From an initial 1165 articles screened after duplicates were removed, 43 were assessed in full text (Figure 1). From the 43 articles, 18 articles were retained. Among those 18 articles, there were 15 cohort studies (1, 3, 9, 22-33) and three cross-sectional studies (1, 2, 34, 35). Methodological quality overall was considered ‘good’ (80%), with cohort studies tending to score higher (82%), than cross-sectional studies (68%). Seven studies assessed injury risk in basic training (16, 22, 25-27, 29, 36), three studies during Advanced Individual Training (AIT) (23, 24, 35), three studies in enlisted personnel more broadly (1, 3, 34), three studies during deployments (2, 32, 33), one study during officer training (9), and one during the first 183 days of service (31). Sixteen of the included studies were conducted in the United States military (1-3, 9, 22-24, 26, 27, 29, 31-36), one in the Israel Defense Forces (30), and one in the British Army (25). A total of 17 potential risk factors for injury were investigated, ranging from demographic and anthropometric factors, such as age, height and weight, to physical performance measures, such as aerobic fitness, or muscle endurance, and to historical factors, such as smoking or injury history, previous activity levels, or deployment history. Factors which were similar, such as running a variety of distances, were grouped for comparison in the synthesis below.
In total, eight studies assessed the influence of age on injury risk in female soldiers (1, 3, 23, 24, 29, 34-36). There were conflicting results, with four studies finding older age was a risk factor for injury, one finding younger age was a risk factor, and three finding no relationship between age and injury risk. Two studies (29, 36) were performed in the basic training context, with varying results. In basic training, female soldiers in the US Army were found to be at a greater injury risk in the age brackets of 25-29.9 years (HR = 1.30 [95% CI = 1.01-1.66], p=0.04) and over 30 years (HR=1.43 [95% CI = 1.12-1.84], p<0.01) when compared to those aged 17-19.9 years (29). Conversely, Knapik et al (36) in 2001 found that age was not associated with injury risk in female recruits undertaking Army basic training when comparing 17–20-year-old recruits with 20-25- and 35-35-year-old recruits.
Two (23, 35) out of three studies performed in the AIT context found that older females were at an increased risk of injury. Women attending AIT in the US Army were significantly more likely to report an injury they had suffered during recruit training which they perceived would affect their current training if they were aged 20-24 years (OR = 1.29 [95% CI = 1.07-1.56], p<0.01) or over 30 years (OR = 2.02 [95% CI = 1.43-2.87], p<0.01) when compared to those aged 17-19 years (23). Likewise, in a study by Henderson et al (35), female Combat Medic AIT trainees aged more than 25 years had a significantly greater (p=0.001) injury incidence (52.9%) than those aged between 20-25 years (21.3%) and younger than 20 years (31.2%). A logistic regression found an OR of 3.5 [95% CI = 1.5-8.1] when comparing odds of injury in those aged more than 25 years to odds in those under 20 years of age (35). Contrasting the aforementioned results, in a population of females attending Ordinance AIT in the US Military, age was not found to be significantly associated with the risk of a time loss injury when comparing those aged 20-24 (HR=0.89 [95% CI = 0.68-1.16], p=0.39) and over 25 years (HR =1.18 [95% CI = 0.86-1.63], p=0.32) to those aged 17-19 years (reference group) (24).
Three studies were conducted on enlisted personnel after completion of both basic training and AIT (1, 3, 34), with these studies finding conflicting results. Age was not found to be associated with injury risk for enlisted females within the US Army in a study by Rappole et al. (1). In the study, the risk of training-related lower extremity injury was not associated with age in 369 female soldiers. Anderson et al. (34) found that younger Army soldiers who were women aged 22 to 26 years were more likely to be injured than both those aged 27 to 30 years and those over 31 years. In total, 57% of the enlisted females in the 22-26 years age bracket suffered an injury, compared with 52% in the 27-30 years age bracket and 48% in the older than 31 years age bracket. This finding was different to that for men in the same study - younger enlisted men were found to be less likely to be injured than those who were older, highlighting possible sex differences in the relationship between age and injury risk. However, another study of US Army soldiers by Bedno et al (3) found older females were at a greater risk of lower limb injury and that, when compared to those who were aged 17-23 years, each increasing age group was at a progressively higher risk of suffering a lower limb injury (Table 2).
