Table 3.
Key findings by risk factors
| Risk factor | Study | Outcomes and key findings |
|---|---|---|
| Physical factors (consistent associations) | ||
| History of LBP | Monnier et al. (2019) |
Incident LBP: Back pain within 6 months prior to course start (ref: no): Yes1: HR 2.47 (1.41; 4.31)* Incident LBP limiting work ability: Back pain within 6 months prior to course start (ref: no): Yes2: HR 3.58 (1.44; 8.90)* |
| Roy and Lopez (2013) |
Brigade Support Battalion: History of LBP (ref: no): Yes: OR 5.03 (1.61; 15.72)* Brigade Special Troops Battalion: History of LBP (ref: no): Yes: OR 8.91 (1.71; 46.46)* Infantry Battalions: History of LBP (ref: no): Yes: OR 2.20 (1.2; 4.04)* |
|
| Previous injury | Taanila et al. (2012) |
Sports injury during last month (ref: no): Yes3: HR 1.7 (1.0; 2.8)* |
| Seay et al. (2017) |
Lower extremity injury4 (ref: no lower extremity injury): HR 1.70 (1.66; 1.74)* Pooled TR 0.90 (0.90; 0.91)* Males with lower extremity injury4 (ref: males with no lower extremity injury): HR 1.76 (1.72; 1.80)* Pooled TR 0.90 (0.89; 0.90)* Females with lower extremity injury4 (ref: females with no lower extremity injury): HR 1.43 (1.36; 1.50)* Pooled TR 0.93 (0.92; 0.94)* |
|
| Time spent on physical training | Monnier et al. (2019) |
Incident LBP limiting work ability: Physical training sessions per week (ref: > 2): ≤ 22: HR 2.96 (1.19; 7.39)* |
| Roy and Lopez (2013) |
Brigade Special Troops Battalion: Strength training (ref: less): More: OR 0.88 (0.78; 0.99)* |
|
| Physical factors (non-associations, single study) | ||
| Body mass index | Taanila et al. (2012) |
BMI (ref: normal 18.5 ≤ BMI < 25.0): Underweight BMI < 18.53: HR 0.2 (0.0; 1.3) Pre-obese 25.0 ≤ BMI ≤ 30.03: HR 0.9 (0.6; 1.3) Obese BMI ≥ 30.03: HR 1.4 (0.8; 2.4) |
| Waist circumference | Taanila et al. (2012) |
WC (ref: normal 80 ≤ WC < 94): Thin WC < 803: HR 0.8 (0.5; 1.4) Increased 94 ≤ WC < 1023: HR 1.3 (0.8; 2.0) High WC ≥ 1023: HR 1.3 (0.7; 2.4) |
| Self-assessed health | Taanila et al. (2012) |
Self-assessed health (ref: good or very good): Average or inferior3: HR 1.1 (0.8; 1.6) |
| Chronic disease | Taanila et al. (2012) |
Chronic disease (ref: no): Yes3: HR 1.2 (0.8; 1.7) |
| Regular medications | Taanila et al. (2012) |
Regular medication (ref: no): Yes3: HR 1.4 (0.9; 2.3) |
| Orthopedic surgery | Taanila et al. (2012) |
Orthopedic surgery (ref: never): Yes3: HR 1.6 (0.9; 2.6) |
| Chronic impairment due to prior MSK injury | Taanila et al. (2012) |
Chronic impairment or disability because of prior MSK injury (ref: no): Yes3: HR 1.4 (0.9; 2.2) |
| Self-assessed physical fitness | Taanila et al. (2012) |
Self-assessed physical fitness (ref: good or very good): Average or inferior3: HR 1.3 (0.8; 1.9) |
| Physical factors (inconsistent associations) | ||
| Poor performance on physical fitness tests | Monnier et al. (2019) |
Incident LBP: Pull-up (number of repetitions) (ref: ≥ 4): ≤ 35: HR 1.87 (1.17; 3.01)* |
| Taanila et al. (2012) |
