Army Trainees Research Articles

The Role Of Reverse Causation In The Relationship Between NSAIDs And Stress Fractures In Army Trainees

The Role Of Reverse Causation In The Relationship Between NSAIDs And Stress Fractures In Army Trainees

The repeatability of stride time variability, regularity, and long-range correlations

BackgroundDetrended fluctuation analysis (DFA) and sample entropy (SE) measure the long-term correlations and regularity of gait patterns, respectively, having previously been used to identify participants at risk of falling, previous history of injury, or patients with motor diseases. Since these measures are more sensitive to gait impairment than linear measures (e.g., the standard deviation [SD] of stride time), they can be potentially used in military medicine to identify soldiers at risk of injury. However, clinometric properties are yet to be established. Research QuestionWhat is the repeatability of DFA, SE, and traditional linear measures of stride time variability (SD and coefficient of variation [CV]) under various load and speed constraints? MethodsFourteen Australian Army trainee soldiers (age: 25.6 ± 5.9 y, height: 1.74 ± 0.08 m, body mass: 77.2 ± 15.1 kg, service: 1.5 ± 1.8 y) attended three sessions over two weeks, completing four 12-minute walking trials on an instrumented treadmill in each session. Participants walked with a combination of 0 kg or 23 kg loads at a self-selected or 5.5 km/h speed. Heel contacts from the right foot were identified using treadmill-embedded force plates. From 512 stride time intervals, linear (SD and CV), and non-linear (DFA and SE) measures were obtained. To assess the between-session repeatability, intraclass correlations (ICC 2,1) were employed. Results and SignificanceThere was poor-to-moderate repeatability for the SD (ICC: 0.357–0.545) and CV (ICC: 0.371–0.529). DFA showed poor-to-moderate repeatability (ICC: 0.013–0.504), while SE had poor repeatability (ICC: 0.133–0.226). Previous studies have shown that differences of > 0.19 in DFA and > 0.66 in SE can differentiate between healthy and pathological gait. These values are greater than this study's reported standard error of measurement, indicating that clinically meaningful changes may still be detectable despite low repeatability.

The Agreement between Wearable Sensors and Force Plates for the Analysis of Stride Time Variability.

The variability and regularity of stride time may help identify individuals at a greater risk of injury during military load carriage. Wearable sensors could provide a cost-effective, portable solution for recording these measures, but establishing their validity is necessary. This study aimed to determine the agreement of several measures of stride time variability across five wearable sensors (Opal APDM, Vicon Blue Trident, Axivity, Plantiga, Xsens DOT) and force plates during military load carriage. Nineteen Australian Army trainee soldiers (age: 24.8 ± 5.3 years, height: 1.77 ± 0.09 m, body mass: 79.5 ± 15.2 kg, service: 1.7 ± 1.7 years) completed three 12-min walking trials on an instrumented treadmill at 5.5 km/h, carrying 23 kg of an external load. Simultaneously, 512 stride time intervals were identified from treadmill-embedded force plates and each sensor where linear (standard deviation and coefficient of variation) and non-linear (detrended fluctuation analysis and sample entropy) measures were obtained. Sensor and force plate agreement was evaluated using Pearson's r and intraclass correlation coefficients. All sensors had at least moderate agreement (ICC > 0.5) and a strong positive correlation (r > 0.5). These results suggest wearable devices could be employed to quantify linear and non-linear measures of stride time variability during military load carriage.

Sex- and age-related differences in kinetics and tibial accelerations during military-relevant movement tasks inU.S. Army trainees.

