Study aim: To assess the generation changes in somatic and motor variables in menstruating and non-menstruating girls from Eastern Poland.Material and methods: Two cohorts of girls aged 10 - 15 years from Eastern regions of Poland were studied in 1986 (n = 2554) and in 2006 (n = 5563). The age at menarche was determined in girls by probit method employing the status quo technique. The girls were subjected to the International Physical Fitness Test battery and the results were classified into two categories: those of girls who already menstruated (M) or who have not yet (N).Results: Mean menarcheal age significantly (p>0.001) decreased in 2006 compared with 1986 (12.77 and 13.41, respectively). This was accompanied by marked, significant increases in body height, significant changes in body mass and significant increases in the slimness. Physical fitness generally decreased, especially in girls aged over 12 years, but in the handgrip and in sit-ups significant improvements were noted in both groups of girls.Conclusions: The results seem to support the view that the secular advancement of somatic traits was associated with decreasing physical fitness.