A Multiple Intervention Strategy for Reducing Femoral Neck Stress Injuries and Other Serious Overuse Injuries in U.S. Army Basic Combat Training

MILITARY MEDICINE, 177, 9:1081, 2012 A Multiple Intervention Strategy for Reducing Femoral Neck Stress Injuries and Other Serious Overuse Injuries in U.S. Army Basic Combat Training LTC Shawn J. Scott, SP USA*; MAJ David N. Feltwell, SP USA ; MAJ Joseph J. Knapik, MS USA (Ret.) ; Lt Col Colleen B. Barkley, USAFR BSC (Ret.) ; LTC Keith G. Hauret, SP USA (Ret.) ; LTC Steven H. Bullock, SP USA (Ret.) ; COL Rachel K. Evans, SP USA ABSTRACT We hypothesized that the use of evidence based injury prevention strategies would lead to a reduction in the incidence of femoral neck stress injuries (FNSIs) and other serious overuse injuries in U.S. Army Basic Combat Training (BCT). An injury prevention strategy began in late 2008 that included: (1) leadership education, (2) leadership enforcement of proven methods, and (3) injury surveillance and reporting. Data on FNSI and removal from training for injury were analyzed based on the fiscal year 2006 through 2010 (n = 210,002). For men, FNSI were reduced from 13 to 20 cases/10,000 recruits per year (2006 2008) to 8 cases/10,000 recruits in 2010 (p < 0.01); for women, FNSI were reduced from 35 to 41 cases/10,000 recruits per year (2006 2008) to 18 cases/10,000 recruits per year in 2010 (p < 0.01). For men, removals from training for injury were reduced from 0.8 to 1.1 cases/100 recruits per year (2006 2008) to 0.5 cases/100 recruits in 2010 (p < 0.01); for women removal from training for injury was reduced from 2.3 to 2.4 cases/100 recruits (2006 2008) to 1.0 case/100 recruits per years in 2010 (p < 0.01). The time course of the changes suggests that following specific injury prevention methods was effective in reducing injuries. INTRODUCTION A growing challenge for military trainers involves transforming an increasingly overweight and less fit civilian population into a physically effective fighting force. 1 3 This challenge is compounded by the increased risk of injury associated with poor physical fitness and low physical activity before Basic Combat Training (BCT). 4 6 One underlying physiological effect of insufficient preservice physical activity is inadequate adaptation of bone and other connective tissues to high impact activity such as running, cutting, and jumping. 7 According to Wolff s Law, bone remodels in response to stresses placed on it over a long period of time. 8 Therefore, those who are less physically active before military training may not have adequately stressed their bones to develop the strength or geometry required for rigorous military training. 9,10 Army Accessions Command (U.S. Army Recruiting Command website frequently asked questions http://www.2k.army.mil/faqs.htm#costper) estimated in 2010 that the cost to recruit, medically clear, and train a new recruit until assignment to first duty station is between $54,000 and $73,000. 11 Lower extremity bone stress injuries during BCT can result *Tripler Army Medical Center, 1 Jarrett White Road, Honolulu, HI 96859. 171st Infantry Brigade, 4500 Stuart Street, Fort Jackson, SC 29207. U.S. Army Institute of Public Health, 5158 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5422. Moncrief Army Community Hospital, 4500 Stuart Street, Fort Jackson, SC 29207. Brooke Army Medical Center, Center for the Intrepid, 3551 Roger Brooke Drive, San Antonio, TX 78234. ku.s. Army Institute for Environmental Medicine, Kansas Street, Building 42 Natick, MA 01760. in considerable additional costs and significantly delay completion of training. 12,13 Many new recruits who incur bone stress injuries are removed from training and reassigned to the Physical Training and Rehabilitation Program (PTRP). At the PTRP, time is provided for the injury to heal and for physical fitness training to match the phase of BCT the soldier will resume when medically cleared. Lower extremity bone stress injuries account for approximately three-quarters of the transfers from BCT into the PTRP. 12,13 The average length of stay for PTRP soldiers from 2001 to 2010 was 93 days at Fort Jackson, South Carolina. Although rehabilitation efforts currently result in approximately a 70% return to duty rate, there is an added cost in time and money related to rehabilitating and retraining a soldier in the PTRP. This cost must be added to the net loss that occurs when approximately 30% of PTRP participants are unable to resume training