Lower extremity injuries are prevalent in military trainees, especially in female and older trainees. Modifiable factors that lead to higher injury risk in these subgroups are not clear. The purpose of this study was to identify whether external loading variables during military-relevant tasks differ by age and sex in U.S. Army trainees. Data was collected on 915 trainees in the first week of Basic Combat Training. Participants performed running and ruck marching (walking with 18.1kg pack) on a treadmill, as well as double-/single-leg drop landings. Variables included: vertical force loading rates, vertical stiffness, first peak vertical forces, peak vertical and resultant tibial accelerations. Comparisons were made between sexes and age groups (young, ≤19years; middle, 20-24years; older, ≥25years). Significant main effects of sex were found, with females showing higher vertical loading rates during ruck marching, and peak tibial accelerations during running and ruck marching (p≤0.03). Males showed higher vertical stiffness during running and peak vertical tibial accelerations during drop landings (p<0.01). A main effect of age was found for vertical loading rates during running (p=0.03), however no significant pairwise differences were found between age groups. These findings suggest that higher external loading may contribute to higher overall injury rates in female trainees. Further, higher stiffness during running may contribute to specific injuries, such as Achilles Tendinopathy, that are more prevalent in males. The lack of differences between age groups suggests that other factors contribute more to higher injury rates in older trainees.

Sex Does Not Affect Changes in Body Composition and Insulin-Like Growth Factor-I During US Army Basic Combat Training.

Roberts, BM, Staab, JS, Caldwell, AR, Sczuroski, CE, Staab, JE, Lutz, LJ, Reynoso, M, Geddis, AV, Taylor, KM, Guerriere, KI, Walker, LA, Hughes, JM, and Foulis, SA. Sex does not affect changes in body composition and insulin-like growth factor-I during US Army basic combat training. J Strength Cond Res 38(6): e304-e309, 2024-Insulin-like growth factor 1 (IGF-I) has been implicated as a biomarker of health and body composition. However, whether changes in body composition are associated with changes in IGF-I is unclear. Therefore, we examined the relationship between body composition changes (i.e., fat mass and lean mass) and total serum IGF-I levels in a large cohort of young men ( n = 809) and women ( n = 397) attending US Army basic combat training (BCT). We measured body composition using dual energy x-ray absorptiometry and total serum IGF-I levels during week 1 and week 9 of BCT. We found that pre-BCT lean mass ( r = 0.0504, p = 0.082) and fat mass ( r = 0.0458, p = 0.082) were not associated with pre-BCT IGF-I. Body mass, body mass index, body fat percentage, and fat mass decreased, and lean mass increased during BCT (all p < 0.001). Mean (± SD ) IGF-I increased from pre-BCT (176 ± 50 ng·ml -1 ) to post-BCT (200 ± 50 ng·ml -1 , p < 0.001). Inspection of the partial correlations indicated that even when considering the unique contributions of other variables, increases in IGF-I during BCT were associated with both increased lean mass ( r = 0.0769, p = 0.023) and increased fat mass ( r = 0.1055, p < 0.001) with no sex differences. Taken together, our data suggest that although changes in IGF-I weakly correlated with changes in body composition, IGF-I, in isolation, is not an adequate biomarker for predicting changes in body composition during BCT in US Army trainees.

Profiling of serum factors associated with Staphylococcus aureus skin and soft tissue infections as a foundation for biomarker identification.

People living in close quarters, such as military trainees, are at increased risk for skin and soft tissue infections (SSTI), especially those caused by methicillin-resistant Staphylococcus aureus (MRSA). The serum immune factors associated with the onset of SSTI are not well understood. We conducted a longitudinal study of SSTIs, enrolling US Army trainees before starting military training and following up for 14 weeks. Samples were collected on Day 0, 56, and 90. Serum chemokines and cytokines among 16 SSTI cases and 51 healthy controls were evaluated using an electro-chemiluminescence based multiplex assay platform. Of 54 tested cytokines, 12 were significantly higher among SSTI cases as compared to controls. Among the cases, there were correlations between factors associated with vascular injury (i.e., VCAM-1, ICAM-1, and Flt1), the angiogenetic factor VEGF, and IL-10. Unsupervised machine learning (Principal Component Analysis) revealed that IL10, IL17A, C-reactive protein, ICAM1, VCAM1, SAA, Flt1, and VGEF were indicative of SSTI. The study demonstrates the power of immunoprofiling for identifying factors predictive of pre-illness state of SSTI thereby identifying early stages of an infection and individuals susceptible to SSTI.

Sex differences in iron status during military training: a prospective cohort study of longitudinal changes and associations with endurance performance and musculoskeletal outcomes.

