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Table 3 Hazard ratios (HR) for any overuse injury (OI) and severe overuse injury (severe OI) incidence by most important socioeconomic, health and health behaviour variables at baseline

From: Risk factors of acute and overuse musculoskeletal injuries among young conscripts: a population-based cohort study

Baseline variable Category Total number (% of experienced OI; % of experienced severe OI) HR for OI incidence (n = 721)* HR for OI incidence (n = 634)** HR for severe OI incidence (≥7 service days lost) (n = 251)* HR for severe OI incidence (≥7 service days lost) (n = 212)**
Socioeconomic variables      
Age 18–19 years 1052 (50; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  20–28 years 359 (54; 19) 1.2 (1.0–1.4) 1.2 (1.0–1.5) 1.2 (0.9–1.6) 1.1 (0.8–1.5)
Father's occupation Not physical 488 (49; 16) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Physical 590 (51; 19) 1.1 (0.9–1.3) 1.0 (0.8–1.2) 1.2 (0.9–1.6) 1.1 (0.8–1.5)
  Unclear or unemployed 302 (55; 19) 1.3 (1.0–1.6) 1.3 (1.0–1.6) 1.2 (0.8–1.7) 1.3 (0.9–1.8)
School success (educational level and grades combined) Excellent1 218 (36; 10) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good2 608 (53; 18) 1.7 (1.4–2.2) 1.6 (1.2–2.0) 1.9 (1.2–3.1) 1.5 (0.9–2.4)
Satisfactory3 467 (54; 21) 1.9 (1.5–2.4) 1.4 (1.1–1.9) 2.4 (1.5–3.9) 1.4 (0.9–2.4)
  Poor4 96 (60; 22) 2.4 (1.7–3.4) 1.9 (1.3–2.7) 2.8 (1.5–5.1) 1.9 (1.0–3.6)
Company Anti–tank company 263 (52; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Signal company 540 (56; 20) 1.2 (1.0–1.4) 1.2 (0.9–1.4) 1.3 (0.9–1.8) 1.2 (0.8–1.7)
  Mortar company 363 (39; 12) 0.9 (0.7–1.1) 1.0 (0.7–1.2) 0.9 (0.6–1.4) 0.8 (0.5–1.3)
  Engineer company 245 (56; 21) 1.1 (0.9–1.4) 1.2 (0.9–1.5) 1.3 (0.9–1.9) 1.2 (0.8–1.9)
Health variables       
Body mass index5 (BMI = (kg)/(m)2) Underweight (<18.5) 56 (61; 25) 1.5 (1.1–2.1) 1.7 (1.1–2.4) 1.8 (1.0–3.1) 2.0 (1.1–3.5)
Normal (18.5 − 25.0) 812 (49; 16) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Pre–obese (25.0 − 30.0) 300 (49; 13) 1.0 (0.8–1.2) 1.0 (0.8–1.2) 0.8 (0.6–1.1) 0.8 (0.5–1.1)
  Obese (≥30.0) 104 (60; 25) 1.4 (1.1–1.9) 1.3 (1.0–1.8) 1.7 (1.1–2.5) 1.3 (0.8–2.2)
Waist circumference (WC, cm) Thin (<80 cm) 271 (48; 17) 1.0 (0.8–1.3) 1.1 (0.9–1.3) 1.2 (0.9–1.7) 1.2 (0.9–1.8)
Average (80 – 93.5 cm) 739 (50; 16) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Increased (94 – 101.5 cm) 178 (52; 15) 1.1 (0.9–1.4) 1.1 (0.8–1.4) 0.9 (0.6–1.4) 0.8 (0.5–1.3)
  High (≥102 cm) 122 (58; 24) 1.4 (1.1–1.8) 1.5 (1.1–2.0) 1.7 (1.1–2.6) 1.7 (1.1–2.7)
Self–assessed health6 Good or very good 743 (47; 14) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Average or inferior 646 (56; 22) 1.5 (1.3–1.7) 1.1 (0.9–1.3) 1.9 (1.4–2.4) 1.2 (0.9–1.6)
Sum factor of musculoskeletal symptoms Minimal symptoms7 440 (42; 10) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Mild symptoms8 548 (51; 18) 1.4 (1.2–1.7) 1.5 (1.2–1.9) 1.9 (1.3–2.8) 2.1 (1.4–3.2)
Clear symptoms9 400 (61; 26) 2.0 (1.6–2.4) 1.9 (1.6–2.4) 3.1 (2.2–4.4) 3.3 (2.2–5.0)
Chronic disease No 1012 (50; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Yes 377 (53; 20) 1.1 (0.9–1.3) 1.1 (0.9–1.3) 1.2 (0.9–1.6) 1.2 (0.9–1.6)
Orthopaedic surgery Never 1273 (50; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Yes 114 (60; 24) 1.3 (1.0–1.6) 1.3 (1.0–1.7) 1.4 (1.0–2.1) 1.5 (1.0–2.3)
Chronic impairment or disability10 No 1165 (49; 16) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Yes 219 (60; 26) 1.5 (1.2–1.8) 1.2 (1.0–1.5) 1.8 (1.4–2.4) 1.5 (1.1–2.1)
