Total physical activity and risk of chronic low back and knee pain in middle-aged and elderly Japanese people: The Murakami cohort study

Background Specific components of physical activity, such as vigorous exercise and heavy occupational work, are known to increase the risk of chronic low back pain (CLBP) and chronic knee pain (CKP), but impacts of other components are less known. This study aimed to assess the relationship between total physical activity and risk of CLBP and CKP from a public health perspective. Methods Participants were 7,565 individuals, aged 40-74 years, who did not have CLBP or CKP, and who participated in the 5-year follow-up survey. A self-administered questionnaire was used to obtain information on demographics, body size and lifestyle (including physical activity) in the baseline survey in 2011-2013, and on CLBP and CKP using Short Form 36 (SF-36) in the follow-up survey. Sitting, standing, walking and strenuous work for occupational activity were assessed for total physical activity, and walking slowly, walking quickly, light to moderate exercise and strenuous exercise were assessed for leisure-time physical activity using metabolic equivalent hours/day (METs score). Results Mean age of participants was 60.1 years (SD, 8.8). Participants with higher METs scores had a significantly higher risk of CKP (p for trend = 0.0089, OR of 4th quartile = 1.29, 95% CI: 1.04-1.59 vs. 1st quartile), but not CLBP. An intermediate leisure-time METs score was associated with a lower risk of CLBP (OR = 0.75, 95%CI: 0.61-0.92 vs. 0 METs-group). Conclusions A high level of total physical activity may increase the risk of CKP, whereas an intermediate level of leisure-time physical activity may decrease the risk of CLBP, in middle-aged and elderly individuals. Significance Evidence on the longitudinal association between total physical activity and CLBP and CKP in middle-aged and elderly people is lacking. We conducted a cohort study to assess this association, and found that high levels of total physical activity increased risk of CKP, and intermediate levels of leisure-time physical activity decreased risk of CLBP. This suggests that the effect of physical activity on chronic pain differed by pain site.