Research shows that the involvement of majority of Lithuanian schoolchildren in sports activities is insufficient. Lack of physical activity has an adverse effect on their growth and maturity. Scientists, who have studied the issue of physical activity of children in Lithuania, envisage obviously declining trends of physical activity. Research data show that physical activity of more than 50% of boys and over 60% of girls in Lithuania are not sufficient (Skurvydas, 2017). Physical activity is defined as any bodily movement produced by skeletal muscles that’s requires energy expenditure. The objective of the research: to assess the impact of strengthening exercises on the functioning of quadriceps muscle for teenagers children who are involved in sports activity or not involved in sports activity. Conclusions: 1. After application of strength exercises the increase in thigh volume, quadriceps muscle thickness and strength were statistically significant (p<0.05) in both groups: sporting and non-sporting. Quadriceps muscle thickness and muscle strength were statistically significantly greater (p<0.05) in sporting group, and thigh volume increase was statistically insignificant greater (p>0.05) in non-sporting group. 2. Difference in thigh volume, quadriceps muscle thickness and strength between the dominant and non-dominant leg was statistically insignificant (p>0.05) prior to and after the application of strength exercises. 3. The closest correlation was between the quadriceps muscle thickness and thigh volume as well as between the quadriceps muscle strength and thickness. The relation between the quadriceps muscle strength and thigh volume was average or weak.

BACKGROUND: Physical activity is the key factor in a child’s development and strong health. This includes physical, mental and functional body states. In Lithuania, as in the whole world, the physical activity of children is decreasing and this affects their growth and maturation.OBJECTIVE OF STUDY: To evaluate the effect of exercises on the thickness and function of the quadriceps thigh muscle of sporting and non-sporting children 11-13 years of age.METHODS: The research was carried out at one of Kaunas basic schools. Two tests were performed for this purpose before and after the study. In the study, a dominant leg measuring test and the thickness, volume and strength measuring of the quadriceps thigh muscle was performed. The received data was processed using SPSS 17.0 and a mathematical calculator in Microsoft Office Excel. The study lasted 5 months and a leg muscle strengthening exercise program was performed for 30 minutes twice a week. The participants performed 30 exercises in total.RESULTS: The study involved 36 participants, which were grouped in two groups of 18 participants. Assessing the results of a study between a dominant and non-dominant leg, we found that the results of all measurements in both groups were not significantly different (p>0.05). By analyzing the results of sporting and non-sporting groups before as well as after the study and after calculation of Pearson correlation coefficients, a greater link between the measured parameters was determined in the sporting group.CONCLUSION: The results showed that the studied parameters (thickness, force and volume of the quadriceps thigh muscle) statistically increased significantly after strength exercises.