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. 2024 Oct 21;37(6):517–526. doi: 10.1080/08995605.2024.2403826

Low psychological resilience and physical fitness predict attrition from US Marine Corps Officer Candidate School training

Jennifer N Forse 1,✉, Kristen J Koltun 1, Matthew B Bird 1, Mita Lovalekar 1, Evan D Feigel 1, Elizabeth J Steele 1, Brian J Martin 1, Bradley C Nindl 1
PMCID: PMC12562803  PMID: 39433479

ABSTRACT

The objective is to examine the predictors of attrition in male and female candidates undergoing a 10-week early career military training program. 1006 candidates (79.5% male, 24.7 ± 3.2 years) consented to participating in a larger study examining predictors of injury during US Marine Corps Officer Candidates School (OCS). Participants completed a blood draw, demographic and psychological characteristics questionnaires, and two fitness tests. Participants were then grouped based on successful completion of OCS or not. Associations between potential predictors and attrition were analyzed using simple logistic regression analyses, followed by a backward stepwise elimination method. Area under the curve (AUC) of the receiver operating characteristic (ROC) curve was used to determine the accuracy of the attrition prediction model. 260 candidates (25.8%) attritted over the 10-week training, with the highest number of discharges during week 5. Musculoskeletal injury (MSKI) was the most common cause of attrition (30%), followed by non-MSKI medical (21.5%), and volitional withdrawals (19.6%). Sex, body mass index (BMI), resilience, initial physical fitness test score, combat fitness test (CFT) score, and prior military service were all significantly associated with attrition from OCS (all p < .05). The final prediction model of attrition included CFT score (p = .027) and resilience (p = .018). Multiple demographic, psychological, and fitness characteristics are associated with attrition from an early career military training course (OCS) and may be utilized as part of early screening procedures to identify and provide guidance for individuals at risk for not completing OCS.

KEYWORDS: Risk factors, military training, physical fitness, psychological resilience, military personnel

What is the public significance of this article?— This study demonstrates that individuals with low BMI, no prior military service, low resilience, and low fitness levels are more at risk to be discharged from USMC OCS. Specifically, higher psychological resilience and better military relevant physical fitness were the most predictive of successful completion of USMC OCS. USMC leadership can use this information to implement better screening measures at the beginning of OCS training to identify individuals who may be at risk for dropping out from training, as well as use this information to create preparatory training plans that help potential candidates get in shape prior to entry into OCS.

Introduction

Early career military training programs are physically and mentally challenging environments designed to prepare and assimilate Service members with necessary physical, mental, and tactical readiness skills. During training, individuals are deliberately and strategically exposed to mental and physical stressors designed to prepare for their career as a Service member (Nindl et al., 2018). However, many individuals are unable to successfully complete training. In recent years, rates of attrition from military training in the United States has ranged from 8% in Army Basic Combat Training to 16% in Marine Corps Basic Training (Harkins & Cox, 2020) and result from a variety of reasons including musculoskeletal injury, self-selection to leave, not meeting training standards, medical issues, or poor psychological adjustment (Farina et al., 2019; Kiernan et al., 2015; Moran et al., 2011; Reis et al., 2007). The rate at which trainees attrit, or drop-out, from training remains cause for concern due to the rising human and financial costs associated with military training and development, as well as current trends for lesser willingness and eligibility for military service (Kimmons, 2018). Therefore, due to the considerable amount of resources allocated to training Service members, it may be of interest to military leaders to identify pertinent factors associated with attrition from military training (Lee et al., 2011).

