Table 2 Study characteristics

MacGregor et al., 2012, United States

Historical cohort (pre-existing data)

Low risk of bias

N = 36,680 (34,879 M, 95%)

Sample size calculation: N/A

Missing data: N/A

Age: 18+ years

Population: US Marines; identified from records from Defense Manpower Data Center

Inclusion: First deployment to Operation Iraqi Freedom between January 2005 and November 2008; without second deployment within 365 days of the end-date of their first deployment

Exclusion: Previous back-related diagnosis (ICD-9-CM 724 series); missing demographic information; died during deployment

New-onset diagnosis of LBP: presence of an ICD-9-CM code of 724.2 (lumbago) over the course of deployment or within 1 year of end of deployment

F/u period: Over course of deployment (greater than 1 month and less than 18 months) or within 1 year of end of deployment

Age (18–24, ≥ 25 years); rank (junior, midlevel, senior); sex (male, female); location country of deployment (Iraq, Kuwait); time deployed (1–7 months, > 7 months); blast injury (no, yes); occupation (administrative/other, communications/intelligence, infantry, service/supply, electrical/mechanical/craftsworker)

Multivariate logistic regression

Risk marker

Sociodemographic, occupational

Knox et al., 2014, United States

Historical cohort (pre-existing data; comparison group: nonvehicle operators)

Low risk of bias

N = 213,024 person-years (186,084 M, 87.4%)

Sample size calculation: N/A

Missing data: N/A

Population: US Military; identified from Defense Medical Epidemiology Database

Inclusion: Ambulatory first encounters during 1998–2006 for ICD-9 code 742.20 (LBP)

Exclusion: Repeat coding of same initial diagnosis for multiple visits for LBP provided to a single service member during study period

First occurrence of ICD-9 code 724.20 (LBP)

1 exposure year defined as 1 year that the service member was exposed to the risk factors for LBP while enlisted

F/u period: 8 years (database searched from 1998–2006)

Military vehicle operator; age (< 20, 20–29, 30–39, > 40); sex (male, female); race (black, white, other); marital status (single, married, other); rank group (junior, senior); military service (Army, Air Force, Marine)

Multivariate Poisson regression

Risk marker

Sociodemographic, occupational

Taanila et al., 2012, Finland

Prospective cohort

Low risk of bias

N = 982 (982 M, 100%)

Sample size calculation: Not reported

Response rate: 1489/1513 (98%)

Missing data: 304/982, 31% lost to follow-up

Age (median): 19 years

Population: Finnish Defence Forces; male conscripts; anti-tank, signal, mortar, engineer companies; data collected July 10, 2006–July 4, 2008)

Inclusion: Young; healthy; male; medical checkup by a clinician during the 12 months before entering the military

Exclusion: Female; ≥ 1 day of LBP during the last month before military entry; unanswered pre-information questionnaire; upper back pain

LBP occurring during active service hours, leisure time, or on the way to or from the garrison for leave

ICD-10 diagnoses: M54 (dorsalgia), M54.5 (LBP), M41 (scoliosis), M54.9 (dorsalgia, unspecified), M54.3 (sciatica)

Confirmed by physician based on computerised patient records

F/u period: 6 months

Father’s occupation (not physical, physical, unemployed/retire); level of education (high, lower); degrees achieved in school (high, low or average); urbanisation level of place of residence (countryside, small population centre, midsize town or city, bigger city); age (18–20, 21–28); company (anti-tank, signal, mortar, engineer); body mass index (underweight, normal, pre-obese, obese); waist circumference thin, normal, increased, high); height (shortest quartile, second quartile, third quartile, tallest quartile); self-assessed health (good or very good, average or inferior); presence of chronic disease (no, yes); use of regular medication (no, yes); previous orthopedic surgery (never, yes); presence of chronic impairment or disability (no, yes); sports injury during the last month (no, yes); other MSK symptoms (minimal, mild, clear); smoking habits (never regularly, has smoked regularly); use of alcohol (< 1 time per month, 1–2 times per week, ≥ 3 times per week); frequency of drunkenness before military service (< 1 time per week, ≥ 1 time per week); agreeing that soldier needs good physical fitness (yes, no); frequency of sweating exercise per week (≥ 3 times per week, 1–2 times per week, only leisured exercise, no physical exercise); participation in individual aerobic sports (yes at least sometimes, no); belonging to a sports club (yes an active member, no); participation in competitive sports (yes, no); last degree in school sports (good or excellent, poor or fair); self-assessed physical fitness (good or very good, average or inferior); Cooper test (12-min running test) (excellent, good, fair, poor); pull-up test (excellent, good, fair, poor); standing long jump test (excellent, good, fair, poor); sit-up test (excellent, good, fair, poor); push-up test (excellent, good, fair, poor); back-lift test (excellent, good, fair, poor); combination of push-up and Cooper test (excellent, good, fair, poor); combination of back lift and Cooper test (excellent, good, fair, poor); combination of sit-up and push-up test (excellent, good, fair, poor); combination of push-up and back lift test (excellent, good, fair, poor)

Multivariate Cox regression

Risk marker

Physical, sociodemographic, occupational

Seay et al., 2017, United States

Historical cohort

(pre-existing data; comparison group: no lower extremity injury)

Low risk of bias

N = 1,066,535; average of 213,307 included in each of 5 yearly cohorts (959,721 M, 90%)

Sample size calculation: N/A

Missing data: N/A

Population: US Army soldiers; identified from Total Army Injury and Health Outcomes Database

