Effects of prolonged training, overtraining and detraining on skeletal muscle metabolites and enzymes.

The research examines the impact of prolonged and intensive training, overtraining, and detraining periods on the metabolism and enzyme activity in the muscles of thirteen Standardbred horses. It suggests that while intense training led to performance improvements and enhanced metabolic efficiency, overtraining reduced the horses’ running time and despite metabolic adaptations, it might not be the cause of poor performance.

Study Design and Process

• The research involved thirteen Standardbred horses who underwent intensive training for 34 weeks and a detraining period of 12 weeks.
• The researchers studied the effects of this training and detraining on various aspects of muscle metabolism and enzyme activities, including creatine kinase (CS), alpha-ketoglutarate dehydrogenase (HAD), and lactate dehydrogenase (LDH).
• The horses were made to perform a standardized exercise test until they were fatigued at a speed of 10m/s, which was equivalent to their VO2 max or maximum oxygen consumption.

Impact of Training

• The study found that the intensive training significantly depleted the horses’ levels of ATP, PCr, and muscle glycogen, while increasing the accumulation of lactate, NH3, and muscle temperature.
• After undergoing training, the horses experienced an enhanced run time to fatigue by 148%, with a decrease in muscle glycogen depletion. Simultaneously, there was an increase in the levels of NH3 and muscle temperature at fatigue.
• Training led to a 19% higher muscle buffering capacity and increased enzyme activities of CS and HAD by 29% and 32% respectively.
• The study also noticed lower glycogen utilization after training (from 1.32 mmol/s in week 1 to 0.58 mmol/s in week 32).
• While plasma lactate levels at fatigue tended to increase with training, this was not true for muscle lactate, suggesting that the horse’s ability to remove lactate from their muscles improved upon training.

Effect of Overtraining

• Overtraining led to a reduced run time and related effects in horses that were overtrained.
• Horses that were overtrained had lower muscle glycogen prior to exercise, but the study noted that glycogen utilization per second was not reduced in these horses. Therefore, the lower initial muscle glycogen may not have caused the reduced running time.

Underlying Changes

• The study concluded that high-intensity and prolonged training primarily induced aerobic adaptations in the horses.
• Interestingly, despite these metabolic changes, poor performance associated with overtraining may not be due to metabolic disturbances.

Taking these findings into consideration, the research provides important insights into how training intensity and duration impact muscle metabolism and athletic performance in horses, and raises questions on the complex effects of overtraining.