Relationship between levator ani contraction and motor unit activation in the urethral sphincter

The purpose of this study was to evaluate the relationship between levator ani contraction and motor unit action potential activation in the striated urethral sphincter.

One hundred eight women who underwent preoperative evaluation at our referral center were studied. All women gave a urogynecologic history and underwent physical examination, multichannel urodynamic testing, and urethral sphincter electromyography. Manual muscle testing was used to grade levator ani contractions as poor, moderate, or strong; quantitative electromyography software was used to analyze motor unit action potential activation in the urethral sphincter.

Levator ani contractions were graded as poor in 46% of the women, moderate in 31% of the women, and strong in 23% of the women. Manual muscle grade was not related to quantitative electromyography values in the urethral sphincter at rest or with voluntary pelvic floor contraction. Poor manual muscle grade was associated with detrusor instability (P =.004) and more advanced stages of prolapse (P =.037). Levator ani strength was not significantly related to age, genuine stress incontinence, urethrovesical junction hypermobility, menopausal status, or surgical cure rates.

The ability to contract the levator ani does not appear to be related to the ability to activate motor unit action potentials in the urethral sphincter, which suggests that the function of the levator ani in maintaining urinary continence is independent from the role of the urethral sphincter.