Use of simple measures of physical activity to predict stress fractures in young men undergoing a rigorous physical training program

[Stress fractures in the military context]

BACKGROUND

Soldiers, especially as recruits, are exposed to significantly elevated stress patterns of the foot due to occupation-related marching and excessive running. This can lead to military-specific stress fractures of the metatarsals, i.e., marching fractures. The treatment and prevention of stress fractures are of particular importance in the military context due to the impact on operational capability and treatment costs. A uniform classification of these fractures does not yet exist.

OBJECTIVE

Review of stress fractures in the military setting with presentation of the incidence, risk factors, classification, treatment and prevention possibilities.

MATERIAL AND METHODS

A PubMed®-based review of the current literature on stress fractures in the military context was conducted and the results were discussed with a focus on specific military medical treatment options.

RESULTS

There are several possibilities to classify stress fractures, the most well-known being a 4-level magnetic resonance imaging (MRI)-based classification. Prevention and treatment possibilities are multifaceted but so far insufficiently validated.

CONCLUSION

Military-specific stress fractures should be grouped according to a 4-level and MRI-based classification. The treatment options include both conservative and surgical measures and should be implemented taking the patient's individual requirements into account. Preventive measures play a key role in the military context. They include the adaptation of screening tools, training and equipment and require continuous evaluation and development.

Epidemiology of Musculoskeletal Injuries in the Navy: A Systematic Review

Objectives: This study aimed to critically review the results of recent studies that investigated the epidemiology of noncombat-related musculoskeletal injuries (MSIs) in the Navy. Methods: A systematic search was conducted of three major databases (Pubmed, Embase, and Cochrane) to identify epidemiological studies on MSIs in the Navy. Study selection and risk of bias assessment were conducted. Results: The overall prevalence of MSIs ranged from 12.69% to 48.81%. And the prevalence of head and face injuries, upper extremity injuries, spine injuries, chest injuries, and lower extremity injuries were 0.11%-0.66%, 0.53%-11.47%, 0.75%-12.09%, 0.43%-0.95%, and 0.4%-21.17%, respectively. For the specific MSIs, the incidence ranged from 0.03/1000 person-years to 32.3/1000 person-years in the Navy and Marines. The ankle-foot, lumbopelvic, knee and lower leg, and shoulder were identified as the most frequent location for MSIs. Conclusion: This systematic review summarized that the Navy population had a high prevalence of MSIs. And different risk factors for MSIs varied from different anatomic locations. This systematic review also provided valuable information on MSIs for sports medicine specialists.

Bone stress injuries

Bone stress injuries, including stress fractures, are overuse injuries that lead to substantial morbidity in active individuals. These injuries occur when excessive repetitive loads are introduced to a generally normal skeleton. Although the precise mechanisms for bone stress injuries are not completely understood, the prevailing theory is that an imbalance in bone metabolism favours microdamage accumulation over its removal and replacement with new bone via targeted remodelling. Diagnosis is achieved by a combination of patient history and physical examination, with imaging used for confirmation. Management of bone stress injuries is guided by their location and consequent risk of healing complications. Bone stress injuries at low-risk sites typically heal with activity modification followed by progressive loading and return to activity. Additional treatment approaches include non-weight-bearing immobilization, medications or surgery, but these approaches are usually limited to managing bone stress injuries that occur at high-risk sites. A comprehensive strategy that integrates anatomical, biomechanical and biological risk factors has the potential to improve the understanding of these injuries and aid in their prevention and management.

Worldwide epidemiology of foot and ankle injuries during military training: a systematic review

INTRODUCTION

Musculoskeletal foot and ankle injuries are commonly experienced by soldiers during military training. We performed a systematic review to assess epidemiological patterns of foot and ankle injuries occurring during military training.

METHODS

A review of the literature was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The search, done on 14 February 2019, resulted in 1603 reports on PubMed, 565 on Embase and 3 on the Cochrane Library. After reading the remaining full-text articles, we included 91 studies.

RESULTS

Among a population of 8 092 281 soldiers from 15 countries, 788 469 (9.74%) foot and ankle injuries were recorded. Among the 49 studies that reported on length of training, there were 36 770/295 040 (18.17%) injuries recorded among women and 248 660/1 501 672 (16.56%) injuries recorded among men over a pooled mean (±SD) training period of 4.51±2.34 months. Ankle injuries were roughly 7 times more common than foot injuries, and acute injuries were roughly 24 times more common than non-acute injuries. Our findings indicated that, during a 3-month training period, soldiers have a 3.14% chance of sustaining a foot and ankle injury. The incidence of foot or ankle injury during military parachutist training was 3.1 injuries per thousand jumps.

CONCLUSIONS

Our findings provide an overview of epidemiological patterns of foot and ankle injuries during military training. These data can be used to compare incidence rates of foot and ankle injuries due to acute or non-acute mechanisms during training. Cost-effective methods of preventing acute ankle injuries and non-acute foot injuries are needed to address this problem.

Models to predict injury, physical fitness failure and attrition in recruit training: a retrospective cohort study

BACKGROUND

Attrition rate in new army recruits is higher than in incumbent troops. In the current study, we identified the risk factors for attrition due to injuries and physical fitness failure in recruit training. A variety of predictive models were attempted.

METHODS

This retrospective cohort included 19,769 Army soldiers of the Australian Defence Force receiving recruit training during a period from 2006 to 2011. Among them, 7692 reserve soldiers received a 28-day training course, and the remaining 12,077 full-time soldiers received an 80-day training course. Retrieved data included anthropometric measures, course-specific variables, injury, and physical fitness failure. Multivariate regression was used to develop a variety of models to predict the rate of attrition due to injuries and physical fitness failure. The area under the receiver operating characteristic curve was used to compare the performance of the models.

RESULTS

In the overall analysis that included both the 28-day and 80-day courses, the incidence of injury of any type was 27.8%. The 80-day course had a higher rate of injury if calculated per course (34.3% vs. 17.6% in the 28-day course), but lower number of injuries per person-year (1.56 vs. 2.29). Fitness test failure rate was significantly higher in the 28-day course (30.0% vs. 12.1%). The overall attrition rate was 5.2 and 5.0% in the 28-day and 80-day courses, respectively. Stress fracture was common in the 80-day course (n = 44) and rare in the 28-day course (n = 1). The areas under the receiver operating characteristic curves for the course-specific predictive models were relatively low (ranging from 0.51 to 0.69), consistent with "failed" to "poor" predictive accuracy. The course-combined models performed somewhat better than the course-specific models, with two models having AUC of 0.70 and 0.78, which are considered "fair" predictive accuracy.

CONCLUSION

Attrition rate was similar between 28-day and 80-day courses. In comparison to the 80-day full course, the 28-day course had a lower rate of injury but a higher number of injuries per person-year and of fitness test failure. These findings suggest fitness level at the commencement of training is a critically important factor to consider when designing the course curriculum, particularly short courses.

Ability of fitness testing to predict injury risk during initial tactical training: a systematic review and meta-analysis

Objective

Tactical personnel (Military, Law Enforcement, Emergency Responders) require physical fitness levels sufficient for training and occupational duty. Physical conditioning aimed at increasing fitness levels during training presents an injury risk, but unfit trainees may struggle to meet occupational performance standards, further increasing injury risk to themselvesor others. Therefore, the aim of this review was to determine if fitness, asquantified by tactical fitness tests, effectively predicts injury risk during training.

