Association between isokinetic abdominal muscle strength, pelvic floor muscle strength and stress urinary incontinence severity

OBJECTIVES

Studies have shown that there is co-activation between abdominal and pelvic floor muscles (PFM) in physiological conditions. This study aimed to assess pelvic floor and isokinetic trunk flexors function in non-active incontinent women, and to investigate the association between the strength of these muscle groups and the severity of stress urinary incontinence (SUI).

METHODS

A cross-sectional study was carried out. Twenty-five incontinent women were enrolled after one-hour pad test results and compared to twenty asymptomatic women. The severity of SUI was determined by the Pad test and Urinary Distress Inventory, Short Form (UDI-6). PFM function was assessed using the modified Oxford Scale, intra-vaginal PFM electromyography, and PFM endurance according to the PERFECT scheme. Trunk flexors strength was assessed using a Cybex Norm II dynamometer.

RESULTS

Incontinent women had a weaker PFM and isokinetic abdominal muscle strength compared to continent women (P<0,05). SUI severity was negatively correlated with PFM strength (r=-0,620, P=0,001), isokinetic trunk flexors strength (r=-0,605, P=0,001), and PFM endurance (r=-0,561, P=0,003) in incontinent women. A positive correlation between PFM function and isokinetic trunk flexors strength was found in incontinent women (r=0,488, P=0,013).

CONCLUSION

Non-active incontinent women had weaker pelvic floor muscles and isokinetic trunk flexors strength compared to continent ones. The positive correlation found between these two muscle groups may be explained by their synergic activity. These findings suggest that the severity of SUI could be related not only to PFM strength but also to abdominal muscle weakness. Further research is needed to recommend abdominal wall training as an alternative method to treat SUI.

LEVEL OF PROOF

3.

Muscle function and fatigability of trunk flexors in males and females

BACKGROUND

Optimal function of the abdominal muscles is necessary for several life functions including lifting and carrying tasks. Sex differences in strength and fatigability are established for many limb muscles and back extensor muscles, but it is unknown if sex differences exist for the abdominal muscles despite their functional importance.

METHODS

Eighteen females (24.3 ± 4.8 years) and 15 males (24.1 ± 6.6 years) performed (1) isometric trunk flexion maximal voluntary contractions (MVCs) in a range of trunk positions to establish a torque-angle curve and (2) submaximal (50% MVC), intermittent isometric contraction (6 s on, 4 s off) until task failure to determine fatigability of the trunk flexor muscles. Dual X-ray absorptiometry quantified body fat and lean mass. Physical activity levels were quantified with a questionnaire. Torque-angle curves, electromyography (EMG), MVC torque, and torque steadiness were compared with repeated measures ANOVA with sex as a between-subjects factor.

RESULTS

For the torque-angle curve, MVC torque was reduced as the trunk angle increased toward flexion (p < 0.001). Males had greater MVC torque than females at the extended positions (31% difference), with no sex differences in torque in upright sitting (p > 0.05). Time-to-task failure for the submaximal fatigability task in upright sitting was similar between males and females (12.4 ± 7 vs 10.5 ± 6 min). Time-to-task failure was positively associated with strength (r = 0.473, p = 0.005) and self-reported physical activity (r = 0.456, p = 0.030). Lean mass in the trunk was positively associated with trunk flexor strength (r = 0.378, p = 0.011) and self-reported physical activity (r = 0.486, p = 0.007). Finally, torque steadiness [coefficient of variation of torque (CV)] during submaximal isometric contractions decreased with contraction intensity and was similar for males and females across all intensities.

CONCLUSIONS

Unlike many limb muscle groups, males and females had similar fatigability and torque steadiness of the trunk flexor muscles during isometric contractions. Stronger individuals, however, exhibited less fatigability. Lower self-reported physical activity was associated with greater fatigability of trunk flexor muscles. The relationship between strength and fatigability of the trunk flexor muscles and physical activity supports the importance of abdominal muscle strengthening to offset fatigability in both males and females.