Karen A. Keenan

Injury Epidemiology of U.S. Army Special Operations Forces

Musculoskeletal injuries have long been a problem in general purpose forces, yet anecdotal evidence provided by medical, human performance, and training leadership suggests musculoskeletal injuries are also a readiness impediment to Special Operations Forces (SOF). The purpose of this study was to describe the injury epidemiology of SOF utilizing self-reported injury histories. Data were collected on 106 SOF (age: 31.7 ± 5.3 years, height: 179.0 ± 5.5 cm, mass: 85.9 ± 10.9 kg) for 1 year before the date of laboratory testing and filtered for total injuries and those with the potential to be preventable based on injury type, activity, and mechanism. The frequency of musculoskeletal injuries was 24.5 injuries per 100 subjects per year for total injuries and 18.9 injuries per 100 subjects per year for preventable injuries. The incidence of musculoskeletal injuries was 20.8 injured subjects per 100 subjects per year for total injuries and 16.0 injured subjects per 100 subjects per year for preventable injuries. Preventable musculoskeletal injuries comprised 76.9% of total injuries. Physical training (PT) was the most reported activity for total/preventable injuries (PT Command Organized: 46.2%/60.0%, PT Noncommand Organized: 7.7%/10.0%, PT Unknown: 3.8%/5.0%). Musculoskeletal injuries impede optimal physical readiness/tactical training in the SOF community. The data suggest a significant proportion of injuries are classified as preventable and may be mitigated with human performance programs.

Test-retest reliability and descriptive statistics of geometric measurements based on plantar pressure measurements in a healthy population during gait.

Previous studies have demonstrated that pressure, force, area, and time measurements can be reliably collected from pedobaragraphic platforms, but no studies have analyzed geometric measurements. The purpose of this study was to establish the test-retest reliability of geometric measurements obtained during gait at a self-selected speed using a two-step approach. Data were collected on both feet for 10 healthy participants using the emed-x platform. Reliability of 15 geometric measurements was assessed using intraclass correlation coefficients (ICC). All 15 measurements were demonstrated to be reliable (ICC>0.8), with 12 measurements ICC>0.90. Collection of geometric measurements at a self-selected pace with the emed-x platform was found to be reliable and can be used for investigation in research settings.

Lumbar spine and hip flexibility and trunk strength in helicopter pilots with and without low back pain history

BACKGROUND Low back pain (LBP) is one of the most common musculoskeletal issues facing military helicopter pilots. It is clinically important to identify differences in musculoskeletal characteristics between pilots with and without a LBP history for formulating effective interventions. OBJECTIVE To compare lumbar spine and hip flexibility and trunk strength in pilots with and without a LBP history. METHODS A total of 30 pilots with a LBP history were matched with pilots without a LBP history. An isokinetic dynamometer and a digital inclinometer were used to evaluate trunk and hip strength and a range-of-motion (ROM), respectively. All tests were performed bilaterally, if applicable, and agonist/antagonist ratios and side-to-side (low/high) symmetries were calculated. Paired t-tests or Wilcoxon tests were used to assess group differences (p <  0.050). RESULTS The LBP group demonstrated significantly lower trunk extension strength and trunk extension/flexion strength ratio (p <  0.008). The LBP group demonstrated significantly less lateral flexion ROM as well as greater lateral flexion and rotation side-to-side asymmetry (p <  0.009). The LBP group demonstrated significantly greater total hip rotation side-to-side asymmetry (p = 0.037). CONCLUSIONS Given the results, specific exercises that are targeted to improve trunk strength, ROM, and side-to-side symmetries could be developed to reduce LBP in helicopter pilots.

