Fatigability of the external anal sphincter muscles using a novel strength training resistance exercise device

Abstract

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. Twelve nulliparous (21 ± 2.7 yr) women were studied. We evaluated fatigue during 40 repetitive 3-s contractions and 30-s 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. Exercise against a resistive load showed significant decrease in anal contractile integral (CI) and maximum squeeze pressure during repetitive short squeeze contractions compared with 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). In conclusion, repetitive contractions against a compressible load induce fatigue and thus have 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.NEW & NOTEWORTHY Fecal incontinence is a distressing disorder with a mainstay of treatment being pelvic floor muscle exercises. However, none of these exercises has proven occurrence of fatigability, which is an important prerequisite for successful muscle strengthening in rehabilitative exercises. In this study, we proved that we can fatigue the external anal sphincter muscles more efficiently by providing a resistive load during anal repetitive short squeeze contractions and long squeeze contraction exercise.

Keywords: Kegel exercises; external anal sphincter; fecal incontinence.

Graphical abstract

Figure 1.

Continence muscle resistance exerciser device.

Figure 2.

Schematic diagram of the study protocol.

Figure 3.

Space-time box showing the contractile integral of the anal contraction on the Manoview analysis software.

Figure 4.

Change of anal contractile integral (anal CI ± SE) over 40 consecutive anal squeeze exercises, no load vs. with load. N = 12 subjects. The y-axis is the anal contractile integral (mmHg·cm·s), and the x-axis is the order of contractions, which are grouped into 8 epochs. Data were analyzed using repeated two way analysis of variance. Consecutive anal squeeze against a resistive load showed significant decrease in anal CI (P < 0.0001). Linear regression analysis showed a significant negative correlation between anal CI and successive squeeze exercise against load. There was no significant change in anal CI during exercise without load.

Figure 5.

Change of anal maximum squeeze pressure (max ± SE) over 40 consecutive anal squeeze exercises, no load vs. with load. N = 12 subjects. The y-axis is the anal maximum squeeze pressure (mmHg), and the x-axis is the order of contractions, which are grouped into 8 epochs. Data were analyzed using repeated two way analysis of variance. Consecutive anal squeeze against a resistive load showed significant decrease in maximum anal squeeze pressure (P < 0.0001). Linear regression analysis showed a significant negative correlation between maximum anal squeeze pressure and successive squeeze exercise against load. There was no significant change in maximum anal squeeze pressure during exercise without load.

Figure 6.

Paired plot data of the individual’s FR, no load vs. with load. N = 12 subjects. Data were analyzed using paired t test. The y-axis represents the pressure change in 20 s. FR was significantly more negative in sustained squeeze against a resistive load than without load. FR, fatigue rate.