Background: The reduction of the pelvic floor muscles (PFM) strength is a major cause of stress urinary incontinence (SUI). Objective: To compare active and passive forces, and vaginal cavity aperture in continent and stress urinary incontinent women. Method: The study included a total of thirty-two women, sixteen continent women (group 1 - G1) and sixteen women with SUI (group 2 - G2). To evaluate PFM passive and active forces in anteroposterior (sagittal plane) and left-right directions (frontal plane) a stainless steel specular dynamometer was used. Results: The anteroposterior active strength for the continent women (mean±standard deviation) (0.3±0.2 N) was greater compared to the values found in the evaluation of incontinent women (0.1±0.1 N). The left-right active strength (G1=0.43±0.1 N; G2=0.40±0.1 N), the passive force (G1=1.1±0.2 N; G2=1.1±0.3 N) and the vaginal cavity aperture (G1=21±3 mm; G2=24±4 mm) did not differ between groups 1 and 2. Conclusion: The function evaluation of PFM showed that women with SUI had a lower anteroposterior active strength compared to continent women.164314319Keller, S.L., Urinary incontinence: Occurrence, knowledge, and attitudes among women aged 55 and older in a rural Midwesten setting (1999) J Wound Ostomy Continence Nurs., 26 (1), pp. 30-38Guarisi, T., Pinto Neto, A.M., Osis, M.J., Pedro, A.O., Paiva, L.H.C., Faúndes, A., Incontinência urinária entre mulheres climatéricas brasileiras: Inquérito domiciliar (2001) Rev Saúde Pública., 35 (5), pp. 428-435Kenton, K., Mueller, E.R., The global burden of female pelvic floor disorders (2006) BJU Int., 98 (1), pp. 1-5Wagner, T.H., Hu, T.W., Economic costs of urinary incontinence in 1995 (1998) Urology., 51 (3), pp. 355-361DeLancey, J.O., The pathophysiology of stress urinary incontinence in women and its implications for surgical treatment (1997) World J Urol., 15 (5), pp. 268-274Dumoulin, C., Bourbonnais, D., Lemieux, M.C., Development of a dynamometer for measuring the isometric force of the pelvic floor musculature (2003) Neurourol Urodyn., 22 (7), pp. 648-653Bø, K., Sherburn, M., Evaluation of female pelvic-floor muscle function and strength (2005) Phys Ther., 85 (3), pp. 269-282Balmforth, J.R., Mantle, J., Bidmead, J., Cardozo, L., A prospective observational trial of pelvic floor muscle training for female stress urinary incontinence (2006) BJU Int., 98 (4), pp. 811-817Peschers, U.M., Gingelmaier, A., Jundt, K., Leib, B., Dimpfl, T., Evaluation of pelvic floor muscle strength using four different techniques (2001) Int Urogynecol J Pelvic Floor Dysfunct., 12 (1), pp. 27-30Bø, K., Pelvic floor muscle strength and response to pelvic floor muscle training for stress urinary incontinence (2003) Neurourol Urodyn., 22 (7), pp. 654-658Amaro, J.L., Moreira, E.C., Gameiro, M.O.O., Padovani, C.R., Pelvic floor muscle evaluation in incontinent patients (2005) Int Urogynecol J Pelvic Floor Dysfunct., 16 (5), pp. 352-354Rett, M.T., Simões, J.A., Herrmann, V., Marques, A.A., Morais, S.S., Existe diferença na contratilidade da musculatura do assoalho pélvico feminino em diversas posições (2005) Rev Bras Ginecol Obstet., 27 (1), pp. 12-19Morin, M., Bourbonnais, D., Gravel, D., Dumoulin, C., Lemieux, M.C., Pelvic floor muscle function in continent and stress urinary incontinent women using dynamometric measurements (2004) Neurourol Urodyn., 23 (7), pp. 668-674Verelst, M., Leivseth, G., Force and stiffness of the pelvic floor as function of muscle length: A comparison between women with and without stress urinary incontinence (2007) Neurourol Urodyn., 26 (6), pp. 