Are fatigue and disturbances in pre-programmed activity of pelvic floor muscles associated with female stress urinary incontinence?

AIMS: To investigate whether there is a difference between a continent versus a stress urinary incontinent group of women regarding: (i) fatigue in pelvic floor muscles, and (ii) pre-activation times between pelvic floor and abdominal muscles during coughing.
METHODS: Twenty-six continent and 20 stress urinary incontinent parous women were examined. Fatigue was measured with an intravaginal device. Time to 10% decline of the initial reference force (RF) was defined as time-to-fatigue. Simultaneous recordings of force developed in levator ani muscle and electromyographic activity in the external oblique abdominal muscle were performed to determine whether contraction of pelvic floor muscles precedes activity in abdominal muscles during coughing.
RESULTS: Time-to-fatigue was identical in the two groups (10.5 sec in the continent and 11.5 sec in the incontinent group, median values). Normalized force was significantly reduced in the incontinent group. The pelvic floor muscles contracted 160 msec before the abdominal muscles in both groups. In 24% of the continent and in 30% of the incontinent women, however, abdominal muscle activity preceded activity of pelvic floor muscles.
CONCLUSIONS: Muscular fatigue, defined as rate of force loss, does not seem to be associated with urinary stress incontinence. Moreover, muscular activity recruitment patterns were equal in both groups suggesting that other factors than disturbances of ordered muscle recruitment, that is, pelvic floor followed by abdominal muscles, may be responsible for stress urinary incontinence. It is likely that reduced normalized force, as found in the incontinent group, is an important contributing factor. Copyright 2004 Wiley-Liss, Inc.