PURPOSE: Cough and more generally abdominal strain determine a pelvic floor contraction which allows an increase in sphincter pressure to prevent leakage during stress. Many electrophysiological studies have demonstrated this reflex (formally cough anal reflex). We postulated that the perineal muscle contraction following cough is not a simple binary response but proportional to the intensity of the cough. MATERIALS AND METHODS: A total of 16 women (mean age 52 years) without neurological disease or stress urinary incontinence, referred for frequency and urgency without urge incontinence, underwent urodynamic investigation. Vesical pressure was compared to electromyographic activity of the anal sphincter during 4 successive coughs of different intensity, namely gentle, moderate, strong and very strong efforts. These 4 graded coughs were repeated at 0, 100, 200, 300 and 400 ml of filling during cystometry. RESULTS: All patients were able to determine a graded cough at each level of filling. In all patients and at each level of filling a strict relationship between intravesical pressure (intensity of cough) and integrated electromyographic value was demonstrated. The greater the intensity of the cough the greater the electromyographic response of the anal sphincter. There is a strict correlation between vesical pressure and integrated electromyographic value at rest at O (R2 = 0.983) or at 100 ml (R2 = 0.970), 200 (R2 = 0.918) or 300 ml (R2 = 0.960). Bladder filling does not modify the responses. CONCLUSIONS: Pelvic floor muscle contraction increases with the importance of intra-abdominal pressure generated during stress. This gradual adaptation of pelvic floor muscles is probably 1 of the main factors which contributes to stress urinary and fecal continence in women. It must be preprogrammed by the central nervous system to maintain continence during various stresses.