Methods

Literature databases were search and relevant articles extracted. 27 Publications were included for qualitative review and seven studies reporting a timed run were included in meta-analysis.

Results

The combined risk ratio was 2.34 (95% CI 2.02 to2.70). Muscular endurance tests were less conclusive in their predictive abilities. Functional strength or power tests were effective predictors, but few studies reported on strength or power, indicating a need for further study inthis area.

Conclusions

The meta-analysis results are supported by the occupational relevance of run tests; tactical trainees are required to perform frequent bouts of distance weight bearing activity. However, given the diverse physical requirements of tactical personnel, measures of strength and power should alsobe evaluated, especially given their effectiveness in the studies that included these measures.

Risk Factors Associated With Musculoskeletal Injury: A Prospective Study of British Infantry Recruits

Background:

Musculoskeletal Injury (MSKI), a common problem in both military and physically active civilian populations, has been suggested to result from both extrinsic and intrinsic factors.

Objective:

To investigate prospectively whether gait biomechanics, aerobic fitness levels and smoking status as well as entry military selection test variables can be used to predict MSKI development during recruit training.

Methods:

British infantry male recruits (n = 562) were selected for the study. Plantar pressure variables, smoking habit, aerobic fitness as measured by a 1.5 mile run time and initial military selection test (combination of fitness, Trainability score) were collected prior to commencement of infantry recruit training. Injury data were collected during the 26 week training period.

Results:

Incidence rate of MSKI over a 26 week training period was 41.28% (95 % CI: 37.28 - 45.40%). The injured group had a higher medial plantar pressure (p < 0.03), shorter time to peak heel rotation (p < 0.02), current smoking status (p < 0.001) and a slower 1.5 mile run time (p < 0.03). In contrast, there were no significant differences (p > 0.23) in lateral heel pressure, age, weight, height, BMI and military selection test. A logistic regression model predicted MSKI significantly (p= 0.03) with an accuracy of 34.50% of all MSK injury and 76.70% of the non-injured group with an overall accuracy of 69.50%.

Conclusion:

The logistic regression model combining the three risk factors was capable of predicting 34.5% of all MSKI. A specific biomechanical profile, slow 1.5 mile run time and current smoking status were identified as predictors of subsequent MSKI development. The proposed model could include evaluation of other potential risk factors and if validated then further enhance the specificity, sensitivity and applicability.

Estimation of energy balance and training volume during Army Initial Entry Training

BACKGROUND

Adequate dietary intake is important for promoting adaptation and prevention of musculoskeletal injury in response to large volumes of physical training such as Army Initial Entry Training (IET). The purpose of this study was to evaluate training volume and dietary intake and estimate energy balance in Army IET soldiers.

METHODS

Dietary intake was assessed by collecting diet logs for three meals on each of three, non-consecutive days during the first week of IET. Training volume was measured across 13 weeks of training using Actigraph wGT3X accelerometers. Training intensity was classified using Sasaki vector magnitude three cut points. Energy expenditure estimates were calculated during weeks two and three of training using the modified Harris-Benedict equation and by estimation of active energy expenditure using metabolic equivalents for each classification of physical activity. All data is presented as mean ± standard deviation.

RESULTS

A total of 111 male soldiers (ht. = ± 173 ± 5.8 cm, age = 19 ± 2 years, mass = 71.6. ± 12.4 kg) completed diet logs and were monitored with Actigraphs. IET soldiers performed on average 273 ± 62 min low, 107 ± 42 min moderate, 26 ± 22 min vigorous, and 10 ± 21 min of very vigorous intensity physical activity daily across 13 weeks. The estimated total daily energy expenditure was on average 3238 ± 457 kcals/d during weeks two and three of IET. Compared to week one caloric intake, there was a caloric deficit of 595 ± 896 kcals/d on average during weeks two and three of IET. Regression analysis showed that body weight was a significant predictor for negative energy balance (adj. R2 = 0.54, p < 0.001), whereby a 1 kg increase in body mass was associated with a 53 kcal energy deficit.

CONCLUSIONS

Based on week one dietary assessment, IET soldiers did not consume adequate calories and nutrients to meet training needs during red phase (weeks one through three). This may directly affect soldier performance and injury frequency. IET soldiers undergo rigorous training, and these data may help direct future guidelines for adequate nourishment to optimize soldier health and performance.

Development of a Prediction Model for Stress Fracture During an Intensive Physical Training Program: The Royal Marines Commandos

BACKGROUND

Stress fractures (SFs) are one of the more severe overuse injuries in military training, and therefore, knowledge of potential risk factors is needed to assist in developing mitigating strategies.

PURPOSE

To develop a prediction model for risk of SF in Royal Marines (RM) recruits during an arduous military training program.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

RM recruits (N = 1082; age range, 16-33 years) who enrolled between September 2009 and July 2010 were prospectively followed through the 32-week RM training program. SF diagnosis was confirmed from a positive radiograph or magnetic resonance imaging scan. Potential risk factors assessed at week 1 included recruit characteristics, anthropometric assessment, dietary supplement use, lifestyle habits, fitness assessment, blood samples, 25(OH)D, bone strength as measured by heel broadband ultrasound attention, history of physical activity, and previous and current food intake. A logistic least absolute shrinkage and selection operator (LASSO) regression with 10-fold cross-validation was used to select potential predictors among 47 candidate variables. Model performance was assessed using measures of discrimination (c-index) and calibration. Bootstrapping was used for internal validation of the developed model and to quantify optimism.

RESULTS

A total of 86 (8%) volunteer recruits presented at least 1 SF during training. Twelve variables were identified as the most important risk factors of SF. Variables strongly associated with SF were age, body weight, pretraining weightbearing exercise, pretraining cycling, and childhood intake of milk and milk products. The c-index for the prediction model, which represents the model performance in future volunteers, was 0.73 (optimism-corrected c-index, 0.68). Although 25(OH)D and VO₂max had only a borderline statistically significant association with SF, the inclusion of these factors improved the performance of the model.

CONCLUSION

These findings will assist in identifying recruits at greater risk of SF during training and will support interventions to mitigate this injury risk. However, external validation of the model is still required.

Low serum 25-hydroxyvitamin D is associated with increased risk of stress fracture during Royal Marine recruit training

The aim of this study was to investigate vitamin D status and stress fracture risk during Royal Marine military training. Poor vitamin D status was associated with an increased risk of stress fracture. Vitamin D supplementation may help to reduce stress fracture risk in male military recruits with low vitamin D status.

INTRODUCTION

Stress fracture is a common overuse injury in military recruits, including Royal Marine (RM) training in the UK. RM training is recognised as one of the most arduous basic training programmes in the world. Associations have been reported between serum 25-hydroxyvitamin D (25(OH)D) and risk of stress fracture, but the threshold of 25(OH)D for this effect remains unclear. We aimed to determine if serum 25(OH)D concentrations were associated with stress fracture risk during RM training.

