(Over)training effects on quantitative electromyography and muscle enzyme activities in standardbred horses.

This study investigates the effects of over-training on horses by using needle electromyography and monitoring muscle enzyme activities. The results suggest electromyography is a more sensitive tool to detect adaptation to training though it can’t differentiate between over-training and regular training at certain levels. It also suggests the diminished performance often found after intensive training is more likely due to central (brain) factors rather than physical ones.

Introduction and Methodology

• The purpose of this study was to assess whether quantitative needle electromyography (QEMG) could effectively measure the effects of training, or over-training, in horses compared to monitoring muscle enzyme activities.
• The research involved 12 Standardbred geldings split into pairs by age, breed, and sex, who underwent a 32-week training program.
• The training consisted of a habituation phase and a normal training phase. These phases were then followed by an intensified training group and a control group. Lastly, all horses took part in a reduced training phase.
• An hour before each standardized exercise test (SET), a QEMG analysis and biochemical enzyme activity test was conducted, focusing mainly on the vastus lateralis and pectoralis descendens muscles to identify any changes in training performance and potential muscle adaptations.

Results

• The study found that normal training led to significant adaptation in QEMG parameters. However, there was a marked decrease in hexokinase activity within the muscle biopsies.
• It was observed that the intensive training led to greater adaptation in the QEMG variables, potentially indicating a synchronization of individual motor unit fibre action potentials.
• Despite a 19% decrease in performance during the SET post intensive training, the enzyme activities of 3-hydroxyacyl dehydrogenase and citrate synthase showed similar increases in both the control and intensified training groups.

Conclusion

• The researchers concluded that QEMG analysis is a more effective tool to monitor training adaptation versus muscle enzyme activities. However, it couldn’t distinguish between normal training adaptation and overreaching at identified training levels.
• The study suggests that the reduction in performance post intensive training is likely due to central (brain-based) factors, rather than physical issues from an overworked peripheral system (muscles).