ABSTRACT
Objective
To investigate the association between weight loss before joining the U.S. Army and rates of musculoskeletal injury (MSKI) during physically demanding Basic Combat Training (BCT).
Methods
Self‐reported weight loss was collected on 3168 Army trainees who were followed through electronic medical records for diagnosis of any and region‐specific MSKI. Cox regression models were stratified by sex and COVID‐19 pandemic and adjusted for age, height, maximum‐ever BMI, race/ethnicity, smoking history, prior physical activity, and history of injury.
Results
A total of 829 trainees (26.16%) reported losing weight to enter the Army with mean (SD) weight loss of 9.06 (8.62) kg, most commonly through exercise (83.72%). Trainees who lost weight to enter the Army had lower rates of any (HR: 0.86; 95% CI: 0.74, 0.99) and lower extremity (HR: 0.84; 95% CI: 0.72, 0.98) MSKI during BCT compared to trainees who did not lose weight. Rate of weight loss (mean [SD]: 1.27 [1.06] kg/week) was not associated with any or region‐specific MSKI.
Conclusions
Results indicate that losing excess weight before military training may minimize injuries during training and the relatively gradual rate of weight loss in these trainees did not pose a higher risk of injury.
Keywords: military training, musculoskeletal injury, weight loss
Study Importance.
- What is already known?
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○The rise in obesity limits the number of people eligible for the military based on weight and height criteria, posing a risk to national security.
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○Mainstream media have reported stories on recruits who lost significant weight, but little is known about how many recruits lose weight before enlisting and its influence on musculoskeletal injuries during military training.
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- What does this study add?
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○This study found that approximately a quarter of trainees reported losing weight to join the Army.
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○Weight loss was associated with lower rates of musculoskeletal injuries, particularly lower extremity injuries, enforcing the benefits of losing excess weight on musculoskeletal injuries during military training.
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○Results for rate of weight loss suggest that these trainees' relatively gradual weight loss did not pose a higher risk and that further studies may be needed to assess the long‐term stability of weight loss as well as any potential health consequences and impact of more rapid weight loss.
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○
1. Introduction
The obesity epidemic in the U.S. poses a national security risk for the military by limiting the pool of eligible recruits based on weight‐for‐height and body fat percentage screening criteria. Less than half of the military‐aged population between 17 and 42 years old was considered eligible to enter the military by body mass index (BMI) alone between 2015 and 2020 [1]. When considering all reasons for ineligibility, only 29% of 17– to 24‐year‐olds—the age group accounting for 90% of military recruits—would have been able to join the military in 2018, with having overweight or obesity among the top reasons [2].
Recent programs by the U.S. Army have expanded recruitment to applicants who exceed body fat standards, specifically by no more than 2% for the Assessment of Recruitment Motivation and Strength 2.0 program and between 2% and 6% for the Future Soldier Preparatory Course [3]. Overweight recruits who are not eligible for these programs would have to independently lose weight in order to pass the screening criteria, in some cases with the help of recruiters [4]. However, the percentage of recruits who lose weight to be eligible, how much weight they lost, and by what means they lost weight to join the Army are largely unknown.
Overall weight loss has been associated with reduced musculoskeletal pain in people enrolled in weight loss programs or interventions [5, 6]. Weight loss that occurs too rapidly, however, has been found to be detrimental with regard to muscle damage and injuries in athletes [7, 8, 9]. For instance, the Army Body Composition Program recommends a safe weight loss rate of 3–8 lb or 1% body fat per month for soldiers who exceed the Army's body fat standards [10]. These findings may be relevant to the Basic Combat Training (BCT) environment, a 10‐week physically demanding course for newly enlisted Army soldiers. High percent body fat has long been associated with higher incidence of any injury during BCT [11], and musculoskeletal injuries (MSKIs) are especially prevalent during BCT [12, 13]. To understand the influence of weight loss on injury risk, we investigated whether overall weight loss and the rate of weight loss before enlistment were associated with rates of medically documented MSKIs among Army BCT trainees.