Pull-up test (consecutive repeats without time limit) (ref: excellent ≥ 14): Good ≥ 103: HR 1.6 (0.8; 3.1) Fair ≥ 63: HR 1.3 (0.7; 2.5) Poor < 63: HR 1.2 (0.7; 2.3) Standing long jump test (two attempts, best result observed) (ref: excellent ≥ 240 m): Good ≥ 220 m3: HR 0.9 (0.5; 1.5) Fair ≥ 200 m3: HR 1.1 (0.7; 1.7) Poor < 200 m3: HR 0.9 (0.5; 1.5) Sit-up test (repeats/60 s) (ref: excellent ≥ 48): Good ≥ 403: HR 1.5 (0.8; 2.8) Fair ≥ 323: HR 1.4 (0.8; 2.4) Poor < 323: HR 1.7 (0.9; 3.0) Push-up test (repeats/60 s) (ref: excellent ≥ 38): Good ≥ 303: HR 1.3 (0.8; 2.1) Fair ≥ 223: HR 1.2 (0.8; 1.9) Poor < 223: HR 1.6 (1.0; 2.6) Back-lift test (repeats/60 s) (ref: excellent ≥ 60): Good ≥ 503: HR 1.2 (0.8; 1.9) Fair ≥ 403: HR 1.2 (0.7; 1.8) Poor < 403: HR 1.6 (0.9; 2.8) Combination of push-up and Cooper test (ref: excellent): Good3: HR 1.4 (0.8; 2.3) Fair3: HR 1.5 (0.8; 2.5) Poor3: HR 2.1 (1.1; 4.2)* Combination of back lift and Cooper test (ref: excellent): Good3: HR 1.3 (0.8; 2.1) Fair3: HR 1.5 (0.9; 2.5) Poor3: HR 2.4 (1.1; 5.4)* Combination of sit-up and push-up test (ref: excellent): Good3: HR 1.5 (0.8; 2.8) Fair3: HR 1.6 (0.9; 3.0) Poor3: HR 2.2 (1.1; 4.5)* Combination of push-up and back lift test (ref: excellent): Good3: HR 1.4 (0.8; 2.2) Fair3: HR 1.3 (0.8; 2.0) Poor3: HR 2.8 (1.4; 5.9)* |
|
| Height | Monnier et al. (2019) |
Incident LBP: Body height (ref: > 1.80 m): ≤ 1.80m1: HR 1.98 (1.19; 3.29)* Incident LBP limiting work ability: Body height (ref: > 1.80 m): ≤ 1.80m2: HR 4.48 (2.01; 9.97)* |
| Taanila et al. (2012) |
Height (cm) (ref: shortest quartile ≤ 176): Second quartile 177–1803: HR 1.2 (0.7; 1.8) Third quartile 181–1853: HR 0.9 (0.5; 1.4) Tallest quartile ≥ 1853: HR 1.1 (0.7; 1.8) |
|
| Sociodemographic factors (consistent associations) | ||
| Female | MacGregor et al. (2012) |
Sex (ref: male): Female6: OR 1.94 (1.61; 2.34)* |
| Knox et al. (2014) |
Sex# (ref: male): Female7: IRR 1.45 (1.39; 1.52)* |
|
| Sociodemographic factors (associations, single study) | ||
| ‘Single’ marital status | Knox et al. (2014) |
Marital status# (ref: married): Single8: IRR 0.87 (0.84; 0.91)* Other8: IRR 1.01 (0.91; 1.12) |
| Lower education level | Taanila et al. (2012) |
Level of education (ref: higher—secondary school graduates, polytechnic, university student): Lower—comprehensive or vocational school)3: HR 1.6 (1.1; 2.3)* Degrees achieved in school (ref: high): Low or average3: HR 1.5 (1.0; 2.2)* |
| Sociodemographic factors (non-associations) | ||
| Father’s occupation | Taanila et al. (2012) |
Father’s occupation (ref: not physical): Physical3: HR 1.2 (0.8; 1.9) Unemployed or retired3: HR 1.4 (0.9; 2.2) |
| Urbanisation level of place of residence | Taanila et al. (2012) |
Urbanisation level of place of residence (ref: countryside): Small population centre3: HR 1.1 (0.6; 2.0) Midsize town or city3: HR 1.0 (0.6; 1.7) Bigger city3: HR 1.2 (CI 0.7; 2.0) |
| Smoking habits | Taanila et al. (2012) |
Smoking habits (ref: never regularly): Smoked regularly3: HR 1.1 (0.8; 1.6) |