The conflicting results across these studies regarding the relationship between age and injury risk in female soldiers do not seem to form any clear patterns, and indicate it is currently unclear whether younger or older age is a risk factor for injury and that other factors may be more important predictors of injury risk.
Body Mass Index
Body Mass Index (BMI) and its relationship to injury risk were considered in seven studies (1, 3, 26, 27, 29, 35, 36). BMI was not found to be significantly associated with injury risk in female personnel in all but one (27) of the four studies conducted during basic training (26, 27, 29, 36), in the one study conducted during AIT (35), and in the two studies involving enlisted personnel (1, 3). In the basic training environment, injury risk in female US Army recruits was not significantly associated with any quartile of BMI in the study by Jones et al (26). Likewise, in two separate studies, Knapik et al (29, 36) found that BMI was not a significant risk factor for injury in female recruits undertaking US Army basic training. Henderson et al (35), found that injury incidence was not significantly different between any levels of BMI during Combat Medic AIT training. BMI was also not a significant predictor of lower limb musculoskeletal injury in the study by Bedno et al. (3), when comparing risk in enlisted female soldiers who were considered to be underweight (<18kg/m2), overweight (25-29.9 kg/m2) or obese (≥30 kg/m2) to risk in those who were considered to be of normal weight (18-24.9 kg/m2). In contrast, in the same study, BMI was found to be a significant predictor amongst male personnel, with underweight, overweight, and obese male soldiers more likely to suffer a lower limb musculoskeletal injury when compared to those considered to be of normal weight. Rappole et al. (1) found a similar result, where BMI was not found to be associated with injury risk in enlisted female soldiers in the US Army.
In contrast, in a large study of 41,727 female recruits undertaking basic training, Jones et al (27) did find a significant bimodal relationship, with low and high BMI associated with increased injury risk. Both the low BMI group of <20.7kg/m2 and high group of > 25.6kg/m2 were found to be at an increased risk of injury when compared to those considered to be in the ‘normal’ range for BMI. This finding suggests that perhaps BMI has not been identified as a significant risk factor in studies with smaller sample sizes due to lower statistical power of those studies to detect such a relationship. However, overall, the volume of evidence suggests that BMI is not a strong and consistent risk factor for injury in female soldiers and that other factors may be more important in predicting injury risk.
Body fat percentage is thought to be a more accurate representation of body composition than BMI (37) and was investigated in five studies (1, 26, 30, 34, 36), with four studies (1, 26, 34, 36) finding no relationship between body fat percentages and injury risk. Body fat percentage was found not to be a predictor of injury risk during basic training for female soldiers in the US Army in two studies (26, 36), and was also not found to be associated with injury risk in a study of enlisted female US Army personnel (1). In a study by Anderson et al., (34) no difference in injury rates was found between tertiles of body fat percentage in female soldiers from the US Army. However, in male soldiers, those in the middle and highest tertile were injured more commonly than those in the lowest tertile (≤29.05%), suggesting while body fat percentage might be a risk factor for male soldiers, it is not an important risk factor in female soldiers.
In contrast to this finding, Kodesh et al (30) found a significant difference (p=0.047) in body fat levels between those female soldiers who were injured (median 23.7%) when compared to those who were not injured (median 22.5%), during a three month Combat Fitness Instructor Course in the IDF. Nevertheless, the volume of evidence suggests that body fat percentage, in general, is not a strong risk factor for injury in female soldiers.
Body mass was examined as a potential risk factor for female soldiers in three studies (26, 35, 36), with only one finding a significant relationship between body mass and injury risk (35). Weight was not found to be a risk factor for injury during army basic training in the US Army in the study by Jones et al (26) nor in the study by Knapik et al (36). In a separate study, female personnel who weighed between 69 and 95kg had a greater incidence of injury during Combat Medic AIT when compared to those weighing less (35). A regression analysis found an OR for injury of 2.4 [95% CI = 1.1-5.0] for those of that weight category when compared to lighter female soldiers (35). Noting the broad confidence interval for this OR and the non-significance of body weight as a risk factor for injury in female recruits in the other two studies, it would appear body mass is unlikely to be a strong risk factor for injury in female soldiers.
