Abstract
We tested the hypothesis that, similar to humans and rodents, exercise training would enhance mitochondrial (Mt) biogenesis and function in skeletal muscle of young horses. Twenty-four Quarter Horse yearlings were randomly assigned to either submaximal exercise training or no forced exercise (untrained). Biopsies were collected from the gluteus medius and triceps brachii before and after 9 wk of treatment. Citrate synthase activity was lower (P < 0.0001) and cytochrome c oxidase activity per Mt unit was higher (P < 0.0001) in gluteus compared to triceps, but neither changed over the trial period. From wk 0 to 9, intrinsic Mt respiration (PCI, PCI+II; P = 0.008) and electron transport capacity (ECI+II; P = 0.01) increased, and LEAK-related flux control factor (FCFL; P = 0.02) decreased in both muscles. After 9 wk of training, gluteus muscle exhibited higher (P < 0.05) intrinsic PCI, PCI+II, ECI+II, and FCFCI and FCFCI+II, and lower FCFL (P = 0.0002). Mitochondrial content did not change from wk 0 to 9, and also not in response to submaximal exercise training. Improvements in Mt function were most directly related to ongoing growth of horses independent of muscle group, and training further enhanced Mt function in the gluteus medius.
Highlights
Training had no effect on citrate synthase (CS) or cytochrome c oxidase (CCO) activity in either muscle
Citrate synthase activity correlates with Mt density[5], which is typically greatest in type I muscle fibers, followed by type IIa, and lowest in type IIx6,7
Direct support comes from our previous analysis of myosin heavy chain (MyHC) isoform distribution in triceps and gluteus muscles from this same group of horses
Summary
Improvements in Mt function were most directly related to ongoing growth of horses independent of muscle group, and training further enhanced Mt function in the gluteus medius. Exercise training has been shown to enhance mitochondrial (Mt) biogenesis and improve Mt function in human and rodent models[1]. These adaptations have not been clearly elucidated in horses, especially at a young age when it is common for horses to enter performance training. We hypothesized that training would enhance Mt biogenesis as well as improve Mt function, and that these adaptations would be augmented in the gluteus medius compared to the triceps brachii
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