To study the effects of obesity, physical activity, and change in physical activity on the incidence of low back pain and explore whether obesity modifies the effects of physical activity.
As part of the ongoing Young Finns Study, 1224 subjects aged 24-39 years free from low back pain during the preceding 12 months at baseline in 2001 were included. Obesity was defined based on the body mass index (BMI) and waist circumference, and physical activity was assessed by the metabolic equivalent of task (MET) index in 2001 and 2007.
Abdominal obesity, defined by an increased waist circumference, was associated with an increased incidence of radiating low back pain (adjusted odds ratio (OR) = 1.7 and 95% confidence interval (CI) 1.1-2.7), while it had no effect on non-specific low back pain. BMI was associated neither with the incidence of radiating low back pain nor with non-specific low back pain. Compared with subjects who stayed active during follow-up, those with a low level of physical activity (adjusted OR = 2.0 and 95% CI 1.1-3.5) and active subjects who further increased their physical activity during follow-up (OR = 3.1 and 95% CI 1.5-6.7) had a higher incidence of radiating low back pain. Low level of physical activity was associated with an increased incidence of radiating low back pain in obese (OR = 3.3 and 95% 1.1-10.4), but not in non-overweight subjects (OR = 1.1 and 95% CI 0.6-1.9). Physical activity was not associated with non-specific low back pain.
Our findings indicate that both obesity and low level of physical activity are independent risk factors of radiating low back pain. The current findings propose a U-shaped relation between physical activity and radiating low back pain. Moderate level of physical activity is recommended for the prevention of low back pain, especially in obese individuals. In all, our findings imply that obese individuals should stay physically active, even if they may not lose weight.