This study investigated sex differences in Fe status, and associations between Fe status and endurance and musculoskeletal outcomes, in military training. In total, 2277 British Army trainees (581 women) participated. Fe markers and endurance performance (2·4 km run) were measured at the start (week 1) and end (week 13) of training. Whole-body areal body mineral density (aBMD) and markers of bone metabolism were measured at week 1. Injuries during training were recorded. Training decreased Hb in men and women (mean change (-0·1 (95 % CI -0·2, -0·0) and -0·7 (95 % CI -0·9, -0·6) g/dl, both P < 0·001) but more so in women (P < 0·001). Ferritin decreased in men and women (-27 (95 % CI -28, -23) and -5 (95 % CI -8, -1) µg/l, both P ≤ 0·001) but more so in men (P < 0·001). Soluble transferrin receptor increased in men and women (2·9 (95 % CI 2·3, 3·6) and 3·8 (95 % CI 2·7, 4·9) nmol/l, both P < 0·001), with no difference between sexes (P = 0·872). Erythrocyte distribution width increased in men (0·3 (95 % CI 0·2, 0·4)%, P < 0·001) but not in women (0·1 (95 % CI -0·1, 0·2)%, P = 0·956). Mean corpuscular volume decreased in men (-1·5 (95 % CI -1·8, -1·1) fL, P < 0·001) but not in women (0·4 (95 % CI -0·4, 1·3) fL, P = 0·087). Lower ferritin was associated with slower 2·4 km run time (P = 0·018), sustaining a lower limb overuse injury (P = 0·048), lower aBMD (P = 0·021) and higher beta C-telopeptide cross-links of type 1 collagen and procollagen type 1 N-terminal propeptide (both P < 0·001) controlling for sex. Improving Fe stores before training may protect Hb in women and improve endurance and protect against injury.

Associations Between Physical Activity And Drop-landing Tibial Accelerations In U.S. Army Trainees

Associations Between Physical Activity And Drop-landing Tibial Accelerations In U.S. Army Trainees

The Effects Of Age On Drop Landing Tibial Accelerations In U.S. Army Trainees

The Effects Of Age On Drop Landing Tibial Accelerations In U.S. Army Trainees

Age-related Differences In Impacts During Running And Loaded Walking In US Army Trainees

Age-related Differences In Impacts During Running And Loaded Walking In US Army Trainees

Relationships between tibial accelerations and ground reaction forces during walking with load carriage

Peak tibial accelerations (TAs) during running are strongly related to early stance vertical ground reaction forces (GRFs), which are associated with musculoskeletal injury. However, few studies have examined these correlations during walking, and none have evaluated them during walking with loads, a relevant activity for military personnel. Our purpose was to determine the relationships between GRFs and TAs in US Army trainees (n = 649) walking with loads. An inertial measurement unit was attached over their distal antero-medial tibia. Participants walked on an instrumented treadmill at 1.21–1.34 m/s, with a pack loaded with 18.1 kg, for a 3-min warm-up followed by a minimum of 14 strides of data collection. Simple linear regression models were calculated for peak vertical and resultant TAs with vertical and posterior GRF loading rates and peak forces. The strongest relationships were between vertical loading rates and peak vertical TA (R = 0.43–0.50), however the relationships were weaker than has been reported for unloaded walking and running (R > 0.7). All other relationships were trivial to small (R = 0.06–0.27). The weaker relationships for vertical GRFs and TAs may be due to methodological differences between studies, or differences in gait mechanics, such as a longer double-limb support phase in loaded vs. unloaded walking.

Exposure to risk factors for the development of lower limb osteoarthritis during Army infantry training

Background: Osteoarthritis (OA) is a degenerative musculoskeletal condition which affects the joints. Rates of lower limb OA in military personnel have been increasing over time and are becoming more prevalent in younger personnel. This has the potential to lead to personnel discharge and losses in, and impacts on, military capability. Therefore, the purpose of this study was two-fold: (1) to determine the exposure of Army trainees qualifying as infantry soldiers to occupational tasks associated with the development of lower limb OA, and (2) to compare the cumulative exposure to such tasks to minimum exposure thresholds set by the Australian Repatriation Medical Authority (RMA) for the development of lower limb OA.

