Effects of 12-Month Training Intervention on Physical Fitness, Body Composition, and Health Markers in Finnish Navy Soldiers.

BACKGROUND: Most Western adults do not meet the recommendations for sufficient activity, and obesity is a global problem. Similar trends are also seen among Western military personnel. Many successful physical training interventions have been carried out in military environments, but the interventions have been quite short term, and the training has been supervised. Therefore, the aim of this study was to investigate the effects of a 12-month voluntary motivational training intervention among the Finnish Defence Forces' (FDF) Navy soldiers. METHODS: In total, 77 FDF Navy soldiers, serving in missile patrol boats, took part in the study. The intervention group (IG) contained 45 participants and the control group (CG) contained 32 participants. The IG was divided into four teams that carried out the intervention, while the CG took part in only the measurements. RESULTS: Most of the participants (65%) in the IG reported that they had increased their exercise volume during the intervention, but no major beneficial impacts on the physical fitness, body composition, or health markers were observed. Nevertheless, there was a clear diversity visible between the subgroups in the IG. The team that reported the most exercise had the best motivation and the most motivated team coach and also had the most improved physical fitness and body composition results. CONCLUSIONS: The present study points out that in military environments, long-term voluntary training interventions may not be as successful as short-term supervised interventions. The results also suggest that in voluntary training interventions among military personnel, the participants' motivation to exercise is a key factor when improving physical fitness.

The Effects of Individual Characteristics of the Naval Personnel on Sleepiness and Stress during Two Different Watchkeeping Schedules.

BACKGROUND: Naval service can have a significant impact on the wellbeing of seafarers, and the operation of warships is highly dependent on the personnel on board. Nevertheless, there is a lack of knowledge concerning the impact of seafarers' individual characteristics on their wellbeing in a naval environment. Therefore, the aim of this study was to investigate individual characteristics of the naval personnel that may be associated with the amount of sleepiness, fatigue and stress responses experienced during shift work and irregular working hours in a naval environment. METHODS: The study took place on a Finnish Defence Forces' Navy missile patrol boat on which 18 crewmembers served as study participants. The measurement periods lasted two separate weeks (seven days and six nights) during shift work with two different watchkeeping systems (4:4, 4:4/6:6). The onboard measurements consisted of the Karolinska Sleepiness Scale, salivary stress hormones, cognitive tests (Sustained Attention to Response Task and N-back Task) and heart rate variability. RESULTS: Participants of older ages or with a longer history in naval service were associated with a greater amount of sleepiness, fatigue and stress responses on board. On the contrary, increased physical activity and a higher level of physical fitness, especially standing long jump, were associated with a lower amount of sleepiness, fatigue and fewer stress responses. In addition, an athletic body composition together with a healthy lifestyle may be beneficial, considering the stress responses on board. CONCLUSION: The present results are well in line with the previous literature regarding shift work and irregular working hours. The results highlight the importance of regular physical activity and good physical fitness during service in the naval environment.

Effects of operational assessment of the 4:4 and 4:4/6:6 watch systems on sleepiness, fatigue, and stress responses during patrolling on a navy missile patrol boat.

The operation of naval vessels involves watchkeeping 24 h per day, which is globally carried out by a variety of different watch systems. In this study, the rotating 4:4 and fixed 4:4/6:6 two-section watch systems were compared in terms of sleepiness, fatigue, and stress responses. The data collection took place on a Finnish Defence Forces' (FDF) Navy missile patrol boat with 15 crew members serving as study participants. The data collection periods lasted two separate weeks (7 days, 6 nights) with the different watch systems. The subjective sleepiness of the participants was assessed before and after every watch using the Karolinska Sleepiness Scale (KSS). Stress responses were assessed daily by the recorded levels of salivary alpha-amylase (sAA), cortisol (sCor), immunoglobulin A (sIgA), and dehydroepiandrosterone (sDHEA). The participants' sustained attention, inhibitory control, and working memory were assessed daily by cognitive tests (SART, N-Back). The heart rate variability (HRV) during an orthostatic test was used as an additional daily marker to assess the amount of psychological stress of the participants. In this study, the difference regarding sleepiness and fatigue between the study weeks was most visible in the subjective KSS, which clearly favored the 4:4/6:6 system. The results of sAA and sIgA also suggested that the subjects were psychologically less stressed during the study week with the 4:4/6:6 watch system. Cognitive test results (SART, N-Back) indicated that there were overall no significant differences in the subjects' sustained attention, inhibitory control, or working memory during the study weeks or between the study weeks. The results of the HRV data during the daily orthostatic tests were inconclusive but there was some indication that the subjects were less stressed during the study week with the 4:4/6:6 watch system. In conclusion, the present study indicates that in navy surface operations: working with the fixed 4:4/6:6 watch system causes less sleepiness, fatigue, and psychological stress than working with the rotating 4:4 watch system. The study result is well in line with previous research regarding watch systems.

