Introduction: Exercises involving pelvic floor muscles including repetitive voluntary contractions of external anal sphincter (EAS) musculature have been used to improve fecal incontinence. Muscle fatigue is a prerequisite for successful strength training. However, muscle fatigue induced by these exercises has not been systematically studied. We aimed to assess the fatigability of EAS muscles during various exercise methods. Methods: Twelve nulliparous (21 ± 2.7 yrs.) females were studied. We evaluated fatigue during 40 repetitive 3 sec contractions and 30 sec long squeeze contractions both with and without an intra-anal compressible resistant load. The sequence of exercises was randomized. This load was provided by the continence muscles Resistance Exerciser Device. Anal canal pressures were recorded by high-resolution manometry. Results: Exercise against a resistive load showed significant decrease in anal contractile integral (CI) and maximum squeeze pressure during repetitive short squeeze contractions compared to exercise without a load. Linear regression analysis showed a significant negative correlation between anal CI and successive contraction against load, suggesting "fatigue". Similar findings were observed for maximum squeeze pressure (slope with load -4.2, P=0.0003 vs without load -0.9, P=0.3). Long squeeze contraction against a load was also more susceptible to fatigue than without a load (p<0.0001). Conclusions: Repetitive contractions against a compressible load induces fatigue and thus has the potential to strengthen the anal sphincter contractile function than contractions without a load. Fatigue rate in long squeeze contraction exercises with a load is significantly faster than that without a load also indicating greater effectiveness in inducing muscle fatigue.
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