and are discharged from active military duty. The vast majority of PTRP discharges are medical separations, which come with monetary compensation. Medical separations remove recruits from military service before they reach the operational force. Arguably, the most devastating bone stress injury seen in BCT is the femoral neck stress injury (FNSI). Based on previous research 14,15 and our observations, FNSIs may provide both an acute sign of overtraining and an index of overall bone stress injuries in the BCT environment. Figure 1A shows a FNSI (Grade IV stress fracture) 16 and the results of the surgical procedure to stabilize the femoral neck (Fig. 1B). FNSIs only represent 5 to 10% of bone stress injuries that occur during initial military training, 14,15 but are by far the most costly. A conservative estimate for the average cost of a FNSI is $100,000. The cost estimate exceeds MILITARY MEDICINE, Vol. 177, September 2012 1081

in FNSI incidence and PTRP referrals among BCT units at Fort Jackson, South Carolina. This approach included: (1) leadership education, (2) leadership enforcement of established injury prevention guidance, and (3) injury surveillance. 28 The purpose of this article is to describe these interventions and their impact on FNSI rates and referrals to the PTRP. FIGURE 1. (A) FNSI with fracture (tension side). (B) Postsurgical fixation using cannulated screws in the same hip. this for a soldier with a FNSI that requires surgery and does not return to training. In these cases, a Medical Evaluation Board must determine disability status and costs include: cost to recruit a replacement soldier, cost of the surgery and rehabilitation, salary during recovery, severance pay, PTRP expenses, and additional medical expenses related to the injury for life. Less tangible are the residual human costs of having a surgical repair. In 2008 and 2009 at Fort Jackson, FNSIs resulted in surgical repairs in 25% and 31% of cases, respectively. Although early detection of this injury can allow conservative management and full recovery after weeks to months of rest and rehabilitation, 17 the risk of avascular necrosis of the femoral neck and osteoarthritis of the hip joint increases for surgical cases that involve fracture of the femoral neck with displacement. 18,19 Lee et al 18 documented this complication in 28% of displaced femoral neck fractures in a military population (n = 42). In the same report, five out of seven patients required femoral head replacement surgery within 6 years of injury. 18 The severity and costs associated with bone stress damage and other types of injuries have resulted in a number of intervention studies directed at reducing the incidence of these maladies in BCT. Successful interventions have included reducing running mileage, 20 wearing an orthotic in the boot, 21 modifying training that requires running and marching, 22 and calcium supplementation. 23 The incidence of training-related injuries has also been reduced as a result of modifications in the BCT physical training program, 24,25 preconditioning of recruits, 3 and the use of mouth guards to protect against orofacial injuries. 26 Medical costs and poor long-term outcomes for bone stress injuries provide an argument for a prevention strategy. A study among soldiers in training for vehicle repair and maintenance specialties showed that the overall incidence of injury could be reduced through a combination of leadership involvement, injury prevention education, injury surveillance, and modified physical training. 27 Based on the above studies and specific recommendations from the Joint Services Physical Training Injury Prevention Working Group (JSPTIPWG), 28 we hypothesized that a multiple intervention strategy was needed to facilitate a decrease MATERIALS AND METHODS BCT Program U.S. Army BCT introduces civilian volunteers into the military lifestyle and develops basic soldiering skills. BCT is currently conducted at five locations in the United States, but Fort Jackson, South Carolina trains the largest number of recruits each year and was selected as the site for this injury prevention intervention. The U.S. is an all volunteer force, but not all volunteers qualify for service. Army Regulation 40-501, Standards of Medical Fitness, is used to determine physical and psychological eligibility. All recruits must pass a physical and medical examination at a Military Entrance Processing Station before enlistment. From calendar year (CY) 2006 through 