Only one study (26) of four that investigated body height as a potential risk factor (9, 26, 35, 36) found a relationship between height and injury risk in female soldiers. Jones et al (26) found that the females in the quartile of shorter stature (~164cm) were at a greater risk of injury during basic training than the taller 75% (RR=1.7 [95% CI = 1.2-2.4], p=0.02). Knapik et al (36) found no significant relationship between stature and injury risk during Army basic training and, likewise, Henderson (35) found no significant differences in injury incidence between female soldiers of varying heights during Combat medic AITs in the US Army. Bijur et al (9) found no relationship between height and injury risk in West Point Officer cadets undertaking their basic training. Height, therefore, does not appear to be a strong risk factor for injury in female soldiers.
Five (3, 22, 24, 29, 36) out of seven of the included studies that investigated smoking as a potential risk factor (3, 22-24, 29, 35, 36) found that smoking was a risk factor for injury among female soldiers. Altarac et al (22) found that female soldiers who had smoked prior to enlisting in the US Army presented with an increased risk of injury overall (OR = 1.61 [95% CI = 1.19-2.17]. This was not found for traumatic injury types (OR=1.05 [95% CI = 0.67-1.64]) but was evident for overuse type injuries (OR = 1.71 [95% CI = 1.26-2.31]), and injuries which were more severe, resulting in greater than ‘one day’ of lost time (OR = 1.44 [95% CI = 1.02-2.02]) or ‘greater than six days’ of lost time (OR = 1.75 [95% CI =1.21-2.51]). Female recruits in US Army basic training who smoked > 20 cigarettes per day were found to be at a significantly greater risk of injury than female recruits who did not smoke (RR = 4.4 [95% CI = 1.9-10.0], p<0.01) (36). In the same study, cigarette smoking was also found to be an independent risk factor for time loss injury in a subsequent multivariate regression analysis (RR = 2.0 [95% CI = 1.2-3.5], p=0.01). A later study in the same environment found an increased risk of injury even with fewer cigarettes per day, with as few as 1-9 cigarettes per day leading to an increased injury risk in female soldiers (HR = 1.44 [95% CI = 1.19-1.73], p<0.01) when compared to those who did not smoke (29). In a similar manner, Bedno et al. (3) found that female US Army soldiers who were currently serving and smoking were at a greater risk of lower limb injury (OR 1.30 [95% CI = 1.23-1.36]) than serving female soldiers who were not smoking.
Grier et al. (24) reported that, overall, females who were both occasional (HR = 1.08 [95% CI = 0.67-1.73], p=0.77) and frequent smokers (HR = 1.27 [95% CI = 0.98-1.63], p=0.07] prior to initial training were not at a significantly increased risk of time loss injury when compared to those who did not smoke. However, when the female soldiers were stratified by the number of cigarettes smoked, a significantly greater risk was evident for those who smoked 20 cigarettes or more per day in the 30 days prior to basic training when compared to those who smoked fewer than 20 cigarettes per day (HR = 1.71 [95% CI=1.12-2.59], p=0.01). In contrast, Grier et al. (23), in their earlier work published in 2010, found that among female soldiers, neither occasional smokers nor frequent smokers were at a significantly greater risk of injury when compared to those who did not smoke, and that comparisons of groups based on number of cigarettes smoked per day did not suggest increases in smoking were associated with an increased risk of injury. Likewise, Henderson et al (35) found no evidence that those female soldiers who reported they were current smokers were at an increased risk of injury during combat medic AIT when compared to those who were not (p=0.190). The volume of evidence nevertheless suggests that smoking is a significant risk factor for injury in female army personnel.
Four studies examined the association between history of previous injury and future injury risk in female soldiers (2, 24, 29, 35), with three (2, 24, 29) showing a significant relationship. Female personnel who had suffered a previous self-reported injury were found to be at an increased risk of subsequent injury during US Army Basic Training (RR = 1.41 [95% CI = 1.13-1.75], p<0.01 (29). Likewise, those who had reported a previous injury were at a greater risk of suffering a ‘time loss’ injury than those who did not report a previous injury during US Army Ordinance school training (HR = 1.67 [95% CI = 1.21-2.30], p<0.01) (24). Enlisted female US Army soldiers were shown to be an increased risk of injury if they had a history of injury (RR=2.6 [95%CI =2.06-3.28]) (2). Conversely, work by Henderson et al (35) found that an injury suffered in basic training did not lead to a higher injury incidence in AIT training for combat medics. In the AIT training, those who reported a previous injury had an injury incidence of 29.5%, whereas those who reported no injury, had an injury incidence of 37.4% (p=0.198).
