Effect of growth and training on muscle adaptation in Thoroughbred horses.

The research study investigates how growth and training impact metabolic adaptations in muscle fibers of adolescent Thoroughbred horses, finding that training, rather than growth, is the key factor in muscle fiber changes.

Research Methodology

• The research was carried out on twenty 2-year-old thoroughbred horses, split into two groups: a training group and a control group.
• The horses in the training group underwent a 16-week training period, while the control group horses were left to roam freely in a pasture with no specific training.
• Throughout the study, muscle samples from each horse were taken before and after the training period for analysis, specifically from the gluteus medius muscle, located in the middle section of the horses body.
• The researchers then used quantitative histochemical staining procedures – a method to visualize biological tissues – to determine the composition and activity of the oxidative enzyme, succinic dehydrogenase (SDH), in each muscle fiber.
• Further to this, whole-muscle activities of SDH and glycolytic enzyme (phosphofructokinase) were analyzed biochemically. Myosin heavy-chain isoforms – proteins that play a key role in muscle contraction – were analyzed electrophoretically.

Research Results

• The SDH activity within type-I and -IIA muscle fibers was found to increase during growth, however, the overall activity in the whole muscle did not change.
• Training led to a decrease in the percentage of type-IIX/B muscle fibers, contrastingly, there was an increase in myosin heavy-chain IIa.
• All fiber types experienced an increase in SDH activity during training, with a particularly noticeable increase in type-IIX/B fibers.

Research Conclusions

• The research concluded that the changes observed in the muscle fibers of the adolescent thoroughbred horses were mainly caused by their training regime, not by their growth.
• The most prominent change was found in the SDH activity in type-IIX/B fibers.
• The researchers suggested that these changes in the gluteus medius muscle of the studied Thoroughbreds are likely beneficial adaptations for them, improving their capacity to run middle distances at high speeds.