Risk factors of acute and overuse musculoskeletal injuries among young conscripts: a population-based cohort study.

BACKGROUND: Military service in Finland is compulsory for all male citizens and annually about 80% of 19-year-old men enter into the service. The elevated risk for many chronic diseases and loss of function among those who are inactive and unfit can be often detected already in youth. On the other hand, activity-induced injuries among young are true public health issue. The purpose of the present prospective cohort follow-up study was to evaluate predictive associations between acute or overuse injuries and their various intrinsic risk factors. METHODS: Four successive cohorts of conscripts who formed a representative sample of Finnish young men were followed for 6 months. At the beginning of the service, the risk factors of injuries were measured and recorded and then the acute and overuse injuries treated at the garrison clinic were identified. Predictive associations between injuries and their risk factors were examined by multivariate Cox's proportional hazard models. RESULTS: Of the 1411 participants, 27% sustained an acute injury and 51% suffered from overuse injury. Concerning acute injuries, highest risk for severe injuries were detected among conscripts with low fitness level in both the standing long-jump and push-up tests (hazard rate, HR=5.9; 95% CI: 1.6‒21.3). A history of good degree in school sports was not a protective factor against acute injuries. High waist circumference and, on the other hand, being underweight according to BMI increased the HR for overuse injuries. Brisk leisure time physical activity before military entry was a protective factor against overuse injuries. Poor result in Cooper's test was a warning signal of elevated risk of overuse injuries. CONCLUSION: We confirmed previous findings that low level of physical fitness is predictor for musculoskeletal injuries during intensive physical training. The U-shaped relationship between body composition and overuse injuries was noticed indicating that both obesity and underweight are risk factors for overuse injuries. Persons with excellent sports skills according to their earlier degrees in school sports had similar HR for acute injuries than those with poorer degrees. This indicates that school-age sports skills and fitness do not carry far and therefore preventive programmes are needed to prevent activity-induced injuries.

Comparison of 1.5T and 3T MRI scanners in evaluation of acute bone stress in the foot.

BACKGROUND: Bone stress injuries are common in athletes and military recruits. Only a minority of bone stress changes are available on plain radiographs. Acute bone stress is often visible on MRI as bone marrow edema, which is also seen in many other disease processes such as malignancies, inflammatory conditions and infections. The purpose of this study was to investigate the ability of radiographs, 1.5T and 3T MRI to identify acute bone marrow changes in the foot. METHODS: Ten patients with 12 stress fractures seen on plain radiographs underwent MRI using 1.5T and 3T scanners. T1 FSE and STIR axial, sagittal, and coronal view sequences were obtained. Two musculoskeletal radiologists interpreted the images independently and by consensus in case of disagreement. RESULTS: Of the 63 acute bone stress changes seen on 3T images, 61 were also seen on 1.5T images. The sensitivity of 1.5T MRI was 97% (95% CI: 89%-99%) compared with 3T. The 3T MRI images where, therefore, at least equally sensitive to 1.5T scanners in detection of bone marrow edema. On T1-weighted sequences, 3T images were slightly superior to 1.5T images in visualizing the demarcation of the edema and bone trabeculae. The kappa-value for inter-observer variability was 0.86 in the MRI indicating substantial interobserver agreement. CONCLUSIONS: Owing to slightly better resolution of 3T images, edema characterization is easier, which might aid in the differential diagnosis of the bone marrow edema. There was, however, no noteworthy difference in the sensitivity of the 1.5T and 3T images to bone marrow edema. Routine identification of acute bone stress changes and suspected stress injuries can, therefore, be made with 1.5T field strength.

Genetic predisposition for femoral neck stress fractures in military conscripts.

