Table 4.
Instruments used in the reviewed studies to measure pelvic floor muscle strength
| Measures common name (review article) | What is assessed | Reliability | Validity | |
|---|---|---|---|---|
| Subjective | Vaginal digital examination [23, 26] | Grading contraction, pressure around finger/s (4-point scale) | – | – |
| Modified Oxford scale [18] | Grading contraction, pressure around fingers, Poisson effect (as muscle is contracted, it expands a bulging up) (6-point scale) |
r = 0.27–0.95 (inter-rater) [49–53] r = 0.93 (test–retest) [50] |
Correlation with perineometric pressure 0.79 [50] Contaminated by IAP |
|
| A self-rated PFM strength question [20] | Self-reported improvement of PFM strength | – | – | |
| Objective | Perineometer-like devices [16, 24] | Maximum voluntary vaginal closure pressure (mm Hg) | r = 0.79–0.80 (inter-rater) [54] |
Good agreement with Brink digital exam score [55] Contaminated by IAP |
| Intravaginal balloon-like device [15, 17, 21] | Maximum voluntary vaginal closure pressure (mm Hg) | r = 0.52–0.85 (test–retest) [56] | Contaminated by IAP [57] | |
| Needle EMG: quantitative EMG [22] | Muscle electrical activity from individual motor units (in microvolt units) |
r = 0.89 (range 0.78–0.95) [22] hard to repeat |
Not possible to measure contractile force using EMG [58] Contaminated by IAP |
|
| Surface EMG (vaginally): quantitative EMG [25] | Muscle electrical activities from summated from many motor units (millivolt) | Between-visit ICC ranging 0.76–0.97 [59] |
Measured PFM activity other than vaginal closure pressure |
|
| A handheld dynamometer (mTasMF-01, ANIMA, Japan) [19] | Hip adductor muscle strength | – | Not measure PFM strength | |
| Sagittal dynamic (perineal) ultrasound [27] | Cephalic displacement (in mm) of the bladder neck in a sagittal view available as biofeedback (as opposed to caudal movement observable when she pushes down instead) | r = 0.52–0.96 (intra-rater) [62] | Visual “lift” of the bladder neck with a correct PFM contraction |
—, Information was not available; IAP, intraabdominal pressure; PFM, pelvic floor muscle; EMG, electromyography; ICC, intra-class correlation coefficients