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Table 5 Hazard ratios (HR) for any overuse injury (OI) and severe overuse injury (severe OI) incidence by physical fitness 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 = 721)** HR for severe OI incidence (≥7 service days lost) (n = 251)* HR for severe OI incidence (≥7 service days lost) (n = 251)**
Self-assessed physical fitness1 Good or very good 323 (46; 14) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Average or inferior 1066 (53; 19) 1.4 (1.1–1.6) 1.1 (0.9–1.3) 1.5 (1.1–2.1) 1.0 (0.7–1.5)
Cooper’s test (12-min running test) Excellent (≥3000 m) 51 (43; 12) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good (≥2600 m) 330 (44; 13) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Fair good (≥2200 m) 630 (50; 15) 1.3 (1.1–1.5) 1.1 (0.9–1.3) 1.2 (0.9–1.7) 1.1 (0.7–1.6)
  Poor (<2200 m) 358 (59; 26) 1.8 (1.5–2.2) 1.4 (1.1–1.8) 2.4 (1.7–3.4) 1.9 (1.3–3.0)
Push-up test (repeats per 60 seconds) Excellent (≥38) 450 (48; 14) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good (≥30) 312 (52; 19) 1.2 (1.0–1.5) 1.1 (0.8–1.3) 1.3 (0.9–1.9) 1.1 (0.7–1.6)
Fair good (≥22) 350 (49; 17) 1.1 (0.9–1.4) 1.0 (0.8–1.2) 1.3 (0.9–1.8) 0.9 (0.6–1.4)
  Poor (<22) 266 (57; 22) 1.5 (1.2–1.8) 1.1 (0.8–1.4) 1.7 (1.2–2.5) 1.0 (0.7–1.5)
Standing long jump test (two attempts, best result) Excellent (≥2,40 m) 241 (45; 12) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good (≥2,20 m) 363 (50; 17) 1.2 (0.9–1.5) 1.1 (0.9–1.4) 1.6 (1.0–2.5) 1.5 (0.9–2.4)
Fair good (≥2,00 m) 442 (52; 17) 1.2 (0.9–1.6) 1.1 (0.9–1.4) 1.5 (1.0–2.3) 1.4 (0.9–2.2)
  Poor (<2,00 m) 332 (56; 23) 1.6 (1.2–2.0) 1.2 (0.9–1.6) 2.3 (1.5–3.6) 1.8 (1.1–3.0)
Back lift test (repeats per 60 seconds) Excellent (≥60) 660 (46; 13) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good (≥50) 284 (50; 22) 1.1 (0.9–1.4) 0.9 (0.8–1.2) 1.7 (1.3–2.4) 1.4 (1.0–2.0)
Fair good (≥40) 291 (54; 20) 1.3 (1.1–1.5) 1.1 (0.9–1.3) 1.5 (1.1–2.2) 1.2 (0.8–1.7)
  Poor (<40) 143 (68; 25) 1.9 (1.5–2.4) 1.5 (1.1–1.9) 2.1 (1.5–3.2) 1.4 (0.9–2.2)
Conscript’s muscle fitness index2 Excellent (13–15 points) 169 (43; 13) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good (9–12 points) 361 (45; 13) 1.2 (0.9–1.6) 1.1 (0.9–1.5) 1.0 (0.6–1.7) 0.9 (0.6–1.6)
  Fair good (5–8 points) 472 (53; 18) 1.5 (1.1–1.9) 1.2 (0.9–1.6) 1.5 (1.0–2.5) 1.2 (0.7–2.0)
  Poor (0–4 points) 376 (57; 23) 1.7 (1.3–2.3) 1.3 (1.0–1.8) 2.1 (1.3–3.3) 1.3 (0.8–2.2)
Conscript’s physical fitness index3 Excellent (≥21,00) 69 (39; 9) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good (17.00 − 20.99) 409 (44; 13) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
  Fair good (13.00 − 16.99) 590 (53; 17) 1.3 (1.1–1.5) 1.2 (1.0–1.5) 1.2 (0.9–1.7) 1.2 (0.8–1.7)
  Poor (<13.00) 297 (59; 26) 1.8 (1.5–2.2) 1.4 (1.1–1.8) 2.4 (1.7–3.4) 1.7 (1.1–2.7)
Combination of standing long jump and back lift test Excellent4 177 (45; 12) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good5 523 (46; 14) 1.1 (0.8–1.4) 1.1 (0.9–1.4) 1.2 (0.7–2.0) 1.1 (0.7–1.9)
Fair good6 607 (54; 21) 1.4 (1.1–1.8) 1.2 (1.0–1.6) 1.9 (1.2–3.0) 1.5 (0.9–2.5)
  Poor7 71 (70; 27) 2.5 (1.7–3.5) 1.7 (1.2–2.6) 2.9 (1.6–5.4) 1.7 (0.8–3.6)
Combination of back lift and push–up test Excellen 4 335 (44; 13) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good5 440 (48; 17) 1.2 (1.0–1.5) 1.0 (0.8–1.3) 1.4 (0.9–2.0) 1.1 (0.8–1.7)
Fair good6 536 (55; 20) 1.5 (1.2–1.8) 1.1 (0.9–1.4) 1.7 (1.2–2.4) 1.1 (0.7–1.7)
  Poor7 67 (67; 31) 2.4 (1.7–3.4) 1.7 (1.2–2.5) 3.2 (1.9–5.5) 1.7 (0.9–3.2)
Combination of standing long jump and Cooper’s test Excellent4 136 (42; 8) 1 (Referent) 1 (Referent) 1 (Referent) 1 (Referent)
Good5 504 (47; 15) 1.3 (1.0–1.7) 1.1 (0.8–1.5) 2.1 (1.1–4.0) 1.9 (1.0–3.6)
Fair good6 550 (54; 19) 1.6 (1.2–2.1) 1.3 (0.9–1.7) 2.6 (1.4–4.8) 2.0 (1.1–3.9)
  Poor7 175 (59; 26) 2.1 (1.5–2.9) 1.5 (1.0–2.2) 4.4 (2.2–8.4) 3.3 (1.6–7.0)
  1. Variable distribution was charted in 1411 male conscripts during the first two weeks 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. 1Compared to age mates.
  6. 2Muscle fitness index is the sum of individual muscle fitness test results including push-up, sit-up, pull-up, standing long jump and back lift tests.
  7. 3Conscript's physical fitness index (CPFI) = (12-min running test result (m) + 100 × muscle fitness test points) / 200.
  8. 4Excellent or good result in Cooper's test and excellent result in selected muscular fitness test.
  9. 5Excellent result in selected muscular fitness test and fair good or poor result in Cooper's test; or excellent result in Cooper's test and good, fair good, or poor result in selected muscular fitness test;
  10. or good result in Cooper's test and good or fair good result in selected muscular fitness test; or fair good result in Cooper's test and good result in selected muscular fitness test.
  11. 6Poorer results than aforementioned, except the combination of poor results in both tests.
  12. 7Poor result in both tests.