2010, over 210,000 individuals were processed into the Army at Fort Jackson for the 9 to 10-week BCT course (Table I). (BCT was 9 weeks from 2006 through October of 2009 and 10 weeks thereafter). The additional week of training was added to provide commanders the discretion to revisit any area of training that was not adequately addressed during the training cycle (this could be as a result of scheduling conflicts at training locations, inclement weather, poor performance, etc.). In spite of this change, the record Army Physical Fitness Test (APFT) was administered during week 7 of training for the entire period of this program evaluation. Approximately 35% of recruits were women. Men and women were integrated into the same platoons (four platoons per company) and performed all training together. To graduate, a recruit must successfully accomplish the following requirements: (1) qualify with the M-16 rifle (5.56 mm); (2) qualify on a hand grenade range; (3) perform foot marches with equipment; (4) perform climbing and rappelling on high towers; (5) complete obstacle and confidence courses, live fire exercises, convoy operations, and a 5-day field training exercise; (6) demonstrate proficiency in common soldiering tasks; and (7) pass the APFT. Retesting is allowed up until graduation day. For this program evaluation, participants were all BCT recruits who trained at Fort Jackson, from CY 2006 through 2010. This project was reviewed and endorsed by the Institutional Review Board of the Eisenhower Army Medical Center, Fort Gordon, GA 30905. TABLE I. Number of BCT Soldiers at Fort Jackson CY 2006 2010 Year 2006 2007 2008 2009 2010 Means SD Men 26,921 24,628 26,630 29,325 28,446 27,190 1,809 Women 15,032 13,891 18,244 16,048 10,844 14,812 2,447 Totals 41,953 38,519 44,874 45,373 39,290 42,002 2,796 1082 MILITARY MEDICINE, Vol. 177, September 2012

Outcome Measures Staff at the Fort Jackson Medical Treatment Facility and the PTRP maintain a database that contains information on all injured recruits referred to the PTRP and includes injury diagnosis. For the purposes of this article, we compiled the total number of PTRP referrals, and the subset of PTRP referrals with a diagnosis of FNSI per the existing Clinical Management Guidelines (CMG) (Fig. 2), for CYs 2006 through 2010. Since meaningful injury prevention interventions were initiated in 2009, CYs 2006 2008 provided historic information on injury rates before the program changes. Outcomes for men and women were evaluated separately because of historical differences in injury rates for men and women (injury rates for women were about twice that of men in other prospective studies). 5,20,29,30 Data on the number of trainees each year were obtained from the Fort Jackson Directorate of Plans, Training and Mobilization (Table II). Interventions Several injury prevention initiatives were introduced at Fort Jackson from late 2008 to 2010 as described below. The time line of major events is illustrated in Figure 3. Leadership Education The first intervention involved leadership education. 28 During a quarterly meeting between medical and military leadership on Fort Jackson, injury prevention recommendations of the JSPTIPWG were described by the principal author. These recommendations included (Based on Sufficient Scientific Evidence, as described in Bullock et al, 2010): (1) Prevent overtraining (strongly recommended); (2) perform multiaxial, neuromuscular, proprioceptive, and agility training; (3) wear mouth guards during high-risk activities; (4) wear semirigid ankle braces for high-risk activities; (5) consume nutrients to restore energy balance within 1 hour following high-intensity activity; and (6) wear synthetic blend socks to prevent blisters were supported by a review of the literature. 28 In spite of evidence that these interventions reduced injury without compromising physical fitness, many of these recommendations were not systematically known or followed on Fort Jackson. Although this meeting did not result in immediate action, it set the tone for later meetings with Fort Jackson leadership. Based on those meetings, the effort to educate leadership was later refined and expanded to include formal training for future Training and Doctrine Command (TRADOC) leaders who attended precommand training at Fort Jackson s Victory FIGURE 2. Fort Jackson CMG for hip pain. MILITARY MEDICINE, Vol. 177, September 2012 1083

