Lifetime Physical Loading and Magnetic Resonance-Derived Intervertebral Disc Health in Adults With Chronic Low Back Pain: A Cross-Sectional Study

Background: The intervertebral disc (IVD) is a mechanosensitive structure influenced by physical loading (physical activity/sport/exercise); however, the optimal type and parameters of physical loading for IVD health remain unclear. The Bone Physical Activity Questionnaire is validated to predict bone mineral density from lifetime exposure to physical loading; therefore, we explored the association between lifetime physical loading and IVD health. Methods: This cross-sectional study recruited 40 individuals with chronic low back pain. Outcomes were magnetic resonance imaging-derived IVD measures reported as both averages and across individual spinal levels T11/T12–L5/S1, including T2 (ms, measure of hydration), height-to-vertebral-body ratio, nucleus-to-annulus signal intensity ratio, volume (cm³), and Pfirrmann grade (0–5 points). Multiple linear regression examined lifetime physical loading and IVD health while controlling for significant covariates (age, body mass index, current and past occupational sitting, and physical labour). Results: Lifetime bone-related physical loading was not associated with IVD health across average spine values, except nucleus-to-annulus signal intensity ratio, which was negatively associated (β [95% CI]: −0.00 [−0.01, −0.00], p = 0.030). At L5/S1, IVD T2 (−0.30 [−0.56, −0.05], p = 0.022) and nucleus-to-annulus signal intensity (−0.02 [−0.03, −0.01], p = 0.007) were negatively associated, and Pfirrmann grade (0.02 [0.01, 0.03], p = 0.006) was positively associated with physical loading. Conclusions: Physical activity loading necessary for improved IVD health appears to differ from loading previously reported for optimal bone health. Specifically, lifetime activity levels considered beneficial for bone were associated with less favourable L5/S1 IVD characteristics, highlighting distinct loading requirements across these tissues. Future studies could develop a questionnaire that captures optimal physical loading for IVD health, such as moderate physical loading.