Current Physical Activity
There are conflicting results regarding the association between reported current level of physical activity performed by female soldiers and injury risk. Rappole et al. (1) found that female soldiers doing more unit physical training (PT), but less personal running and interval training, were at an increased risk of injury. The female enlisted US Army soldiers who were doing unit PT more than once a week were reported to be at a greater risk of injury than those who were doing fewer sessions (OR = 1.96 [95% CI = 1.20-3.21), p<0.01) (1). However, those who were not doing personal running of at least one mile per week or personal interval training at least once per week were found to be at increased risk of injury when compared to those who were doing one of these types of personal training, though the differences were of marginal statistical significance (OR = 1.57 [0.98-2.52], OR = 1.64 [95% CI = 1.00-2.71], respectively).
Conversely, in the study by Roy et al. (2), enlisted female soldiers in the US Army were found to be at an increased risk of injury if they did not do any unit runs each week, when compared to those who did one to two runs per week (RR= 1.53 [95% CI = 1.07-2.19]) (2). In addition, those female soldiers who did one to two personal resistance training sessions per week were reported to be at a greater injury risk than those who did none (RR = 1.42 [95% CI = 1.08-1.87]).
Previous Physical Activity
Four studies assessed the relationship between previous levels of physical activity performed by female soldiers prior to basic training (26, 29, 36) and AIT (35) and injury risk. Only one of the studies conducted during basic training (29) showed an association between self-reported previous activity and injury risk; those who reported that they participated in sport or exercise less than once per week prior to basic combat training were found to be at a greater risk of injury than those who reported greater than five episodes of sport or exercise per week (RR=1.41 [95% CI = 1.09-1.82], p<0.01). A similar result was seen for self-reported running or jogging in the same study, with those reporting a history of less than one session per week being at a greater risk of injury than those two reported five or more sessions per week (RR= 1.62 [95% CI = 1.16-2.27], p<0.01) (29). Conversely, the self-reported amount or duration of physical activity prior to enlistment was not found to be associated with injury incidence in female soldiers undertaking combat medic training (35), or in female recruits undertaking basic training in two other studies (26, 36).
The relationship between deployment history and injury risk was investigated in two studies (2, 3), while individual risk factors for injury during operations in Afghanistan were the focus of two other studies (32, 38). Female soldiers of US Army units who had not been deployed were found to have higher injury rates than those who had been deployed at least twice (RR = 1.48 [95% CI = 1.02-2.13]) (2). A similar finding was reported by Bedno et al. (3), whereby those who had been on one deployment were less likely to be injured than those who had not been deployed (OR =0.65 [95% CI = 0.58-0.72], p<0.001).
Heavy Occupational Tasks
Whilst on deployment, there have been several risk factors reported as increasing the likelihood of injury among female soldiers. Self-reported physically demanding work, walking more than four miles per day, wearing loads greater than 30 pounds, carrying loads for more than 25 feet, lifting objects to waist height or lower, wearing armour for more than an hour a day, wearing a backpack, and lifting an average weight of greater than 50 pounds were all found to be associated with an increased risk of injury in female soldiers deployed in Afghanistan, in two studies by Roy et al (32, 38).
Two studies (2, 3), both involving enlisted, female army personnel, investigated the relationship between injury risk and overall score on the Army Physical Fitness Test (APFT), comprised of a 2-mile run, push-ups, and sit-ups in 2 minutes. Female soldiers who had a score lower than 270 points on the APFT were found to be at an increased risk of lower limb injury, with a gradual increase in risk for those scoring 240-269 points (OR 1.11 [95% CI = 1.03-1.20], p=0.006), 215-239 points (OR = 1.17 [95% CI = 1.09-1.27], p<0.001) and less than 215 points (OR = 1.45 [95% CI = 1.35-1.57], p<0.001) (3). Roy et al (2) found an increased risk even in those scoring up to 290 points, with 290 points being used as a threshold level beyond which risk of injury was lower than that observed in those scoring below that score (Table 2).
