Training and growth induced changes in the middle gluteal muscle of young Standardbred trotters.

This research studied the impact of six months of training on the middle gluteal muscle of young Standardbred trotters. Results define a shift in muscle fiber types, increase in capillaries, and metabolic changes enhancing aerobic capacity. Growth was found not to influence these aspects but to decrease capillaries per area, and modify the activities of certain enzymes.

Research Methodology

• The study involved two groups of Standardbred trotters: a training group consisting of five horses, aged two years, and a growth group of five horses aged three years.
• The impact of a six-month training regime and growth effects were evaluated on the middle gluteal muscle of these horses.
• Repeated needle biopsy samples were taken for analysis throughout this period.

Training and Muscle Fiber Type Distribution

• The research found that after the training period, there was an increase in the distribution of slow twitch (ST) fibers from 18% to 25%, and fast twitch (FTa) fibers from 36% to 45%.
• Simultaneously, there was a decrease in another type of fast twitch fibers (FTb) from 46% to 30%.
• The initial two months of training resulted in a roughly 18% decrease in the cross-sectional area of all fiber types.
• This was followed by an increase to approximately pretraining levels at the end of the period, indicating an initial phase of muscle adaptation.

Capillaries and Metabolic Adaptations

• The training also resulted in an increase in the number of capillaries per each muscle fiber—from 1.7 to 2.4. This capillary proliferation occurred in fibers of all types.
• Metabolic changes also occurred, with enhanced enzyme activities that improve the process whereby fats and sugars are converted into energy. These included increases of 50% and 31% in 3-hydroxy-acyl-CoA dehydrogenase (HAD) and citrate synthase activities respectively.

Effects of Growth on Muscle and Metabolic Activities

• The research found that growth did not influence the fiber type distribution or the amount of capillaries per fiber.
• However, as the mean fiber area increased by 36%, primarily due to increases in FT fibers, there was a decrease in the number of capillaries per square millimeter.
• Enzyme activities including phosphorylase and HAD increased with growth, while there was a decrease in the activity of hexokinase.

Conclusions

• The research concluded that the adaptations to training, including changes in muscle fiber types, number of capillaries, and metabolic modifications, led to an improvement in the aerobic capacity of the muscle.
• Growth was found to impact enzyme activities and decrease capillary density but did not influence the overall muscle fiber distribution