Attributes associated with attrition from military training include demographic, anthropometric, behavioral and lifestyle characteristics, and physical fitness (Larson et al., 2002; Lee, 2010; Lee et al., 2011; Moran et al., 2011; Pope et al., 1999; Sefidan et al., 2021). Gender and age are two demographic variables known to play a significant role in the dropout rates of recruits undergoing military training. In USMC training populations, female recruits had significantly higher rates of dropout from training (18.2%) than their male counterparts (11.9%) and those older than 23 years old had significantly higher rates of dropout (16.2%) compared to recruits that were younger than 19 years old (11.7%) and between 19 and 23 years old (9%) (Reis et al., 2007; Wolfe et al., 2005). Baseline anthropometric assessment of recruits undergoing basic training showed that high body mass index (BMI), in this case greater than 30, was a significant predictor of dropout from the program compared to those with normal BMIs, which were between 18.5 and 25 (Lee, 2010). In the same study, lifestyle characteristics were also examined and those that were current smokers were at an increased odds of being released from training (Lee, 2010). Although the aforementioned factors associated with attrition from training comprised some nonmodifiable attributes (i.e., sex and age), modifiable characteristics such as mental and physical strength may also provide great insight into the reasons individuals drop out of training.

One of the most prevalent reasons for attrition from military training is musculoskeletal injuries (Knapik et al., 2001; Reis et al., 2007). Previous research has shown that a history of injury before entering training significantly increased the risk of attrition from the training program, highlighting this as important information for the military to take into account when an individual begins training (Larson et al., 2002; Reis et al., 2007). Another physical aspect of military training is the rigorous fitness testing demands that focus on performance across different physical fitness domains and military specific fitness tests (Pope et al., 1999). Those that cannot maintain adequate levels of physical fitness standards can be discharged from training or service (National Research Council, 2006). In basic training studies with both the United States Army and Marine recruits, physical fitness test (PFT) events (e.g., run time, upper body strength, core strength) were related to dropout from training or early discharge from service (Knapik et al., 2001; Saxon et al., 2020). This shows that screening for baseline fitness may provide insight into those that will have the physical qualities needed to complete training.

As previously mentioned, military training deliberately induces stress in individuals, and other risk factors for attrition from military training include psychological and physiological measures of adaptation to stressors. Individuals with prior military service have gone through at least one training program, and, therefore, may have already developed skills to adapt to the stressors of military training. Previous research has not yet examined how this relates to successful completion of other training programs. However, the tools needed to adapt to training, such as psychological resilience, may be playing a role. Psychological resilience is an individual’s ability to promote positive adaptation to the negative effects of stress and is an attribute that has been used to predict successful completion of both basic and special operations military training (Bartone et al., 2008; Ledford et al., 2020; León-Guereño et al., 2020; Sefidan et al., 2021). While psychological resilience may help understand how recruits mentally adapt to stressors during training, objective physiological measures of stress should also be considered. If psychological or physiological stress is prolonged, it leads to a disruption in homeostasis, activation of the hypothalamic-pituitary-adrenocortical (HPA) axis, and alterations in the hormones that it produces (Kamin & Kertes, 2017). An individual’s physiological reaction to stress can be measured using hormonal biomarkers released by the HPA axis during stress response, such as cortisol and dehydroepiandrosterone (DHEA). Previous research has demonstrated that both are significantly associated with attrition from training (Ledford et al., 2020; Vaara et al., 2020).

Although the factors described above have been associated with attrition from training in the previous research, there is evidence that these risk factors are specific to a given training environment, such that certain risk factors may predict attrition in one population but have no predictive value in a different population. US Marine Corps (USMC) Officer Candidate School (OCS) is a unique training pipeline in which candidates are typically older in age and with higher education levels due to the requirement that candidates be working toward or have completed a college degree. Additionally, a 2020 USMC Doctrine Publication focused on the topic of learning, and leadership describe the branch as an organization that is willing and needs to have continuous learning occurring in order and adapt to the ever changing demands of warfare (United States Marine Corps, 2020) and the USMC is unique in that it is a smaller service branch that can more easily receive research supported guidance and enact changes that better the branch (United States Marine Corps, 2020). Given this learning environment and willingness to change in order to better the Marine Corps, data in the USMC OCS population may lead to actionable changes that can be implemented in the immediate future. Previous research has also been limited by consisting of very specific military training populations (e.g., Swiss males entering civic duty, Israeli special forces, etc.), almost exclusively focused on males, and a lack of knowledge of the specific reason that an individual is discharged from training (Moran et al., 2011; Sefidan et al., 2021).

