Skeletal muscle transcriptome profiles related to different training intensities and detraining in Standardbred horses: A search for overtraining biomarkers

Training horses improves athletic capabilities by inducing skeletal muscle-specific and systemic adaptations. However, rest is required to recover from exercise or else overtraining may occur and affect performance and welfare. Biomarkers would be useful to identify early chronic overtraining in animals. The objective of the current study was to investigate skeletal muscle gene expression patterns and underlying biological mechanisms related to training of different intensities and detraining. Untrained 20 month-old Standardbred geldings were exercised at varying intensities (endurance and sprint) followed by detraining (n = 5 per phase). The results indicated that training mainly affected skeletal muscle-specific protein metabolism and increased CO2 export from the tissues. Intensive training increased energy metabolism and affected heart and adipose tissues, while having an adverse effect on stress, apoptosis and immune capacity. The intensity of the training could be related to decreased expression of extra cellular matrix proteins (ECM), cell–cell contacts and intracellular signalling pathways. During detraining, most mechanisms were reversed, but heart tissue-related changes and increased expression of skeletal muscle-specific proteins were still evident. The study suggested that changes to ECM expression and cell–cell contact mechanisms may be long-lasting and related to multifactorial aspects of training and detraining. These biomarkers may be useful to identify horses in the early stages of chronic overloading or early overtraining