Electrode Placement of the Abdominal Muscles
By Jeffrey R. Cram, PhD
In placing sEMG electrodes in the abdominal area, there is a multibellied muscle for the rectus, but the belly of the obliques muscle is impossible to find. This article will focus on placement and recording for the rectus abdominis and the external abdominal obliques.
Rectus Abdominis Placement
Recording from this muscle is considered to yield specific recordings. The only mitigating factor of this specificity is the thickness of the adipose tissue. Its primary action is that of trunk flexion, and clinically, the pelvic tilt.
This multibellied muscle arises from the third to fifth rib and the xiphoid process and inserts into the crest of the pelvic bone. It is innervated by the intercostal nerves via the ventral rami from T5 to T12. Its clinical uses typically are to treat abdominal and back pain.
Fig. 1. Electrode placement for the rectus abdominis placement. (illustrations/courtesy Clinical Resources, Nevada City).
To place electrodes over this muscle, palpate the abdominal wall in the area close to
the umbilicus. Locate, to the best of your ability, the muscle mass.
A thick pad of adipose tissue may be a problem. The electrodes are placed 3
cm apart and parallel to the muscle fibers of the rectus abdominis such that they are located approximately 2 cm lateral and across from the umbilicus over
the muscle belly (Fig. 1).
This site is affected by the
degree of anterior vs. posterior pelvic tilt. It has its greatest level of activation when the body weight is carried on the back rather than the thighs.
Values may differ greatly as the patient moves from the sitting to standing posture. During a sit-up, the greatest level of activation is noted during the first 45 degrees of flexion (Fig. 2).
Fig. 2. sEMG recordings from the rectus abdominis and abdominal obliques are shown during a curl up (partial sit-up) at midline from a supine position.
External Abdominal Oblique Placement
Recordings from this site are considered quasispecific due to possible cross talk from quadratus lumbar, latissimus dorsi and internal obliques. Its primary function is that of flexion, rotation and side bending of the torso. This rather broad muscle arises from the fifth to 12th ribs, interdigitating with serratus anterior on the upper ribs and with the latissimus dorsi on the lower ribs, passes downward and medially inserting on the iliac crest and the abdominal aponeurosis at the midline. It is innervated by the intercostal nerve via the ventral rami from T8 to T12. Its clinical use is in the assessment and treatment of back pain and urinary incontinence.
To place electrodes at this site, palpate the iliac crest and locate the anterior superior iliac spine (ASIS).
Two active electrodes are placed 2 cm apart, lateral to the rectus abdominis directly above the ASIS, half-way between the crest and the ribs, at a slightly oblique angle that they run parallel to the muscle fibers (Fig. 3).
While this placement will primarily record from the external oblique due to its superficial nature, recording from the internal obliques may be significant in some individuals and probably depends upon the depth of adipose tissue and movement strategy.
When the pelvis is fixed, the ipsilateral external obliques are known to rotate the homolateral shoulder forward. However, most of the internal obliques rotate the homolateral shoulder backward. Thus, when studying rotational movement patterns at this site, paradoxical results may be found.
The resting values at this site may vary dramatically as one goes from the sitting to the standing posture. The degree of pelvic tilt may also moderate the resting sEMG levels.
Leg length discrepancies would certainly alter the horizontal axis of the pelvis thus providing a basis for asymmetries at this site, as would scoliosis. The practitioner should also be alert to the possibility of antalgic postures that could affect the resting sEMG levels and alter timing issues during dynamic movement.
Fig. 3. Electrode placement for external abdominal obliques.
* For more information, call (530) 478-9660.
Dr. Cram is the director of the Sierra Health Institute in Nevada City, CA, where he treats patients and teaches workshops on surface EMG. He is the co-author of three books on surface EMG including Introduction to Surface EMG (Frederick, MD: Aspen Publishers).