To address these limitations, the purpose of this investigation was to characterize reasons for attrition and identify risk factors for attrition in a large cohort of male and female candidates undergoing USMC OCS, a 10-week early career military training program. The first aim of the study was to descriptively analyze reasons of attrition from OCS. The second aim of the study was to identify variables associated with attrition from OCS. We first hypothesized that, similar to previous research, attrition from OCS would occur at a higher rate for females, smokers, those with higher BMI, those with higher baseline stress levels, lower psychological resilience, and those with a history of injury before OCS. One factor that has not been examined is how the previous military training relates to success in an early career military training, but not basic training, such as OCS. We hypothesized that a history of previous military service would be protective of attrition from OCS as they would have had experience in training settings before and therefore may be better suited to adapt. We also hypothesized that attrition would be associated with a mix of demographic, psychological, and physical fitness variables, which could be used to create a multidisciplinary model of prediction for future use at OCS. Results of this investigation will provide beneficial information to military leadership for screening at-risk candidates who might not complete training or develop preparatory training interventions to improve retention.

Methods

Study Design and Procedures

This prospective cohort study is a secondary analysis of a larger investigation that occurred during OCS in Quantico, VA. Data were collected during six iterations of USMC OCS between September 2020 and March 2023. Inclusion criteria for participation included any healthy female or male currently enrolled in OCS, aged 18 or older. All candidates attended an informed consent briefing about the study at the beginning of training before their medical in-processing occurred. To eliminate the threat of coercion, no military leadership was present at the briefing, and candidates were given ample time to review the consent documents and ask questions before enrolling in the study. All briefings were attended and observed by an ombudsman. All data collected during the study was de-identified and confidentiality was protected by providing leadership with reports of combined data, never individual data. This study was approved by the University of Pittsburgh Institutional Review Board, Office of Naval Research (ONR) Human Research Protection Office, and endorsed by the USMC Human Research Protection Program. All research was performed in accordance with the Declaration of Helsinki.

Measured Variables

Demographics and Anthropometrics

Sex and age were obtained via questionnaire at the beginning of testing. Prior military service was measured as a binary yes or no outcome to the question, “Did you have any history of prior service before entering OCS?” History of nicotine use was measured with a questionnaire that asked individuals if they currently used, previously used, or never used cigarettes, cigars, smokeless tobacco, and/or e-cigarettes. Injury history was collected via questionnaire asking questions related to the individual’s date of injury, anatomic location of injury, type of injury (i.e., sprain, strain, and fracture), and cause of injury (i.e., running, landing, and crushing). Height (cm) and weight (kg) were measured before testing began using a digital scale with a stadiometer (Health o meter Professional, McCook, Illinois, USA). BMI was calculated from collected height and weight measurements (kg/m2).

Psychological Resilience

Resilience was measured using the Connor-Davidson Resilience Scale (CD-RISC), which is a 25-item self-report scale that measures an individual’s agreement toward statements related to coping ability, response to failure, optimism, and faith (Connor & Davidson, 2003). Responses are given on a five-point Likert scale from “0 – not true at all” to “4 – true nearly all the time.” All items are totaled for a final resilience score between 0 and 100, with higher scores indicating higher levels of perceived resilience. The CD-RISC has good internal consistency (Cronbach’s α = 0.89–0.96), test–retest reliability (intraclass correlation coefficient = 0.87), and convergent and divergent validity in general and military populations (Connor & Davidson, 2003; Green et al., 2014). Internal consistency for the CD-RISC in this study was α = 0.88.

