Human musculoskeletal system is a tool of his physical, in particular sport, activity - consists entirely of mesenchymal derivatives. Connective tissue dysplasia is a group of its systemic diseases of genetically determined, mono-or polygenic multifactorial nature, stipulated by the impaired development of mesenchymal derivatives in the embryonic and postnatal periods, and is characterized by self-assembly tissue defects on the basis of its anomalies of recognizing it proteins or bio-regulators and their receptors. The purpose of the present study was to establish the relationship of muscle mass, thyroid function and the features of the marfanoid phenotype in individuals of different sexes and ages. Young athletes with the marfanoid phenotype prone to autoimmune thyroiditis should be considered at high risk. Normalization of thyroid function in athletes may provide the basis for increasing their sports potential and sports longevity. At the same time, thyroid hormones in any way can not be equated to doping f