TABLE II. FNSIs and PTRP Referrals, 2006 2010 FNSIs PTRP Referrals Gender Year n Incidence/10,000 RR (95%CI) p-value n Incidence/100 RR (95%CI) p-value Men 2006 35 13.0 0.65 (0.43 1.00) 0.05 204 0.76 0.86 (0.71 1.03) 0.11 2007 44 17.9 0.90 (0.60 1.34) 0.60 261 1.06 1.20 (1.07 1.45) 0.04 2008 53 19.9 1.00 235 0.88 1.00 2009 52 17.7 0.89 (0.61 1.31) 0.55 189 0.64 0.73 (0.60 0.88) <0.01 2010 24 8.4 0.42 (0.26 0.69) <0.01 91 0.32 0.52 (0.42 0.65) <0.01 Women 2006 53 35.3 0.97 (0.68 1.40) 0.89 360 2.39 1.03 (0.89 1.18) 0.67 2007 57 41.0 1.13 (0.80 1.62) 0.48 333 2.40 1.03 (0.90 1.19) 0.67 2008 66 36.2 1.00 424 2.32 1.00 2009 91 56.7 1.57 (1.14-2.15) <0.01 310 1.93 0.83 (0.72 0.96) 0.01 2010 20 18.4 0.51 (0.31 0.84) <0.01 109 1.01 0.43 (0.35 0.53) <0.01 Significantly lower compared to reference year (2008). Significantly higher compared to 2008. University (where military trainers matriculate before taking on training responsibilities). This was accomplished with the support of senior leaders at Fort Jackson and in TRADOC who acknowledged the need to proactively reduce all overuse injuries. In July 2009, an injury prevention curriculum was added to the precommand courses that included information on current fitness levels of recruits, injury risk factors, injury trends, and the cost of overtraining injuries. FNSIs were presented to leaders as an extreme example of poor adherence to exercise principles. Results of studies that support a standardized approach to physical fitness programming (schedule) for BCT soldiers were also presented. 24,25,31 Throughout 2009 and 2010, leadership education and updates of the injury prevention efforts at Fort Jackson were also provided at various conferences and presentations for those already in command throughout TRADOC. Leadership Enforcement of Injury Prevention Guidelines In July 2009, leadership enforcement of evidence-based injury prevention practices was implemented through assignment of a physical therapist to the brigade in charge of Fort Jackson s reception station (where recruits are in-processed before entering BCT) and the PTRP. This subject matter expert on injury evaluation and treatment worked with Fort Jackson, brigade, and PTRP leadership to provide consistent visibility and emphasis for ongoing injury prevention efforts in all Fort Jackson training units. For example, the brigade physical therapist provided case reviews of soldiers who were FIGURE 3. Time line of major injury prevention events at Fort Jackson. DCG-IMT = deputy commanding general of initial military training. 1084 MILITARY MEDICINE, Vol. 177, September 2012

transferred to the PTRP for FNSI to the brigade and Fort Jackson chain of command, which in turn, provided guidance to BCT cadre regarding unstructured high-risk exercise sessions. Fort Jackson training policies and practices were adapted in December 2009 to decrease corrective action (i.e., exercise used as reinforcement to correct minor disciplinary infractions) that included high-impact activities such as running and jumping. In January 2010, leadership enforcement of injury reduction policies and practices was enhanced with the introduction and mandatory inclusion of Physical Readiness Training (PRT). The final draft Training Circular (TC) 3-22.20 for Army PRT served as a unifying document for BCT installations to standardize the physical training programs. Major elements of this standardized exercise program (schedule) were described in previous studies, 24,25 and outcomes of these studies included a significant reduction in overuse injuries and achievement of the same or better APFT success as the control groups. Injury Surveillance and Reporting A third intervention involved injury surveillance and reporting. Starting in the spring of 2009, FNSI reports were distributed by the PTRP database manager to commanders via e-mail showing injury occurrences at the end of each training quarter (3-month period). These reports included graphs, by gender, comparing FNSI for each battalion for the previous quarter and compared to the previous 2 years for the same quarter. Annual reporting provided comparisons to previous fiscal years for each brigade by company (Fig. 4). Injury reporting was enhanced in August 2009 with the implementation of near real-time surveillance and reporting of FNSIs to unit leadership and the installation safety office. This system involved providing a written notification to battalion and company level commanders for each FNSI that required convalescent leave (30-day rest at home for healing) or assignment to the PTRP. This