The relationship between spontaneous physical activity, physical fitness and serum high density lipoprotein cholesterol concentration (HDL-C), triglycerides and creatine kinase activity was examined in a group of 3-5 year old children. Their somatic development, skinfold thickness, modified step test performance, psychological development and fine motor control were within the limits of values observed in previous studies. Food intake corresponded to recoimmended allowances except for fat intake, which appeared higher by 10%. The activity of creatine kinase in the blood was about half of the adult value. No significant differences in the above-mentioned characteristics were found between boys and girls except for body weight. A significant relationship was established between the index of lean body mass kg/10 cm body height on one side, and the index of cardiac efficiency, or the activity of creatine kinase, or fat intake on the other side. Cholesterol, HDL-C and LDL-C, and triglyceride blood levels corresponded to values found in other child populations of comparable age. Children characterized by the permanently highest level of spontaneous physical activity tended to have lower weight and fatness, smaller arm circumference, higher ectomorphy, better step test performance and cardiac efficiency indices, higher energy, fat and carbohydrate intakes, a slightly higher level of psychological development and fine motor control, and a significantly higher level of HDL-C (n = 8; 1.38 ± 0.20) as compared to inactive children (n = 9; 1.1 ± 0.25 mmole/1, p \u3c 0.05)