METHODS

We prospectively followed 1082 RM recruits (males aged 16-32 years) through the 32-week RM training programme. Troops started training between September and July. Height, body weight and aerobic fitness were assessed at week 1. Venous blood samples were drawn at weeks 1, 15 and 32. Serum samples were analysed for 25(OH)D and parathyroid hormone (PTH).

RESULTS

Seventy-eight recruits (7.2 %) suffered a total of 92 stress fractures. Recruits with a baseline serum 25(OH)D concentration below 50 nmol L(-1) had a higher incidence of stress fracture than recruits with 25(OH)D concentration above this threshold (χ(2) (1) = 3.564, p = 0.042; odds ratio 1.6 (95 % confidence interval (CI) 1.0-2.6)). Baseline serum 25(OH)D varied from 47.0 ± 23.7 nmol L(-1) in February, to 97.3 ± 24.6 nmol L(-1) in July (overall mean 69.2 ± 29.2 nmol L(-1), n = 1016). There were weak inverse correlations between serum 25(OH)D and PTH concentrations at week 15 (r = -0.209, p < 0.001) and week 32 (r = -0.214, p < 0.001), but not at baseline.

CONCLUSION

Baseline serum 25(OH)D concentration below 50 nmol L(-1) was associated with an increased risk of stress fracture. Further studies into the effects of vitamin D supplementation on stress fracture risk are certainly warranted.

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.

Stress fracture injury in female endurance athletes in the United Kingdom: A 12-month prospective study

Studies of stress fracture (SF) incidence are limited in number and geographical location; this study determined the incidence of SF injury in female endurance athletes based in the United Kingdom. A total of 70 athletes aged between 18 and 45 years were recruited and prospectively monitored for 12 months. Questionnaires at baseline and 12 months assessed SF, menstrual and training history, eating psychopathology, and compulsive exercise. Peak lower leg muscle strength was assessed in both legs using an isometric muscle rig. Bone mineral density (BMD) of total body, spine, hip, and radius was assessed using dual X-ray absorptiometry. Among the 61 athletes who completed the 12-month monitoring, two sustained a SF diagnosed by magnetic resonance imaging, giving an incidence rate (95% confidence intervals) of 3.3 (0.8, 13.1) % of the study population sustaining a SF over 12 months. The SF cases were 800 m runners aged 19 and 22 years, training on average 14.2 h a week, eumenorrheic with no history of menstrual dysfunction. Case 1 had a higher than average energy intake and low eating psychopathology and compulsive exercise scores, while the reverse was true in case 2. BMD in both cases was similar to mean values in the non-SF group. The incidence of SF in our female endurance athlete population based in the United Kingdom was 3.3%, which is lower than previously reported. Further work is needed to confirm the current incidence of SF and evaluate the associated risk factors.

Diagnosis, treatment, and rehabilitation of stress fractures in the lower extremity in runners

Stress fractures account for between 1% and 20% of athletic injuries, with 80% of stress fractures in the lower extremity. Stress fractures of the lower extremity are common injuries among individuals who participate in endurance, high load-bearing activities such as running, military and aerobic exercise and therefore require practitioner expertise in diagnosis and management. Accurate diagnosis for stress fractures is dependent on the anatomical area. Anatomical regions such as the pelvis, sacrum, and metatarsals offer challenges due to difficulty differentiating pathologies with common symptoms. Special tests and treatment regimes, however, are similar among most stress fractures with resolution between 4 weeks to a year. The most difficult aspect of stress fracture treatment entails mitigating internal and external risk factors. Practitioners should address ongoing risk factors to minimize recurrence.

Management and prevention of bone stress injuries in long-distance runners

SYNOPSIS

Bone stress injury (BSI) represents the inability of bone to withstand repetitive loading, which results in structural fatigue and localized bone pain and tenderness. A BSI occurs along a pathology continuum that begins with a stress reaction, which can progress to a stress fracture and, ultimately, a complete bone fracture. Bone stress injuries are a source of concern in long-distance runners, not only because of their frequency and the morbidity they cause but also because of their tendency to recur. While most BSIs readily heal following a period of modified loading and a progressive return to running activities, the high recurrence rate of BSIs signals a need to address their underlying causative factors. A BSI results from disruption of the homeostasis between microdamage formation and its removal. Microdamage accumulation and subsequent risk for development of a BSI are related both to the load applied to a bone and to the ability of the bone to resist load. The former is more amenable to intervention and may be modified by interventions aimed at training-program design, reducing impact-related forces (eg, instructing an athlete to run "softer" or with a higher stride rate), and increasing the strength and/or endurance of local musculature (eg, strengthening the calf for tibial BSIs and the foot intrinsics for BSIs of the metatarsals). Similarly, malalignments and abnormal movement patterns should be explored and addressed. The current commentary discusses management and prevention of BSIs in runners. In doing so, information is provided on the pathophysiology, epidemiology, risk factors, clinical diagnosis, and classification of BSIs.

LEVEL OF EVIDENCE

Therapy, level 5.

Tibial stress changes in new combat recruits for special forces: patterns and timing at MR imaging

PURPOSE

To characterize the incidence, location, grade, and patterns of magnetic resonance (MR) imaging findings in the tibia in asymptomatic recruits before and after 4-month basic training and to investigate whether MR imaging parameters correlated with pretraining activity levels or with future symptomatic injury.

MATERIALS AND METHODS

This study was approved by three institutional review boards and was conducted in compliance with HIPAA requirements. Volunteers were included in the study after they signed informed consent forms. MR imaging of the tibia of 55 men entering the Israeli Special Forces was performed on recruitment day and after basic training. Ten recruits who did not perform vigorous self-training prior to and during service served as control subjects. MR imaging studies in all recruits were evaluated for presence, type, length, and location of bone stress changes in the tibia. Anthropometric measurements and activity history data were collected. Relationships between bone stress changes, physical activity, and clinical findings and between lesion size and progression were analyzed.

RESULTS

Bone stress changes were seen in 35 of 55 recruits (in 26 recruits at time 0 and in nine recruits after basic training). Most bone stress changes consisted of endosteal marrow edema. Approximately 50% of bone stress changes occurred between the middle and distal thirds of the tibia. Lesion size at time 0 had significant correlation with progression. All endosteal findings smaller than 100 mm resolved or did not change, while most findings larger than 100 mm progressed. Of 10 control subjects, one had bone stress changes at time 0, and one had bone stress changes at 4 months.

CONCLUSION

Most tibial bone stress changes occurred before basic training, were usually endosteal, occurred between the middle and distal thirds of the tibia, were smaller than 100 mm, and did not progress. These findings are presumed to represent normal bone remodeling.