A state-by-state and regional analysis of the direct medical costs of treating musculoskeletal injuries among US Army trainees

IntroductionLow physical activity (PA) and physical fitness (PF) are well-known factors for chronic diseases generally and cardiovascular diseases specifically. The economic burden from these chronic diseases is also well documented, as is their disproportionate prevalence among states in the Southern region of the U.S. Low PA and PF have also become recognized factors impacting military readiness and national security. Specifically, low PA and PF are highly correlated with musculoskeletal injures (MSKIs), now considered the greatest medical impediment to military readiness. Prior research shows low PF and MSKI incidence are greater among Army recruits from Southern states, however no previous research has investigated the economic impact of MSKIs at the state- and regional-level. The aim of this study was to determine the economic impact of MSKIs among U.S. Army initial military trainees on a state- and regional-basis. MethodsRosters for recruits entering U.S. Army Initial Military Training (IMT) for fiscal year 2017 were obtained (n = 103,487). Roster data included the unique personal identifier, demographics with postal zip code, training start/end dates, and height and weight and were subsequently linked to medical encounters and cost data from the Military Health System Data Repository. Trainees with one or more MSKIs were considered injury cases (n = 33,509) and were stratified by gender. The percent of trainee MSKI cases was calculated as number of injury cases divided by total number of trainees. For each injury case, the direct medical cost for MSKIs was calculated. The percent of trainees and direct medical costs for MSKIs were aggregated to home-state and regional-levels for the four U.S. Census tract regions. A test for equality of proportions was performed at state- and regional-levels to investigate differences in percent of trainees with MSKIs by state/region. A one-way ANOVA was used to investigate possible differences in medical cost/trainee by region. Results34% (n = 33,509) of all trainees sustained at least one MSKI. State-specific MSKI percentages showed ten states having the greatest percentage of trainees with at least one MSKI, eight of which were from the South region (AL, FL, GA, LA, MS, NC, SC, TN). The South was the only region to have a statistically significantly higher percentage of trainees with MSKIs at 34% (p < 0.001), as compared to all other regions. The total direct medical cost of treating MSKIs among all trainees was $14,891,563. The South was the costliest region ($7,168,997), accounted for nearly 50 % of the total national cost, and had the highest mean MSKI cost/trainee. DiscussionThis study was the first in demonstrating the disproportionate economic burden Southern states pose to the U.S. Department of Defense resulting from its significantly higher MSKI cost. PA and PF are known to ameliorate chronic disease and MSKI burden among general and military populations. Therefore, increasing PA and PF among all young Americans, and specifically those living in Southern states, is imperative for improving public health and reducing the economic and practical burden of MSKIs on military readiness and national security.

Combining sport and conventional military training provides superior improvements in physical test performance

Training for both sporting and military performance is common practice within army trainee populations, although it is currently unknown what effect this combination of training methods may have on the physical attributes required for overall physical preparedness. This study examined the effects of sport-specific training on general fitness in a professional military population. Four hundred and twenty-three Greek male army cadets completed a 12-week training regimen involving standard physical training (callisthenics, strength and endurance running exercises) and either general military training (GMT) or sport military training (SMT). A series of physical tests took place before and after the training period: a mile run, pull-ups, 50 m swim and an obstacle course run. Both the GMT and SMT groups showed significant (p &lt; 0.001) improvements in all physical tests. However, the SMT group produced significantly greater improvements in all four tests (pull-ups [p &lt; 0.001], 50 m swim [p &lt; 0.05], obstacle course [p &lt; 0.01] and mile run [p &lt; 0.01]) compared to the GMT group. Furthermore, different types of SMT (e.g. rock climbing and track sprinting) achieved greater improvements (p &lt; 0.001–0.01) in certain physical tests when compared to other forms of SMT (e.g. Pankration, Fencing). These results indicate that cadets undertaking concurrent participation in general and sport military training are overall better prepared for physical performance than their counterparts who undertake only general military training. Military conditioning personnel should be aware of the positive interplay between general and sports specific training in forming a preparation strategy designed for physical performance.

Virological and Serological Assessment of US Army Trainees Isolated for Coronavirus Disease 2019.