Physiological Stress Biomarkers

To measure physiological stress biomarkers, standard venipuncture procedures were employed using a 21-gauge needle to collect 6 mL of whole blood in a serum collection tube (Becton, Dickinson and Company, Franklin Lakes, NJ). Serum was left to clot for 30 min before centrifugation at 1500 × g for 15 min at room temperature. Supernatant was aliquoted into Eppendorf tubes before being stored on dry ice for transport back to the laboratory. Samples were stored at −80°C until enzyme-linked immunosorbent assays (ELISAs) were conducted for cortisol (ALPCO, Salem, NH) and DHEA (Eagle Biosciences, Amherst, NH). Sensitivity for cortisol and DHEA assays were 0.4 μg/dL and 0.15 ng/mL, respectively. All samples were measured in duplicate with intra-assay coefficients of variation of 10% or less for cortisol and 15% or less for DHEA, based on variance values reported by manufacturers.

Fitness

Measures of physical fitness were obtained from the inventory physical fitness test (iPFT) and USMC combat fitness test (CFT). The iPFT was completed within the first few days of training onset and comprised a 3-mile run time, the candidate’s choice of push-ups or pull-ups, and the candidate’s choice of abdominal crunches or plank time. The CFT, which was designed to simulate real-life combat operations to enhance physical and tactical readiness, was completed approximately 5 weeks into training and comprised a timed movement-to-contact run, maximum 30-pound ammunition can overhead lift repetitions in 2 min, and a timed maneuver-under-fire event. For both fitness tests, candidates were scored using an age and sex adjusted scale from 0 to 100 for each of the three tests, for a total score out of 300. More detailed explanations of these fitness tests have been described elsewhere (Keefer & Debeliso, 2020).

Attrition

Information about candidates who were discharged from training was received directly from OCS leadership at the end of each class in the form of a Drop Report. The Drop Report included which participants were discharged from training, the date they attritted, and the reason for which they were discharged. In total, there were 23 reasons for attrition from OCS, which were reduced into 6 categories: musculoskeletal injury (MSKI), non-MSKI medical, volitional withdrawal, Marine Corps standards, physical training, and cannot be categorized.

Statistical Analyses

The dependent variable in the main analysis was attrition. Participants were placed into two groups based on their attrition status: discharged from training (DT) or not discharged from training (ND). Mean and SD were calculated for all continuous variables while relative frequency (percentage) was calculated for binary variables. Associations between the potential risk factors and attrition were analyzed using simple logistic regression analyses. The independent variables of interest included sex, age, BMI, prior military service, history of injury, history of nicotine use, resilience, cortisol, DHEA, iPFT total score, and CFT total score. Following the analysis of independent risk factors of attrition, a backward stepwise method was used to identify the variables that were most important for risk of attrition. Area under the curve (AUC) of the receiver operating characteristic (ROC) curve was used to determine the accuracy of the attrition prediction model. Statistical analyses were conducted using Stata (Release 18; StataCorp LLC, College Station, TX) and significance was set a priori at α = 0.05

Results

Descriptive Analyses

Data were collected from 1006 participants who completed pre-testing during the first week of training. The sample included 800 male candidates (age 24.6 ± 3.1 yrs, height 176.6 ± 7.0 cm, weight 80.2 ± 9.4 kg, BMI 25.7 ± 2.2 kg/m2) and 206 female candidates (age 24.7 ± 3.3 yrs, height 163.8 ± 6.0 cm, weight 64.4 ± 7.2 kg, BMI 24.0 ± 2.1 kg/m2).

Two hundred and sixty candidates attritted from OCS over the 10-week training period and included 79 female candidates (30.4%) and 181 male candidates (69.6%). Of those who attritted from training, 11.3% had a history of prior service, while 88.7% had no history of prior service. Candidates attritted in each of the 10 weeks, but the number of discharges peaked during week 5 (21.5%). Among those that were discharged, approximately half of candidates attritted by the end of week 4 (50.8%), and that number rose to 72.3% by the end of week 5. After performing Kaplan–Meier survival estimates for those discharged from training, mean survival time was 4.4 weeks (Figure 1). Kaplan–Meier estimates were also completed for those discharged from OCS split by sex (Figure 2), demonstrating that male and female candidates were not different in mean survival time across the 10 weeks of training (males: 4.3 weeks, females: 4.6 weeks, log-rank p = .233).

