Regular Physical activity (PA) is important counteracting decline of physiological and molecular parameters in elderly, while among younger age groups it is also crucial maintaining proper age matched physical fitness. According to WHO physical inactivity is one of the most important causes of deaths and long-lasting sicknesses. The aim of our study was to measure biological effects of regular PA among young healthy adults. Previously inactive individuals, 20-25 years old females (N= 18) enrolled in a six-month exercise program conducted by a personal trainer. During the study 60 min complex exercises were conducted, 3x/week, average time 180 min/week. Intensity of strength training and aerobic exercise was calculated with HRmax, regularly adjusted to the actual fitness of participants. Field and laboratory tests (body composition, cardiovascular parameters, 6MWT, activity measurements) were applied determining health-related physical fitness. Immune (cortisol, CRP, lymphocytes, hTREC) and metabolic parameters (glucose, insulin, HDL, LDL) were assessed from blood samples. Body composition, cardiovascular, metabolic and immune parameters showed improvement. After 3 months of training mostly blood parameters changed and correlated significantly, while after 6 months many hormonal and metabolic changes were found in the whole population. Correlation of CRP-CK (P=0.036) was found, CRP-Insulin (P=0.033), WBC-Glucose (P=0.046), Monocytes correlated with RDW (P=0.046), Monocytes-Glucose (P=0.028), Monocytes-MPV (P=0.015). Glucose correlated with MPV (P=0.037), with Biceps (P=0.042), Triceps (0.013). BF% and Muscle mass% (P=0,001) has a strong correlation at each measured time point, just like Cortisol-Insulin levels after sixth months of training (P=0.000). Muscle mass% and BF% (P=0.000) are strongly correlated, insulin level correlated parameters of body composition, muscle mass% (P=0.002), Bodyfat% (P=0.010), and Subscapula (P=0.029). Cortisol-Biceps (P=0.005) correlation was also found. Data show that moderate regular PA is essential to counteract senescence of metabolism and early regression of fitness in young, healthy individuals, becoming the basis of healthy ageing.