2. Methods
2.1. Study Population
The current analysis includes 3168 Army BCT trainees from the ARIEM Reduction in Musculoskeletal Injury (ARMI) Study, an observational cohort study conducted at Fort Jackson, South Carolina, and Fort Sill, Oklahoma, from 2017 to 2023 [14]. In short, trainees were eligible to participate if they were between 17 and 42 years old, did not have physical activity‐limiting injuries, did not have a history of an endocrine disorder or bone‐modifying disorder, had not had a glucocorticoid drug prescription within 2 years, did not have metal in their bodies that could interfere with bone and body composition scans, and were not pregnant or breastfeeding. Trainees with prior service experience were excluded in the analyses. Research procedures were approved by the U.S. Army Medical Research and Development Command Institutional Review Board, and all participants provided signed informed consent to participate in the study and to access their Army records. The investigators adhered to the policies for protection of human subjects as prescribed in Army Regulation 70–25, and the research was conducted in adherence with the provisions of 45 CFR Part 46.
2.2. Questionnaire and Body Composition
Trainees completed a baseline questionnaire on demographics, including age, sex, race/ethnicity (categorized as Hispanic, non‐Hispanic Black, non‐Hispanic White, and non‐Hispanic other), and smoking history (categorized as ever smoker vs. never smoker). Prior physical activity was assessed as the amount of physical activity prior to entering BCT compared to others of the same age and sex (much less active, somewhat less active, about the same, somewhat more active, much more active). Self‐reported history of injury included any ache, pain, or discomfort in the bones, muscles, ligaments, and tendons that lasted more than 7 days or any stress fracture, broken bone, or concussion.
As part of the baseline questionnaire, trainees were asked, “Did you lose weight to enter the Army?” with follow‐up questions on the amount (“How much weight did you lose?”), duration (“How long did it take you to lose weight before entering BCT?”), and methods of weight loss (“How did you lose weight before BCT?”). Trainees were instructed to select all weight loss methods that applied. Among trainees who reported weight loss, the rate of weight loss was calculated as kilograms (kg)/week from the amount and duration of weight loss. Trainees also reported their maximum‐ever weight at their current height, from which the maximum‐ever BMI was calculated.
Weight and height at the beginning of BCT were measured using a stadiometer and calibrated electronic scale, respectively. Body fat percentage and lean mass were measured via dual‐energy x‐ray absorptiometry (Lunar Prodigy, GE Healthcare).
2.3. Injury Assessment
MSKIs during BCT were defined based on International Classification of Diseases, Tenth Revision, Clinical Modification diagnosis codes from the Military Health System Data Repository inpatient and outpatient medical records. Specific diagnosis codes from G‐, M‐, S‐, and T‐series categorized as MSKI and Neuro‐MSKI in the Defense Centers for Public Health‐Aberdeen's Taxonomy of Injuries were included in the analysis [15]. MSKIs were assessed as any injury and by body region: lower extremity, upper extremity, spine/back, and other including torso and head/neck due to small frequencies. MSKIs during BCT were captured from medical records throughout BCT and up to 6 weeks after BCT to include incident MSKIs that might have occurred during BCT but were not medically documented until after BCT.
2.4. Statistical Analyses
In this prospective cohort study, Cox regression models using time on study as the time scale were conducted for each MSKI outcome to report hazard ratios (HR) and 95% confidence intervals (95% CI). Two separate models were conducted for (i) weight loss as a dichotomous variable, comparing trainees who lost weight to trainees who did not lose weight, among the entire study population and (ii) rate of weight loss as a continuous variable among trainees who reported weight loss. Trainees were followed from the start of BCT to date of MSKI outcome, date of separation, or 6 weeks after BCT, whichever occurred first. A total of 264 trainees who filled the baseline questionnaire on weight loss but did not have linked medical records to ascertain MSKI outcomes were censored at the start of BCT. The models were adjusted for age, height, maximum‐ever BMI, race/ethnicity, smoking history, prior physical activity, and history of injury. Continuous covariates age, height, and maximum‐ever BMI were modeled as restricted cubic splines with four knots. Sex and the indicator variable for whether data collection occurred before or after March 2020 due to the COVID‐19 pandemic were included as stratifying variables in the models because they did not meet the proportional hazards assumption.
