Abstract
[Purpose] This study investigated the effects of co-contraction resistance exercises of the transverse abdominal and pelvic floor muscles in middle-aged females with stress urinary incontinence. [Participants and Methods] We included 32 females with stress urinary incontinence and divided them into two groups: the inner muscle training group and the pelvic floor muscle group. The thickness of the transverse abdominal muscle was measured during four tasks: (1) rest, (2) maximum contraction of the transverse abdominal muscle, (3) maximum contraction of the pelvic floor muscle, and (4) maximum co-contraction of the transverse abdominal and pelvic floor muscles. In the latter three tasks, measurements were obtained while the participants performed resistance movements using a Thera-band®. A home program was conducted in both groups, and the intervention lasted for 8 weeks. [Results] The cure rates for SUI were 87.5% and 68.8% in the inner muscle training and pelvic floor muscle groups, respectively. After the intervention, the thickness of the transverse abdominal muscle significantly increased in the inner muscle training groups performing maximum co-contraction of the transverse abdominal and pelvic floor muscles and maximum contraction of the transverse abdominal muscle. [Conclusion] Inner muscle training exercises are more effective than pelvic floor muscle exercises in improving inner muscle function and urinary incontinence in middle-aged females.
Keywords: Urinary incontinence, Transversus abdominis, Co-contraction resistance exercise
INTRODUCTION
The overall prevalence of urinary incontinence during pregnancy is estimated to be around 58% and stress urinary incontinence (SUI) affects 31–42% of females (nulliparous and multiparous)1). Several studies have reported that the pelvic floor muscle (PFM; the inner unit) along with the transverse abdominal muscle (TAM), multifidus, and diaphragm maintain the stability of the trunk. The PFM exercise have been used in the management of SUI2,3,4). The PFM exercises are 50–69% effective in reducing episodes of urine loss in women5,6,7). The PFM exercises generally relax the abdominal muscle when the PFM contracts8,9,10). However, the principle of effective muscle training requires overload, and we believe that contracting only the PFM while relaxing the abdominal muscle may not have a sufficient effect as load strength. In our previous study, we found a significant relationship between the thickness of the TAM and the iEMG of the levator ani muscle11). The TAM and PFM co-contraction exercise intervention has been reported to increase the thickness of the TAM12). This result suggests that changes in the thickness of the TAM may be used to indicate changes in the electrical activity of the PFM.
Our hypothesis is that the intervention effect on SUI of both the TAM and PFM muscles co-contraction resistance exercise is better than the PFM only exercise. The purpose of this study was to investigate the effects co-contraction resistance exercises of the TAM and PFM on middle-aged females with SUI.
PARTICIPANTS AND METHODS
The required number of samples was calculated using G*Power software, the effect size was set to 0.5 and power (1-β=0.8), the required number of samples was fourteen for each group. We included 32 females who had experienced one or more episodes of SUI in the past one month13). They were randomly divided into two groups: the TAM and PFM co-contraction resistance group (inner muscle training [IMT] group; n=16) and the PFM group (n=16). All participants provided informed consent to participation in this study. This study was approved by the International University of Health and Welfare Ethics Review Committee (approval number: 20-Io-167).
All participants completed a questionnaire on UI, delivery history, delivery method and menstrual cycle. The thickness of the TAM was measured using ultrasound (SonoSite 180 PLUS, B mode,5-MHz linear transducer, USA). The thickness of the TAM was measured in all participants in the supine position under eight conditions at random. The reliability of the measurement method was verified from our previous research10).
1) Resting state
2) Maximum contraction of the TAM: The participants were instructed to draw in the lower abdominal wall toward the spine (an action that specifically activates the TAM), and breathe in a relaxed manner without moving the lumbar spine.
3) Maximum contraction of the PFM: The participants were instructed to contract the muscles around the vagina “like a drawstring”, and lift them internally without tilting the pelvis posteriorly. There was no instruction regarding the use of the abdominal muscle.
4) Maximum co-contraction of the TAM and PFM: The participants were instructed to draw in the lower abdominal wall toward the spine, an action that specifically activates the TAM. When the TAM sustained isometric contraction, the participants were instructed to contract the muscles around the vagina “like a drawstring” to lift them internally and maintain the position for 5 seconds. During the above four tasks, measurements were taken while performing resistance movements using a Thera-band®. The resistance forces were measured by two hand-held dynamometers (ANIMA uTas MT1, HHD, Japan) held in both knees inside of the Thera-band® using the tester function of HHD. The resistance force was controlled at 1.5 kg.
