a lower muscle oxidative capacity and rely more on glycolysis for energy, leading to more lactate accumulation.

Study Objective and Method

• The primary objective of this research was to investigate the skeletal muscle metabolism in horses with various cardiocirculatory capacities. The focus was on how energy is metabolized during a near-maximal exercise test in relation to muscle fiber composition.
• During this standardised near-maximal exercise test, the horses, regardless of their differing capacities, were made to perform the same amount of work.

Findings Related to Substrate Utilisation and Lactate Accumulation

• The study found significant differences in the amount of glycogen utilised, triglycerides burned, and lactate accumulated among horses, showing variance in energy utilization and metabolic processes.
• There was a positive correlation between both blood and muscle lactate accumulation and the amount of glycogen utilized. The more glycogen was used, the higher level of lactate was accumulated.

Impact of Muscle Fibre Type

• The muscle fibre composition also had an impact on the metabolic process. Thus, glycogen use and lactate accumulation were positively linked to the proportion of Type IIB fibres and negatively connected to the percentage of Type IIA fibres.
• Type IIB fibers were observed to have lower oxidative enzyme activities (such as citrate synthase and 3-hydroxyacyl-CoA-dehydrogenase) and higher lactate dehydrogenase activity.

Metabolic Properties and Muscle Fiber Recruitment

• It was inferred that horses with a higher proportion of Type IIB fibers have less muscle oxidative capacity and depend more on glycolysis for energy production. This reliance on glycolysis resulted in an increased lactate accumulation compared to those with a higher proportion of Type IIA fibres.
• The different metabolic properties of muscle fibre types suggest that the pattern of muscle fibre recruitment could significantly impact intramuscular substrate utilization, thereby influencing horses’ athletic performance and endurance.