ICS 1999, Denver
Informally discussed posters
Pelvic floor
EMG Evidence of abdominal muscle activity during pelvic floor muscle contraction

V. Gill and P. Neumann
School of Physiotherapy, University of South Australia, Adelaide, Australia

Isolation of pelvic floor muscle (PFM) activity, specifically eliminating abdominal muscle activity, is incorporated in many guidelines for PFM exercise. Abdominal muscle activity is regarded as undesirable because it may increase intrabdominal pressure (IAP) and cause a Valsalva response.

Abdominal muscle activity during PFM exercise has been detected via palpation of the abdominal wall, surface EMG recording techniques and monitoring of IAP. PFM contraction had been measured vaginally with surface EMG techniques and pressure recorded via a vaginal balloon.

Only one small study had investigated the electrical evidence of concormitant activity in the abdominal and pelvic floor muscle group. Using surface EMG recording, an increase inlower Rectus Abdominis (RA) activity was considered to be unavoidable in efficient PFM training (1). However, the abdominal wall is comprised of muscle layers with different actions. Three of its four muscles can be evaluated using surface EMG (SEMG) recording techniques. Due to its deep position, Transversus Abdominis (TA) must be investigated using intramuscular needle electrodes.

Despite the still-common advice to eliminate abdominal muscle activity during PFM exercise, there are no investigations of the resulting PFM contraction.

Aim of Study: Development of a method to identify activity in abdominal muscles and PFM during:

1. maximum PFM contraction;
2.PFM contraction with specific inhibition of abdominal muscle activity.

Method: Subjects were four women aged 25-42 years (mean 34), lean, nulliparous and continent. Subjects were trained and tested vaginally by an experienced physiotherapist to contract the PFM correctly.

Test activities were FPM contractions in lying and standing positions.

Measurements were the simultaneous recording of:

1.Intra abdominal pressure (IAP)
2.Intra vaginal pressure (IVP)
3.Surface EMG (SEMG) overlying:
a)Lower Rectus Abdominis (LRA)
b)External Oblique Abdominis (EOA)
c)Internal Oblique Abdominis (IOA)
4.Intramuscular EMG (IEMG) of Transversus Abdominis (TA).
5.Surface EMG of PFM.

To assess reliability, all tests were repeated one week later.

All EMG data was normalized prior to descriptive analysis of muscle activity.

Test re-test reliability was investigated using Pearson's Correlation Co-efficient r and t tests.

Results: Abdominal muscle activity was identified with all PFM contractions in lying and standing positions. Greatest EMG activity occured in the deepest muscles of the abdominal wall (TA and IOA), with minimal recruitment of superficial muscles (RA and EOA). IAP remained below 22 cm H₂O during PFM contractions.

Attempts to inhibit abdominal muscle activity were largely unsuccessful.

Test-retest reliability was higher for surface than intramuscular EMG recording, but satisfactory.

Conclusion: Strong PFM contractions simultaneously activated the deep muscles of the abdominal wall (TA and IOA). Minimal activity was shown in the superficial muscles (EOA and RA) of all four trained subjects.

It was possible to reduce, but not eliminate, abdominal muscle activity when contracting the PFM. However, minimizing abdominal muscle activity resulted in PFM contractions so low in intensity that no principles of strength training would be satisfied.

The results of this small study challenge instructions, which recommend relaxing the abdominal wall during PFM exercise.

Further investigation of apparent synergistic interaction of the deep abdominal muscles with PFM contraction is warranted.

(1) Bø et al (1990): Pelvic floor muscle exercise for the treatment of female stress urinary incontinence: 11. Validity of vaginal pressure measurements of pelvic floor muscle strength and the necessity of supplementary methods for control of correct contraction. Neurourology & Urodynamics 9:479-487.