Research Review by Dr. Shawn Thistle©

Date:

Aug. 2005

Study Title:

Abdominal muscle recruitment during a range of voluntary exercises

Authors:

Urquhart DM, Hodges PW, Allen TJ, Story IH

Publication Information:

Manual Therapy 2005; 10: 144-153.

Summary:

Treatment of low back pain has recently shifted toward restoring proper muscular function of the abdominal wall and low back muscles - the ever popular "core muscles". Despite this common approach to the treatment or prevention of low back pain, little is known about the exact muscle recruitment patterns during commonly used exercises.
This study examined the activation of different regions of the transverse abdominus (TrA), internal and external obliques (IO and EO respectively), and rectus abdominus (RA), as well as lumbar spine and pelvic movement during four commonly used, basic movements:
  1. inward movement of the lower abdominal wall
  2. abdominal bracing (lateral and anterior flaring of the abdominal wall)
  3. posterior pelvic tilting
  4. combined inward movement of the upper and lower abdominal wall
All movements were done in prone and supine positions, and were performed with a "mild" muscular effort (2 rating on a Borg exertion scale), mimicking contemporary exercise interventions which focus on low level contractions of the stabilizing muscles. Fine needle EMG electrodes were used to record muscular activity and were inserted using real-time ultrasound imaging to ensure accuracy.

Lumbar spine and pelvic motion were recorded using digital video and LED markers on the spinous process of L3 and the anterior superior iliac spine (ASIS). EMG signals were normalized using maximal contractions (MVC), and each movement was performed three times in random order.

Pertinent Results:

  1. TrA activation was best achieved during inward movement of the lower abdominal wall in a supine position - activation was 70%, 100%, and 65% greater that IO, EO, and RA respectively in this position
  2. during abdominal bracing, EO activity was greater than that of the upper TrA, IO, and RA
  3. lumbar spine and pelvic motion was minimal and did not differ between tasks (except posterior pelvic tilting)
  4. there was a significant negative correlation between lumbar spine and pelvic motion and activation of the TrA, while pelvic and lumbar spine motion seemed to increase EO activity

Conclusions & Practical Application:

Although this study did not investigate common exercises per se (such as McGill's "big three") it did investigate some basic movements and instructions that are often given prior to exercise, or very early in low back pain rehabilitation programs. One of the main advantages of this study was that fine needle electrodes were utilized to obtain the EMG recordings.

This technique is commonly thought to provide more accurate readings than surface EMG, particularly in the abdominal wall region. However, due to the invasive nature of this study, only seven subjects were used. Although this is consistent with similar studies in this area, it may limit the statistical power of this study.

From a clinical perspective, this study provides some useful information:
  1. if the goal is to preferentially activate the TrA, inward movement of the lower abdominal wall in a supine position seems to work best
  2. further, in order to minimize EO activity, lumbar spine and pelvic motion should be minimized to maximally activate the TrA
  3. abdominal bracing is not appropriate if the goal of an exercise or movement is to activate the TrA
Preventing and treating low back pain is a complex clinical task. This small study investigated what I consider early phase techniques in a rehabilitation program - that is, establishing proper activation patterns and motor control of the core region. This is usually followed by coordinated incorporation of movements and exercises that functionally train the entire body.

More research is needed to determine the exact movements and instructions we can provide to patients to achieve optimal activation of the abdominal wall muscles to provide stability to the lumbar spine region, and also the best way to progress patients through stability exercises.