Figure 1.

Figure 1.

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Weekly incidence of attrition from the 260 candidates who did not complete the 10-week OCS training program.

Figure 2.

Figure 2.

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Weekly incidence of attrition from the 181 male and 79 female candidates who did not complete the 10-week OCS training program.

Across the six categories of reasons for attrition in this study (Table 1), MSKI was the most common cause (n = 78, 30%). The majority of MSKI discharges occurred between weeks 3 and 6 of training, with the highest number of MSKI discharges occurring in weeks 5 and 6 (n = 15, 19.2% each week). The next most common reason for attrition (n = 56, 21.5%) was classified as non-MSKI medical issues and over three quarters of these candidates were discharged between weeks 1 and 4. The highest number of non-MSKI medical discharges happened in week 1, which aligns with the medical screening done during the in-processing stage of OCS. The third most common reason for attrition was volitional withdrawal (n = 51, 19.6%), which accounted for the highest number of discharges during week 5 of training, and more than half of volitional withdrawal discharges occurred between weeks 4 and 5 (n = 10, 19.6% and n = 21, 41.2%, respectively). The fourth most common reason for attrition was Marine Corps standards (n = 38, 14.6%), for which the most candidates were discharged during week 5 (n = 10, 26.3%); however, three quarters of the candidates were discharged during the last 5 weeks of training. Finally, cannot be categorized and physical training discharges were the fifth and sixth most common reasons for attrition (n = 19, 7.3% and n = 18, 6.9%, respectively). Over half of the candidates who were discharged for physical training reasons attritted during week 1 (n = 10, 55.6%). Cannot be categorized was the only category that attrition was equally distributed across all 10 weeks of OCS.

Table 1.

The 23 reasons for attrition from OCS grouped into six categories for descriptive analysis.

Category (total n) Reason for attrition (n)
MSKI (78) Orthopedic – evident (78)
Non-MSKI medical (56) OB/GYN (1), blood pressure (2), psychological (2), cardio (4), internal medicine (7), heat (8), respiratory (32)
Volitional Withdrawal (51) Personal (1), no longer interested in program (50)
Marine Corps Standards (38) Academics (1), combative/belligerent (1), drug use (1), UCMJ Article 134 (1), integrity (2), inability to adapt (5), leadership (7), inability to evaluate (20)
Physical training (18) Physical training (1), fail inventory PFT (17)
Cannot be categorized (19) Missing data (2), double category (4), other (13)
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MSKI = musculoskeletal injury, OB/GYN = obstetrics and gynecology, UCMJ = the Uniform Code of Military Justice.

Predictors of Attrition

The simple logistic regression analysis of risk factors associated with attrition from OCS is included in Table 2. Simple logistic regression analyses revealed that sex, BMI, resilience, iPFT total score, CFT total score, and prior military service were all significantly associated with attrition from OCS. Age, history of nicotine use, cortisol concentration, DHEA concentration, and history of injury were not significantly associated with attrition from OCS.

Table 2.

Summary of univariate associations between risk factors and attrition from OCS.