Seven studies investigated the relationships between push-up performance and injury risk in female personnel. In trainees, three (27, 29, 36) of four studies (26, 27, 29, 36) reported a relationship between low push-up performance and injury risk during basic training while the remaining study failed to find a significant association.
Of the studies investigating the trainee populations, a study published in 1993 by Jones et al (26) reported no significant differences in injury incidence in female trainees completing basic training in the US Army regardless of quartile of push-up performance. A more recent study by the same authors (27) found an increase in injury risk from 31.6% in those female recruits in the quintile who could perform the most push-ups to 48.8% in the quintile with the lowest push-up performance (RR= 1.5 [95% CI = 1.49-1.61]), with a significant trend linking increasing injury risk to decreasing push up ability (p<0.00001). In the aforementioned more recent study by Jones et al (27), low BMI combined with low push-up ability were also found to be associated with increased injury risk with an injury rate of 50% in basic training for this group (RR 1.7 [95% CI = 1.6-1.9]) when compared to those with normal BMI in the highest push-up quintile. Likewise, female recruits in US Army Basic Training who performed fewer than 14 push-ups were found to be at an increased risk of injury when compared to those female recruits who completed 14 or more push-ups (RR = 1.6 [95% CI = 1.1-2.4], p=0.02) (36). A later study in the same environment found similar results, with female trainees who could only perform between 0-4 push-up repetitions in a 2 minute period being at an increased risk of injury when compared to female trainees who could perform more than 23 repetitions (HR = 1.92 [95% CI = 1.41=2.59], p<0.01) (29).
A study by Grier et al (24), involving 498 female soldiers, investigated push-up performance and injury risk during US Army AIT at the Ordinance School. The authors found that females who could perform more than 37 push-ups were at a decreased risk of time loss injury when compared to those who could perform between 24 and 30 repetitions (HR = 1.44 [95% CI = 1.02-2.04], p=0.04) and less than 23 repetitions (HR = 1.47 [95% CI = 1.03-2.09], p=0.03) (24).
Both studies of enlisted female Army personnel serving after completion of initial training failed to find any association between push-up performance and injury risk (1, 34). The number of push-ups completed as part of the APFT by enlisted female soldiers in the US Army was not found to be associated with risk of injury (1). In line with that finding, no difference was found in injury rates between any tertiles of push-ups within female enlisted US Army soldiers; this contrasts with the finding for male soldiers, in whom risk of injury was found to be increased for male soldiers who performed less than 62 repetitions (RR=1.31 [95% CI = 1.19-1.44], p<0.01) (34). The volume of evidence suggests that low push-up performance may be a risk factor for injury within female soldiers during basic training but potentially not for female soldiers serving after completion of basic training.
Four studies examined sit-up performance in two minutes as a potential risk factor for injuries in female soldiers during basic training (26, 27, 29, 36), one during AIT (24), and two in enlisted soldiers (1, 34). Two studies conducted by Jones et al in 1993 (26) and 2017 (27) did not find an association between sit-up performance and injury risk in basic training. Likewise, Knapik et al (36) found that the number of sit-up repetitions completed was not associated with injury risk during US Army Basic training in 2001. Later, in 2009, Knapik et al (29) found that the number of sit-ups in 2 minutes was a risk factor for injury, with risk increased in those female personnel who could only perform 0-20 repetitions (HR = 1.75 [95% CI = 1.29-2.37] p<0.01), when compared to those who could perform more than 47 repetitions.
Later in the training progression of a soldier, the maximal number of sit-up repetitions was not found to be a risk factor for injury in female soldiers undertaking Ordnance School AIT in the US Army. In the study by Grier et al (24), female soldiers who could perform between 0 and 23 sit-up repetitions were not found to be at a significantly increased risk of injury compared to those who were able to do more than 68 repetitions (HR 1.28 [95% CI = 0.91-1.76], p=0.16).
