The core of the Finnish Defence Forces is based on mandatory military service. Although the majority of European countries count on professional soldiers in their defence strategy, the Finnish conscription system has maintained its high coverage: approximately 80% of young men in Finland enter into military service. The purpose of this dissertation was to investigate the occurrence, nature, severity, injury mechanisms and risk factors of musculoskeletal disorders (MSDs) including low back pain (LBP) and medical discharge in physically active male Finnish conscripts, and examine whether a neuromuscular training with injury prevention counseling, designed to enhance body control, motor skills and knowledge of prevention methods, was effective in preventing acute musculoskeletal injuries and LBP in conscripts during military training.
First, the occurrence, anatomical location, severity and etiology including injury mechanisms and intrinsic risk factors for MSDs among conscripts were examined in studies I and II. Two successive cohorts of 18 to 28-year-old male conscripts (N = 944, median age 19) were followed for six months. MSDs, including overuse and acute injuries, treated at the garrison clinic were identified and analysed. Associations between MSDs and risk factors were examined by multivariate Cox’s proportional hazard models. Among 944 conscripts, there were 1629 MSDs and 2879 health clinic visits due to MSDs. The event-based incidence rate for MSD was 10.5 (95% confidence interval (CI): 10.0–11.1) per 1000 person-days. Most MSDs were in the lower extremities (65%) followed by the back (18%), upper extremities including shoulders (11%), head (2%) and other parts of the body (3%). Overuse-related MSDs (70%) were more than twice as prevalent as traumatic MSDs (30%). The majority (69%) of disorders were classified as minor leading to a maximum 3-day exemption from military training, while mild (4-7 off-duty days) MSDs accounted for 20%, moderate (8-28 off-duty days) for 8% and severe (>28 off-duty days) for 3% of all cases. Fractures, bone stress injuries, dislocations and internal knee injuries represented the most severe injuries.
Of the traumatic causes of acute MSDs, falling down (17%) and collision with an object (16%) were most commonly associated with MSDs. Marching and running (36%) were the most common activities associated with overuse-related MSDs, followed by carrying and lifting loads (10%). Predictive associations between intrinsic risk factors and MSDs were examined using multivariate Cox’s proportional hazard models. The strongest baseline factors associated with MSDs were poor result in the combined outcome of a 12-minute running test and back lift test (hazard ratio (HR) 2.9; 95% CI: 1.9–4.6). In addition, obesity measured as high waist circumference (WC) (HR 1.7; 95% CI: 1.3–2.2) or high body mass index (BMI) (HR 1.8; 95% CI: 1.3–2.4), earlier musculoskeletal symptoms (HR 1.7; 95% CI: 1.3–2.1) and poor school success (educational level and grades combined; HR 2.0; 95% CI: 1.3–3.0) were associated with MSDs.
Further and more specifically, the third study examined incidence, severity and predictors of LBP. Four successive cohorts of male conscripts without LBP before military entry (N = 982) were followed for 6 months. Conscripts who suffered from LBP were identified and treated at the garrison clinic.
The cumulative incidence of LBP was 16%. Of those 27% (n=42) had recurrent LBP, while the LBP incidence rate was 1.2 (95% CI: 1.0–1.4) per 1000 person-days. The majority (75%) of LBP was classified as minimal, leading to a maximum 3-day exemption from military training, while mild LBP accounted for 15%, moderate for 7%, and severe for 3% of all cases. Five previously symptomless conscripts were discharged prematurely due to LBP. Conscripts with low educational level had increased risk for incidence of LBP (HR 1.6, 95% CI: 1.1–2.3). Moreover, conscripts with low dynamic trunk muscle endurance and low aerobic endurance simultaneously (i.e. having co-impairment) at baseline had increased risk for incidence of LBP. The strongest risk factor was co-impairment of trunk muscular endurance in tests of back-lift and push-up (HR 2.8; 95% CI: 1.4–5.9). The fourth study examining occurrence, reasons and risk factors of military discharge found that low physical fitness is a strong predictor of health problems leading to premature discharge from military service. Of 1411 participants, 9.4% (n=133) were discharged prematurely for medical reasons after the 2-week run-in period, mainly musculoskeletal (44%, n=59) and mental and behavioral (29%, n=39) disorders. Low levels of physical fitness assessed with a 12-min running test (HR 3.3; 95% CI: 1.7–6.4), poor school success (HR 4.6; 95% CI: 2.0-11.0), poor self-assessed health (HR 2.8; 95% CI: 1.6–5.2), and not belonging to a sports club (HR 4.9; 95% CI: 1.2–11.6) were most clearly associated with medical discharge in a graded manner.