Multiple imputation using fully conditional specification methods was used to account for missingness in overall weight loss (0.98%), rate of weight loss (3.35%) due to missing information on amount or duration of weight loss, and covariates whose missingness ranged from 0.47% for prior physical activity to 1.86% for maximum‐ever BMI. Results were pooled across 10 imputations. A sensitivity analysis was conducted restricting to injuries that occurred during BCT and not including the 6 weeks of follow‐up after BCT. All analyses were conducted using SAS 9.4 (SAS Institute Inc.).
3. Results
Trainees were on average 20.96 (standard deviation, SD: 3.82) years old, predominantly non‐Hispanic White (40.81%), male (62.34%), and never smokers (76.07%) (Table 1). Trainees who reported losing weight tended to have higher levels of maximum‐ever BMI, body fat percentage, and lean mass compared to trainees who did not. Of the 3168 trainees, 874 (27.59%) self‐reported history of any injury before BCT. By the end of follow‐up, 1078 out of 2308 (46.71%) trainees who did not report losing weight to enter the Army had at least one medically documented MSKI in 152,725 person‐days, and 360 out 829 (43.43%) trainees who reported losing any weight to enter the Army had at least one medically documented MSKI in 55,439 person‐days. Overall, lower extremity MSKIs made up the most injured region (40.69%), followed by spine/back (7.32%).
TABLE 1.
Trainee characteristics at baseline and frequency of MSKI during BCT (n = 3168).
| Self‐reported weight loss a | |||
|---|---|---|---|
| All (n = 3168) | No (n = 2308) | Yes (n = 829) | |
| Age, years, mean (SD) | 20.96 (3.82) | 20.74 (3.62) | 21.58 (4.30) |
| Body mass, kg, mean (SD) | 72.49 (13.81)1 | 69.55 (12.50)2 | 80.57 (13.93)3 |
| Height, cm, mean (SD) | 170.48 (9.67)4 | 170.67 (9.64)5 | 169.89 (9.73) |
| Maximum‐ever BMI, kg/m2, mean (SD) | 26.71 (4.97)6 | 25.10 (3.99)7 | 31.15 (4.67)8 |
| Body fat, %, mean (SD) | 26.67 (7.65)9 | 25.07 (7.53)10 | 31.20 (6.05)11 |
| Lean mass, kg, mean (SD) | 51.45 (10.68)9 | 50.42 (10.37)10 | 53.92 (11.06)11 |
| Sex, n (%) | |||
| Female | 1193 (37.66) | 850 (36.83) | 335 (40.41) |
| Male | 1975 (62.34) | 1458 (63.17) | 494 (59.59) |
| Race/ethnicity, n (%) | |||
| Black non‐Hispanic | 675 (21.31) | 515 (22.31) | 152 (18.34) |
| White non‐Hispanic | 1293 (40.81) | 964 (41.77) | 318 (38.36) |
| Hispanic | 774 (24.43) | 511 (22.14) | 254 (30.64) |
| Other non‐Hispanic | 426 (13.45) | 318 (13.78) | 105 (12.67) |
| Smoking history, n (%) | |||
| Ever smoker | 734 (23.17) | 529 (22.92) | 191 (23.04) |
| Never smoker | 2410 (76.07) | 1761 (76.30) | 633 (76.36) |
| Missing | 24 (0.76) | 18 (0.78) | 5 (0.60) |
| Prior physical activity, n (%) | |||
| Much less active | 382 (12.06) | 268 (11.61) | 111 (13.39) |
| Somewhat less active | 808 (25.51) | 561 (24.31) | 243 (29.31) |
