Research Review By Dr. Christopher M. Coulis©

Date Posted:

June 2009

Study Title:

Postural control during prolonged standing in persons with chronic low back pain

Authors:

Lafond D et al.

Author's Affiliations:

University of Quebec, Trois Rivieres, Canada

Publication Information:

Gait & Posture 2009; 29: 421-427.

Background Information:

Numerous factors are involved in the onset of low back pain. One important factor is prolonged standing. Prolonged standing is thought to be associated with negative physical and psychological outcomes and work related low back pain. To illustrate, it is believed that 50% of the healthy population will experience LBP after 2 hours of prolonged standing.

During prolonged standing, healthy individuals are able to alter their postural position through weight shift and sway. Such alteration in posture is believed to reduce stress and fatigue on the musculoskeletal system, thus preventing the onset of discomfort and pain. Conversely, CLBP patients have a decreased ability to shift weight and achieve a single leg stance. They also display decreased postural control adaptability when challenged on a labile surface. It is believed that this makes them more vulnerable to discomfort and pain during prolonged standing.

This paper aimed to investigate postural control strategies during prolonged standing and test whether CLBP patients have a higher frequency of postural alterations and increased sway during prolonged standing compared to healthy subjects.

Pertinent Results:

All participants were able to stand for 30 minutes and made postural changes during that period. However, the number of shifting and drifting patterns in the anterior-posterior and medial-lateral direction, and the speed and frequency of postural changes was significantly different for both groups:

Main Findings
  • CLBP patients exhibited less postural changes during the 30 minutes of prolonged standing, most notably in the Anterior-Posterior direction
  • CLBP patients swayed less than the control group
  • During the 60 second quiet standing period (no movement allowed), subjects with CLBP had greater postural sway than healthy subjects
  • 30 minutes of prolonged standing (PS) did not alter the control group’s ability to stand “quietly” for 60 seconds post-PS, however, the CLBP group increased sway during the post-PS quiet period
  • There was no increase or change in the number or amplitude of positional changes during the entire 30 PS period; a comparison of first 15 min to the second 15 min was the same for each individual group

Clinical Application & Conclusions:

This study utilized 2 distinct methods to assess the sensory-motor function of patients with CLBP. Prolonged standing (PS) was used to test an individual’s ability to voluntarily control their posture and limit musculoskeletal fatigue and discomfort while quiet standing was used to determine the amount of “noise” in the postural control system and its related sub-systems. During both tasks the CLBP group displayed a different response compared to the control group. This may be explained by previous work which has demonstrated a postural “stiffness” in CLBP patients and geriatric subjects. This locomotor “stiffness” has been shown to reduce an individual’s ability to shift weight and achieve a single leg stance and diminish a patient’s postural adaptability to a labile surface (1).

Alternatively, altered proprioceptive input, increased visual dependency and reduced effects of vibratory perturbations on postural control have all been associated with balance dysfunction in subjects with CLBP(2). This may explain the inability to maintain a “silent” posture during the quite period.

Individuals with CLBP have altered sensory motor function. Further work is needed to determine if neuromuscular re-education in conjunction with passive treatment (i.e. spinal manipulation/mobilization, myofascial release, etc.) could improve function and mobility and improve treatment outcomes in these patients.

Study Methods:

12 adults with CLBP and 12 healthy adults without a history of musculoskeletal disorders were recruited for the study.

Inclusion Criteria:
  • LBP for at least 6 months
  • radiating pain (if present) no further than the buttocks
  • normal neurological exam
Exclusion criteria:
  • history of neurological disease
  • history of dizziness and medication with known effects on balance
The subjects were required to stand on a force plate for 32 minutes. Initially for 60 seconds of “quiet” standing without movement, followed by 30 minutes with sway and shift of body weight, followed by another 60 seconds of “quiet” standing. Ground reaction forces were acquired from the force plate and recorded. Three center of pressure (COP) postural patterns were detected:
  1. Shifting – fast movement from one region to another
  2. Fidgeting – fast and large displacement followed by return to original position
  3. Drifting – slow continuous movement
COP patterns were analyzed for direction (A-P and M-L directions), speed, power, and area covered.

Study Strengths / Weaknesses:

Weaknesses of this study:
  • The authors did not assess the perception of low back discomfort, general fatigue, and alterations in proprioceptive input before and immediately after the PS period
  • The authors did not monitor the occupational or recreational activities of the subjects, these could play a role in lumbar spine strength and endurance
  • The sample size was small, and there was no mention if power was attained

Additional References:

  1. Byl NN, Gray JM. Complex balance reactions in different sensory conditions: adolescents with and without idiopathic scoliosis. J Orthop Res 1993; 11:215-27.
  2. Mok NW, Brauer SG, Hodges PW. Hip strategy for balance control in quiet standing is reduced in people with low back pain. Spine. 2004; 29:E107-112.