Extrinsic risk factors for injury during sports participation are not inherent to the individual participant. Extrinsic factors that are specific to military units and military occupations can be more difficult to comprehend. Reducing these extrinsic risk factors is a relatively simple process in theory, but in practice there are many unique military obstacles to implementation. Equipment, playing surface, coaching, and rules enforcement are known extrinsic factors associated with sports injury [30]. In a military setting, mitigating these risk factors can be difficult as sports and physical training are often secondary concerns behind mission-specific training.

Military units vary from location to location by the type of unit, operational tempo, and training cycle. There may be a time during the year when a military unit is training at a high operational pace in preparation for an upcoming deployment, prolonged field training exercise (FTX), or skills validation assessment. Some unit leaders believe that offering a sports activity during physical training can be a way to reward soldiers for their hard work and give them a break from the normal rigors of physical training. This practice is also common when a unit returns from a deployment or long field training exercise. While commanders may feel that unit sports participation is a reward for a job well done, the risk of injury is higher due to lower levels of conditioning and fitness. The unit operational tempo is a modifiable extrinsic risk factor for sports injury. Commanders must be aware of this risk and produce a physical training plan accordingly. Furthermore, taking steps to ensure that known risk factors are accounted for when adding sports to the training calendar is critical in mitigating these risks .

Another extrinsic risk factor for sports injury is the use of appropriate safety equipment. In collegiate and professional athletics , it is mandatory for safety equipment to be utilized. For instance, in American football it is unheard of for a player to participate without a helmet or shoulder pads [32]. During military training , a soldier would never conduct a mission without appropriate protective equipment including a ballistic vest, helmet, or weapon. However, when these same soldiers participate in an organized game of flag football, they often wear their normal running shoes. Not wearing appropriate footwear greatly increases the risk of slipping and twisting injuries. The same footwear issue is present when military members participate in other sports as well. Wearing running shoes while playing basketball or softball can also lead to lower extremity injury. Running is perhaps the most popular military sport, and multiple studies indicate that appropriate footwear can help reduce injury. In the basic training environment, running injuries have been investigated in multiple settings with inappropriate footwear being cited as a significant contributing factor [33, 34].

The playing surface is another extrinsic modifiable risk factor for injury in the military setting. Typically, military sports are played in any available open space. These include grassy areas never designed or inspected for organizational sports use, and even large areas of concrete such as empty parking lots. Flag football participation by military personnel results in a considerable injury rate [16]. A major factor in many of these injuries revolves around the playing surface. Often times, open areas on military installations serve multiple purposes, are not level, and are filled with tire ruts and other obstacles that are not easily seen. Combining a poor playing surface with inappropriate equipment only increases the risk of injury. Commanders and unit leaders should take appropriate steps to ensure that appropriate facilities are available for organized sports activities that are added to the training calendar. Furthermore, unit leaders should ensure that the facilities are inspected for potential hazards prior to engaging in sports activities, and any noted deficiencies should be addressed to reduce injury risk .

In addition to equipment and playing surface, the lack of appropriate officiating and coaching are also risk factors for injury. It is common practice for military units to play a particular sport during unit physical training without a trained official. Military units also lack trained coaches or conditioning staff to ensure that members are prepared for sport participation. If the sport is conducted as part of a daily physical training program, there may be no officials or coaches and the responsibility lies with the participants to control the game. With this, it is fairly common for games to become increasingly competitive and physical. This style of play, that is often void of fundamentals and performed by unconditioned participants, creates an environment of increased injury risk. Planning sports activities where the rules of engagement are clarified prior to participation, and assigning personnel to monitor the rules during play, are relatively simple steps that can be taken by unit leaders to enhance the safety of these activities and reduce injury risk .

Intrinsic risk factors are those that are particular to the individual athlete. In some instances these factors may be modifiable; regardless, intrinsic risk factors require identification and subsequent mitigation if appropriate. Hamstring injuries are very common among sports participants and the risk factors for hamstring injury are widely published [35, 36]. Among the intrinsic risk factors, some of the most widely reported are age, flexibility, strength, fitness, and past history of injury [35, 36]. These intrinsic risk factors exist for military members participating in sports and physical training as well.

The first factor to consider is the overall fitness level of the sports participant. One might assume that a high level of fitness is required to join and remain in the military. While there are fitness requirements for military service, these requirements vary from service to service and the enforcement of these standards can vary from unit to unit. As a result, there are individuals in the military that do not meet height/weight or basic fitness standards. Military research indicates that current fitness levels can be a significant risk factor for future injury during military training [23−25]. Increasing the fitness level of military recruits prior to entry into their initial training can reduce the rate of musculoskeletal injury [29, 37]. Identifying members that possess an inadequate level of aerobic fitness and enforcing standards in place concerning passing fitness tests can also ensure that poor fitness becomes less of an impact on injury in the military. A factor often associated with low levels of aerobic fitness is obesity which can also increase the risk of injury [28, 38].

Obesity is another intrinsic risk factor for military and civilian athletes alike [30]. While there are height and weight standards across the military, the enforcement of these standards often varies from unit to unit. Fitness levels and obesity are both modifiable risk factors that are constantly measured as part of the normal unit physical training plan [28]. Identifying these individuals and implementing a plan for improvement prior to unit sports participation is vital to preventing musculoskeletal injury. Another easily identifiable risk factor for injury is history of previous injury.

