Objectives: In physiotherapeutic practice, special attention is being given to the reciprocal anatomical, physiological, and biomechanical relationship of the pelvis and the structures connected to it. However, the scientific literature shows mainly the theoretical information about their mutual connections. The lack of information about these relations from a practical aspect coupled with the paucity of scientific papers on the impact of posture changes on the pelvic floor led the authors to conduct this study. The primary aim of this study was to compare the resting and functional bioelectrical activities of pelvic floor muscles (PFMs) depending on three different positions of the lower limbs (positions A, B, and C) in the supine position. Materials and methods: This was a prospective observational study evaluating resting and functional activities of the PFM depending on the position of the lower limbs. The study was carried out at the Department and Clinic of Urology, University Hospital in Wroclaw, Poland and the target group were women in the menopausal period. Bioelectrical activity of PFM was recorded using a surface electromyographic instrument in the supine position. Results of the values obtained in A, B, and C positions were compared using a one-way analysis of variance. Results: In position A, the average resting surface electromyography (sEMG) activity of PFM was 6.9 +/- 2.6 mu V; in position B, the result was 6.9 +/- 2.5 mu V and in position C, the resting sEMG activity was 5.7 +/- 1.8 mu V (P=0.0102). The results of the functional bioelectrical activity of PFM were as follows: position A - 20.3 +/- 11.8 mu V, position B - 19.9 +/- 10.6 mu V, and position C - 25.3 +/- 10.9 mu V (P=0.0104). Conclusion: The results showed that in the supine position, the PFM achieved the lowest resting activity and the highest functional activity. Therefore, the supine position can be recommended for the diagnosis and therapy of weakened PFM.