| Use of alcohol | Taanila et al. (2012) |
Use of alcohol (ref: < 1 time/month): 1–2 times/week3: HR 0.8 (0.5; 1.2) ≥ 3 times/week3: HR 0.6 (0.3; 1.2) |
| Frequency of drunkenness before military service | Taanila et al. (2012) |
Frequency of drunkenness before military service (ref: < 1 time/week): ≥ 1 time/week3: HR 0.7 (0.5; 1.1) |
| Agreeing that soldiers need good physical fitness | Taanila et al. (2012) |
Agrees that soldier needs good physical fitness (ref: yes): No3: HR 1.0 ( 0.7; 1.4) |
| Amount of time spent on sweating exercises | Taanila et al. (2012) |
Sweating exercise (brisk leisure time sport) (ref: ≥ 3 times/week): 1–2 times/week3: HR 0.7 (0.5; 1.1) Only leisured exercise3: HR 1.3 (0.8; 2.1) No physical exercise3: HR 1.0 (0.6; 1.7) |
| Participation in individual aerobic sports | Taanila et al. (2012) |
Participates in individual aerobic sports (ref: yes, at least sometimes): No3: HR 1.1 ( 0.7; 1.5) |
| Belonging to a sports club | Taanila et al. (2012) |
Belongs to a sports club (ref: yes, active member): No3: HR 1.1 ( 0.7; 1.8) |
| Participation in competitive sports | Taanila et al. (2012) |
Participates in competitive sports (ref: yes): No3: HR 1.1 ( 0.7; 1.7) |
| Last degree in school sports | Taanila et al. (2012) |
Last degree in school sports (ref: good or excellent): Poor or fair3: HR 0.8 (0.5; 1.3) |
| Race | Knox et al. (2014) |
Race# (ref: other): Black9: IRR 1.07 (1.00; 1.14) White9: IRR 1.06 (1.00; 1.13) |
| Sociodemographic factors (inconsistent associations) | ||
| Age | Knox et al. (2014) |
Age# (ref: 30–39): < 2010: IRR 1.24 (1.15; 1.36)* 20–2910: IRR 0.96 (0.91; 1.01) > 4010: IRR 1.23 (1.0; 1.38) |
| Ernat et al. (2012) |
Infantrymen stratified by age (ref: control): < 2011: IRR 0.61 (0.59; 0.63)* 20–2911: IRR 0.66 (0.65; 0.67)* 30–3911: IRR 0.86 (0.83; 0.88)* > 4011: IRR 0.91 (0.86; 0.97)* |
|
| Taanila et al. (2012) |
Age (ref: 18–20): 21–283: HR 1.8 (1.0; 3.4) |
|
| MacGregor et al. (2012) |
Age (ref: 18–24): ≥ 256: OR 1.13 (0.94, 1.36) |
|
| Occupational factors (consistent associations) | ||
| Lower rank | Knox et al. (2014) |
Rank# (ref: senior E5–E9): Junior E1–E412: IRR 1.60 (1.52; 1.70)* |
| MacGregor et al. (2012) |
Rank (ref: junior E1–E3): Midlevel E4–E56: OR 0.73 (0.64; 0.83)* Senior E6–E96: OR 0.98 (0.76; 1.26) |
|
| Occupational factors (associations, single study) | ||
| Blast injury | MacGregor et al. (2012) |
Blast injury (ref: no): Yes6: OR 2.29 (1.64; 3.19)* |
| Job duties | Roy and Lopez (2013) |
Brigade Support Battalion: Lifting objects (ref: < 30 lbs): > 30 lbs: OR 1.30 (1.06; 1.60)* Brigade Special Troops Battalion: Body armour (ref: no): Yes: OR 1.23 (1.03; 1.47)* Reconnaissance, Surveillance, and Target Acquisition Squadron: Body armour (ref: no): Yes: OR 1.30 (1.11; 1.53)* Infantry Battalions: Body armour (ref: no): Yes: OR 1.14 (1.07; 1.21)* |
| Service type | Knox et al. (2014) |
Military service# (ref: Marine): Army13: IRR 2.74 (2.60; 2.89)* Air Force13: IRR 1.98 (1.84; 2.14)* |