Sports injury during last month No 1254 (50; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Yes 130 (65; 23) 1.5 (1.2–1.9) 1.4 (1.1–1.9) 1.4 (1.0–2.1) 1.3 (0.8–1.9)
Health behaviour variables      
Smoking habits Never smoked regularly 735 (46; 15) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Has smoked regularly 650 (57; 21) 1.4 (1.2–1.6) 1.1 (0.9–1.3) 1.6 (1.2–2.0) 1.2 (0.9–1.6)
Use of alcohol11 <3 times per week 1148 (49; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  ≥3 times per week 240 (61; 23) 1.3 (1.1–1.6) 1.2 (1.0–1.4) 1.4 (1.0–1.9) 1.2 (0.8–1.6)
Drunkenness before military service <1 time per week 1075 (48; 17) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
≥1 time per week 313 (60; 19) 1.4 (1.2–1.7) 1.4 (1.2–1.7) 1.2 (0.9–1.6) 1.1 (0.8–1.5)
Sweating exercise (Brisk leisure time sport) ≥3 times per week 438 (42; 13) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
1–2 times per week 415 (54; 17) 1.4 (1.1–1.7) 1.2 (1.0–1.5) 1.3 (0.9–1.9) 1.1 (0.8–1.7)
Only leisured exercise 257 (55; 19) 1.6 (1.3–2.1) 1.3 (1.0–1.7) 1.6 (1.1–2.4) 1.0 (0.7–1.6)
  No physical exercise 278 (57; 26) 1.9 (1.5–2.3) 1.3 (1.0–1.7) 2.5 (1.8–3.6) 1.7 (1.1–2.6)
Belongs to a sports club Yes, active member 206 (40; 14) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  No 1177 (53; 18) 1.6 (1.3–2.0) 1.5 (1.2–2.0) 1.5 (1.0–2.2) 1.2 (0.8–1.8)
Participates in competitive sports No 1206 (51; 19) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Yes 180 (51; 17) 0.9 (0.7–1.1) 1.5 (1.1–2.1) 1.0 (0.7–1.5) 1.9 (1.2–3.0)
Last degree in school sports Good or excellent 1101 (49; 16) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Poor or fair 286 (59; 23) 1.5 (1.3–1.8) 1.2 (1.0–1.5) 1.6 (1.2–2.2) 1.2 (0.8–1.6)
  1. Variable distribution was charted in 1411 male conscripts during the first week of military service and discharge outcomes were registered during the following 6-month military service.
  2. Statistically significant (p< 0.05) findings are indicated with bold type.
  3. *Adjusted for age (univariate).
  4. **Adjusted for age, company, smoking (previous or current smoker), frequency of drunkenness, baseline medical conditions (sum factor of earlier musculoskeletal symptoms and sports injury during the last month before military entry, previous orthopaedic operations), school success (educational level and grades combined), father’s occupational group, belonging to a sport’s club, waist circumference and physical fitness measured as a standing long jump test result.
  5. 1Attended upper secondary school, polytechnic, or university and reported excellent or good grades.
  6. 2Other subjects from upper secondary school, polytechnic, or university and conscripts from vocational school whose grades were excellent or good.
  7. 3Respondents with poorer grades in vocational school.
  8. 4Attended only comprehensive school or had interrupted vocational or upper elementary school.
  9. 5Not adjusted by waist circumference since BMI and WC are strongly interconnected (χ2-test, p < 0.001).
  10. 6Compared to age-mates.
  11. 7‘Minimal symptoms’: maximum of 7 days in one anatomical region during the last month before military entry.
  12. 8'Mild symptoms’: maximum of 7 days in 2 to 6 anatomical regions during the last month before military entry.
  13. 9'Clear symptoms’: included the remaining conscripts i.e. those with symptoms more than 8 days or more.
  14. 10Due to earlier musculoskeletal injury.
  15. 11Not adjusted by frequency of drunkenness since drunkenness and use of alcohol are strongly interconnected (χ2-test, p < 0.001).