Prevalência e fatores associados à ocorrência de lesões durante a prática de atividade física

INTRODUÇÃO: Embora estudos demonstrem a importância da atividade física na prevenção e manutenção de um padrão de vida saudável, a prática pode determinar um aumento no risco da ocorrência de lesões entre aqueles praticantes de atividades desportivas.OBJETIVO: Determinar a prevalência e os fatores associados à ocorrência de lesões durante a prática de atividade física no tempo de lazer na cidade de Pelotas, RS, Brasil.MÉTODOS: Estudo transversal de base populacional realizado na área urbana do município de Pelotas, RS, Brasil. Uma amostra levando em consideração os diversos conglomerados foi selecionada. Características sociodemográficas, econômicas, comportamentais, nutricionais e relacionadas à ocorrência de lesões durante a prática de atividade física foram coletadas por meio de questionário padronizado e pré-codificado.RESULTADOS: O percentual de lesões em sujeitos praticantes de atividade física no lazer foi de 21,9% (IC95% 18,3 - 25,9). As lesões mais prevalentes foram contusões (39,6%), luxações (30,2%) e distensões (11,3%) e a prática de futebol e musculação foram as atividades onde mais ocorreram lesões. As lesões estiveram associadas ao sexo masculino, idades mais jovens e a indivíduos de cor da pele preta e parda.CONCLUSÃO: Embora a prevalência de lesões entre praticantes seja importante, os benefícios decorrentes de um estilo de vida ativo superam os riscos.

Stress fractures in runners

Stress fractures, were first described in military recruits but in recent years have increasingly been described in runners. In most surveys they comprise between 10 and 20% of all running injuries. The tibia is the most common site of all stress fractures although recent studies involving track and field athletes show an increased incidence of navicular stress fractures. The diagnosis is based on the clinical findings of a history of exercise-related bone pain with local bony tenderness on examination. The diagnosis is often confirmed by a typical appearance on an isotope bone scan or plain radiograph. In general, treatment consists of relative rest from the aggravating activity until symptom-free and then graduated resumption of activity. Attention also needs to be paid to correction of possible causative factors. These include excessive training, low bone density, low calcium intake, menstrual abnormalities in females and biomechanical features such as excessive sub-talar pronation. Certain stress fractures, such as those in the navicular, require specific management, e.g. six weeks non-weight bearing cast immobilization.

A prospective investigation of injury incidence and risk factors among army recruits in combat engineer training

BACKGROUND

United States Army combat engineer (ENG) training is an intense 14-week course designed to introduce new recruits to basic soldiering activities, Army values and lifestyle, and engineering skills and knowledge. The present investigation examined injury rates and injury risk factors in ENG training.

METHODS

At the start of their training, 1,633 male ENG recruits were administered a questionnaire containing items on date of birth, height, weight, tobacco use, prior physical activity, and injury history. Injuries during training were obtained from electronic medical records and the training units provided data on student graduation and attrition. Risk factors were identified using Cox regression.

RESULTS

Ninety-two percent of the recruits successfully graduated from the course and 47% of the recruits experienced one or more injuries during training. Univariate Cox regression demonstrated that recruits were at higher injury risk if they reported that they were older, had a higher or lower body mass index, had smoked in the past, had performed less exercise (aerobic or muscle strength) or sports prior to ENG training, had experienced a previous time-loss lower limb injury (especially if they had not totally recovered from that injury), or had a lower educational level.

CONCLUSIONS

The present investigation was the first to identify injury rates and identify specific factors increasing injury risk during ENG training. The identified risk factors provide a basis for recommending future prevention strategies.

A prospective investigation of injury incidence and injury risk factors among Army recruits in military police training

BACKGROUND

United States Army military police (MP) training is a 19-week course designed to introduce new recruits to basic soldiering skills, Army values and lifestyle, and law enforcement skills and knowledge. The present investigation examined injury rates and injury risk factors in MP training.

METHODS

At the start of training, 1,838 male and 553 female MP recruits were administered a questionnaire containing items on date of birth, height, weight, tobacco use, prior physical activity, injury history, and menstrual history. Injuries during training were obtained from electronic medical records and the training units provided data on student graduation and attrition.

RESULTS

Successfully graduating from the course were 94.3% of the men and 83.7% of the women. Experiencing at least one injury during training were 34.2% of the men and 66.7% of the women (risk ratio (women/men) = 1.95, 95% confidence interval = 1.79-2.13). Recruits were at higher injury risk if they reported that they were older, had smoked in the past, or had performed less frequent exercise or sports prior to MP training. Men were at higher injury risk if they reported a prior injury and women were at higher risk if they reported missing at least six menstrual cycles in the last year or had previously been pregnant.

CONCLUSION

The present investigation was the first to identify injury rates and identify specific factors increasing injury risk during MP training.

Step test performance and risk of stress fractures among female army trainees

BACKGROUND

Stress fractures and other musculoskeletal injuries are major sources of morbidity among female military trainees. Several risk factors have been postulated, particularly pre-existing fitness, usually assessed with post-entry run time for ≥ 1.0 mile.

PURPOSE

Physical fitness is not formally evaluated prior to Army entry. If a valid and simple test that identified women at increased risk of stress fracture were available and could be applied prior to entry, it would facilitate cost-benefit studies of deferral or interventions. These analyses were undertaken to determine if a 5-minute step test conducted before entry identified women at increased risk.

METHODS

A prospective study was conducted of weight-qualified women entering the Army in 2005-2006, with analyses completed in 2011. At the pre-entry examination, information was collected on age, BMI, smoking, race, and activity level. Everyone took the step test. All outpatient medical encounters were captured, and stress fractures and other musculoskeletal injuries identified. Women with stress fractures and those with other musculoskeletal injuries were evaluated separately.

RESULTS

1568 women were included in the study; 109 developed stress fractures and 803 other musculoskeletal injury. Women who failed the step test had a 76% higher stress fracture incidence and a 35% higher incidence of other musculoskeletal injuries. There was effect modification between age and test failure for stress fracture.

CONCLUSIONS

A step test that can be administered before military entry identifies women with increased incidence of stress fracture and other musculoskeletal injury. This test could be used pre-entry to defer or target high-risk recruits for tailored fitness training before or after military entrance.

Injury rates and injury risk factors among Federal Bureau of Investigation new agent trainees

BACKGROUND

A one-year prospective examination of injury rates and injury risk factors was conducted in Federal Bureau of Investigation (FBI) new agent training.

METHODS

Injury incidents were obtained from medical records and injury compensation forms. Potential injury risk factors were acquired from a lifestyle questionnaire and existing data at the FBI Academy.

RESULTS

A total of 426 men and 105 women participated in the project. Thirty-five percent of men and 42% of women experienced one or more injuries during training. The injury incidence rate was 2.5 and 3.2 injuries/1,000 person-days for men and women, respectively (risk ratio (women/men) = 1.3, 95% confidence interval = 0.9-1.7). The activities most commonly associated with injuries (% of total) were defensive tactics training (58%), physical fitness training (20%), physical fitness testing (5%), and firearms training (3%). Among the men, higher injury risk was associated with older age, slower 300-meter sprint time, slower 1.5-mile run time, lower total points on the physical fitness test (PFT), lower self-rated physical activity, lower frequency of aerobic exercise, a prior upper or lower limb injury, and prior foot or knee pain that limited activity. Among the women higher injury risk was associated with slower 300-meter sprint time, slower 1.5-mile run time, lower total points on the PFT, and prior back pain that limited activity.

CONCLUSION

The results of this investigation supported those of a previous retrospective investigation emphasizing that lower fitness and self-reported pain limiting activity were associated with higher injury risk among FBI new agents.