information alerted commanders of individual occurrences of these serious injuries and trends within a training cycle. Earlier notification of injury provided commanders with a new way to monitor training practices from an injury prevention standpoint. Statistical Analysis To determine the effectiveness of the interventions, the yearly incidence of FNSI was calculated as: (cases referred to PTRP/total number of recruits+10,000 (cases/10,000 recruits). Incidence of PTRP referrals was calculated as: (cases referred to PTRP/total number of recruits (cases/100 recruits). c 2 p-values, risk ratios (RRs), and 95% confidence intervals were calculated using the 2 Epidemiological Calculator, version 2.3.1 (http://www.openepi + 100 + 2 Tables Modules in the.com/menu/open EpiMenu.htm). For all comparisons, CY 2008 was selected as the reference year since the major training interventions were initiated in 2009 and carried over to 2010. RESULTS Table II shows incidence of FNSIs and PTRP referrals and statistical results from CY 2006 through CY 2010. Among the men, FNSI incidence was highest in 2008, similar in 2007 and 2009, and reached their lowest level in 2010. Among the women, FNSI incidence was highest in 2009, just shortly after the interventions began, but declined to their lowest point by 2010. PTRP referrals among the men were the highest in 2007 but progressively declined from that point reaching their lowest level in 2010. From 2006 to 2008, PTRP referral incidence reached a plateau at a high level among the women but started to decline in 2009 and reached its lowest point in 2010. Compared to 2008, the FNSI incidence in 2010 was 58% and 50% lower among men and women, respectively. A similar result was seen from 2008 to 2010 for PTRP referrals with a reduction of 64% for men and 57% for women (all adjusted for differences in sample sizes). There were 75 fewer FNSI in 2010 compared to 2008. From a financial standpoint, when adjusted for fewer soldiers in training in 2010 and using $100,000 as the cost basis for each injury, this represented a $5.3 million ($2 million for women and $3.3 million for men) savings for FNSI alone. The additional reduction in PTRP referrals accounted for a savings that has yet to be determined. DISCUSSION We monitored injury outcomes following implementation of a combination of injury prevention interventions that included leadership education, leadership enforcement of established injury prevention guidance, 27,28 and injury surveillance with reporting. Because several interventions were put in place over time, and because most overlapped, it is difficult to separate the effects of each individually. This is a typical challenge when assessing program evaluations involving multiple interventions. Nonetheless, the time course of the changes in the outcome measures provides insight into injury reduction methods that might have been most effective (Fig. 2). Based on the time line, the intervention that is most closely related to a consistent reduction in our outcome variables was the enforcement of the Army PRT exercise program in January 2010. In 2004, a standardized fitness program, very similar to PRT was mandated for all BCT locations, including Fort Jackson, but lack of oversight and resistance from trainers may have led to a dilution of the PRT concepts and ultimately a lack of compliance by 2006. The mandatory reintroduction of PRT in early 2010 coincided with the largest reductions in FNSI and PTRP referrals from 2009 to 2010 ( p = 0.01 for both genders). Demonstrated or MILITARY MEDICINE, Vol. 177, September 2012 1085

FIGURE 4. Comparison of annual FNSI incidence for the 2 BCT brigades at Fort Jackson, fiscal year 2009 2010. A categorical rating system was used to provide feedback to commanders regarding incidence of injury. Commanders received color coded bars: Red > 3 (above average injury rate), Amber 2 3 (high average), Green 0 1 (desirable). 1086 MILITARY MEDICINE, Vol. 177, September 2012

