Predictors of low back pain in physically active conscripts with special emphasis on muscular fitness

Background context: Association between low physical fitness and low back pain (LBP) is contradictory in previous studies. Purpose: The objective of the present prospective cohort study was to investigate the predictive associations of various intrinsic risk factors in young conscripts for LBP, with special attention to physical fitness. Study design: A prospective cohort study. Patient sample: A representative sample of Finnish male conscripts. In Finland, military service is compulsory for male citizens and 90% of young men enter into the service. Outcome measures: Incidence of LBP and recurrent LBP prompting a visit at the garrison health clinic during 6-month military training. Methods: Four successive cohorts of 18- to 28-year-old male conscripts (N=982) were followed for 6 months. Conscripts with incidence of LBP were identified and treated at the garrison clinic. Predictive associations between intrinsic risk factors and LBP were examined using multivariate Cox proportional hazard models. Results: The cumulative incidence of LBP was 16%, the incidence rate being 1.2 (95% confidence interval [CI], 1.0-1.4) per 1,000 person-days. Conscripts with low educational level had increased risk for incidence of LBP (hazard ratio [HR], 1.6: 95% CI, 1.1-2.3). Conscripts with low dynamic trunk muscle endurance and low aerobic endurance simultaneously (ie, having coimpairment) at baseline also had an increased risk for incidence of LBP. The strongest risk factor was coimpairment of trunk muscular endurance in tests of back lift and push-up (HR, 2.8: 95% CI, 1.4-5.9). Conclusions: The increased risk for LBP was observed among young men who had a low educational level and poor fitness level in both muscular and aerobic performance.