852-857Peng, Q., Jones, R., Shishido, K., Omata, S., Constantinou, C.E., Spatial distribution of vaginal closure pressures of continent and stress urinary incontinent women (2007) Physiol Meas., 28 (11), pp. 1429-1450Nunes, F.R., Martins, C.C., Guirro, E.C.O., Guirro, R.R.J., Reliability of bidirectional and variable-opening equipment for the measurement of pelvic floor muscle strength (2011) PM R., 3 (1), pp. 21-26Dumoulin, C., Gravel, D., Bourbonnais, D., Lemieux, M.C., Morin, M., Reliability of dynamometric measurements of the pelvic floor musculature (2004) Neurourol Urodyn., 23 (2), pp. 134-142Hundley, A.F., Wu, J.M., Visco, A.G., A comparison of perineometer to brink score for assessment of pelvic floor muscle strength (2005) Am J Obstet Gynecol., 192 (5), pp. 1583-1591Bø, K., Pelvic floor muscle exercise for the treatment of female stress urinary incontinence: Validity of vaginal pressure measurements of pelvic floor muscle strength and the necessity of supplementary methods for control of correct contraction (1990) Neurourol Urodyn., 9 (5), pp. 479-487Cram, J.R., Kasman, G.S., Haltz, J., (1998) Introduction to surface electromyography, , Maryland: Aspen PublishersGuirro, R.R.J., Forti, F., Bigaton, D.R., Proposal for electrical insulation of the electromyographic signal acquisition module (2006) Electromyogr Clin Neurophysiol., 46 (6), pp. 355-363Sarwar, R., Niclos, B.B., Rutherford, O.M., Changes in muscle strength, relaxation rate and fatiguability during the human menstrual cycle (1996) J Physiol., 493 (PART 1), pp. 267-272DeLancey, J.O.L., Trowbridge, E.R., Miller, J.M., Morgan, D.M., Guire, K., Feener, D.E., Stress urinary incontence: Relative importance of urethral support and urethral closure pressure (2008) J Urol., 179 (6), pp. 2286-2290Constantinou, C.E., Omata, S., Direction sensitive sensor probe for the evaluation of voluntary and reflex pelvic floor contractions (2007) Neurourol Urodyn., 26 (3), pp. 386-391Nishiyama, M., Kimura, Y., Nishiyama, Y., Terazima, M., Pressure-induced changes in the structure and function of the kinesin-microtubule complex (2009) Biophys J., 96 (3), pp. 1142-1150Mørkved, S., Salvesen, K.A., Bø, K., Eik-Nes, S., Pelvic floor muscle strength and thickness in continent and incontinent nulliparous pregnant women (2004) Int Urogynecol J Pelvic Floor Dysfunct., 15 (6), pp. 384-390Thompson, J.A., O'Sullivan, P.B., Briffa, N.K., Neumann, P., Assessment of voluntary pelvic floor muscle contraction in continent and incontinent women using transperineal ultrasound, manual muscle testing and vaginal squeeze pressure measurements (2006) Int Urogynecol J Pelvic Floor Dysfunct., 17 (6), pp. 624-630Verelst, M., Leivseth, G., Force-lenght relationship in the pelvic floor muscles under transverse vaginal distension: A method study in healthy women (2004) Neurourol Urodyn., 23 (7), pp. 662-667Rahn, D.D., Ruff, M.D., Brown, S.A., Tibbals, H.F., Word, R.A., Biomechanical properties of the vaginal wall: Effect of pregnancy, elastic fiber deficiency, and pelvic organ prolapse (2008) Am J Obstet Gynecol., 198 (5), pp. 590+e1-6Nunes, F.R., Guirro, E.C.O., Martins, C.C., Guirro, R.R.J., Influence of visual feedback on pelvic floor muscle strength (2010) Eur J Obstet Gynecol Reprod Biol., 151 (2), pp. 217-220Hannestad, Y.S., Rortveit, G., Sandvik, H., Hunskaar, S., Epidemiology of Incontinence in the County of Nord-Trøndelag. A community-based epidemiological survey of female urinary incontinence: The Norwegian EPINCONT Study. Epidemiology of Incontinence in the County of Nord-Trøndelag (2000) J Clin Epidemiol., 53 (11), pp. 1150-1157. , Norwegian EPINCONT study