Predictor N Discharged from training Not discharged from training β Standard error OR (95% CI) p
Sex (Female)a 1006 38.3% 61.7% 0.76 0.17 2.13 (1.54–2.95) <.001
Age 989 24.61 ± 3.09 24.88 ± 3.13 −0.01 0.02 0.99 (0.95–1.04) .701
BMI (kg/m2)a 896 24.83 ± 2.24 25.47 ± 2.44 −0.11 0.03 0.90 (0.84–0.96) .001
Prior military service (Yes)a 832 10.1% 89.9% −1.08 0.25 0.34 (0.21–0.56) <.001
History of injury (Yes) 1003 24.9% 75.1% −0.11 0.14 0.90 (0.68–1.19) .466
History of nicotine use (Yes) 874 22.8% 77.2% −0.18 0.16 0.84 (0.61–1.15) .268
Resiliencea,b 628 80.92 ± 10.57 82.69 ± 9.62 −0.02 0.01 0.98 (0.97–0.99) .048
Cortisol (µg/dL) 605 10.65 ± 3.99 10.74 ± 4.37 −0.01 0.02 1.00 (0.95–1.04) .822
DHEA (ng/mL)a 594 3.97 ± 1.66 4.29 ± 2.23 −0.08 0.05 0.92 (0.84–1.02) .099
iPFT total scorea 962 262.58 ± 26.33 269.59 ± 18.22 −0.02 0.00 0.99 (0.98–0.99) <.001
CFT total scorea,b 749 262.30 ± 20.29 278.27 ± 18.12 −0.04 0.01 0.96 (0.94–0.98) <.001
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OR = odds ratio; CI = confidence interval. Predictors may not sum to the total sample size due to missing data.

aIncluded in the backwards stepwise analysis.

bVariables in final prediction model.

Female candidates were 2.13× more likely to be discharged from OCS than their male counterparts. In fact, 38.3% of the female candidates attritted compared to only 22.6% of the male candidates. Higher BMI seems to offer some protection against attrition from OCS, as a one-point increase in BMI is associated with decreased odds of attrition by 0.90×, or 10%. Likelihood of attrition was 0.34× lower in candidates with prior military service where only 10.1% of the participants with a history of prior service attritted from training while 24.8% of the candidates with no prior military service attritted from training.

Candidates with higher perceived psychological resilience were also less likely to be discharged. Every one-point increase in CD-RISC total score was associated with 0.98×, or 2%, decrease in the odds of attrition.

Higher performance on the iPFT and CFT was also protective against attrition. For every one-point increase in iPFT total score, candidates had 0.99×, or 1%, decrease in the odds of attrition while for CFT total, one-point increase in total score had 0.96×, or 4%, decrease in the odds of attrition from OCS.

After running the multivariate backward stepwise analysis, the final prediction model included psychological resilience and CFT total score as predictors for attrition (χ2 = 11.38, p = .0034). The likelihood of attrition decreased by 8.1% for each unit increase in self-reported resilience and decreased by 3.5% for each point increase in CFT total score (Table 3).

Table 3.

Final prediction model*.

Predictor β Standard error OR (95% CI) p
CFT total score −0.036 0.02 0.96 (0.93-0.99) 0.027
Resilience −0.086 0.04 0.92 (0.86-0.99) 0.018
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OR = odds ratio; CI = confidence interval.

The AUC was 78.13% which is best understood as the percentage of randomly selected participants whose outcome, discharged from training or not discharged from training, was successfully predicted with the model (Figure 3).

Figure 3.

Figure 3.

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Accuracy of the prediction model of attrition from OCS, based on the two most significant variables. AUC for this model was 0.7813, which is shown above from using the ROC curve. Created with Stata.

Discussion

High rates of attrition from military training are a concerning problem in the military, given the financial and personnel burdens (Kimmons, 2018). Individuals may drop out of training due to injuries caused by physical training, inability to adapt to military environments, or personal choice. This study examined 11 variables for their associations with attrition from OCS (Table 2) and identified 6 as significant: sex, BMI, prior military service, psychological resilience, iPFT score, and CFT score. The main finding from this investigation was that the prediction of attrition from USMC OCS, although multifactorial, may be best determined from psychological resilience and military specific fitness. This suggests that successful candidates comprise high proficiency across psychological and physical domains. By examining risk factors, future considerations can be made to adapt training or provide leadership with useful screening measures to reduce attrition frequency.