Under each condition, the participants were asked to assume the supine position with their knees flexed at 90° and a pillow under their heads. To correctly perform the inner muscle contraction, a Biofeedback Stabilizer was used to provide visual feedback. The participants were asked to maintain the baseline at 40 mmHg. Except during the resting state, whenever the pressure of the Biofeedback Stabilizer decreased during the tasks, abdominal muscle re-education was provided by a physical therapist.
Ultrasound images of the anterolateral abdominal wall were obtained using a SonoSite ultrasound. The gel was interposed between the transducer and the skin. The transducer was positioned adjacent and perpendicular to the abdominal wall 25 mm anteromedial to the midpoint between the ribs and ilium on the midaxillary line and parallel to the muscle fibers of the transversus abdominis12). The same physical therapist took the measurements to avoid inter-rater errors. Ultrasound images were saved as still images. All thickness measurements were of muscle only, that is, between the fascia boundaries. To assess its effect, measurements were taken before and after the intervention. As a single-blind test, the measurer performed measurement and instruction, subject grouping was unknown. All measurements were performed by a licensed physical therapist.
A home program was conducted in the two groups. Participants in the IMT group performed TAM and PFM co-contraction training, with lateral resistance added to both knees using a Thera-band®, and 40 repetitions (two sets of 20 repetitions) of a 5-second co-contraction were prescribed. Females in the PFM group performed PFM training with 40 repetitions (two sets of 20 repetitions) of a 5-second contraction. They were instructed to perform one exercise session three times per week, and the intervention lasted for 8 weeks.
To determine whether there were differences in terms of participant characteristics between the exercise and control groups, an independent t-test was used. To determine the differences in the results of the questionnaire survey between the IMT and the PFM groups, the χ2 test was used. Two-way repeated measures ANOVA was used to test for statistically significant differences, and the factors were intervention and group. Where a significant interaction was found, a paired t-test was used to compare the results before and after the intervention. Data were analyzed using SPSS Ver. 17.0 for Windows and the level of statistical significance was set at p<0.05.
RESULTS
There were no significant differences between the IMT and PFM group in terms of participant characteristics and measures before the intervention (Table 1).
Table 1. Characteristics of the participants.
| IMT groupa | PFM groupb | Sum total | |
| (n=16) | (n=16) | ||
| Age (years) | 50.9 ± 5.1 | 44.6 ± 10.2 | 47.8 ±8.5 |
| Height (cm) | 161.6 ± 4.4 | 160.3 ± 4.2 | 160.9 ± 4.3 |
| Weight (kg) | 63.9 ± 6.9 | 58.9 ± 3.6 | 61.4 ± 5.9 |
Values are presented as means ± standard deviation. There were no significant differences between groups at the 0.05 level.
a: IMT group: inner muscle training group.
b: PFM group: pelvic floor muscles exercise group.
The delivery history, delivery method, and menstrual cycle were not significantly different between the groups (Tables 2, 3, 4).
Table 2. Delivery history.
| IMT groupa | PFM groupb | Sum total | |
| (n=16) | (n=16) | ||
| Primiparity | 15 | 13 | 28 |
| Para | 1 | 3 | 4 |
| Sum total | 16 | 16 | 32 |
χ2 test. There were no significant differences between groups at the 0.05 alpha level.
a: IMT group: inner muscle training group.
b: PFM group: pelvic floor muscles exercise group
Table 3. Delivery method.
| IMT groupa | PFM groupb | Sum total | |
| (n=16) | (n=16) | ||
| Natural childbirth | 12 | 13 | 25 |
| Cesarean section | 4 | 3 | 7 |
| Sum total | 16 | 16 | 32 |
χ2 test. There were no significant differences between groups at the 0.05 alpha level.
a: IMT group: inner muscle training group.
b: PFM group: pelvic floor muscles exercise group.
Table 4. Menstrual cycle.
| IMT groupa | PFM groupb | Sum total | |
| (n=16) | (n=16) | ||
| Steady | 6 | 8 | 14 |
| Irregular | 3 | 3 | 6 |
| Menopause | 7 | 5 | 12 |
| Sum total | 16 | 16 | 32 |
χ2 test. There were no significant differences between groups at the 0.05 alpha level.
a: IMT group: inner muscle training group.
b: PFM group: pelvic floor muscles exercise group.