presumed injury prevention concepts in PRT included a reduction in the amount of running, 20 a greater variety of exercise, taking advantage of the cross-training principle, 32 and enforcement of gradual progressive overload. 33 In January 2010, a final draft of the Army s new PRT manual (TC 3-22.20) was provided to all TRADOC units for immediate implementation. In March 2010, the PRT manual was published and, shortly after, became the Army s official physical training doctrine. The other event that was closely associated with the downward trend in FNSI was the policy on corrective action, implemented in December 2009. Elimination of high-impact physical training outside of the prescribed program of training may have stabilized injury outcomes similar to those seen during previous PRT validation studies. 24,25 Constraining corrective action may play an important role in keeping injury rates down as excessive physical activity (intensity or volume (frequency +duration)) can increase injury rates, especially among individuals with initially low fitness levels. 34 Command emphasis on injury reduction was increased as a result of a combination of leader education and injury surveillance with consistent reporting. Action taken after initial efforts to educate leaders was negligible until April 2009, when the Fort Jackson leadership was briefed on injury surveillance and reporting from the PTRP database. These data showed an increase in FNSI over the two quarters after the October 2008 meeting. This underscored the need to use a systematic, multiple intervention approach to complement leadership education. Although enforcement of PRT and modified corrective action were closely associated with the reductions in the injury outcomes, injury surveillance with reporting was also likely of critical importance. By providing battalion commanders with information regarding their FNSI relative to other battalions, an environment favorable to soldier injury prevention was facilitated. Before this project, commanders did not know the relative injury risk that soldiers in their units faced. Given information regarding elevated FNSI rates, some commanders took action on their own to identify modifiable training risks, whereas others sought council from their physical therapist or athletic trainers. For example, one battalion made a significant change to training in the summer of 2009 by incorporating hip strengthening exercises, eliminating flutter kicks and days with two run sessions, and having the least fit runners train only on soft surfaces during the first 3 weeks of training. The intervention was designed by the battalion athletic trainer and led by drill sergeants. The result was a reduction in FNSIs from seven in the previous cycle to zero during the intervention cycle. Other commanders may have instituted their own training modifications, but overall injury trends did not reflect a significant reduction until CY 2010. Based on discussions with battalion commanders (J. Callahan; L. Murray; S. Heintzelman; C. Fortier, Fort Jackson, personal communications, 2010), early notification to senior leadership improved compliance with prescribed activity guidelines among companies whose higher injury rates reflected possible noncompliance. The results of our program evaluation support findings from a previous study conducted among soldiers in advanced mechanical training, where the overall incidence of injuries was reduced through leadership emphasis, surveillance and reporting, and modified physical training. 27 Our program evaluation expands on this previous study by using a separate population (new recruits in training) and a different metric (FNSI and PTRP referrals). The results of these two reports emphasizes that the use of these specific multiple interventions reduce both overall injury rates and the rates of serious bone stress injuries during military training. Limitations Army assignment rotations are such that over the course of 3 years, each company had a complete change of leadership and cadre. This may have lead to some differences in training procedures over time. However, the training program of instruction (POI) for BCT is highly standardized and commanders are held responsible for following the POI. Further, the major interventions, PRT and the policy on corrective action, became policy and were enforced throughout the training command. An important PTRP admission criterion was also changed during the program evaluation. Starting in September 2009, the PTRP Commander required all soldiers to have 30 days of convalescent leave before being transferred to his company. During convalescent leave, soldiers were allowed to return to their home of residence for rest and rehabilitation. Previously, some soldiers went directly to PTRP without taking convalescent leave and others took 30 days convalescent leave first, depending on their unit Commander s preference. This change could have lead to the reduction that we saw in PTRP referrals that preceded the reduction that we saw in FNSI. This is as a result of the fact that some soldiers with minor bone stress injuries heal enough in 30 days to return to training without the need to go to the PTRP. Another limitation was that we did not collect data on the many covariates known to influence injury rates in BCT. These include physical fitness, prior cigarette smoking, prior physical activity, prior injuries, menstrual history, and other factors. 