Croatian Society of Medical Biochemistry and Laboratory Medicine

Introduction: Intensive exercising may significantly damage muscles which is refl ected in pain, fatigue and the increase of muscle proteins concentrations in blood such are creatinin kinase (CK), lactic dehydrogenase (LD), myoglobin (MB) and other biochemical parameters including urea serum concentration (SU). Biochemical markers vary with age, sex, race, muscle mass, physical activity and climate conditions. They also assist us in determining the limit between the capacity for adaptation to given training process which results in su-percomepensation and in condition of overtrain-ing (OT), in the case of load that exceeds the physi-ologic potential of regeneration. Concerning the problem of diagnosis and explanation of the symptoms of overtraining, markers that can apply reliably and with suffi cient sensitivity and simplicity of interpretation in the praxis are sought. It is critical to take into account diff erence among individuals and groups that could hamper the interpretation .