BACKGROUND: Stress fractures are a significant problem among athletes and soldiers and may result in devastating complications or even permanent handicap. Genetic factors may increase the risk, but no major susceptibility genes have been identified. The purpose of this study was to search for possible genetic factors predisposing military conscripts to femoral neck stress fractures. RESULTS: Eight genes involved in bone metabolism or pathology (COL1A1, COL1A2, OPG, ESR1, VDR, CTR, LRP5, IL-6) were examined in 72 military conscripts with a femoral neck stress fracture and 120 controls. The risk of femoral neck stress fracture was significantly higher in subjects with low weight and body mass index (BMI). An interaction between the CTR (rs1801197) minor allele C and the VDR C-A haplotype was observed, and subjects lacking the C allele in CTR and/or the C-A haplotype in VDR had a 3-fold higher risk of stress fracture than subjects carrying both (OR = 3.22, 95% CI 1.38-7.49, p = 0.007). In addition, the LRP5 haplotype A-G-G-C alone and in combination with the VDR haplotype C-A was associated with stress fractures through reduced body weight and BMI. CONCLUSIONS: Our findings suggest that genetic factors play a role in the development of stress fractures in individuals subjected to heavy exercise and mechanical loading. The present results can be applied to the design of future studies that will further elucidate the genetics of stress fractures.

An association of serum vitamin D concentrations < 40 nmol/L with acute respiratory tract infection in young Finnish men.

BACKGROUND: The effects of vitamin D in regulating bone mineralization are well documented. The action of vitamin D as a key link between Toll-like receptor activation and antibacterial responses in innate immunity has recently been shown. The data suggest that differences in the ability of human populations to produce vitamin D may contribute to susceptibility to microbial infection. OBJECTIVE: We aimed to explore whether an association exists between vitamin D insufficiency and acute respiratory tract infection in young Finnish men. DESIGN: Young Finnish men (n = 800) serving on a military base in Finland were enrolled for this study. Their serum 25-hydroxyvitamin [25(OH)D] concentrations were measured in July 2002. They were followed for 6 mo, and the number of days of absence from duty due to respiratory infection were counted. RESULTS: The mean (+/- SD) serum 25(OH)D concentrations were 80.2 +/- 29.3 nmol/L (n = 756). Subjects with serum 25(OH)D concentrations < 40 nmol/L (n = 24) had significantly (P = 0.004) more days of absence from duty due to respiratory infection (median: 4; quartile 1-quartile 3: 2-6) than did control subjects (2; 0-4; n = 628; incidence rate ratio 1.63; 95% CI: 1.15, 2.24). We found a significant (P = 0.004) association between serum 25(OH)D concentrations and the amount of physical exercise before induction into military service. We also found significantly (P < 0.001) lower serum 25(OH)D concentrations in subjects who smoked (72.8 +/- 26.6 nmol/L; n = 192) than in control subjects (82.9 +/- 29.7 nmol/L; n = 537). CONCLUSION: Clinical trials of vitamin D supplementation are needed to investigate whether it enhances immunity to microbial infections.

Displaced femoral neck fatigue fractures in military recruits.

BACKGROUND: Displaced fatigue fractures of the femoral neck are uncommon, but they can lead to substantial patient morbidity. This study was performed to examine the incidence, long-term consequences, radiographic findings, risk factors, and complications associated with this fracture. METHODS: Between 1975 and 1994, twenty-one military recruits sustained a displaced fatigue fracture of the femoral neck. Nineteen patients were followed for an average of eighteen years. Data regarding the population at risk, hospital records, initial and follow-up radiographs, and physical findings were analyzed. The impact of instructions from the Finnish Defense Forces, Department of Medical Services, provided in 1986 for prevention of femoral neck fatigue fractures was assessed. RESULTS: At our institution, the incidence of displaced fatigue fractures of the femoral neck was 5.3/100,000 service years from 1975 to 1986, prior to the introduction of the prevention regimen in 1986, and it was 2.3/100,000 service years (95% confidence interval, 0.11 to 1.31) from 1987 to 1994. The rate of Garden type-IV fractures decreased from 3.8 to 0/100,000 service years (95% confidence interval, 0 to 0.66) between the first and second time-periods. The detection of nondisplaced symptomatic fatigue fractures of the femoral neck increased from 15.5 to 53.2/100,000 service years (95% confidence interval, 2.27 to 5.21) between the two time-periods. Eighteen of the nineteen patients had had prodromal symptoms prior to the fracture displacement. Following fracture treatment, six patients had delayed union or nonunion of the fracture. Osteonecrosis of the femoral head developed in six patients and was significantly associated (p = 0.001) with shortening of the femoral neck. Severe osteoarthritis developed in eight patients. CONCLUSIONS: A displaced fatigue fracture of the femoral neck leads to long-term morbidity in a high percentage of patients. Most patients have prodromal symptoms, which provide an opportunity to prevent fracture displacement. Our results indicate that, in a military setting, an educational program can diminish the incidence of fatigue fracture displacement by increasing the awareness of these fractures and their prodromal symptoms and by facilitating diagnosis in the early stages before displacement occurs. LEVEL OF EVIDENCE: Therapeutic Level III.

