Muscles are one of the most important components in the horse body and one of the largest proportion of it's body weight. Skeletal muscles perform different roles in horse body, but basically they all work the same way, by changing the period of contraction or shortening of muscle fibers and a period of relaxation or extension of the muscle fibers. For muscle contraction it is necessary to have an energy source, in other words adenosine triphosphate (ATP), which can be brought from creatine phosphate, glycolysis or oxidative metabolism. Biochemical disturbances in these processes of creating energy for muscle work leads to the appearance of metabolic myopathy. Metabolic myopathies are usually genetically related to certain mutations which consequently leads to a lack of certain enzymes or accumulation of metabolites. They are characterized by episodes of muscle tremors, generalized or local spasms, muscle stiffness, rhabdomyolysis and myoglobinuria and if they do not react in time may lead to irreversible changes and even death of the animal. With horses which have this genetic disorder, clinical symptoms can be prevented by feeding the alternative sources of energy, such as fats. The good news is that muscles are very flexible and with protocol of exercise and periods of rest they can be prepared for the various activities in such a way that they function is very effective.