The aim of the study was to estimate the influence of trunk inclination on muscle activity during sitting on forward inclined seats without backrest. The group consisting of thirteen healthy women was examined. Based on anthropometrical data two types of sitting position were adopted with two different angles between thighs and trunk: 120 and 135 degrees. Bioelectrical activity of five muscles was recorded. There was observed statistical influence of the trunk inclination on erector spinae, gastrocnemius lat. and tibialis anterior (p < 0.05). Especially, the inclination of seat pan influenced tibialis anterior activity (10%), although EMG measured during sitting did not exceed 20% of MVC.