Female enlisted US Army personnel who performed in the bottom two thirds of sit-up repetitions for the APFT were found to be at an increased risk of injury when compared to those in the upper third (OR = 1.68 [95% CI = 0.96-2.93]), however APFT sit-up repetitions did not feature in a multivariate regression model for prediction of injury in that population (1). Enlisted female soldiers who could not perform more than 62 sit-ups were found to be at a greater risk of injury than those who could perform more than 62 (RR = 1.35 [95% CI = 1.01-1.80], p=0.03) (34). A similar relative risk of injury was found in enlisted men who were unable to complete that number (RR = 1.31 [95% CI = 1.19-1.44], p<0.01) (34). Overall, the volume of evidence suggests sit-up performance may be a weak predictor of injury risk in female soldiers, but the findings are inconsistent.
Strength, Power and Speed Assessments
Kodesh et al. (30) conducted a barrage of power and speed assessments on female soldiers completing a combat fitness instructors’ course in the Israel Defense Forces (IDF). Neither the 10m sprint time nor any parameters measured for the drop jump and the counter movement jump were found to be significantly associated with injury risk. The single leg triple hop distance was found to be significantly associated with injury risk (p=0.029 on the left and p=0.047 on the right). Knapik et al (36) also assessed a variety of strength and power measurements in female recruits undertaking basic training, including incremental dynamic lift strength, upper and lower body strength, upright pull static strength, and a vertical jump assessment, and found no relationship between any measurement and injury risk. Overall, the evidence at this stage does not support or suggests only weak associations between low levels of strength, power or speed and injury risk in female military personnel.
Knapik et al (36) assessed flexibility in females undertaking basic training with the sit-and-reach test and found no significant difference in injury risk for those who scored less (-6cm to 31cm RR = 0.7 [95% CI = 0.4-1.3], p=0.27), or more (40-55cm RR = 0.9 [95% CI = 0.5-1.5], p=0.64) than the referent group of 32-39cm. In contrast, the male trainees did show a relationship between their sit-and-reach performance and injury risk, with a bimodal curve evident in which those who were most and least flexible were at greater risk of injury.
Aerobic fitness, as measured by runs of varying distances, including 3.2km / 2mile (2, 24, 27, 29, 36), 2.4km / 1.5mile (25), 2km (30), or 1 mile (26), a 5 minute step test (31), or average time per mile (9), was found to be related to injury risk in eleven studies that investigated this potential risk factor for injury, and at all stages of a female soldiers career. The one exception was the study by Rappole et al (1), in which the run distance was 2 miles, and completed by 369 female soldiers.
Knapik et al (36) in 2001 found that the slowest two quartiles of 3.2km run times were associated with increased risks of injury in female soldiers when compared to the fastest quartile of 10.38-15.40 mins (RR=1.6 [95% CI = 1.0-2.3], p=0.04, RR = 1.9 [95% CI = 1.2-2.8], p<0.01, respectively). A low peak relative VO2, in the range of 29.9-37.0ml/kg/min was also found to be an independent risk factor for time loss injury in a multivariate cox regression (RR=2.8 [95% CI = 1.4-5.6], p<0.01). A similar result was found by Knapik et al (29) again in 2009, with the slower quartile exhibiting an elevated injury risk (HR=2.18 [95% CI = 1.60-2.98], p<0.01) when compared to those with the quicker run times over 2 miles.
A similar result has also been reported in the British Army for 2.4km / 1.5 mile run times, with female recruits who were injured having a mean time of 12 minutes and 43 seconds, compared to those who were not injured achieving 12 minutes 13 seconds. A subsequent regression analysis found that every 10 second increase in run time was associated with an 8.3% greater injury risk (25). This is in line with the finding of increased incidence of time loss injuries in the slower two quartiles of the 1 mile run during US Army basic training (RR = 2.40 [95% CI = 1.2-4.8] and RR = 2.18 [95% CI = 1.1-5.0] respectively) (26). A more recent study by Jones and colleagues (27) showed the same trend of increasing injury incidence with slower run times. The quintile with the fastest 2-mile run time (<16.2 minutes) had an injury incidence of 26.5% across the basic training period, which increased to 56.0% in the slowest quintile (>19 minutes), with an associated risk ratio of 2.2 [95% CI = 2.0-2.2]. When combined with a low BMI, those who had a slower run time had an injury incidence of 63.1% (RR=2.6 [95% CI = 2.3-2.8], p<0.00001, when compared to those with normal BMI and fastest run time).