History of a prior musculoskeletal injury is one of the major predisposing non-modifiable risk factors for injury development [39, 40]. While there is no consensus answer as to why this risk factor exists, one theory is that athletes return to sports prior to fully recovering from their previous injury [40−45]. Athletes or military members with a history of prior injury can be assessed by the sports medical staff to determine any rehabilitative needs prior to sports participation. In the military setting, recovery from injury is often focused on being cleared to participate in unit physical training and complete the mandatory physical fitness tests. These fitness tests are not sports-specific, so significant strength, mobility, or motor control deficits can still exist despite being cleared for full participation in military physical training. While past history of injury is not a modifiable risk factor, the intrinsic deficits that remain after injury may be modifiable, if identified. Furthermore, secondary prevention becomes much more important in military service members with a history of musculoskeletal injury .

Age is another intrinsic risk factor for sports injury development [46, 47]. While the youngest members of the military can be of a similar age to many civilian college athletes, the more experienced members of the military often approaches 45–50 years of age. Increasing years of experience are often associated with promotion and career advancement. Not surprisingly, a higher enlisted rank is found to correlate with increased injury during deployment [48]. Age may also be associated with the type of sports-related injuries experienced by military service members. A recent review reported that acute traumatic joint injuries and fractures seem to be more common in younger military service members, and the risk of these injuries decreases with increasing age. Conversely, the risk for chronic overuse injuries, injuries to the fibrocartilage in the knee and shoulder, and degenerative joint disease and osteoarthritis (OA) is lowest in younger age groups and increases with increasing age [49]. While age is not a modifiable risk factor for injury, it is an easily identifiable risk factor. Unit leaders must decide if the benefits of sports participation are worth the increased risk of injury for their more seasoned military members.

The final intrinsic risk factors to be discussed here include strength, flexibility, and neuromuscular control [50]. Arguably the most important aspect of physical training is the warm-up and cool-down periods. In the military setting, these are often neglected due to time constraints. Strength training in the military is often left to the individual members. Group strength training is rarely performed. When strength training is integrated into a fitness plan, the focus is on fitness test performance and not sports-specific skills. The concept of neuromuscular control has received considerable attention in the civilian sports medicine research literature. Not only is neuromuscular control a known risk factor for injury, integrating an intervention program to improve neuromuscular control can reduce injury risk specifically in the knee [51]. As noted previously, the knee is one of the most common sites for sports-related injury among military service members .

With all of the risk factors for injury discussed, the largest contributor to injury in the military population may be inadequate planning and execution, which can clearly be modified with appropriate command interest and support. A published physical training plan can ensure that participants arrive in the appropriate footwear. Inspecting the playing area prior to the day of competition can identify environmental risks for injury. Ensuring that all participants know the rules of engagement prior to participating in sports activities and that someone is designated to ensure these rules are followed to mitigate injury risk are all important strategies that can make sports participation safer in military populations. Appropriate planning can also help reduce the role that fatigue plays in injury production [23]. There are several studies looking at professional sports teams that identify fatigue as a significant intrinsic risk factor for various injuries [52−56]. Understanding the role of fatigue in a military setting may be best illustrated with an example. A service member on deployment may conduct daily patrols for 12–18 h per day carrying equipment that may exceed 85 pounds. In addition to the physical stresses associated with these missions, there are also significant mental stressors that can lead to fatigue and lack of focus. Upon return to their base, these military members may engage in a sporting activity to help recovery mentally from these stressful missions. Participating in a disorganized sports activity, while physically and mentally fatigued, can increase the risk of musculoskeletal injury.

The majority of research studies focusing on sports injury prevention and management involve civilian athletes at the collegiate and professional levels. Military health-care providers specializing in the delivery of sports medicine, including physical therapists, orthopedists, and sports-trained physicians routinely integrate these research findings into the evaluation and management of injured soldiers. Advancements in the care of civilian athletic populations can have direct implications in the management of military athletes. Looking at the spectrum of care provided to civilian athletes, and comparing that level of care to that provided to military athletes might offer some insight into the management of military sports and fitness injuries.

In 2003, a collegiate football player competing for a nationally ranked university created a national controversy when responding to a question regarding his aggressive style of play. While his language was a bit more colorful than described here, the essence of his response included references to protecting yourself from other players attempting to harm you, competing in a war, and being a soldier on the playing field. His comments came at a time when American military members were involved in actual combat operations in both Afghanistan and Iraq. His realization that college athletics are not combat operations, along with words of advice from the university leadership, resulted in an immediate apology. This was not the first or last reference credited to athletes at all levels of competition alluding to battles occurring on the playing field. We provide care for civilian athletes in a manner consistent with their required level of performance when they step onto these proverbial battlefields. How can we provide that same level of care to military members whose ultimate performance is judged on actual battlefields? Perhaps the answer lies in integrating a civilian model of sports care for our military members [49].

Civilian athletes are afforded structured training programs specific for their sport, top notch training facilities, and readily available access to high quality sports medicine assets that are typically co-located in the training environment. Military service members are constantly preparing for situations where much more is at stake than a simple win or loss. The high rate of sports and fitness injuries prevalent in the military indicates a need to alter the model of health care provided to our military athletes [57]. While personnel and training issues represent seemingly insurmountable obstacles to implementation, integrating aspects of sports care proven effective in the civilian community can only help to improve upon musculoskeletal injury rates observed in the military environment.