It’s well known in the low back pain (LBP) field that conservative interventions have small to moderate effects at best.[1] Frustration with these small effects has prompted researchers to shift their attention to identifying prognostic factors. Prognostic factors are baseline factors that are associated with a worse or better disease outcome at a given time. Studies investigating prognostic factors are useful for clinicians because they can use this information to help patients to better understand the disease process and predict disease outcome more accurately, to identify target groups for treatment, or to target specific factors that could be modified using intervention.[2]
Our group recently published a paper in the European Journal of Pain investigating the prognostic value of leisure-time physical activity in people seeking care for LBP.[3] As we would expect, engaging in physical activity during one’s leisure time offers a long list of health benefits. There are a few population-based studies which have shown that participation in leisure-time physical activity is associated with increased muscle strength, decreased bone loss and better physical functioning. We should also bear in mind that the benefits of physical activity extend far beyond the physical domain. There is some evidence, for instance, that leisure-time physical activity improves mood and quality of life and prevents social isolation and loneliness. Leisure-time physical activity is a modifiable factor and may have an important place as a self-management strategy for LBP. However, whether levels of leisure-time physical activity would influence the course of back pain in those patients seeking care for chronic and persistent LBP was not clear – and this was the question which drove our research.
This study was an interesting collaboration between Denmark, Brazil and Australia: it was led by a Brazilian PhD student from an Australian research institute (The George Institute for Global Health – University of Sydney), it used data from a Danish outpatient spine centre, and it had co-authors from the University of Southern Denmark and the University of Sydney. This was a longitudinal study with 1-year follow-up, and it included data from more than 800 patients with LBP. Our aim was to investigate whether levels of leisure-time physical activity predict pain and disability at 1-year follow-up in people seeking care for LBP.
What did we find? Our results revealed that people with back pain who engaged in moderate-to-vigorous leisure-time physical activity showed less pain and disability one year later than those patients in the sedentary group. Although this result showed statistical significance, it is also important to look at the size of the effect (i.e. mean difference) and its precision (i.e. 95% confidence interval). So, let’s look at the size of the effect: our results for the outcome disability (measured on a 0 to 100 self-rating scale) showed that the ‘moderate’ group scored an average of 9 points lower than the ‘sedentary’ group. Although I would argue that nearly 10% difference in disability between groups could be considered a clinically important prognostic factor (my own opinion based on the proposed threshold for minimal clinically important change in the LBP field), the wide 95% confidence interval of the mean difference shows considerable imprecision: the true mean difference in disability between groups could be as low as 3 points or as high as 14 points. This lack of precision might be due to several factors. One is that this study used a self-reported measure of leisure-time physical activity. Although this measure has been shown to be valid and reliable, it is a single, non-specific question involving a combination of physical activity domains – not only leisure time or recreational activities, but also exercise/sport (i.e. more vigorous activities than usual everyday activities) and household (i.e. home activities and/or gardening) activities. Another issue related to self-reported measures is that they are prone to recall bias and are less precise than objective measures for recording the intensity, frequency and duration of physical activity.[4]
Our results also allowed us to compare the prevalence of sedentarism in our cohort with that found by previous studies that used the same questionnaire. We found that around a fifth (21%) of the cohort sample were classified as sedentary. Other studies have reported a comparable proportion of sedentary people (17-23%) in the general population and general working population. This finding is contrary to the view that patients’ activity levels may decrease after pain onset. Our result, therefore, adds to mounting evidence that it is unclear whether physical reconditioning might be considered as a potential target for effective intervention in people suffering from chronic back pain. This is the opposite of what we would expect, for instance, in the area of non-communicable diseases such as coronary heart disease and diabetes in which sedentarism is highly prevalent and associated with decreased life expectancy. In this case, regular physical activity is considered a guideline endorsed treatment and prevention strategy.
What is the next step then? My research group now located at the São Paulo State University in Brazil (Universidade Estadual Paulista – UNESP) is now conducting a series of studies looking at the role of objective measures as well as different domains of physical activity in LBP prognosis. We have been collaborating with a few researchers from Australia and the Netherlands. There is a long road ahead to explore, so we would welcome anyone interested in this topic. Feel free to contact me directly or leave a comment below.
About Rafael Zambelli Pinto
Dr Rafael Zambelli Pinto is a Brazilian physiotherapist who travelled all the way to Australia for his PhD. Rafael completed his PhD in mid-2013 at The George Institute of Global Health in Sydney. Soon after that he joined the Pain Management Research Institute where he stayed for just more than a year. He found a home back in Brazil as a lecturer in the physiotherapy department at the São Paulo State University where he keeps his research alive. Rafael can be contact at: rafael.z.p@fct.unesp.br
References
[1] Keller A, Hayden J, Bombardier C, & van Tulder M (2007). Effect sizes of non-surgical treatments of non-specific low-back pain. Eur Spine J, 16 (11), 1776-88 PMID: 17619914
[2] Altman DG, & Lyman GH (1998). Methodological challenges in the evaluation of prognostic factors in breast cancer. Breast cancer Res Treat, 52 (1-3), 289-303 PMID: 10066088
[3] Pinto RZ, Ferreira PH, Kongsted A, Ferreira ML, Maher CG, & Kent P (2014). Self-reported moderate-to-vigorous leisure time physical activity predicts less pain and disability over 12 months in chronic and persistent low back pain. Eur J Pain, 18 (8), 1190-8 PMID: 24577780
[4] Janz KF (2006). Physical activity in epidemiology: moving from questionnaire to objective measurement. Br J Sports Med, 40 (3), 191-2 PMID: 16505072