Inclusion: Active duty from January 1, 2007 to December 31, 2011

Exclusion: History of lower-extremity MSK injury; history of LBP or back injury; nonmusculoskeletal back pain

Incident LBP identified by ICD-9-CM code (353.4, 720.2, 721.3, 721.42, 722.10, 722.52, 722.73, 722.93, 724.02, 724.03, 724.2, 724.3, 724.4, 724.5, 724.6, 738.4, 739.3, 739.4, 756.11, 756.12, 839.20, 846.1, 846.8, 846.9, 847.2, 847.3)

F/u period: From January 1 of calendar year until either: (1) incident LBP; (2) end of active duty; (3) December 31 of respective year

Lower extremity injury (yes, no); sex (female, male)

Extended Andersen–Gill Cox regression

Risk marker

Physical

Monnier et al., 2019, Sweden

Prospective cohort

Low risk of bias

N = 53 (48 M, 91%)

Sample size calculation: Not reported

Response rate: 53/56 (95%)

Missing data: 2/53, 3.8% withdrew from course

Age (mean (SD)): 21.8 years (3.4 years)

Population: Marines in Swedish Armed Forces in training course

Inclusion: Entering with intention to complete 4 month marine training course; not seeking medical care

Exclusion: Ongoing LBP at baseline lasting ≥ 5 consecutive weeks adjacent to the course start

Occurrence of any self-rated pain in the lower back (from twelfth ribs to lower gluteal folds) within the preceding week, as reported during the weekly follow-up

LBP limiting work ability: occurrence of any self-rated pain in the lower back within the preceding week that had limited work ability

F/u period: Weekly, for 16 weeks

Body weight; body height (> 1.80 m, ≤ 1.80 m); back pain within 6 months prior to course start (no, yes); hip/knee pain within 6 months prior to course start (no, yes); neck/shoulder pain within 6 months prior to course start (no, yes); mental distress GHQ-12 score (< 4, ≥ 4); current work ability with regard to best ever (≥ 9, < 9); direct (within 3 months) from basic military training (no, yes); physical training sessions per week (> 2, ≤ 2); muscular strength training sessions per week (2–4, ≤ 1, ≥ 5); aerobic fitness training sessions per week (> 1, ≤ 1); kettlebell lift (kg x repetitions) (> 760, ≤ 760); number of pull-ups (≥ 4, ≤ 3); double leg lift and power (pass, fail); double leg lift and alternate leg extension (pass, fail)

Andersen-Gill repeated time-to-event regression

Risk marker

Physical

Roy and Lopez, 2013, United States

Prospective cohort

Low risk of bias

N = 805 (approximately 758 M, 94%)

Sample size calculation: Not reported

Response rate: 1194/3500 (34%)

Missing data: 55/1194, 4.6% medically evacuated

Age: Brigade Support Battalion (27.7 ± 6.4 years); Brigade Special Troops Battalion (25.8 ± 4.9 years); Reconnaissance, Surveillance, and Target Acquisition Squadron (25.8 ± 5.6 years); Field Artillery (26.9 ± 6.2 years); Infantry Battalions (24.9 ± 4.9 years)

Population: US Army

Inclusion: All soldiers deploying as a member of the Brigade Combat Teams from June 2009–August 2010

Exclusion: Current LBP

Self-reported LBP: pain interfering with the performance of occupational tasks

F/u period: 12 months

Number of hours per week spent on cardiovascular training, core training, and strength training; history of LBP (yes, no); hours per day or week spent on occupational tasks including wearing body armour, lifting objects weighing more than 30 lbs, dismounted patrolling, riding in tactical vehicles, or desk work; and average weight of equipment worn

Logistic regression

Risk marker

Physical, occupational

Ernat et al., 2012, United States

Historical cohort (pre-existing data; comparison group: noninfantry soldiers)

Low risk of bias

N = 791,526 person-years of data

Sample size calculation: N/A

Missing data: N/A

Population: US Military; infantrymen; identified from records from Defense Medical Epidemiology Database

Inclusion: Junior (E1–E4) and senior (E5–E9) enlisted infantry members

Exclusion: Officers

ICD-9-CM code 724.20 for ambulatory patients’ initial visits for “lumbago” (LBP)

F/u period: 8 years (database searched from 1998–2006)

Infantrymen; age (< 20, 20–24, 25–29, 30–34, 35–39, > 40); marital status (single married, other); race (white, black, other); rank (junior, senior); and branch of military service (Army, Air Force, Marine)

Multivariate Poisson regression

Risk marker

Sociodemographic, occupational

Zack et al., 2018, Israel

Historical cohort (pre-existing data)

Low risk of bias

N = 80,599 (80,599 M, 100%) total; 73,989 (73,989 M, 100%) with no history of LBP

Sample size calculation: N/A

Missing data: N/A

Age (mean (SD)): 19.06 years (1.4 years)

Population: Soldiers drafted to Israel Defense Forces

Inclusion: Drafted between January 1, 1997 to December 31, 2006; served in administrative or driving professions for a full 36-months period during study period

Exclusion: Not specified

Newly reported LBP evaluated by certified orthopedic surgeon in accordance with medical parameters defined in the military medical book of profiles (based on reported LBP, findings on physical examination, and radiologic findings)

F/u period: 36 months

Occupational groups, consisting of administrative units, professional car drivers, and professional truck drivers

Incidence and relative risk rates

Risk marker

Occupational