Musculoskeletal disorders in the Swedish armed forces marines : back pain epidemiology and clinical tests

The present work was conducted in order to lay the foundation for effective evidence-based prevention of one of the most common musculoskeletal disorders (MSDs) in the Swedish Armed Forces (SAF) marines. The overall aim of this thesis was therefore to estimate the occurrence of and identify risk factors for back pain and related limitations in work ability, at different stages of the SAF marine’s career. The aim further included an evaluation of clinical useful tests and exposures assessment of occupational physical activity.

The work presented in this thesis is based on one study with a cross-sectional, population-based design (study I, n=272) and two studies with prospective observational cohort designs (study III; n=163, study IV; n= 53). These studies aimed to establish the occurrence of MSDs (study I) and back pain in SAF marines, and identify risks associated with back pain (study I, III, IV). A fourth study (study II; n=33) used a test-retest design to evaluate clinically- relevant movement-control tests with regard to their intra- and inter-observer reliability. Study participants were recruited from the main marine regiment in the SAF, the 1st Marine Regiment at Berga, Sweden. Included personal- and work-related potential risks were measured with structured self-report questionnaires (study I, III,IV), and clinical movement control (study II, III, IV) and muscular strength (study IV) tests. Occupational physical activity and worn load during the marine training course (study IV) were monitored using accelerometers combined with schedules and self-reports.

The results from these studies revealed that MSDs were common among SAF marines, limiting work ability to some extent in every other marine within six months. Here, the back (low and/or thoracic) emerged among the most prevalent pain regions, with more than 50% of active duty marines experiencing back pain within 12 months (study III). Additionally, 79% of the marines in the four-month long training course experienced back pain (study IV). Serving as a combat craft crew member (study III) or having work tasks that include occupational sitting (study III) and computer work (study I) emerged as associated factors for back pain. Of the risks related to personal factors, a history of previous back pain and body height emerged as risks for back (study III) and low back pain (study IV). While a lack of physical training (study I, IV) emerged as a risk for back/low back pain that limited work ability, only insufficient upper body strength, as tested with pull-ups (study IV), emerged from the clinical tests as related to back pain. In addition to a low predictive validity (study III, IV), while the movement control test showed good inter- observer reliability, the intra-observer reliability were lower (study II). While only addressing a limited part of the marine training course, results indicate that ambulation was low for parts of the course, but combat loads were carried for more than half of the work time.

In conclusion, MSDs are common in active duty SAF Marines, with the back among the most commonly reported pain region. Preventive actions targeting significant risks related to the work marines perform as well as the characteristics of marines – including physical training – are warranted to curb further back pain episodes. While pain history and demographic characteristics can be used to identify marines at risk, the specific relation of these risks to back pain needs to be further clarified. However, movement control tests do not seem to be valid for inclusion in preventive back pain screenings for marines.

List of scientific papers

I. Monnier A, Larsson H, Djupsjöbacka M, Brodin L-Å, Äng BO. Musculoskeletal pain and limitations in work ability in Swedish marines: a cross-sectional survey of prevalence and associated factors. BMJ Open. 2015;5(10): e007943.
https://doi.org/10.1136/bmjopen-2015-007943

II. Monnier A, Heuer J, Norman K, Äng B. Inter- and intra-observer reliability of clinical movement-control tests for marines. BMC Musculoskeletal Disorders. 2012;13(1):263.
https://doi.org/10.1186/1471-2474-13-263

III. Monnier A, Djupsjöbacka M, Larsson H, Norman K, Äng BO. Risk factors for back pain in marines; a prospective cohort study. BMC Musculoskeletal Disorders. 2016;17(1):1-12.
https://doi.org/10.1186/s12891-016-1172-y

IV. Monnier A, Larsson H, Nero H, Djupsjöbacka M, Äng B, O. Low back pain in the marine training course: A study of incidence, risk factors and occupational physical activity. [Manuscript]