| About the same | 728 (22.98) | 517 (22.40) | 205 (24.73) |
| Somewhat more active | 860 (27.15) | 662 (28.68) | 192 (23.16) |
| Much more active | 375 (11.84) | 295 (12.78) | 75 (9.05) |
| Missing | 15 (0.47) | 5 (0.22) | 3 (0.36) |
| History of injury, n (%) | |||
| Yes | 874 (27.59) | 644 (27.90) | 230 (27.74) |
| No | 2246 (70.90) | 1647 (71.36) | 588 (70.93) |
| Missing | 48 (1.52) | 17 (0.74) | 11 (1.33) |
| MSKI during BCT, n (%) | |||
| Any | 1447 (45.68) | 1078 (46.71) | 360 (43.43) |
| Lower extremity | 1289 (40.69) | 964 (41.77) | 318 (38.36) |
| Upper extremity | 177 (5.59) | 123 (5.33) | 50 (6.03) |
| Spine/back | 232 (7.32) | 173 (7.50) | 57 (6.88) |
| Other | 107 (3.38) | 78 (3.38) | 29 (3.50) |
Abbreviations: BCT, basic combat training; MSKI, musculoskeletal injury.
Missing for 31 trainees, n = 3138; 1 n = 3140; 2 n = 2286; 3 n = 823; 4 n = 3159; 5 n = 2299; 6 n = 3109; 7 n = 2275; 8 n = 826; 9 n = 3100; 10 n = 2260; 11 n = 816.
Among the 829 trainees who reported losing any weight to enter the Army, the most frequently reported methods of weight loss were exercising more (83.72%), changing diet (61.04%), skipping meals (39.32%), and sweating using a sauna or rubber suit (25.57%) (Table 2). A total of 506 (53.80%) trainees reported both exercising more and changing diet as methods of weight loss. Mean (SD) weight loss was 9.06 (8.62) kg at a rate of 1.27 (1.06) kg/week among 723 trainees with complete information on amount and duration of weight loss. Overall, trainees lost more weight at longer durations of weight loss (Figure 1). A small number of trainees (n = 47, 6.50%) reported losing weight rapidly within 1 week with an average of 2.78 kg.
TABLE 2.
Reported methods of weight loss to join the U.S. Army (n = 829).
| Weight loss method | n (%) |
|---|---|
| Exercising more | 694 (83.72) |
| Changing diet | 506 (61.04) |
| Skipping meals | 326 (39.32) |
| Sauna/rubber suit | 212 (25.57) |
| Weight loss supplements | 105 (12.67) |
| Laxatives | 93 (11.22) |
| Liquid or bar diet | 58 (7.00) |
| Weight loss program | 31 (3.74) |
| Commercial diet | 29 (3.50) |
| Vomiting | 6 (0.72) |
| Missing | 12 (1.45) |
FIGURE 1.
Mean and SD of weight loss (kg) reported prior to entering the Army by quintile of weight loss duration (weeks).
Compared to trainees who did not lose weight to enter the Army, trainees who lost weight had lower rates of any MSKI (HR: 0.86; 95% CI: 0.74, 0.99) and lower extremity MSKIs (HR: 0.84; 95% CI: 0.72, 0.98) during BCT, but no difference in rates of upper extremity MSKIs, spine/back MSKIs, or other MSKIs (Table 3). A higher rate of weight loss was not associated with rates of any MSKI or region‐specific MSKIs (Table 3). Results were similar but less robust for overall weight loss after restricting analyses to the weeks of BCT and not including the 6 weeks after BCT (Table S1).
TABLE 3.
