Inclusion Criteria:  for athletes' groups (master - 65 - 75 years old, and young athletes - 20 - 30 years old)  more than 150 minutes of running activity which is by ACSM considered as vigorous intensity of endurance running for young athletes at least 3 years and for master athletes at least 15 years body mass index (BMI index) - range 18.5-30 kg/m2  for groups less active than recommended (sedentary young and elderly)  no history of regular physical activity training and no more practice than 150 minutes of moderate or 75 minutes of vigorous intensity per week body mass index (BMI index) - range 18.5-30 kg/m2  Exclusion Criteria  recent or current infection malignant disease uncontrolled hypertension (higher than 160 / 95mmHG) congestive heart failure (NYHA grade III and IV) unstable angina pectoris recent myocardial infarction (during the last 6 months) severe cardiac arrhythmia (anamnestic) chronic obstructive pulmonary disease presence of severe pulmonary, pleural or pericardial disease severe asthma recent sudden stroke (during the last 6 months) epilepsy insulin-dependent diabetes mellitus unstable bone lesions with a high risk of fractures other chronic diseases, at the discretion of the responsible doctor states of mental incompetence (severe anxiety and depression, dementia, alcoholism , or other dependencies, mental retardation) conditions complicating regular physical activity (uncontrollable pain, severe arthritis, planned knee / hip endoprosthesis, pathological fractures (last 6 months), amputation, use of walker, wheelchair pharmacological interference (e.g., steroids, nonsteroidal anti-inflammatory agents, immunosuppressive and antineoplastic drugs, beta blockers, statins) the use of performance-enhancing drugs in the past and during the study period