In terms of the frequency of UI, all participants had mild SUI at least once a week. Behavior during UI was 27% when coughing or sneezing, 20% when laughing out loud, 12% when lifting a heavy object, 12% when running, and 12% when exercising.
The cure rates of SUI were 87.5% (14/16) in the IMT group, and 68.8% (11/16) in the PFM group after 8 weeks of the intervention.
Table 5 shows the thickness of the TAM. The main effect was observed before and after 8 weeks of exercise (p<0.05). There were significant differences in the thickness of the TAM during maximum co-contraction of the TAM and PFM in active exercise in the IMT group (p<0.01). There were significant differences in the thickness of the TAM during maximum contraction of the TAM in resistance exercise using a Thera-band® in both the IMT (p<0.05) and the PFM (p<0.01) groups.
Table 5. Comparison of TAMa thickness before and after intervention.
| IMT groupb | PFM groupc | ||||||
| (n=16) | (n=16) | ||||||
| Before | After | Before | After | ||||
| TAM thickness (active exercise) | Resting state | 2.7 ± 0.7 | 2.9 ± 0.9 | 2.3 ± 0.4 | 2.3 ± 0.4 | ||
| Maximal contraction of TAM | 4.1 ± 1.0 | 4.4 ± 0.7 | 3.9 ± 0.6 | 4.2 ± 0.9 | |||
| Maximal contraction of PFM | 3.3 ± 0.9 | 3.3 ± 0.9 | 2.8 ± 0.4 | 2.8 ± 0.8 | |||
| Maximal co-contractiod | 4.6 ± 0.9 | 5.1 ± 0.7 | ** | 4.1 ± 0.7 | 4.4 ± 1.0 | ||
| TAM thickness (resistance exercise) | Resting state | 2.8 ± 0.7 | 3.0 ± 0.9 | 2.4 ± 0.5 | 2.6 ± 0.4 | ||
| Maximal contraction of TAM | 4.1 ± 1.0 | 4.7 ± 0.7 | * | 3.6 ± 0.5 | 4.4 ± 0.7 | ** | |
| Maximal contraction of PFM | 3.5 ± 0.9 | 3.4 ± 0.9 | 2.7 ± 0.3 | 2.8 ± 0.5 | |||
| Maximal co-contractiond | 4.6 ± 1.2 | 5.1 ± 0.9 | 4.0 ± 1.1 | 4.7 ± 0.9 | |||
Values are presented as means ± standard deviation (unit: mm).
*p<0.05; **p<0.01 (before and after 8 weeks).
a: TAM: transverse abdominal muscle.
b: IMT group: inner muscle training group.
c: PFM group: pelvic floor muscle group.
d: Maximal co-contraction: maximal co-contraction of both the TAM and PFM.
DISCUSSION
We investigated the effects co-contraction resistance exercises of the TAM and PFM on middle-aged females with SUI. Participants in the IMT group and the PFM group showed not only an increased thickness of the TA but also improved SUI. The SUI cure rate in the IMT group was higher than that in the PFM group after intervention. In prior studies, PFM exercises had a cure rate of 50–69% for SUI treatment in females14, 15). Similar results were required in the PFM group.
In our previous study, the TAM output during simultaneous contraction and resistance movements was larger than that of the individual muscles16). The TAM was contracted by “belly-in” and the pelvis was in retroversion, raising the intra-abdominal pressure. The TAM contraction is a resistance exercise with raised intra-abdominal pressure, which increases PFM contraction. In addition, the six deep external rotators of the hip were contracted by resistance exercise using a Thera-band®. The internal obturator muscle was connected to the levator ani muscle at the pelvic obturator foramen. Based on the theory of muscle cooperative movement, a possible explanation is that internal obturator muscle contraction promotes levator ani muscle contraction.
Although the absolute amount of the TAM did not increase after eight weeks of intervention, there was an increase in the expansion rate of muscle contraction, an increase in activity of the TAM, and an improvement in the function of the inner muscle. In middle-aged females, IMT exercises are more effective than PFM exercises in improving inner muscle function and urinary incontinence.
The limitation is to consider how to control the resistance of the Thera-band®. Further investigations are required to increase the number of samples.
Funding
No funding was provided for this study.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
The author is grateful to the participants and co-authors for assistance with data acquisition.
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