BackgroundLaboratory screening for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a key mitigation measure to avoid the spread of infection among recruits starting basic combat training in a congregate setting. Since viral nucleic acid can be detected persistently after recovery, we evaluated other laboratory markers to distinguish recruits who could proceed with training from those who were infected.MethodsRecruits isolated for coronavirus disease 2019 (COVID-19) were serially tested for SARS-CoV-2 subgenomic ribonucleic acid (sgRNA), and viral load (VL) by reverse transcriptase polymerase chain reaction (RT-PCR), and for anti- SARS-CoV-2. Cluster and quadratic discriminant analyses of results were performed.ResultsAmong 229 recruits isolated for COVID-19, those with a RT-PCR cycle threshold >30.49 (sensitivity 95%, specificity 96%) or having sgRNA log10 RNA copies/mL <3.09 (sensitivity and specificity 96%) at entry into isolation were likely SARS-CoV-2 uninfected. Viral load > 4.58 log10 RNA copies/mL or anti- SARS-CoV-2 signal-to-cutoff ratio < 1.38 (VL: sensitivity and specificity 93%; anti- SARS-CoV-2: sensitivity 83%, specificity 79%) had comparatively lower sensitivity and specificity when used alone for discrimination of infected from uninfected.ConclusionsOrthogonal laboratory assays used in combination with RT-PCR may have utility in determining SARS-CoV-2 infection status for decisions regarding isolation.

Psychological Hardiness and Grit Are Associated with Musculoskeletal Injury in U.S. Army Trainees

Musculoskeletal injuries (MSKIs) during U.S. Army Basic Combat Training (BCT) are pervasive, costly, and erode training effectiveness. Research has explored factors, particularly physical and demographic characteristics, which contribute to injury risk in military trainees. Psychological traits, such as hardiness and grit, have been associated with positive performance outcomes and retention during military training, but their relationship to injury risk is unclear. In this study, 2275 U.S. Army trainees completed validated measures of hardiness and grit at the start (T1) and end (T2) of BCT, and reported injuries sustained during BCT via weekly survey. A majority of trainees (70%) reported an injury during BCT. Trainees reporting high scores on grit and positive hardiness subscales at T1 had 20–30% lower odds of self-reported injury during training; those reporting high scores on negative hardiness subscales at T1 had 20–40% greater odds of self-reported injury. Trainees who reported an injury during BCT also reported higher scores on negative hardiness subscales at T2 compared to uninjured trainees. These findings provide novel evidence supporting an association between positive psychological traits and MSKI risk in military trainees, and underscore the importance of considering psychological resilience when assessing MSKI risk in military populations.

Prior Physical Activity Influences Changes In Tibial Bone Microarchitecture During U.S. Army Basic Combat Training

Bone stress injuries (BSIs) are common among military personnel due to heightened physical activity. Whereas we have previously shown significant tibial bone adaptation following 8 weeks of Basic Combat Training (BCT), it is not known whether prior exercise habits influence the skeletal response to BCT. PURPOSE: Determine the relationship between exercise history and changes in tibial bone microarchitecture induced by BCT. METHODS: We collected high-resolution peripheral quantitative computed tomography images of the distal tibia, pre- and post-BCT, on U.S. Army trainees. We created low (LOW; 0-2 days/wk, n = 312), moderate (MOD; 3-4 days/wk, n = 597), and high (HIGH; 5+ days/wk, n = 696) exercise groups based on self-reported average days/wk of exercise during the 2 months prior to BCT. Linear mixed models were used to estimate within and between group differences from pre- to post-BCT controlling for sex, race, age, height, and weight. RESULTS: We enrolled 552 female and 1053 male trainees (20.7 ± 3.7 yrs) with normal BMI (24.7 ± 3.5 kg/m2). Trabecular thickness (Tb.Th), cortical thickness (Ct.Th), Ct area (Ct.Ar), total volumetric bone mineral density (Tt.vBMD), Tb.vBMD and Ct.vBMD increased significantly among all exercise groups over the BCT period (0.46-1.9%; all p < 0.0001, Fig 1). However, there was a greater increase in Ct.Th (p < 0.0001), Ct.Ar (p = 0.02), Tb.vBMD (p < 0.0001) and Tt.vBMD (p = 0.001) in LOW vs. HIGH. Similarly, MOD had greater increases in Tb.Th (p = 0.003), Ct.Th (p = 0.004), Ct.Ar (p = 0.001), Tb.vBMD (p = 0.0001), and Tt.vBMD (p < 0.0001) compared to HIGH. There were no differences between LOW and MOD CONCLUSION: All groups saw improved bone microarchitecture in response to BCT. LOW compared to MOD had greater increases than HIGH, perhaps due to a greater relative increase in novel physical activity during BCT experienced by LOW and MOD. Ongoing work will determine whether a more robust skeletal response to BCT reduces BSI incidence.