Associations of overall weight loss and rate of weight loss with MSKI during BCT.
| MSKI | Overall weight loss a | Rate of weight loss b |
|---|---|---|
| HR (95% CI) | HR (95% CI) | |
| Any | 0.86 (0.74, 0.99) | 1.06 (0.94, 1.19) |
| Lower extremity | 0.84 (0.72, 0.98) | 1.04 (0.93, 1.17) |
| Upper extremity | 1.09 (0.71, 1.66) | 0.80 (0.60, 1.07) |
| Spine/back | 0.78 (0.54, 1.13) | 1.08 (0.87, 1.33) |
| Other | 0.94 (0.54, 1.63) | 0.99 (0.69, 1.43) |
Note: Cox regression models were adjusted for age, sex, race/ethnicity, smoking history, prior physical activity, history of injury, and maximum‐ever BMI and stratified by sex and whether data collection occurred during the COVID‐19 pandemic.
Abbreviations: BCT, basic combat training; HR, hazard ratio; MSKI, musculoskeletal injury.
Comparing trainees who lost weight to trainees who did not lose weight among the entire study population.
Per kg/week increase in rate of weight loss among trainees who reported weight loss.
4. Discussion
In a population of trainees from two basic training sites, 26% of trainees reported losing weight to join the Army. Trainees who reported losing weight had reduced rates of any MSKI during BCT by approximately 14%, driven by lower rates of lower extremity MSKIs. Lower extremity MSKIs typically account for the majority of MSKIs during BCT, particularly injuries to the knee and ankle [16]. Among trainees who reported losing weight to join the Army, the rate of weight loss was not associated with rates of MSKIs.
While there are individual success stories in mainstream media of recruits losing weight to enlist in the Army [4, 17, 18], there is little data on the number of trainees who had to lose weight to meet enlistment eligibility under the body composition standards. Approximately a quarter of trainees in this study reported losing weight of an average of about 9 kg per trainee. This indicates a considerable number of trainees lost excess weight to enter the Army, but it cannot be ascertained directly in this study whether they lost weight to pass weight‐for‐height accession standards or to be healthier overall before joining the Army. Though a smaller percentage of trainees lost weight quickly within a week, which may reflect water weight, most trainees lost weight over longer durations with increasing amounts of weight lost. The most common methods of weight loss were exercising more and changing diet, although more unhealthy methods such as skipping meals, laxatives, and vomiting were also reported, which warrants further study in relation to injury risk. A study of current soldiers who failed to meet body composition standards reported high prevalence of unhealthy weight loss methods as well that included diet pills (48.7%), skipping meals/fasting (45.3%), and laxatives (22.4%) [19].
Previous studies have shown that weight loss was associated with reduced musculoskeletal pain [5, 6, 20]. Increased body fat and musculoskeletal pain have been observed across cross‐sectional and longitudinal studies for widespread pain as well as site‐specific pain in the low back, knee, and foot [21]. A potential mechanism underlying body fat and musculoskeletal pain is biomechanical stress on load‐bearing joints; in a study of adults with overweight or obesity and knee osteoarthritis, each pound of weight lost was associated with a fourfold reduction in the knee‐joint forces [22]. Other proposed mechanisms include upregulation of cytokines secreted by adipose tissue that are associated with pain and impaired ability to repair joint cartilage and increase in systemic inflammation in obesity associated with chronic pain and structural joint changes [21]. In addition, other studies have found adverse associations of less lean mass with reduced knee and hip strength [23] and more knee pain [24, 25]. As trainees who reported losing weight had more absolute lean mass than trainees who did not at the start of BCT, even after accounting for sex (data not shown), lean mass might have a role in the observed association. There could also be differences in lifestyle factors between the two groups of trainees; for instance, most trainees reported exercising more to lose weight. The ramp‐up of physical activity during BCT for trainees who had been exercising before BCT would likely be more gradual and less intense compared to trainees who did not, potentially putting them at a lower risk for injuries [26]. Prior physical activity level was included in the models, but it might not have fully captured the difference in physical fitness or the influence of the ramp‐up of physical activity between the two groups.