5,6 The relative consistency in BCT entry criteria during the period suggests that differences in these factors across the years might have been minimal. Finally, the use of MRI was not practiced widely before 2008 because of lack of inclusion on the CMG for hip pain; so, it is likely that hip pain with underlying boney edema to the femoral neck was not diagnosed in many cases (because of normal appearance on radiographs). This leads to the assumption that our data before MILITARY MEDICINE, Vol. 177, September 2012 1087

2008 likely under-reported the injury incidence. If this is the case, our results may have underestimated the actual improvement. CONCLUSION The result of our evaluation suggests that FNSIs and other severe overuse injuries can be mitigated through the application of some of the JSPTIPWG recommendations regarding the prevention of overtraining. Standardized physical training, in this case PRT, appears to be a key factor toward optimizing overall intensity and volume in training for injury prevention. An ongoing high incidence of these largely avoidable injuries represents a threat to a successful BCT program. Albeit undesirable, incidence of FNSIs appears to be a quantitative measure of the effectiveness of injury prevention interventions in the BCT environment. Although early detection of injury and evidence-based treatment are an essential part of medicine, they are inevitably more costly and less timely than the preventive approach that was used at Fort Jackson from late 2008 through 2010 (and is ongoing). The effort to reduce injury through a multiple intervention program requires an investment in injury data collection and reporting coupled with educating current and future generations of Army officers, noncommissioned officers, and health care professionals. Collecting unit injury data and presenting this to commanders as part of leadership education may provide the incentive to participate in the process of injury reduction. ACKNOWLEDGMENTS The authors express special appreciation to TRADOC, the Fort Jackson Medical Command and the Fort Jackson Installation Command for full and active participation in the process to reduce overuse training injuries. Their active participation made positive change achievable. All authors are government employees and received no additional funding to participate in this project. There is no conflict of interest between the authors of this report and commercial associations. REFERENCES 1. Flegal KM, Troiano RP: Changes in the distribution of body mass index of adults and children in the US population. Int J Obes Relat Metab Disord 2000; 24(7): 807 18. 2. Kaufman KR, Brodine S, Shaffer R: Military training-related injuries: surveillance, research, and prevention. Am J Prev Med 2000; 18(3 Suppl): 54 63. 3. Knapik JJ, Darakjy S, Hauret KG, et al: Increasing the physical fitness of low-fit recruits before basic combat training: an evaluation of fitness, injuries, and training outcomes. Mil Med 2006; 171(1): 45 54. 4. Jones BH, Bovee MW, Harris JM 3rd, Cowan DN. Intrinsic risk factors for exercise-related injuries among male and female army trainees. Am J Sports Med 1993; 21(5): 705 10. 5. Knapik JJ, Sharp MA, Canham-Chervak M, Hauret K, Patton JF, Jones BH: Risk factors for training-related injuries among men and women in basic combat training. Med Sci Sports Exerc 2001; 33(6): 946 54. 6. Knapik JJ, Swedler DI, Grier TL, et al: Injury reduction effectiveness of selecting running shoes based on plantar shape. J Strength Cond Res 2009; 23(3): 685 97. 7. Finestone A, Milgrom C: How stress fracture incidence was lowered in the Israeli army: a 25-year struggle. Med Sci Sports Exerc 2008; 40(11 Suppl): S623 9. 8. Chen JH, Liu C, You L, Simmons CA: Boning up on Wolff s Law: mechanical regulation of the cells that make and maintain bone. J Biomech 2010; 43(1): 108 18. 9. Heinonen A, Sievanen H, Kyrolainen H, Perttunen J, Kannus P: Mineral mass, size, and estimated mechanical strength of triple jumpers lower limb. Bone 2001; 29(3): 279 85. 