The following two studies investigated the effect of neuromuscular exercise (NME) with injury prevention counseling to decrease the risk of acute musculoskeletal injuries (study V) and LBP (study VI) during military service. Participants were conscripts of four successive age cohorts (N = 1912). In the pre-study year, before adoption of the intervention, two successive cohorts of four companies (N = 944) were followed prospectively for 6 months to study the baseline incidence of acute injuries and LBP. Then the group randomization was carried out. In the intervention year, two new cohorts of the same companies (N = 968) were followed for 6 months: 501 conscripts participated in NME (intervention group: anti-tank and engineer companies) and 467 conscripts conducted their service as usual in the control group (signal and mortar companies). A NME program and educational counseling were used to reduce acute extremity injuries, and LBP and disability. The NME program was aimed to enhance conscripts’ motor and muscular performance with emphasis on the control of the lumbar neutral zone (NZ) and specifically avoiding full lumbar flexion. Counseling was based on the cognitive-behavior modeling. The aims were to increase awareness of military tasks that could lead to acute injuries or were potentially harmful to the lower back, and to enhance understanding and skills to perform them in a less risky manner.
In the intervention companies, the risk for acute ankle injury decreased significantly compared to the control companies (adjusted HR 0.34; 95% CI: 0.15–0.78, p=0.011). This risk decline was observed in conscripts with low, as well as moderate-to-high, baseline fitness. In the latter group of conscripts, the risk of upper extremity injuries also decreased significantly (adjusted HR 0.37; 95% CI 0.14–0.99, p=0.047). In addition, the intervention companies tended to have fewer time losses due to injuries (adjusted HR 0.55; 95% CI 0.29–1.04).
In the study VI, effectiveness of the NME and counseling for reducing the incidence of LBP and disability was investigated in conscripts with a healthy back, assessed by a questionnaire and routine medical screening by a physician at the beginning of military service. Altogether 472 (23%) conscripts were excluded from the analyses due to previous LBP. Total number of off-duty days due to LBP was significantly decreased in the intervention companies compared to the controls (adjusted HR 0.42; 95% CI 0.18–0.94, p = 0.035). The number of LBP cases, number of health clinic visits due to LBP, and number of the most severe cases showed a similar decreasing trend, but without statistical significance. The findings indicated that exercise and education to improve control of the lumbar NZ had a prophylactic effect on LBP-related off-duty service days in the military environment, and may provide a target for the primary prevention of LBP.
The findings of this thesis indicate that MSDs, especially those involving lower extremities and low back, are common among a population-based sample of Finnish conscripts during physically demanding military service. However, a neuromuscular warm-up program with injury prevention counseling designed to enhance motor skills and body control especially considering lumbar NZ, and knowledge of prevention methods can clearly decrease the risk for acute ankle injuries and LBP. Hence, neuromuscular training programs can be recommended to be included in the weekly training schedules of conscripts. Injury prevention counseling especially at the beginning of military service would help to control the injury risk. A similar neuromuscular training as a warm-up or cool-down program for sports and physical exercise as well as in school sports lessons would offer means to reduce the burden of injuries and LBP, and consequently enhance the positive effects of regular physical activity on health.