Rapid weight loss is common in weight‐categorized sports where athletes would quickly lose around 5% or more of their body weight before competition weigh‐ins [27]. This rapid weight loss has been associated with injuries among wrestlers, judokas, and taekwondo athletes [8, 9, 28]. In addition, several biomarkers of muscle damage—including myoglobin, creatine kinase, aldolase, and lactate dehydrogenase—were elevated in judokas and mixed martial artists undergoing rapid weight loss [7, 29]. Studies have found decrements in musculoskeletal health including declines in lean mass and suppressed bone formation in extreme energy restriction settings such as the U.S. Army Ranger 8‐week training that involved a calorie deficit of at least 1000 kcal/day [30, 31]. The current study did not observe an association between rate of weight loss and any MSKI during BCT among trainees. A possible explanation is that the mean rate of weight loss at 1.27 kg/week might not have been as extreme, for example, in comparison to wrestlers who lost on average 5.52 (1.44) kg over 7.96 (3.31) days [8]. Approximately half of the trainees lost weight at a rate considered to be safe by the Army of at most 8 lb/month, or 0.91 kg/week. This suggests that these trainees as a whole lost weight at a rate that might not have been rapid enough to confer a higher risk of MSKIs during BCT.
Strengths of this study include a large diverse population with detailed information on weight loss and prospective assessment of MSKIs through medical records. There was, however, missingness in weight loss variables and covariates, which was accounted for through multiple imputation to make use of all available data [32]. In addition, information on duration and amount of weight loss was self‐reported, but the measurement error is not expected to be differential with respect to MSKIs which were captured through medical records at the end of BCT. The medical records might not have captured all MSKIs if trainees did not seek medical care due to concerns on timely graduation or being placed on duty limitation profiles [33]. To minimize this potential underestimate, medical records were followed up for up to 6 weeks after the end of BCT in the event that medical care was sought for MSKIs after graduation. This study captured MSKIs occurring during BCT only and did not investigate whether these results hold up after BCT or in the long term after years of military service. Since it has been reported that soldiers tended to gain weight by 1.5–1.8 kg/year after graduation, further research should also address the potential impact of weight regain or weight fluctuations on injury risk [34]. It is also unclear how increased exercise and dietary changes, which were the two most common weight loss approaches reported by trainees, may have influenced the association. In addition, further research may be warranted to investigate sex differences in the association and the potential underlying mechanisms, as female Army trainees have higher rates of injury [35].
In conclusion, overall weight loss was associated with lower rates of MSKIs during BCT in this prospective observational study of Army trainees. The findings highlight that losing excess weight before entering military training may reduce MSKI risk for incoming recruits, enforcing the benefits of healthy weight loss programs. The findings also suggest relatively gradual weight loss did not pose a higher MSKI risk, in contrast to the association between rapid weight loss and the higher injury risk observed in studies of athletes. Further studies should clarify the influence of more extreme weight loss and methods of weight loss on MSKI risk, particularly in the long term, in military settings, as well as the impact of any weight regain.
Conflicts of Interest
S.A.F. and K.G.A. received support from the Medical Research and Development Command's Military Operational Medicine Program. The other authors declare no conflicts of interest.
Supporting information
Table S1.
Acknowledgments
The authors thank all the study participants and support staff of the ARMI Study without whom this study would not have been possible.
Nguyen V. T., Donovan A. A., Taylor K. M., et al., “Weight Loss Before Basic Combat Training and Musculoskeletal Injuries Among U.S. Army Trainees: The ARMI Study,” Obesity 33, no. 10 (2025): 1977–1983, 10.1002/oby.24364.
Funding: This work was supported by U.S. Army Medical Research and Development Command's Military Operational Medicine Program (20300).
The opinions or assertions in this manuscript are the private views of the authors and should not be construed as official policy or reflecting views of the U.S. Army.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Table S1.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.