| Occupational factors (non-associations, single study) | ||
| Location of deployment | MacGregor et al. (2012) |
Location country (ref: Iraq): Kuwait6: OR 1.11 (1.00; 1.24) |
| Time deployed | MacGregor et al. (2012) |
Time deployed (ref: 1–7 months): > 7 months6: OR 1.06 (0.95; 1.19) |
| Occupational factors (inconsistent associations) | ||
| Military occupations | MacGregor et al. (2012) |
Occupation (ref: administrative/other): Communications/intelligence1: OR 0.82 (0.64; 1.06) Infantry6: OR 0.86 (0.73; 1.02) Service/supply6: OR 1.33 (1.12; 1.59)* Electrical/mechanical/craftsworker1: OR 1.31 (1.12; 1.53)* |
| Taanila et al. (2012) |
Company (ref: anti-tank): Signal3: HR 1.4 (0.9; 2.3) Mortar3: HR 1.0 ( 0.5; 1.8) Engineer3: HR 2.0 (CI 1.2; 3.3)* |
|
| Ernat et al. (2012) |
Infantrymen11 (ref: control): IRR 0.69 (95% CI 0.68; 0.70)* Infantrymen stratified by age (ref: control): < 2011: IRR 0.61 (0.59; 0.63)* 20–2911: IRR 0.66 (0.65; 0.67)* 30–3911: IRR 0.86 (0.83; 0.88)* > 4011: IRR 0.91 (0.86; 0.97)* Infantrymen stratified by rank (ref: control): Junior: Unadjusted IRR 0.59 (no CI provided) Senior: Unadjusted IRR 0.80 (no CI provided) Infantrymen stratified by branches of service (ref: control): Army: Unadjusted IRR 0.70 (no CI provided) Marine: Unadjusted IRR 0.59 (no CI provided) |
|
| Driving | Knox et al. (2014) | Military vehicle operator14 (ref: other occupations): IRR 1.15 (1.13; 1.17)* |
| Zack et al. (2018) |
Occupational categories (ref: administrative): Car drivers: RR 1.0 (0.79; 1.28) Truck drivers: RR 0.49 (0.40; 0.60)* |
|
ref, referent category; CI, confidence interval; OR, odds ratio; IRR, incidence rate ratio; ICD-10, International Classification of Diseases, 10th Revision; HR, hazard ratio; BMI, body mass index (kg/m2); WC, waist circumference (cm); MSK, musculoskeletal; m, metres; s, seconds; TR, time ratio; GHQ, General Health Questionnaire; lbs, pounds; RR, relative risk
Variables adjusted for: 1Sex; 2Sex, neck/shoulder pain previous to course start; 3Age, company, smoking, baseline medical conditions (sports injury, sum factor of earlier musculoskeletal symptoms, regular medication, chronic impairment or disability because of prior musculoskeletal injury, orthopedic surgery), education level, school degree level, father’s occupation, participating in individual aerobic sports; 4Sex, age, race, rank, time in service, military occupation specialty physical demands; 5Prior back pain, body height; 6Age, rank, sex, location country, time deployed, blast injury, occupation; 7Age, race, rank, service, marital status; 8Age, sex, race, rank, service; 9Age, sex, rank, marital status, service; 10Sex, service, rank, marital status, race; 11Age, race, rank, service, marital status; 12Age, sex, race, marital status, service; 13Age, sex, race, marital status, rank; 14Sex, race, rank, service, marital status
*Statistically significant; #among vehicle operators in the US military