The relative frequency of attrition for USMC OCS training (25.8%) was higher than previously reported in USMC basic training (10.4–16%) (Harkins & Cox, 2020; Reis et al., 2007). While both training courses assess academic achievement and physical fitness, OCS training focuses on developing leadership qualities whereas USMC basic training focuses on developing tactical training (“Marine Corps Boot Camp and Officer Candidates School: What to Expect,” 2022). Because of the distinction between the primary focus of these trainings, OCS is more selective and sets candidates on different career paths, which may explain the higher attrition in this sample. The highest percentage of candidates (21.5%) attritted during week 5 which occurs during the adaptation phase of training, which focuses on teamwork, accountability, leading your peers, and often includes graded fitness tests. Adaptation occurs after transition, which focuses on conditioning, close order drill, and culture/leadership indoctrination, and the switch between phases may help explain the high percentage of attrition.

Previous studies examined attrition using limited categories (i.e., voluntary vs. forced, behavioral vs. administrative) (Pollack et al., 2009; Reis et al., 2007), but this analysis consolidated 23 different reasons for attrition into 6 categories to highlight the reasons for discharge from OCS. By examining more categories of attrition, USMC leadership may better recognize candidates needing improvement in one or more aspects of their training.

Of the 11 variables examined, two were the most significant in predicting attrition, psychological resilience and CFT total score. Together, the prediction model made up of these two variables was able to accurately predict 78% of attrition in this sample. Both variables are easy to measure, as one is administered through a 5–10-min survey and the other is already a part of OCS training.

Previous research demonstrated that psychological resilience has a significant role in the success of individuals undergoing both basic military training and special operations military training (Ledford et al., 2020; Sefidan et al., 2021). This analysis supported those conclusions and observed high self-reported psychological resilience to be one of the two variables most predictive of successful training completion. The predictive value of psychological resilience may suggest that those with high levels of resilience are able to positively adapt to the stress placed on them during training.

Another factor of interest in this analysis was the fitness level of candidates. In basic training studies with both US Army and Marine recruits, physical fitness events were related to attrition from training or early discharge from service (Canham-Chervak et al., 2001). In this study, we examined two different fitness tests, the iPFT and CFT, which examine both general and military specific fitness tasks. Both fitness tests were significantly associated with attrition from OCS. However, it is important to note that the inventory PFT was carried out in the first few days of training, while the CFT was carried out toward the middle of training. Although the fitness measures were done at two different points in training, it stands to reason that if general fitness was significant early in training, military specific fitness (i.e., CFT) would likely be significant early in training as well since levels of general fitness and military specific fitness are correlated (Hauschild et al., 2017; Saxon et al., 2020). However, it is important to interpret the results of this analysis as it being best to screen individual’s fitness levels using general tests of physical fitness early in training, while military specific training is successful at screening halfway through training.

