The aim of the study was to determine the immediate effect of timing a pelvic muscle contraction with the moment of expected leakage (the Knack maneuver) to preempt cough-related stress incontinence. Women performed a standing stress test using three hard coughs without and then with the Knack maneuver. Volume of urine loss under both conditions was quantified with paper-towel test. Two groups of women were tested: nonpregnant women (n = 64) and pregnant women (n = 29). In nonpregnant women, wetted area decreased from a median (range) of 43.2 (0.2-183.7) cm2 without the Knack maneuver to 6.9 (range of 0 to 183.7 cm2) with it (p < 0.0001); while in pregnant women it decreased from 14.8 (0-169.7) cm2 to 0 (0-96.5) cm2, respectively (p = 0.001). This study confirms the effect from the Knack maneuver as immediate and provides a partial explanation for early response to widely applied pelvic muscle training regimens in women with stress incontinence.