10. Petit MA, McKay HA, MacKelvie KJ, Heinonen A, Khan KM, Beck TJ: A randomized school-based jumping intervention confers site and maturity-specific benefits on bone structural properties in girls: a hip structural analysis study. J Bone Miner Res 2002; 17(3): 363 72. 11. U.S. Army Recruiting Command Website. Frequently Asked Questions. Available at http://www.2k.army.mil/faqs.htm#costper; accessed January 25, 2012. 12. Hauret KG, Shippey DL, Knapik JJ: The physical training and rehabilitation program: duration of rehabilitation and final outcome of injuries in basic combat training. Mil Med 2001; 166(9): 820 6. 13. Hauret KG, Knapik JJ, Lange JL, Heckel HA, Coval DL, Duplessis DH: Outcomes of Fort Jackson s Physical Training and Rehabilitation Program in army basic combat training: return to training, graduation, and 2-year retention. Mil Med 2004; 169(7): 562 7. 14. Armstrong DW 3rd, Rue JP, Wilckens JH, Frassica FJ: Stress fracture injury in young military men and women. Bone 2004; 35(3): 806 16. 15. Talbot JC, Cox G, Townend M, Langham M, Parker PJ: Femoral neck stress fractures in military personnel a case series. J R Army Med Corps 2008; 154(1): 47 50. 16. Zwas ST, Elkanovitch R, Frank G: Interpretation and classification of bone scintigraphic findings in stress fractures. J Nucl Med 1987; 28(4): 452 7. 17. Pihlajamaki HK, Ruohola JP, Weckstrom M, Kiuru MJ, Visuri TI: Long-term outcome of undisplaced fatigue fractures of the femoral neck in young male adults. J Bone Joint Surg Br 2006; 88(12): 1574 9. 18. Lee CH, Huang GS, Chao KH, Jean JL, Wu SS: Surgical treatment of displaced stress fractures of the femoral neck in military recruits: a report of 42 cases. Arch Orthop Trauma Surg 2003; 123(10): 527 33. 19. Pihlajamaki HK, Ruohola JP, Kiuru MJ, Visuri TI: Displaced femoral neck fatigue fractures in military recruits. J Bone Joint Surg Am 2006; 88(9): 1989 97. 20. Jones BH, Knapik JJ: Physical training and exercise-related injuries. Surveillance, research and injury prevention in military populations. Sports Med 1999; 27(2): 111 25. 21. Milgrom C, Giladi M, Kashtan H, et al: A prospective study of the effect of a shock-absorbing orthotic device on the incidence of stress fractures in military recruits. Foot Ankle 1985; 6(2): 101 4. 22. Pope RP: Prevention of pelvic stress fractures in female army recruits. Mil Med 1999;164(5): 370 3. 23. Lappe J, Cullen D, Haynatzki G, Recker R, Ahlf R, Thompson K: Calcium and vitamin d supplementation decreases incidence of stress fractures in female navy recruits. J Bone Miner Res 2008;23(5): 741 9. 24. Knapik JJ, Hauret KG, Arnold S, et al: Injury and fitness outcomes during implementation of physical readiness training. Int J Sports Med 2003; 24(5): 372 81. 25. Knapik J, Darakjy S, Scott SJ, et al: Evaluation of a standardized physical training program for basic combat training. J Strength Cond Res 2005; 19(2): 246 53. 26. dela Cruz GG, Knapik JJ, Birk MG: Evaluation of mouthguards for the prevention of orofacial injuries during United States Army Basic Military Training. Dent Traumatol 2006; 24: 86 90. 27. Knapik JJ, Bullock SH, Canada S, et al: Influence of an injury reduction program on injury and fitness outcomes among soldiers. Inj Prev 2004; 10(1): 37 42. 28. Bullock SH, Jones BH, Gilchrist J, Marshall SW. Prevention of physical training-related injuries recommendations for the military and other active populations based on expedited systematic reviews. Am J Prev Med 2010; 38(1 Suppl): S156 81. 1088 MILITARY MEDICINE, Vol. 177, September 2012

29. Bell NS, Mangione TW, Hemenway D, Amoroso PJ, Jones BH: High injury rates among female army trainees: a function of gender? Am J Prev Med 2000; 18(3 Suppl): 141 6. 30. Blacker SD, Wilkinson DM, Bilzon JL, Rayson MP: Risk factors for training injuries among British Army recruits. Mil Med 2008; 173(3): 278 86. 31. Knapik JJ, Scott SJ, Sharp MA, et al: The basis for prescribed ability group run speeds and distances in U.S. Army basic combat training. Mil Med 2006; 171(7): 669 77. 32. Stamford B: Cross-training: giving yourself a whole-body workout. Phys Sportsmed 1996; 24(9): 103 4. 33. McArdle WD, Katch FI, Katch VL: Exercise Physiology: Energy, Nutrition and Human Performance. Philadelphia: Lippincott, Williams, and Wilkins, 2009. 34. Trank TV, Ryman DH, Minagawa RY, Trone DW, Shaffer RA: Running mileage, movement mileage, and fitness in male U.S. Navy recruits. Med Sci Sports Exerc 2001; 33(6): 1033 8. MILITARY MEDICINE, Vol. 177, September 2012 1089