Baseline characteristics of study subjects
| Characteristics | PMU (n=43) | DBC (n=43) | BB (n=40) |
| Demographic features | |||
| Age, years | 45 (9) | 44 (8) | 45 (7) |
| Male, % | 65 | 72 | 68 |
| Married, % | 81 | 84 | 70 |
| Body mass index, kg/m2 | 26 | 28 | 28 |
| Smoking, % | 31 | 40 | 40 |
| High school diploma or vocational degree, % | 67 | 56 | 58 |
| General health | |||
| Self-rated health status moderate or better, % | 95 | 88 | 95 |
| Previous low back operation, % | 5 | 2 | 8 |
| Duration of LBP, years | 13 | 10 | 14 |
| Previous rehabilitation for LBP or active self-care, % | 28 | 35 | 35 |
| Medical history of chronic morbidity other than LBP, % | 33 | 30 | 30 |
| Physical activity twice or more/week before LBP, % | 77 | 65 | 68 |
| Work related features | |||
| Blue collar, % | 74 | 77 | 90 |
| Shift work, %† | 43 | 28 | 39 |
| Physical work load (1–5)‡ | 3.2 (1.0) | 3.1 (0.8) | 2.7 (0.8) |
| Mental work load (1–5)‡ | 2.5 (0.9) | 2.8 (0.8) | 2.9 (0.8) |
| Work ability (0–10)§ | 6.8 (2.0) | 7.1 (1.7) | 6.8 (2.4) |
| At least some or more work control, % | 65 | 72 | 68 |
| Total sickness absence days in previous year* | 16 | 21 | 19 |
| Screening criteria | |||
| Intensity of pain in past week (VAS, 0–100) | 60 | 55 | 60 |
| LBP radiating below the knee, % | 51 | 51 | 45 |
| Subacute LBP for 2 weeks or more in previous year, % | 56 | 44 | 53 |
| Recurrent LBP (more than once/year), % | 86 | 95 | 93 |
| Self-reported LBP work absence in previous year, % | 33 | 37 | 40 |
| Outcome variable at randomisation | |||
| Intensity of pain (past week) (VAS, 0–100 mm) | 43 (23) | 39 (24) | 34 (25) |
| Physical impairment (RM-18, 0–18) | 8 (5) | 6 (5) | 6 (5) |
| Disability (ODI, 0–100), % | 21 (13) | 17 (12) | 16 (11) |
| Fear of pain (FABQ, 13–78) | 37 (14) | 35 (11) | 32 (12) |
| Depression (DEPS, 0–30) | 6 (4) | 4 (5) | 4 (4.0) |
| HRQoL score (15D, 0–1) | 0.8681 | 0.8884 | 0.8932 |
Values are mean (SD) unless otherwise stated. Range (when applicable) is presented after the variable name in parenthesis.
↵* Register data.
↵† Two-shift or three-shift work.
↵‡ Range 1–5 indicates self-rated load level: 1=very heavy, 2=moderate, 3=intermediate, 4=rather light, 5=very light.
↵§ Range 0–10, where 0 is the is the lowest possible work ability and 10 is the best possible work ability.
BB, Back Book intervention group; DBC, progressive back specific exercises group; HRQoL, health related quality of life; LBP, low back pain; PMU, hospital physical medicine unit group; VAS, visual analogue scale.