Physical and psychological stressors linked with stress fractures in recruit training

This study aimed to measure ambulation in infantry army basic training, and to evaluate if covering more distance can explain stress fractures in a stressor-stress model. Forty-four male combat recruits (18.7 ± 0.7 years) participated in a 6-month rigorous high intensity combat training program. Baseline data included anthropometric measurements, VO(2)max, and psychological questionnaires. Actual distance covered was measured using a pedometer over an 11-week training period. Psychological questionnaires were repeated after 2 months. Sixteen recruits were diagnosed with stress fractures by imaging (SFi = 36.4%). Statistical analysis included comparing measured variables between SFi and those without stress fractures (NSF). The recruits covered 796 ± 157 km, twofold the distance planned of 378 km (P < 0.001). The SFi group covered a distance 16.4% greater than that of the NSF group (866 ± 136 and 744 ± 161 km, respectively, P < 0.01), and also demonstrated greater psychological stress. These data reveal the importance of adherence to or enforcement of military training programs. In the light of these data, the Israeli Defense Forces program needs reappraisal. A stressor-stress response might explain the susceptibility of certain recruits for injury. Using advanced technology, monitoring ambulation may prevent stress fracture development by limiting subjects exceeding a certain level. Psychological profile may also play a role in predicting stress fracture development.

Retrospective examination of injuries and physical fitness during Federal Bureau of Investigation new agent training

Background

A retrospective examination was conducted of injuries, physical fitness, and their association among Federal Bureau of Investigation (FBI) new agent trainees.

Methods

Injuries and activities associated with injuries were obtained from a review of medical records in the medical clinic that served the new agents. A physical fitness test (PFT) was administered at Weeks 1, 7 and 14 of the 17-week new agent training course. The PFT consisted of push-ups, sit-ups, pull-ups, a 300-meter sprint, and a 1.5-mile run. Injury data were available from 2000 to 2008 and fitness data were available from 2004 to early 2009.

Results

During the survey period, 37% of men and 44% of women experienced one or more injuries during the new agent training course (risk ratio (women/men) = 1.18, 95% confidence interval = 1.07-1.31). The most common injury diagnoses were musculoskeletal pain (not otherwise specified) (27%), strains (11%), sprains (10%), contusions (9%), and abrasions/lacerations (9%). Activities associated with injury included defensive tactics training (48%), physical fitness training (26%), physical fitness testing (6%), and firearms training (6%). Over a 6-year period, there was little difference in performance of push-ups, sit-ups, pull-ups, or the 300-meter sprint; 1.5-mile run performance was higher in recent years. Among both men and women, higher injury incidence was associated with lower performance on any of the physical fitness measures.

Conclusion

This investigation documented injury diagnoses, activities associated with injury, and changes in physical fitness, and demonstrated that higher levels of physical fitness were associated with lower injury risk.

Epidemiology of metatarsal stress fractures versus tibial and femoral stress fractures during elite training

BACKGROUND

The training of elite infantry recruits takes a year or more. Stress fractures are known to be endemic in their basic training and the clinical presentation of tibial, femoral, and metatarsal stress fractures are different. Stress fracture incidence during the subsequent progressively more demanding training is not known. The study hypothesis was that after an adaptation period, the incidence of stress fractures during the course of 1 year of elite infantry training would fall in spite of the increasingly demanding training.

MATERIALS AND METHODS

Seventy-six male elite infantry recruits were followed for the development of stress fractures during a progressively more difficult training program composed of basic training (1 to 14 weeks), advanced training (14 to 26 weeks), and unit training (26 to 52 weeks). Subjects were reviewed regularly and those with clinical suspicion of stress fracture were assessed using bone scan and X-rays.

RESULTS

The incidence of stress fractures was 20% during basic training, 14% during advanced training and 23% during unit training. There was a statistically significant difference in the incidence of tibial and femoral stress fractures versus metatarsal stress fractures before and after the completion of phase II training at week 26 (p=0.0001). Seventy-eight percent of the stress fractures during phases I and II training were either tibial or femoral, while 91% of the stress fractures in phase III training were metatarsal. Prior participation in ball sports (p=0.02) and greater tibial length (p=0.05) were protective factors for stress fracture.

CONCLUSION

The study hypothesis that after a period of soldier adaptation, the incidence of stress fractures would decrease in spite of the increasingly demanding elite infantry training was found to be true for tibial and femoral fractures after 6 months of training but not for metatarsal stress fractures. Further studies are required to understand the mechanism of this difference but physicians and others treating stress fractures should be aware of this pattern.

The role of exercise intensity in the bone metabolic response to an acute bout of weight-bearing exercise

We compared the effects of exercise intensity (EI) on bone metabolism during and for 4 days after acute, weight-bearing endurance exercise. Ten males [mean ± SD maximum oxygen uptake (Vo(2max)): 56.2 ± 8.1 ml·min(-1)·kg(-1)] completed three counterbalanced 8-day trials. Following three control days, on day 4, subjects completed 60 min of running at 55%, 65%, and 75% Vo(2max). Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH(2)-terminal propeptides of procollagen type 1 (P1NP), osteocalcin (OC), bone-alkaline phosphatase (ALP)], osteoprotegerin (OPG), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate (PO(4)), and cortisol were measured during and for 3 h after exercise and on four follow-up days (FU1-FU4). At 75% Vo(2max), β-CTX was not significantly increased from baseline by exercise but was higher compared with 55% (17-19%, P < 0.01) and 65% (11-13%, P < 0.05) Vo(2max) in the first hour postexercise. Concentrations were decreased from baseline in all three groups by 39-42% (P < 0.001) at 3 h postexercise but not thereafter. P1NP increased (P < 0.001) during exercise only, while bone-ALP was increased (P < 0.01) at FU3 and FU4, but neither were affected by EI. PTH and cortisol increased (P < 0.001) with exercise at 75% Vo(2max) only and were higher (P < 0.05) than at 55% and 65% Vo(2max) during and immediately after exercise. The increases (P < 0.001) in OPG, ACa, and PO(4) with exercise were not affected by EI. Increasing EI from 55% to 75% Vo(2max) during 60 min of running resulted in higher β-CTX concentrations in the first hour postexercise but had no effect on bone formation markers. Increased bone-ALP concentrations at 3 and 4 days postexercise suggest a beneficial effect of this type of exercise on bone mineralization. The increase in OPG was not influenced by exercise intensity, whereas PTH was increased at 75% Vo(2max) only, which cannot be fully explained by changes in serum calcium or PO(4) concentrations.

Aetiology and risk factors of musculoskeletal disorders in physically active conscripts: a follow-up study in the Finnish Defence Forces

BACKGROUND

Musculoskeletal disorders (MSDs) are the main reason for morbidity during military training. MSDs commonly result in functional impairment leading to premature discharge from military service and disabilities requiring long-term rehabilitation. The purpose of the study was to examine associations between various risk factors and MSDs with special attention to the physical fitness of the conscripts.

METHODS

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.

RESULTS

During the six-month follow-up of two successive cohorts there were 1629 MSDs and 2879 health clinic visits due to MSDs in 944 persons. 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%). 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), high waist circumference (HR 1.7; 95% CI: 1.3-2.2), high body mass index (HR 1.8; 95% CI: 1.3-2.4), poor result in a 12-minute running test (HR 1.6; 95% CI: 1.2-2.2), 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). In addition, risk factors of long-term MSDs (>or=10 service days lost due to one or several MSDs) were analysed: poor result in a 12-minute running test, earlier musculoskeletal symptoms, high waist circumference, high body mass index, not belonging to a sports club and poor result in the combined outcome of the 12-minute running test and standing long jump test were strongly associated with long-term MSDs.

