Physical fitness as a predictor of herniated lumbar disc disease – a 33-year follow-up in the Copenhagen male study

BACKGROUND The role of physical fitness (VO2Max (mlO2*min-1*kg-1)) as a risk factor for herniated lumbar disc disease (HLDD) is unknown. The objective of this study was to examine the association between aerobic (physical) fitness and risk of hospitalisation due to HLDD in a long-term follow up. METHODS The Copenhagen Male Study is a prospective cohort study established in 1970-71. At baseline, 5,249 men answered a questionnaire about their history of back disease, physical and psychosocial working conditions, lifestyle and social class. Height and weight was measured and aerobic capacity (physical fitness) was estimated based on a submaximal bicycle test. Information about hospitalization due to HLDD was obtained from the National Hospital Register covering the period 1977 - 2003. Hazard Ratios (HR) were calculated by Cox's proportional hazard regression model. RESULTS Among 3,833 men without history of low back disorders, 64 were hospitalized due to HLDD. The cumulative incidence of HLDD was 1.7% (n=34) among men with low physical fitness (15-32 ml O2*min-1*kg-1), and 1.7% (n=30) among men with high physical fitness (33-78 ml O2*min-1*kg-1). In a final model, adjusted for relevant confounders, the HR (95% CI) for HLDD for those with high physical fitness was 0.88 (0.51-1.50) compared to those with low physical fitness. In the same model, HR for men often exposed to strenuous work compared to those seldom or never exposed to strenuous work was 3.91(1.82-8.38). Also body height was a significant predictor. CONCLUSIONS Physical fitness is not associated with hospitalisation due to HLDD, and the only modifiable risk factor for hospitalisation due to HLDD seems to be strenuousness at work.