Hypothesis / aims of study
Electromyography (EMG) using intra-vaginal and/or intra-anal probes is widely used and considered a reliable method of assessing the activity of the pelvic floor musculature (PFM). Some authors have questioned the validity of these probes because of the fear of crosstalk. The crosstalk phenomenon is described as the detection by the EMG of a signal originating from a neighbouring muscle rather than exclusively from the muscle under investigation(1).
The activation of muscles surrounding the pelvic floor, such as abdominal or hip musculature, during a PFM contraction has been described before. In literature, it has been emphasized that exercise of the PFM should be performed in isolation without abdominal or hip muscle activity. Contraction of the adductors and gluteal muscles during PFM exercise is considered incorrect as these actions may occur without concurrent PFM muscle activity. Some authors found that it was not possible for continent women to fully contract their PFM without also contracting the transversus abdominis and the internal obliques. Furthermore they were not able to perform a maximal voluntary contraction (MVC) with their PFM without a rise in EMG activity in the lower portion of rectus abdominis. Other authors suggested that cross-talk also could be co-activation of PFM. In a scoping review the authors identified a gap in scientific knowledge regarding to the relation between contractions of muscles surrounding the pelvic floor and pelvic floor muscle activation(2).
A better understanding of how these muscles influence each other could be used to enhance pelvic floor muscle function and benefit patient outcome.
The aim of this study was: To describe the effect of the contractions of the muscles surrounding the pelvic floor and the EMG activity of the pelvic floor muscles (PFM) with a bi-polar EMG probe and the MAPLe(3).
Study design, materials and methods
Healthy Pelvic Floor Physiotherapists without complaints of micturition, defecation, sexual dysfunction and or pain and not having pelvic surgery in the past were approached by mail if they want voluntarily participate in this research.
EMG activity for the abdominal, gluteal, abductor, and adductor muscles on the right side of the volunteers was recorded with surface electrodes. In supine the women lay flat with a pillow under the head and with the thighs slightly abducted..
Surface electrode pairs were oriented along the line of action of the underlying muscle fibres on the right side: rectus abdominis (RA), transversus abdominis (TA), external obliques (EO), internal obliques (IO), abductors and adductors. A reference electrode was placed over the right anterior superior iliac spine (ASIS) (Figure 1).
The volunteers were asked to perform the following activities: one minute rest, 10 MVC’s and three (selectively) provoked contractions of the Adductors, Gluteal, Abductors, Rectus Abdominus, Obliques and Transversus Abdominus were performed. Furthermore, EMG was recorded with a bipolar probe (Periform) and repeated with the MAPLe®, a monopolar probe, both placed intra-vaginally.
During the provoked contractions of the muscles surrounding the Pelvic Floor a MicroFET 2® Handheld Dynamometer was used to record resistance force (Newton) to ensure similar effort during the provoked activation.
For the bipolar probe and the muscles surrounding the pelvic floor, raw EMG signals were acquired at a sample rate of 2,048 Hz. For each bipolar signal, the root mean square was calculated using a window of 205 samples (0.1 sec). For the MAPLe, the raw EMG signals were acquired at a sample rate of 1,000 Hz, the root mean square was calculated using a window of 100 samples (0.1 sec) and an average EMG of all 24 electrodes was taken for the analysis in this abstract. For tone at rest, an average was calculated for both probes. For the MVCs and the activity on the probes during a provoked activation an average of the peaks of individual contractions was calculated. The activation of the PFM was compared to tone at rest and MVC with paired T-Tests to find significant differences.
Fifteen volunteers were included in this study with a mean age of 45, 7 years (range; 28-63). Seven women were premenopausal and 8 postmenopausal with a mean of Gravida 1, 2 (range 0-3) and delivery of 1, 3 (range 0-3).
All contractions of muscles surrounding the pelvic floor result in a co-activation of the PFM.
For the MAPLe peak EMG activity for all contractions of the muscles surrounding the pelvic floor were significantly higher than average tone at rest and lower than MVC peak activity, except the peak activity of the abductors. For the bipolar probe this contraction was also significantly lower (Figure 2). In some cases the average peak EMG activity of co-activation of the PFM was higher than the volunteers’ average peak EMG activity of MVC (for the bipolar probe; 7 cases in 3 volunteers, for the MAPLe: 8 cases in 5 volunteers).
During MVC, an increase in EMG activity of the Abdominal, Obliques (IO/EO) and Rectus Abdominus muscle was recorded in 7 out of 15 volunteers.
Interpretation of results
During contraction of all surrounding muscles separately there was a significant increase in peak EMG activity of the pelvic floor compared to the activity of tone at rest. For all surrounding muscles, the peak EMG activity of MVC was significantly lower except for the peak activity of the MAPLe during abductor muscle contraction. This indicates that there is a co-activation of the PFM which is higher than rest, but lower than MVC and not, as some described in literature, crosstalk from the surrounding muscles. Perhaps the recorded co-activation is an involuntary reflex contraction to counteract the sudden increase in pressure or it could be that there is in fact ‘crosstalk’ across different nerves or nerve branches during these types of contractions, causing a contraction of the PFM. This could also be one of the reasons why in some cases the co-activation was higher than the maximal voluntary contraction.
The relation between the muscles surrounding the pelvic floor and the PFM are in line with findings regarding lower back pain and the high incidence of incontinence (some report up to 70%) which could indicate there is a link between the musculature of the lower back and the PFM.
That some volunteers were unable to perform a PFM contraction without also contracting one or more muscles surrounding the pelvic floor is in line with literature.
What the bipolar probe is actually measuring is still unclear; since the use of a bipolar configuration comparing different sides to one-another in combination with large electrodes covering multiple muscle layers is under debate. Next step will be to look at differentiated EMG nearest to individual muscles on different sides and different depths of the pelvic floor, recorded with the MAPLe, to provide even more insight behind the working mechanisms of (co-activation of) the PFM.