Elsevier

The Spine Journal

Volume 14, Issue 2, 1 February 2014, Pages 209-216
The Spine Journal

2013 Outstanding Paper Winner: Medical and Interventional Science
Does physical activity influence the relationship between low back pain and obesity?

https://doi.org/10.1016/j.spinee.2013.11.010Get rights and content

Abstract

Background context

Evidence supporting an association between obesity and low back pain (LBP) continues to grow; yet little is known about the cause and effect of this relationship. Even less is known about the mechanisms linking the two. Physical activity is a logical suspect, but no study has demonstrated its role.

Purpose

This study was designed to examine the interrelationship between physical activity, obesity, and LBP. The specific aims were to determine if obesity is a risk factor for LBP in the U.S. population, measure the strength of any observed association, and evaluate the role of physical activity in modulating this association.

Study design/setting

A cross-sectional U.S. population-based study.

Patient sample

A cohort of 6,796 adults from the 2003–2004 National Health and Nutrition Examination Survey.

Outcome measures

Demographic information, an in-depth health questionnaire, physical examination details, and 7-day free-living physical activity monitoring using accelerometry (ActiGraph AM-7164; ActiGraph, Pensacola, FL, USA).

Methods

LBP status was determined by questionnaire response. Body mass index (BMI) was calculated during physical examination and divided here into four groups (normal weight <25, overweight 25–30, obese 31–35, and ultraobese 36+). Summary measures of physical activity were computed based on intensity cutoffs, percentile intensities, and bout. Demographics, social history, and comorbid health conditions were used to build adjusted weighted logistic regression models constructed using Akaike Information Criterion. All displayed estimates are significant at level <.05. No external funding was received to support this study. None of the authors report conflicts of interest directly related to the specific subject matter of this manuscript.

Results

In the U.S. population, the risk of low LBP increases in step with BMI from 2.9% for normal BMI (20–25) to 5.2% for overweight (26–30), 7.7% for obese (31–35), and 11.6% for ultraobese (36+). Smoking is consistently the strongest predictor of LBP across the BMI spectrum (odds ratio 1.6–2.9). Physical activity also modulates these risks. In the overall model, the best physical activity predictors of LBP are in the moderate and high intensity ranges with small effects (odds ratio 0.98 and 0.996 per standard deviation increase, respectively). When broken down by BMI, time spent in sedentary and moderate activity ranges demonstrate more robust influences on LBP status in the overweight, obese, and ultraobese groups.

Conclusions

Increased BMI is a risk factor for back pain in Americans. More important, the role of physical activity in mitigating back pain risk is shown to be of greater consequence in the overweight and obese populations.

Introduction

Obesity, like back pain, negatively impacts health-related quality of life and productivity. Combined they are associated with an estimated 30% of U.S. health care expenditures [1], [2]. Studies of back pain often list obesity as a confounding factor, yet research has failed to consistently demonstrate this association [3], [4]. Still, the growing consensus among higher quality studies supports the presence of a positive association. Large population studies in Europe, for instance, have consistently demonstrated a link between obesity and chronic low back pain (LBP) [5], [6], [7], and two independent and well-conducted surveys each found that obese individuals with a body mass index (BMI) >30 are 1.7 times more likely to develop disabling back pain compared with healthy weight individuals [5], [8]

Although evidence of the association between obesity and back pain continues to grow, little is known about the cause-and-effect relationship [9], and even less is known about the potential mechanisms linking the two [3], [4]. Structural, mechanical, metabolic, and behavioral factors are all implicated [4], [10]. Of these factors, physical activity is a logical suspect. An inverse relationship between physical activity and obesity is well documented [11], [12], [13], with a similar inverse relationship to back pain suggested but less well defined [14], [15], [16], [17], [18], [19]. Furthermore, both exercise and weight loss is known to benefit some with back pain [14], [15], [20]. Yet, no study has shown that physical activity plays any role in the relationship between obesity and back pain.

The purpose of this study is to examine the interrelationship between physical activity, obesity, and LBP using the 2003–2004 National Health and Nutrition Examination Survey. Specifically, this study seeks to determine if obesity is a risk factor for back pain in the U.S. population, measure the strength of any observed association, and evaluate the role of physical activity in modulating this association.

Section snippets

Materials and methods

The dataset used in this study is publically available; thus, review board approval was not required. No external funding was received or used to support this study. None of the authors reports conflicts of interest directly related to the specific subject matter of this manuscript.

Results

To better measure the association of physical activity with LBP, we adjust for and remove the influences of known confounders. That is, we incorporate known and measured confounder variables in a multivariate regression model to minimize their effects. Once this is done, we study predictors of adjusted LBP risk as a function of various measures of physical activity as measured by accelerometry.

Weighted logistic regression models were constructed that incorporate age, gender, race, income,

Key findings

The results of this study confirm that increased BMI is a risk factor for low back pain in the general U.S. population. Similar to findings in studies of the British, Danish, and Norwegian populations [5], [6], [7], this investigation demonstrates a stepwise increase in risk of LBP with BMI, up to a fourfold increase in the morbidly obese population (BMI 36+). The magnitude of this effect is in line with that observed in some nationalities [5], but exceeds that of others [6], [7]. Variations in

Conclusions

This study provides strong evidence that increased BMI is a risk factor for back pain in Americans. It also shows that reduced physical activity is an independent risk factor for LBP. Most important, the role of physical activity in mitigating back pain risk is shown to be of greater consequence in the overweight population. Because this is a cross-sectional study, the cause and effect of these relationships cannot be determined; however, the instruments used in this study can be adopted by

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  • Cited by (0)

    FDA device/drug status: Not applicable.

    Author disclosures: MS: Consulting: Arthrocare Corp (B); Speaking and/or Teaching Arrangements: North American Spine Society (Instructional Course Honoraria); Trips/Travel: North American Spine Society (Airfare reimbursement); Board of Directors: The Spine Journal (None); Grants: Cytonics Corp (F, Paid directly to institution/employer). M-CJK: Nothing to disclose. NB: Nothing to disclose. AM-I: Nothing to disclose. JC: Nothing to disclose. CCT-L: Nothing to disclose.

    The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.

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