CONCLUSIONS

The majority of the observed risk factors are modifiable and favourable for future interventions. An appropriate intervention based on the present study would improve both aerobic and muscular fitness prior to conscript training. Attention to appropriate waist circumference and body mass index would strengthen the intervention. Effective results from well-planned randomised controlled studies are needed before initiating large-scale prevention programmes in a military environment.

Effect on injuries of assigning shoes based on foot shape in air force basic training

BACKGROUND

This study examined whether assigning running shoes based on the shape of the bottom of the foot (plantar surface) influenced injury risk in Air Force Basic Military Training (BMT) and examined risk factors for injury in BMT.

METHODS

Data were collected from BMT recruits during 2007; analysis took place during 2008. After foot examinations, recruits were randomly consigned to either an experimental group (E, n=1042 men, 375 women) or a control group (C, n=913 men, 346 women). Experimental group recruits were assigned motion control, stability, or cushioned shoes for plantar shapes indicative of low, medium, or high arches, respectively. Control group recruits received a stability shoe regardless of plantar shape. Injuries during BMT were determined from outpatient visits provided from the Defense Medical Surveillance System. Other injury risk factors (fitness, smoking, physical activity, prior injury, menstrual history, and demographics) were obtained from a questionnaire, existing databases, or BMT units.

RESULTS

Multivariate Cox regression controlling for other risk factors showed little difference in injury risk between the groups among men (hazard ratio [E/C]=1.11, 95% CI=0.89-1.38) or women (hazard ratio [E/C]=1.20, 95% CI= 0.90-1.60). Independent injury risk factors among both men and women included low aerobic fitness and cigarette smoking.

CONCLUSIONS

This prospective study demonstrated that assigning running shoes based on the shape of the plantar surface had little influence on injury risk in BMT even after controlling for other injury risk factors.

Stress fracture and military medical readiness: bridging basic and applied research

PURPOSE

Military recruits and distance runners share a special risk of stress fracture injury. Recent efforts by US and Israeli military-sponsored researchers have uncovered important mechanisms and practical low-cost interventions. This article summarizes key findings relevant to prevention of stress fracture, including simple strategies to identify and to mitigate risk.

METHODS

Published research supported through the Bone Health and Military Medical Readiness research program and related military bone research was analyzed for contributions to preventing stress fracture in military recruits and optimizing bone health.

RESULTS

Thousands of military recruits helped test hypotheses about predictors of risk, safer exercise regimens, and rest, nutrition, gait training, and technology interventions to reduce stress fracture risk. Concurrent cellular, animal, and human laboratory studies were used to systematically investigate mechanisms of mechanical forces acting on bone and interactions through muscle, hormonal and genetic influences, and metabolism. The iterative and sometimes simultaneous process of basic discovery and field testing produced new knowledge that will provide safer science-based physical training.

DISCUSSION

Human training studies evaluating effects on bone require special commitment from investigators and funders due to volunteer compliance and attrition challenges. The findings from multiple studies indicate that measures of bone elasticity, fragility, and geometry are as important as bone mineral density in predicting fracture risk, with applications for new measurement technologies. Risk may be reduced by high intakes of calcium, vitamin D, and possibly protein (e.g., milk products). Prostaglandin E2, insulin-like growth factor 1, and estrogens are important mediators of osteogenesis, indicating reasons to limit the use of certain drugs (e.g., ibuprofen), to avoid excessive food restriction, and to treat hypogonadism. Abnormal gait may be a correctable risk factor. Brief daily vibration may stimulate bone mineral accretion similar to weight-bearing exercise. Genetic factors contribute importantly to bone quality, affecting fracture susceptibility and providing new insights into fracture healing and tissue reengineering.

Calcium and vitamin d supplementation decreases incidence of stress fractures in female navy recruits

INTRODUCTION

Stress fractures (SFx) are one of the most common and debilitating overuse injuries seen in military recruits, and they are also problematic for nonmilitary athletic populations. The goal of this randomized double-blind, placebo-controlled study was to determine whether a calcium and vitamin D intervention could reduce the incidence of SFx in female recruits during basic training.

MATERIALS AND METHODS

We recruited 5201 female Navy recruit volunteers and randomized them to 2000 mg calcium and 800 IU vitamin D/d or placebo. SFx were ascertained when recruits reported to the Great Lakes clinic with symptoms. All SFx were confirmed with radiography or technetium scan according to the usual Navy protocol.

RESULTS

A total of 309 subjects were diagnosed with a SFx resulting in an incidence of 5.9% per 8 wk. Using intention-to-treat analysis by including all enrolled subjects, we found that the calcium and vitamin D group had a 20% lower incidence of SFx than the control group (5.3% versus 6.6%, respectively, p = 0.0026 for Fisher's exact test). The per protocol analysis, including only the 3700 recruits who completed the study, found a 21% lower incidence of fractures in the supplemented versus the control group (6.8% versus 8.6%, respectively, p = 0.02 for Fisher's exact test).

CONCLUSIONS

Generalizing the findings to the population of 14,416 women who entered basic training at the Great Lakes during the 24 mo of recruitment, calcium and vitamin D supplementation for the entire cohort would have prevented approximately 187 persons from fracturing. Such a decrease in SFx would be associated with a significant decrease in morbidity and financial costs.

Injuries and injury risk factors among members of the United States Army Band

BACKGROUND

This project documented injuries in the professional musical performers of the US Army Band and used a multivariate approach to determine injury risk factors.

METHODS

Injuries were obtained from a medical surveillance database. Administrative records from the Band provided fitness test scores, physical characteristics, performing unit (Blues, Ceremonial, Chorale, Chorus, Concert, Strings), and functional group (strings, winds, keyboard, vocal, percussion, brass). A questionnaire completed by 95% of the Band (n=205) included queries on practice time, physical activity, tobacco use, and medical care.

RESULTS

One or more injuries were diagnosed in 44 and 53% of Band members in the years 2004 and 2005, respectively. In univariate analysis, higher injury risk was associated with higher body mass index (BMI), less physical activity, prior injury, unit, functional group, and practice duration. In multivariate analysis, less self-rated physical activity, a prior injury, and functional group were independent risk factors.

CONCLUSION

In the US Army Band, about half the performers had a medical visit for an injury in a 1-year period and injury risk was associated with identifiable factors.

Risk factors for bone stress injuries: a follow-up study of 102,515 person-years

PURPOSE

The aim of the present study was to assess the risk factors for magnetic resonance imaging (MRI)-detected bone stress injuries in the pelvis, hip, thigh, and knee in a large cohort of Finnish conscripts during a follow-up of 102,515 person-years.

METHODS

An epidemiologic prospective cohort study of 152,095 conscripts, including 2345 (1.5%) females, was conducted. Localized pain in the pelvis, hip, thigh, or knee resulted in an orthopedic surgeon's consultation and subsequent MRI examination at the Central Military Hospital, Helsinki, Finland. Risk factors were systematically collected from 1998 to 2004, including data on conscripts' physical fitness and body composition measured at the beginning of their military service.

