Muscle biopsy as a tool for assessing muscular adaptation to training in horses.

OBJECTIVE

To describe an applied method for quantitative estimation of training condition in horses.

ANIMALS

17 sedentary adult (5 to 14 years old) stallions of several breeds endurance trained for 3 months.

PROCEDURE

Muscle biopsy specimens from 2 depths (20 and 60 mm) of the gluteus medius muscle were obtained before and after training and were analyzed for fiber type distribution, mean cross-sectional area, relative fiber area, and mean number of capillaries in contact with each fiber type relative to their mean area. Fiber types were designated as types 1, 2A, and 2B (high, low, and moderate myosin ATPase activities at pH 4.5, respectively). Data were subjected to discriminant and principal component analyses.

RESULTS

77% of the observations were correctly discriminated according to training condition of horses by use of discriminant analyses when histochemical and morphometric data from the 2 muscle biopsy specimens were used. Principal component analysis indicated that the most efficient variables describing muscular adaptation to training are fiber area and number of capillaries in contact with type-1 and type-2A fibers, particularly from the deepest sampling site of the muscle.

CONCLUSION

It is possible to satisfactorily classify an individual horse in a given training category on the basis of a physiologic muscle index.

CLINICAL RELEVANCE

These methods could become a useful aid for evaluation of the individual horse's response to training.