The aim of this study was primarily to determine the reliability and factor validity of four muscular endurance tests, and secondly, to identify gender differences in muscular endurance tests. For this purpose, a new muscular endurance test was constructed for pupils aged between seven and eight (CROCO). The research was done on a sample of 71 pupils aged between seven and eight (35 girls and 36 boys), their body height being 129.2 +/- 1.3 cm for boys and 127.1 +/- 1.4 cm for girls, body weight 29.3 +/- 7.2 kg for boys and 27.1 +/- 6.5 for girls. According to the results, all tests have shown a good level of reliability and factor validity. Also, the present study confirmed the expected gender differences (p < or = 0.05). In all muscular endurance tests, the boys were slightly better than girls (p < or = 0.05). The authors recommend the implementation of the CROCO test and other muscular endurance tests used in this study, both for the implementation in the primary school curricula and in sports because of these tests' satisfactory level of reliability and factor validity. The school curricula need to be adjusted to the age and gender differences of children in order to promote positive health behavior from the earliest age on the one hand, and on the other to be able to objectively measure muscular endurance.