RESULTS

Altogether, 319 MRI-detected bone stress injuries of the pelvis, hip, thigh, or knee were identified in our cohort; thus, the incidence was 311 (95% CI: 277-345) per 100,000 person-years. The female:male ratio varied substantially, depending on the anatomic location of the injury; it was highest for sacral injuries (female:male ratio = 51.1) and lowest for injuries of the femoral condyle (female:male ratio = 0.8). In univariate Cox regression analysis, poor muscle strength and a poor result in a 12-min run were significantly associated with bone stress injuries. In multivariable analysis, the strongest risk factors for bone stress injuries were female gender (hazard ratio 8.2; 95% CI: 4.8-14.2) and higher age (hazard ratio 2.1; 95% CI: 1.4-3.1).

CONCLUSIONS

Female military trainees have a highly increased risk of bone stress injuries of the pelvis and hip compared with male conscripts. Sacral stress fractures are typical bone stress injuries in female military recruits. Physicians should remember the possibility of bone stress injury, especially when examining stress-related pain symptoms of the pelvic area in physically active young adult females.

Bilateral femoral fatigue fracture: an unusual fracture in a military recruit

We present a case report of a military recruit who had bilateral fatigue fractures of the distal femur. Possible predisposing factors and the long-term outcome of these unusual stress fractures also are presented. A 19-year-old recruit experienced knee pain 2 weeks after starting his military service. Bilateral nondisplaced transverse fatigue fractures were detected radiographically in the supracondylar region on the right side and in the distal 1/3 of the femoral shaft on the left side. The fractures were treated with plaster casts for 5 weeks and healed properly. Osteopenia was seen in further examinations. At followup after 31 months followup the patient had fully resumed his previous athletic activity level and was symptom-free. Osteopenia still could be detected at the final examination. Nonoperative treatment with careful followup resulted in a favorable outcome in the nondisplaced bilateral distal fatigue femoral fractures in this patient.

Stress fractures in the female athlete

Stress fractures are common among female athletes, especially runners. Although both intrinsic and extrinsic factors can contribute to stress injury etiology, the female athlete triad--negative energy balance leading to menstrual irregularity, and reduced bone mineral mass--is a significant contributor to the incidence of stress fractures in the female athlete. When combined with impact weight-bearing activity, this triad puts these women at increased risk for stress fractures. Treatment must focus on reversing identified risk factors, in addition to relative rest, and maintenance of fitness. Most stress fractures heal without complication. High-risk stress fractures should be evaluated and treated by a practitioner with expertise in the care of these injuries.

Predictors of stress fracture susceptibility in young female recruits

BACKGROUND

Stress fractures account for substantial morbidity for young women undergoing U.S. Marine Corps basic training.

HYPOTHESIS

Certain pretraining characteristics identify women at increased risk of stress fractures during boot camp.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Data collected included baseline performance on a timed run (a measure of aerobic fitness), anthropometric measurements, and a baseline questionnaire highlighting exercise and menstrual status among 2962 women undergoing basic training at the Marine Corps Recruit Depot, Parris Island, in 1995 and 1996.

RESULTS

One hundred fifty-two recruits (5.1%) had 181 confirmed lower extremity stress fractures, with the most common sites being the tibia (25%), metatarsals (22%), pelvis (22%), and femur (20%). Logistic regression models revealed that having low aerobic fitness (a slower time on the timed run) and no menses during the past year were significantly associated with the occurrence of any stress fracture and with pelvic or femoral stress fracture during boot camp.

CONCLUSION

These findings suggest that stress fractures may be reduced if women entering Marine Corps Recruit Depot training participated in pretraining activities designed to improve aerobic fitness. Furthermore, women reporting no menses during the previous year may need additional observation during training.

CLINICAL RELEVANCE

Consistent with previous studies, we found that low aerobic fitness was the only modifiable risk factor associated with stress fractures during boot camp.

Risk factors for clinical stress fractures in male military recruits: a prospective cohort study

This prospective study was aimed at evaluating risk factors for symptomatic stress fractures among 179 Finnish male military recruits, aged 18 to 20 years. The subjects were studied in the very beginning of the military service of 6 to 12 months in summer. Bone mineral content (BMC) and density (BMD) were measured by dual energy X-ray absorptiometry (DXA) at the lumbar spine and at the hip and heel ultrasound investigation was performed. Blood was sampled for determination of serum total and free testosterone, total and free estradiol, sex hormone-binding globulin (SHBG), procollagen type I N propeptide, total and carboxylated osteocalcin, tartrate-resistant acid phosphatase 5b, 25-hydroxyvitamin D (25-OHD), and intact parathyroid hormone (iPTH), as well as for studying the XbaI and PvuII polymorphisms of the estrogen receptor gene and the CAG repeat polymorphism of the androgen receptor gene. Urine was collected for the determination of N-terminal cross-linking telopeptide of type I collagen. Muscle strength was measured and Cooper's test was performed. Current exercise, smoking, calcium intake, and alcohol consumption were recorded using a questionnaire. During military service, 15 men experienced a stress fracture, diagnosed with X-ray in 14 and with nuclear magnetic resonance in one man. Those who experienced a fracture were taller than those who did not (P = 0.047). The result of Cooper's test was worse in the fracture group than in the non-fracture group (P = 0.026). Femoral neck and total hip BMC and BMD, adjusted for age, weight, height, exercise, smoking, and alcohol and calcium intake were lower (P = 0.021-0.041) for the fracture group. Stress fractures associated with higher iPTH levels (P = 0.022) but not with lower 25-OHD levels. Bone turnover markers as well as sex hormone and SHBG levels were similar for men with and without stress fracture. There was no difference in the genetic analyses between the groups. In conclusion, tall height, poor physical conditioning, low hip BMC and BMD, as well as high serum PTH level are risk factors for stress fractures in male Finnish military recruits. Given the poor vitamin D status of young Finnish men, intervention studies of vitamin D supplementation to lower serum PTH levels and to possibly reduce the incidence of stress fractures are warranted.

Relationship between bone morphology and bone quality in male tibias: implications for stress fracture risk

Biomechanical properties were assessed from the tibias of 17 adult males 17-46 years of age. Tissue-level mechanical properties varied with bone size. Narrower tibias were comprised of tissue that was more brittle and more prone to accumulating damage compared with tissue from wider tibias.

INTRODUCTION

A better understanding of the factors contributing to stress fractures is needed to identify new prevention strategies that will reduce fracture incidence. Having a narrow (i.e., more slender) tibia relative to body mass has been shown to be a major predictor of stress fracture risk and fragility in male military recruits and male athletes. The intriguing possibility that slender bones, like those shown in animal models, may be composed of more damageable material has not been considered in the human skeleton.

MATERIALS AND METHODS

Polar moment of inertia, section modulus, and antero-posterior (AP) and medial-lateral (ML) widths were determined for tibial diaphyses from 17 male donors 17-46 years of age. A slenderness index was defined as the inverse ratio of the section modulus to tibia length and body weight. Eight prismatic cortical bone samples were generated from each tibia, and tissue-level mechanical properties including modulus, strength, total energy, postyield strain, and tissue damageability were measured by four-point bending from monotonic (n = 4/tibia) and damage accumulation (n = 4/tibia) test methods. Partial correlation coefficients were determined between each geometrical parameter and each tissue-level mechanical property while taking age into consideration.