Serological and RT-PCR Surveillance for COVID-19 in an Asymptomatic US Army Trainee Population.

BackgroundSignificant variability exists in the application of infection control policy throughout the US Army initial entry training environment. To generate actionable information for the prevention of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/coronavirus disease 2019 (COVID-19) transmission among new recruits, active enhanced surveillance was conducted for evidence of and exposure to SARS-CoV-2/COVID-19.MethodsWe serially tested recruits with a reverse transcriptase polymerase chain reaction (RT-PCR) COVID-19 and/or total antibody to SARS-CoV-2 tests at days 0, 14, and week 10 upon arrival for basic combat training at a location in the Southern United States.ResultsAmong 1403 recruits who were enrolled over a 6-week period from August 25 through October 11, 2020, 84 recruits tested positive by RT-PCR, with more than half (55%, 46/84) testing positive at arrival and almost two-thirds (63%, 53/84) also testing seropositive at arrival. Similarly, among an overall 146 recruits who tested seropositive for SARS-CoV-2 during the period of observation, a majority (86%) tested seropositive at arrival; no hospitalizations were observed among seropositive recruits, and antibody response increased at week 10.ConclusionsThese findings that suggest serological testing may complement current test-based measures and provide another tool to incorporate in COVID-19 mitigation measures among trainees in the US Army.

Sleep health of incoming army trainees and how it changes during basic combat training

ObjectiveTo examine the sleep health of incoming Army trainees and how it is impacted during basic combat training (BCT). DesignProspective. SettingBCT site (Fort Jackson, SC). ParticipantsA total of 1349 trainees (936 = male, 413 = female, 20.73 ± 3.67 years). MeasurementsParticipants completed the Pittsburgh Sleep Quality Index (PSQI), the Morningness/Eveningness Questionnaire, and the Epworth Sleepiness Scale at the start of BCT and a modified PSQI at the end of BCT. ResultsAt baseline, trainees reported an average sleep duration of 7.65 ± 1.68 hours per night, with 81.8% rating their sleep quality as “Very Good or Fairly Good.” The mean reported Morningness/Eveningness Questionnaire score was 50.63 ± 8.11 and the mean Epworth Sleepiness Scale was 8.60 ± 4.02. Reported sleep duration was significantly less during BCT (6.73 ± 0.90 hours) compared to baseline (P< .001). There was no significant difference in the mean PSQI Global score at the end of BCT compared to the start (5.33 ± 3.00 vs. 5.42 ± 2.85, P = .440), however, 6 of the 7 component scores were significantly different (with Sleep Quality, Sleep Duration, and Daytime Dysfunction scores being higher/worse and Sleep Latency, Sleep Efficiency, and Sleep Medication Use scores being lower/improved [all P < .01]). ConclusionsArmy BCT trainees in this large sample reported good sleep health characteristics at entry to training, including achieving recommended sleep amounts (>7 hours per night) and reporting good sleep quality. During BCT, negative changes were observed in reported sleep duration and quality in trainees. Further investigation into the factors contributing to changes in trainees’ sleep health during BCT and the implications on subsequent readiness, injury risk, and performance is warranted.

Prevalence of Gram-Positive Bacteria Isolated from Nasal Swabs and Hands of Healthy Army Trainees in the Republic of Korea

Prevalence of Gram-Positive Bacteria Isolated from Nasal Swabs and Hands of Healthy Army Trainees in the Republic of Korea