Research Review by Dr. Shawn Thistle©

Date:

June 2007

Study Title:

A clinical tool for office assessment of lumbar spine stabilization endurance: Prone and supine bridge maneuvers

Authors:

Schellenberg KL, Lang JM, Chan KM & Burnham RS

Publication Information:

American Journal of Physical Medicine and Rehabilitation 2007; 86(5): 380-386.

Summary:

There is an abundance of published literature suggesting that dysfunction of the "core musculature" (here defined as the cylinder of muscle surrounding and supporting the lumbar spine) can play a role in the development and proliferation of chronic low back pain (CLBP). Contemporary, evidence-based rehabilitation exercises are now widely in use, aiming to improve the function of these muscles. This type of exercise has shown promise in preventing recurrence and severity in patients suffering from CLBP, particularly those with segmental hypermobility. The exact methods for assessing core stability and implementing rehabilitation strategies is still being determined.

Clinicians are seeking simple in-office methods of measuring spinal stability, but few have been developed and validated. This study aimed to assess the validity and reliability of an office-based measure of lumbar spine stabilization endurance capacity, and establish normative data for two simple exercises in patients with, and without CLBP. There are a variety of exercises thought to be beneficial for training spinal stability, including Dr. Stuart McGill's "Big 3â"- the plank, cross-crawl, and neutral spine curl-up, as well as variations of pelvic or 'glute bridging' - to name a few.

Two simple exercises were investigated in this study - the prone bridge (also known as the "front plank") and supine bridge (also known as a 'glute bridge"'). The first step in this study was to validate the exercises and EMG measurements taken from four muscles: the rectus abdominus, external oblique, hamstring, and lumbar erector spinae. 8 test subjects were involved in the validation before two groups underwent testing – asymptomatic subjects (n=23), and those with CLBP for at least 6 months (n=32).

Asymptomatic subjects were recruited from a local community, and had no history of recent low back pain. CLBP subjects were recruited from primary practice, and had to have LBP for at least six months that was aggravated by activity and relieved by rest. Exclusion criteria were the same for both groups, and included:
  • evidence of spinal infection or neoplasm
  • fracture
  • inflammatory disease
  • neurological impairment
  • history of angina, emphysema
  • shoulder pain in the past 6 months
  • spinal surgery
  • cervical strain or other pain conditions
All subjects completed demographics information, as well as the Oswestry and VAS (Visual Analogue Scale) to indicate pain and disability levels. All subjects performed 2 exercises that were timed to failure or pain (whichever came first). The exercises were performed as follows:
  1. Prone Bridge (Front Plank) - subjects were prone on a mat, propped up on their elbows, which were shoulder width apart, with feet close together but not touching. They then raised their pelvis from the floor into a neutral spine position, maintaining alignment between shoulders, pelvis, hips, and ankles.
  2. Supine Bridge (glute bridge) - in the supine position with knees flexed to 90° with feet flat, the subject would raise their pelvis such that their hips, knees and shoulders were in line. If this position was held for 2 minutes, one leg was straightened in mid air to add rotational torque to the core.
All testing sessions were done with a work:rest ratio of 1:4, and each exercise was repeated to determine test-retest reliability.

Pertinent Results:

  • EMG data indicated that the prone bridge preferentially activated the anterior stabilizers and the supine bridge activated the posterior stabilizers
  • asymptomatic subjects averaged 72 seconds for the prone bridge and 170 seconds for the supine bridge
  • CLBP subjects' times were significantly reduced: average 28 seconds for the prone bridge and 76 seconds for the supine bridge
  • prone:supine time ratios did not differ significantly between groups, and was roughly 0.45
  • males could maintain both bridging positions significantly longer than females
  • bridge duration times were not related to gender, or the subject's reason for stopping (i.e. pain or fatigue)
  • higher prone and supine bridging times correlated with lower levels of pain and disability (from VAS and OSWESTRY)

Conclusions & Practical Application:

Assessing core stability objectively is an important aspect of a comprehensive low back examination. This study not only provided one of the first “normative” data sets for these two exercises, but validated the concept that endurance times on these exercises can separate CLBP patients from those without low back pain. Interestingly, the ratio between prone and supine plank was similar in both groups (roughly 0.45), which suggests that the balance between anterior and posterior core muscle endurance may not be critical in low back pain. This relationship requires further study. Lower endurance times also correlated with higher pain and dysfunction scores on VAS and the OSWESTRY Disability Index.

This study could have been strengthened by utilizing a more detailed EMG evaluation (including gluteus maximus/medius, internal oblique, multifidus, transverse abdominus). This would allow a more detailed description of muscle activation patterns during these exercises, which may shed light on exact roles played by each muscle in stabilizing the spinal column. Recent evidence suggests that optimal stability comes from all of the core muscles working in concert, rather than relying on one or two in particular. This is an important concept to keep in mind when teaching patients these exercises, and monitoring their progress.

The prone and supine bridges are two simple exercises that may be used for assessment, rehabilitation, and outcome monitoring for chronic low back pain patients. Clinicians should familiarize themselves with these, and other core training techniques to better serve this population of patients.