RESULTS

Significant correlations were observed between tibial morphology and the mechanical properties that characterized tissue brittleness and damageability. Positive correlations were observed between measures of bone size (AP width) and measures of tissue ductility (postyield strain, total energy), and negative correlations were observed between bone size (moment of inertia, section modulus) and tissue modulus.

CONCLUSIONS

The correlation analysis suggested that bone morphology could be used as a predictor of tissue fragility and stress fracture risk. The average mechanical properties of cortical tissue varied as a function of the overall size of the bone. Therefore, under extreme loading conditions (e.g., military training), variation in bone quality parameters related to damageability may be a contributing factor to the increased risk of stress fracture for individuals with more slender bones.

Use of Self-Assessed Fitness and Exercise Parameters to Predict Objective Fitness

PURPOSE

The purpose of this prospective study was to examine the effectiveness of self-assessed fitness and exercise in predicting objectively measured physical fitness.

METHODS

Study subjects included 1583 men who entered Marine Corps training in San Diego, CA, between September and November 2002 and completed a questionnaire and an objective fitness test. The questionnaire included demographic and self-assessed fitness/exercise items, and was administered immediately upon entry into the training program. The objective fitness measure was obtained using a standardized test after approximately 1 month of training.

RESULTS

Multivariate modeling found that several measures of self-assessed fitness and exercise (estimated number of pull-ups; good, very good, or excellent self-assessed fitness; sweating quite a lot or most or all of the time during physical activity; and competitive experience) were all associated with the objective fitness score. These results remained statistically significant after controlling for age, race, and body mass index (model adjusted R2 = 0.469, P < 0.01).

CONCLUSION

In this analysis, self-assessed fitness and exercise parameters that can be easily ascertained with a short questionnaire predicted objective fitness scores approximately 1 month later. This information could be used by recruiters to make recommendations for pre-enlistment conditioning.

Quantitative ultrasound: use in screening for susceptibility to stress fractures in female army recruits

QUS measurements were made on 4139 female Army recruits at the beginning of basic training (BT). QUS predicted stress fracture in female recruits as well as it predicts hip fracture in elderly women. Recruits with low QUS values and a history of smoking and not exercising had an extremely high risk of stress fracture.

INTRODUCTION

Stress fractures during basic military training (BT) cause morbidity for the recruits and expense for the Military Services. Females have a higher incidence than males. If recruits at high risk for stress fracture could be accurately identified before they began BT, the military might find it advantageous to provide adaptive training programs for them. Currently no accurate methods of risk identification are available. We measured quantitative ultrasound (QUS) in a population sample of female Army recruits to determine if QUS is a useful tool for determining soldiers at high risk of stress fracture during BT.

MATERIALS AND METHODS

We recruited 93% of the population of female recruits entering BT at Fort Leonard Wood, MO, during a 10-month period. We measured calcaneal QUS and administered a risk factor questionnaire at baseline and ascertained stress fractures during the 8 weeks of BT. Logistic regression was used to calculate relative risk (RR) of stress fracture. The area under the receiver-operating characteristic (ROC) curve was also analyzed to determine the sensitivity and specificity of speed of sound (SOS) in predicting stress fracture.

RESULTS

The incidence of stress fracture was 4.7%. SOS was significantly related to the risk of stress fracture. (p < 0.000) The area under the ROC curve was 0.70. The relative risk (RR) of fracture of those in the lowest quintile (Q1) of SOS was 6.7. The highest risk of stress fracture was found in the subgroup of white women in Q1 of SOS who smoked and didn't exercise (RR, 14.4). Over 16% of the fractures occurred in this subgroup, which indicates that about six of these women would need to be assigned to an alternate BT regimen to prevent one stress fracture.

CONCLUSIONS

The combination of QUS measurements with evaluation of individual risk factors can identify recruits who are at the very highest risk of stress fracture. The military may find these data helpful to determine the cost-effectiveness of alternate BT regimens.

Bone stress injuries in asymptomatic elite recruits: a clinical and magnetic resonance imaging study

BACKGROUND

The occurrence and clinical significance of asymptomatic bone stress injuries is unknown.

HYPOTHESIS

To evaluate by clinical and magnetic resonance imaging follow-up the occurrence of asymptomatic bone stress injuries, their clinical significance, and whether they all progress to stress fractures in subjects undergoing intensive physical training.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 1.

METHODS

Twenty-one male elite-unit military recruits voluntarily underwent clinical examination and magnetic resonance imaging before their intensive training period, 6 weeks into it, and on completion of the 5-month training program.

RESULTS

Based on magnetic resonance imaging, a total of 75 bone stress injuries were detected. Only 40% (30/75) of the bone stress injuries had been symptomatic. Symptoms depended on location and magnetic resonance imaging grade of injury, with higher grades usually more symptomatic. Repeated clinical and magnetic resonance imaging assessment indicated that asymptomatic grade I bone stress injuries healed (21/25, 84%) or remained grade I and asymptomatic (3/25, 12%). The numbers of bone stress injuries, symptomatic cases, and recruits with bone stress injury increased toward the end of the intensive training period.

CONCLUSIONS

Asymptomatic grade I bone stress injuries seem common in subjects undergoing intensive physical training. Such bone stress injuries heal or remain asymptomatic grade I bone stress injuries even if intensive physical activity continues. They are therefore of no clinical significance. Only subjects who exhibit symptoms need undergo imaging studies. Subjects with an asymptomatic grade I bone stress injury may continue training but should be clinically monitored for symptoms.

Stress fracture injury in young military men and women

Approximately 5% of all military recruits incur stress fracture injuries during intense physical training, predominately in the lower extremity. We compared young men and women with stress fracture injury (subjects) to a matched group of uninjured volunteers (controls) during a summer training program at the United States Naval Academy to identify possible risk factors for stress fracture injury. The subject group was composed of 13 female and 18 male plebes with training-induced stress fracture injury verified by plain radiographs and/or nuclear bone scan. The control group was composed of 13 female and 18 male plebes who remained without injury during plebe summer training but who were matched with the 31 injured plebes for the Initial Strength Test (1-mi run time, means: women, 7.9 min; men, 6.4 min) and body mass index (means: women, 23.4; men, 23.8). We found that the subjects lost significant body weight (mean, 2.63 +/- 0.54 kg) between Day 1 and the date of their diagnosis of a stress fracture (mean, Day 35) and that they continued to lose weight until the date of their DEXA scan (mean, Day 49). Among female plebes, there was no evidence of the female athlete triad (eating disorders, menstrual dysfunction, or low bone density). Thigh girth was significantly smaller in female subjects than in female controls and trended to be lower in male subjects than in male controls. Total body bone mineral content was significantly lower in the male subjects than in male controls. Bone mineral density of the distal tibia and femoral neck were not significantly different between the groups. DEXA-derived structural geometric properties were not different between subjects and controls. Because, on average, tibias were significantly longer in male subjects than in male controls, the mean bone strength index in male subjects was significantly lower than that of male controls. We conclude that significant, acute weight loss combined with regular daily physical training among young military recruits may be a significant contributing risk factor for stress fracture injuries in young military men and women.