Female soldiers attending Ordinance School AIT in the US Army were found to be at increased risk of time loss injury if they ran slower than 19.39 minutes for the 2-mile run, when compared to those who completed it in less than 17 minutes (HR = 2.04 [95% CI = 1.45-2.88], p<0.01) (24). An increased risk was also associated with the 17.01-18.08 minutes timeframe (HR = 1.46[95% CI = 1.02-2.08], p=0.04), but not in the 18.09-19.38-minute timeframe (HR = 1.27 [95% CI = 0.88-1.83], p=0.21). Kodesh (30) also reported significant differences in injury risks associated with different 2km run times (OR = 1.007 [95% CI = 1.001-1.014], p=0.022), with a median time of 658 seconds amongst those who were injured, which was significantly slower than the median time of 640 seconds for those who reported no injury. The authors of that same study performed a Receiver Operating Characteristic analysis and identified an optimal diagnostic cut off at 11minutes and 33 seconds for the 2km run, which predicted injury with a sensitivity of 0.40 and specificity of 0.86. Likewise, females enlisted in US Army units who ran 2 miles in 17-18 minutes were at an increased risk of injury when compared to those who were faster (RR = 1.71 [95% CI = 1.07-2.73]) (2).
The same risk factor appears to exist for cadets undertaking officer training. Female West Point cadets who had slower mean run times per mile were at a greater risk of injury, with injury rates increasing from 42.1 injuries per 100 cadets for those whose mean run time was 7.2 minutes, to 126.3 injuries per 100 cadets for those whose mean run time was 9.8 minutes (9).
Krauss et al (31) explored the interaction between body fat, aerobic fitness, and injury risk in female US Army trainees. They found that those who were deemed to be unfit, as measured by a five-minute step test, were more prone to both non stress fracture injury (IRR = 1.32 [95% CI = 1.14-1.53] and stress fracture injury (IRR = 1.62 [1.19-2.21] than those who were fit. Those who were fit but exceeded body fat limits had an increased risk of non-stress fracture injury (IRR = 1.27 [95% CI = 1.07-1.50] but appeared to be less prone to stress fracture (IRR = 0.79 [95% CI = 0.49-1.28] when compared to females who were both fit and of optimal body fat composition. Those who met the body fat limits but were unfit tended to suffer more stress fractures (IRR = 1.62 [95% CI = 1.19-2.21]). Conversely, Rappole et al (1) did not find 2-mile run times to feature in the multivariate model which was predictive of lower extremity, training related injury among enlisted women (n=369) in the US Army, suggesting that in enlisted women serving in the army, aerobic fitness levels may not be strong predictors of injury risk and other factors may be more important in predicting injury risk.
Movement Assessments (FMS & Y Balance)
One study examined the relationships between Functional Movement Screen (FMS) results and injury during a combat fitness instructors course within the Israel Defense Forces (IDF) (30). No significant difference was found in FMS scores between those injured (mean FMS score = 16 [IRQ=12.75-18.0]) and not injured (mean score = 16 [13.25-17.0]). In attempting to find an optimal cut-off score in the FMS which could be used for prediction of injury risk, Kodesh et al. (30) found that with a score of 12, they only achieved 24% sensitivity and 83% specificity, while a score of 14 led to 42% sensitivity and 63% specificity. Their regression model for prediction of injury risk based on FMS scores was not statistically significant, with an OR of 0.95 ([95% CI = 0.87-1.1], p=0.77), leading the authors to suggest that the FMS was not an effective tool in predicting injury risk in female soldiers in the IDF.
Single leg balance ability and its relationship to injury amongst female soldiers deployed in Afghanistan was assessed in one study (32). Roy et al (32) found that those female soldiers who had a composite score of ≤ 95.23 in the Y Balance assessment were at a significantly greater risk of injury than those who scored above this number (RR = 1.71 [95% CI = 1.13-2.60]. There were no other studies which reported associations between injury risk and results of any other movement assessments.