Objectives:
An increase is observed worldwide in the number of children with an incorrect nutritional status. Both underweight and overweight create health risk for children during the period of ontogeny and also later in adulthood. Functional shortening of muscles which occurs often in children and adolescents is the phenomenon associated with an increase in passive stiffness of muscles. The aim of this study was to evaluate how frequently the functional shortening of the lower limbs muscles occurs in children with various nutritional status.

Material and methods:
The study covered 227 children aged 9–12 years, attending primary school in Wysokie Mazowiecki (Podlaskie Province). Anthropometric measurements and lower extremity muscle tests were performed: Thomas Test, Patrick Test and Sciatic Torsion Test. The t-student and chi 2 tests were used to analyze the results, which were calculated using Statistica v. 12.0.

Results:
Girls were significantly more often underweight than boys (p <0.01), while boys more frequently had excessive weight, compared to girls (p <0.01). Functional shortening of the muscles of the lower limbs was significantly more often diagnosed in boys than girls (p <0.01). It was confirmed that among the examined girls, nutritional status had an effect on the occurrence of shortened functioning of the lower limbs.

Conclusions:
1) Muscle contractures of lower limbs tend to occur more often in girls than boys. 2) Correct BMI is associated with a decrease in the occurrence of functional shortening of the muscles of the lower limbs, both in boys and girls. 3) Children with impropriate weight should be encouraged to participate in corrective-compensatory gymnastics classes.