Association between musculoskeletal pain at multiple sites and objectively measured physical activity and work capacity: Results from UK Biobank study

Abstract

Objectives

To describe the cross-sectional association between musculoskeletal pain at multiple sites and physical work capacity (PWC) and objectively measured physical activity (PA).

Design

Observational study.

Methods

Data from a subsample of the UK Biobank were utilised (n = 9856; mean age 58.5 years, mean body mass index 30.2 kg/m², 62% female). PWC was measured by a bicycle ergometer and PA by an accelerometer. Pain experienced in hip, knee, back and neck/shoulder was collected by questionnaire. Linear regression modelling was used with adjustment for potential confounders to estimate the association between pain and PWC and PA.

Results

Increase in number of painful sites was associated with lower PWC, moderate and vigorous PA and increased low intensity PA in a dose-response relationship (all p-values for trend ≤0.001) before and after adjustment for confounders. In site specific analyses, hip pain was associated with an increased low intensity PA (β 52.8 min/week, 95% CI 2.3–103.2) and reduced moderate PA (β −50.1 min/week, 95% CI −98.5 to −1.8). Knee pain was only associated with vigorous PA (β −5.7 min/week, 95% CI −10.0 to −1.3). Pain at neck/shoulder pain and back were not independently associated with PWC and PA.

Conclusions

Greater number of painful sites is consistently associated with poorer PWC, increased low intensity PA and reduced moderate to vigorous PA. Clinicians should address the critical role of being physically active in managing chronic musculoskeletal pain and interventions targeting musculoskeletal pain may be needed to increase PA levels.

Introduction

Musculoskeletal pain is a major public health burden worldwide. It is common in western countries with a prevalence estimated as high as 74% in the general population,¹ leading to restrictions in physical function and mobility impairments including decreased balance and gait speed, reduced quality of life and disability.2, 3 Chronic musculoskeletal pain, generally defined as persistent or recurrent pain lasting more than three months, is typically represented by conditions such as low back pain, neck pain, chronic widespread pain (fibromyalgia) and osteoarthritis.4, 5 A recent study of the global burden of the 328 diseases and injuries reported that low back pain, neck pain, other musculoskeletal disorders and osteoarthritis were ranked 1st, 6th, 7th and 12th, respectively, for years lived with disability (YLDs).⁶ Multiple risk factors have been reported to be associated with chronic musculoskeletal pain.4, 5, 7 There is a difference in pain mechanisms underlying acute and chronic pain. In addition to peripheral tissue injury, evidence is growing that central nervous system factor is of prominent importance in the development and persistence of chronic pain.⁹

In pain research, the concept of ‘multi-site’ or ‘multiple site’ pain (MSP) has been proposed; defined as musculoskeletal pain occurring at more than one site, although, currently, an exact definition is still unclear. The prevalence of MSP is approximately 41–75% depending on study population and number of painful sites measured.¹⁰ MSP has been found to be associated with poorer physical and psychological health, worse health-related quality of life, and more severe depressive symptoms as compared to single-site musculoskeletal pain in both cross-sectional and longitudinal studies.11, 12 In addition, several studies reported the adverse effects of MSP on other health outcomes, including risk of falls,¹³ cognitive impairments¹⁴ and sleep quality.¹⁵ There is also evidence to support more pronounced associations with these outcomes as painful sites increase. Many of these outcomes may result from and lead to reduced physical activity (PA).16, 18, 19

Low PA is the fourth leading cause of mortality worldwide. Lack of PA is associated with an increased risk for cardio-metabolic disorders²⁰ such as diabetes and heart diseases; and common mental disorders,²¹ such as depression and anxiety. A recent meta-analysis of eight studies found that older people with musculoskeletal pain are less likely to engage in PA than those without musculoskeletal pain.²² All included studies have relied on a self-reported PA from which it is hard to quantify total PA across different domains. Self-reported activity levels are however poorly correlated with objective measures of PA participation, i.e. accelerometer, with self-reported PA estimates more likely to be higher than those measured by objectively measured PA.²³ This highlights the need for accurate and reliable measurements of PA in assessing the relationship between PA and health outcomes.

Pain experience is a complex and multifactorial nature with multiple domains involved including peripheral, psychological and neurological.²⁴ This heterogeneity leads to the variation in individual pain perception (including pain intensity, frequency and pattern).²⁵ PA offers a broad range of health benefits; however, the mechanisms by which exercise exerts its effects remain unclear. There is evidence from mechanistically-orientated studies of PA and pain relief to support a variety mechanisms, including changes in both the peripheral and central components of the nervous systems,26, 27, 28 reduced level of chronic inflammation/comorbidities,29, 30, 31 muscle strengthening and aerobic capacity32, 33 and improvements in psychological and cognitive function.32, 34 Whilst the causal direction of PA and pain is hard to discern, awareness is increasing that chronic pain is associated with brain structural change,³⁵ psychosocial issues (e.g. fear-avoidance beliefs and behaviours, fear of falling³² and cognitive impairment³⁶), which in turn contribute to reduced PA. To our knowledge, there are no previous studies reporting on the relationship between pain at multiple sites and objectively measured physical work capacity (PWC) and PA. Based on the relationship that chronic pain negatively affects PA and its potential mechanisms, we hypothesised that there is a relationship between pain at multiple sites and reduced physical work capacity (PWC) and PA, and that the relationship was stronger in those with a greater number of painful sites. Therefore, the aim of this study was to describe the association between MSP and objectively measured levels of PWC and PA in a population-based sample from the UK Biobank.