This analysis also examined other demographic, anthropometric, and lifestyle characteristics that have been associated with being discharged from military training. Similar to previous research, we observed that females were at greater risk and discharged from training at a higher rate than males (Canham-Chervak et al., 2001; Pollack et al., 2009). It is well known that physical differences exist between males and females and, perhaps the most important difference between them in relation to military training, females are at an increased risk for injury (Epstein et al., 2015) which also increases their likelihood of being discharged from training. MSKI was the most common reason for attrition in this analysis, with a higher percentage of females being discharged for an injury (32.9%) than males (28.7%). Previous studies have reported conflicting evidence on how BMI is associated with attrition rates, with both high and low BMI being identified as a risk factor (Pollack et al., 2009; Wolfe et al., 2005). This research suggests that a lower BMI is a risk factor for being discharged from OCS, although it is important to note that BMIs of both attrition groups (24.8 and 25.5 kg/m2) fall in the higher “healthy” range and lower “overweight” range of BMI classification from the World Health Organization and National Institutes of Health (Weir & Jan, 2024). The Marine Corps has the most strict standards for body composition, with the minimum BMI set at 19 for both sexes and maximum BMI for females and males set at 25 and 27.5 kg/m2, respectively (Defense Advisory Committee on Women in the Services, 2016; Department of Defense, 2022). So, while higher BMI was found to offer some protection against attrition from OCS, there are upper limits to the possible BMIs in the dataset, and it should be interpreted as such. Within a BMI range of approximately 19 to 25 or 27.5, those who had higher BMIs were less likely to drop out from training. This trend may be seen because BMI does not take into consideration other aspects of body composition (i.e., fat mass, fat-free mass, and lean mass), and these results may not be capturing the full picture. It is possible that a certain amount of lean body mass is protective against injury and beneficial for physical task performance, and, therefore, is protective against attrition. Recruits with sufficient levels of physical fitness who fell into the “overweight” category for BMI were not at a greater risk of being discharged from training, which these results may be supporting (Niebuhr et al., 2008). As previously mentioned, candidates may have previous military service, and therefore military training experience, prior to OCS. The impact that this prior service has on successful completion of training has not been previously studied. In this study, prior military service was protective against being discharged from training. All other demographic variables of interest (i.e., age, entering training with an injury, and prior nicotine use) were not associated with being discharged from training even though previous research has identified them as risk factors (Lee, 2010; Reis et al., 2007).

When individuals are placed under high levels of stress, the body may begin to respond by HPA axis activation (Kamin & Kertes, 2017). The HPA axis releases cortisol, which increases arousal and energy, and DHEA, which provides anti-inflammatory and neuroprotective effects (Ledford et al., 2020). While previous research reported that higher concentrations of these hormones before training were significantly associated with attrition from training, the current results did not support the same association (Ledford et al., 2020; Vaara et al., 2020). These results may be incongruent with previous research given that the days leading into training are different for every course, so “baseline” measures may be capturing systematically different stress reactions (i.e., an individual who has been in a stressful environment for a few days vs. an individual still in the calm period before training begins). Future research may benefit by measuring physiological stress biomarkers throughout the early stages of training to adequately capture early physiological changes due to stress.

One limitation was that the study was designed to not add burden or disrupt training for OCS leadership and candidates participating in the study. Because of that, hormonal biomarkers were only taken at one timepoint before training began. Significant results may not have been present as these biomarkers are expected to be low when individuals are not under stress and, therefore, we may have been unable to adequately capture how candidates physiologically responded to the initiation of training.

Finally, interpreting the final prediction model should be done with some margin of caution. First, this study was conducted among US Marine Corps Officer Candidates and the predictors identified in this analysis may not be generalized to other Marine Corps personnel, other military personnel, or other populations. Additionally, the CFT was not run until the middle of the class, so we cannot know how this model of prediction would work solely as a baseline screening tool. Also, psychological attributes like resilience should be carefully considered since it is a self-reported tool that subjectively measures how well an individual perceives they would respond to heightened levels of stress.

Conclusion

Sex, BMI, prior military service, and general fitness levels were characteristics of candidates that were associated with attrition from a physically and mentally challenging military training. However, in this training environment (OCS), resilience and military specific performance were most predictive of successful completion. This study adds valuable insight into the current literature as it included both males and females, obtained a large sample size, and was completed with candidates who entered a more specialized form of military training. Findings of this study suggest that there are multiple risk factors for attrition from OCS, some of which are modifiable and can be intervened on (i.e., fitness, BMI, and resilience). This analysis suggests that these variables may be utilized for early screening procedures prior to OCS that identify candidates who may benefit from training in addition to the standardized OCS program.

Funding Statement

This study was funded by the Office of Naval Research [Award #’s N00014-20-C-2020 and N00014-21-1-2725]. The views, findings, and opinions in this report are those of the authors and do not necessarily reflect the views of the United States Government, Department of the Navy, United States Marine Corps, or University of Pittsburgh.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, JF, upon reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, JF, upon reasonable request.

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