Association between serum 25(OH)D concentrations and bone stress fractures in Finnish young men.

UNLABELLED: Low vitamin D level may predict rickets, osteomalacia, or osteoporosis. We examined serum 25(OH)D concentration as a predisposing factor for bone stress fracture in 756 military recruits. The average serum 25(OH)D concentration was significantly lower in the group with fracture, suggesting a relationship between vitamin D and fatigue bone stress fracture. INTRODUCTION: Low vitamin D level may predict rickets, osteomalacia, or osteoporosis. Fatigue bone stress fracture is one of the most frequently seen types of overuse injuries in athletes and military recruits. An association was recently shown between vitamin D and BMC. A correlation has also been found between low femoral BMD and stress fractures. We measured serum 25(OH)D concentration in a population sample of military recruits to determine if vitamin D is a predisposing factor for fatigue bone stress fracture. MATERIALS AND METHODS: We prospectively followed 800 randomly selected, healthy Finnish military recruits with a mean age of 19 years for developing stress fractures in homogenous circumstances. Blood for serum 25(OH)D concentration was drawn at entry into military service, and the weight, height, body mass index (BMI), muscle strength, and 12-minute running were measured for all subjects. Serum 25(OH)D concentrations were measured with enzyme immunoassay. At end of the 90-day follow-up, 756 subjects completed the study. Subjects without fracture constituted controls. RESULTS: Twenty-two recruits with stress fracture were identified (2.9%), the incidence being 11.6 (95% CI: 6.8-16.5) per 100 person-years. In the final multivariate analysis, the significant risk factor for stress fracture in conscripts was a below median serum 25(OH)D level (75.8 nM), OR being 3.6 (95% CI: 1.2-11.1). No significant associations between BMI (p = 0.255), age (p = 0.216), or smoking (p = 0.851) and bone stress fracture were found in this study population. CONCLUSIONS: A lower level of serum 25(OH)D concentration may be a generally predisposing element for bone stress fractures. Considering the obvious need of additional vitamin D in prevention of stress fractures, the effects of vitamin D fortification of foods and supplementation will be subjects of interest for future research.

Fatigue bone injuries causing anterior lower leg pain.

UNLABELLED: Shin splints, or stress-related anterior lower leg pain, seem to arise from numerous causes, including stress fractures. We retrospectively reviewed 154 consecutive military patients who had magnetic resonance imaging during a 5-year period for stress-related anterior lower leg pain. Using magnetic resonance imaging, 143 bone stress injuries were diagnosed in 86 of the 154 (56%) patients. The incidence of bone stress injury requiring orthopaedic consultation and magnetic resonance imaging among recruits during the 5 years was 117 per 100,000 person years in military service. The bone stress injury was located in the tibia in 141 (99%) patients. Of these injuries, 80 (57%) were located in the distal (1/3) of the tibial shaft, 42 (30%) in the middle (1/3), 14 (10%) in the proximal (1/3), and five (3%) in the medial condyle. The locations of tibial stress injuries related to the magnetic resonance imaging grades. Almost all lower leg fatigue bone stress injuries were located in the tibia, and the distal lateral shaft was affected most often. When used early after onset of symptoms, magnetic resonance imaging provides accurate diagnosis to ensure appropriate treatment, especially when dealing with exercise-induced lower leg pain in physically active patients. LEVEL OF EVIDENCE: Diagnostic study, Level II (development of diagnostic criteria on consecutive patients [with universally applied reference "gold" standard]). See the Guidelines for Authors for a complete description of levels of evidence.