Study highlights role of physical activity in the relationship of BMI, low back pain

Moderate and sedentary activity stratified by BMI showed stronger associations with low back pain.

NEW ORLEANS — A study presented at the North American Spine Society Annual Meeting indicated that small increases in moderate physical activity can reduce the risk of back pain in Americans with higher body mass indices.

“We demonstrated that modest reductions in sedentary time and increases in moderate physical activity have a greater impact on low back pain risk in overweight Americans than on the general population,” Matthew Smuck, MD, associate professor of Orthopaedic Surgery at Stanford University Medical Center, said in his presentation.

The research, which Smuck noted confirms the inverse relationship between body mass index (BMI) and low back pain (LBP) in the U.S. population and is the first to detail the role of physical activity in this relationship, won The Spine Journal Outstanding Paper Award for Medical and Interventional Science.

Monitor to measure activity

To confirm and quantify the relationship between BMI and LBP and to describe the role of physical activity in this relationship, Smuck and colleagues used the NHANES database to study nearly 6,800 subjects who are representative of the U.S. population.

Matthew Smuck

The investigators analyzed the subjects’ self reports of LBP, BMI determined by physical examination, and physical activity determined by accelerometry or a continuous activity monitor used for 7 days.

The investigators found a step-wise increase in LBP risk with increased BMI, and Smuck noted in his presentation there was “a four-fold overall increased risk from normal weight to morbidly obese.”

Specifically, the risk of back pain was 2.9% for normal weight, 5.2% for overweight, 7.7% for obese and 11.6% for morbidly obese Americans based on the World Health Organization BMI standards.

Looking at the overall population, the researchers initially discovered weak associations between activity and the odds ratios for LBP with the greatest predictors being in the vigorous and moderate activity levels. However, when they stratified their findings by BMI, Smuck and colleagues found much stronger associations in the moderate activity and sedentary activity ranges.

Impact of activity on LBP

In the study, investigators discovered that for each population standard deviation increase in the number of minutes in sustained, nonsedentary activity, the odds of LBP occurring in overweight subjects decreased by 17%.

“To put that in other terms, the mean sustained, nonsedentary activity time in this cohort was 114 minutes. [By] increasing that by just 7 minutes, they reduce their back pain risk by 17%,” Smuck, who is chief of Physical Medicine & Rehabilitation and is the medical director of Rehabilitation Services for Stanford Hospitals and Clinics, in Stanford, Calif., said.

In that same group, increasing moderate activity by less than 20 minutes a day reduced the risk of LBP by 32%.

The researchers found similar results for morbidly obese subjects.

Smuck cited the use of a pre-existing dataset and the inability to stratify back pain severity among the weaknesses of the study. – by Gina Brockenbrough, MA

Reference:

Smuck M. Does physical activity influence the relationship between low back pain and obesity? Presented at: North American Spine Society Annual Meeting; Oct. 9-12, 2013; New Orleans.

For more information:

Matthew Smuck, MD, can be reached at Orthopaedic Spine Center, 450 Broadway, ST Pavilion A, Floor 1 MC6110, Redwood City, CA 94063; email: msmuck@stanford.edu.
Disclosure: Smuck has no relevant financial disclosures.