The relationship of core strength and activation and performance on three functional movement screens

Abstract Johnson, CD, Whitehead, PN, Pletcher, ER, Faherty, MS, Lovalekar, MT, Eagle, SR, and Keenan, KA. The relationship of core strength and activation and performance on three functional movement screens. J Strength Cond Res 32(4): 1166–1173, 2018—Current measures of core stability used by clinicians and researchers suffer from several shortcomings. Three functional movement screens appear, at face-value, to be dependent on the ability to activate and control core musculature. These 3 screens may present a viable alternative to current measures of core stability. Thirty-nine subjects completed a deep squat, trunk stability push-up, and rotary stability screen. Scores on the 3 screens were summed to calculate a composite score (COMP). During the screens, muscle activity was collected to determine the length of time that the bilateral erector spinae, rectus abdominis, external oblique, and gluteus medius muscles were active. Strength was assessed for core muscles (trunk flexion and extension, trunk rotation, and hip abduction and adduction) and accessory muscles (knee flexion and extension and pectoralis major). Two ordinal logistic regression equations were calculated with COMP as the outcome variable, and: (a) core strength and accessory strength, (b) only core strength. The first model was significant in predicting COMP (p = 0.004) (Pearsons Chi-Square = 149.132, p = 0.435; Nagelkerkes R-Squared = 0.369). The second model was significant in predicting COMP (p = 0.001) (Pearsons Chi-Square = 148.837, p = 0.488; Nagelkerkes R-Squared = 0.362). The core muscles were found to be active for most screens, with percentages of “time active” for each muscle ranging from 54–86%. In conclusion, performance on the 3 screens is predicted by core strength, even when accounting for “accessory” strength variables. Furthermore, it seems the screens elicit wide-ranging activation of core muscles. Although more investigation is needed, these screens, collectively, seem to be a good assessment of core strength.

Effects of Deployment on Musculoskeletal and Physiological Characteristics and Balance.

Despite many nonbattle injuries reported during deployment, few studies have been conducted to evaluate the effects of deployment on musculoskeletal and physiological characteristics and balance. A total of 35 active duty U.S. Army Soldiers participated in laboratory testing before and after deployment to Afghanistan. The following measures were obtained for each Soldier: shoulder, trunk, hip, knee, and ankle strength and range of motion (ROM), balance, body composition, aerobic capacity, and anaerobic power/capacity. Additionally, Soldiers were asked about their physical activity and load carriage. Paired t tests or Wilcoxon tests with an α = 0.05 set a priori were used for statistical analyses. Shoulder external rotation ROM, torso rotation ROM, ankle dorsiflexion ROM, torso rotation strength, and anaerobic power significantly increased following deployment (p < 0.05). Shoulder extension ROM, shoulder external rotation strength, and eyes-closed balance (p < 0.05) were significantly worse following deployment. The majority of Soldiers (85%) engaged in physical activity. In addition, 58% of Soldiers reported regularly carrying a load (22 kg average). The deployment-related changes in musculoskeletal and physiological characteristics and balance as well as physical activity and load carriage during deployment may assist with proper preparation with the intent to optimize tactical readiness and mitigate injury risk.

Residual Impact of Previous Injury on Musculoskeletal Characteristics in Special Forces Operators

Background Musculoskeletal injuries are a significant burden to United States Army Special Operations Forces. The advanced tactical skill level and physical training required of Army Special Operators highlights the need to optimize musculoskeletal characteristics to reduce the likelihood of suffering a recurrent injury. Purpose To identify the residual impact of previous injury on musculoskeletal characteristics. Study Design Cross-sectional study; Level of evidence, 3. Methods Isokinetic strength of the knee, shoulder, and back and flexibility of the shoulder and hamstrings were assessed as part of a comprehensive human performance protocol, and self-reported musculoskeletal injury history was obtained. Subjects were stratified based on previous history of low back, knee, or shoulder injury, and within-group and between-group comparisons were made for musculoskeletal variables. Results Knee injury analysis showed no significant strength or flexibility differences. Shoulder injury analysis found internal rotation strength of the healthy subjects (H) was significantly higher compared with injured (I) and uninjured (U) limbs of the injured group (H, 60.8 ± 11.5 percent body weight [%BW]; I, 54.5 ± 10.5 %BW; U, 55.5 ± 11.3 %BW) (P = .014 [H vs I] and P = .05 [H vs U]). The external rotation/internal rotation strength ratio was significantly lower in the healthy subjects compared with injured and uninjured limbs of the injured group (H, 0.653 ± 0.122; I, 0.724 ± 0.121; U, 0.724 ± 0.124) (P = .026 [H vs I] and P = .018 [H vs U]). Posterior shoulder tightness was significantly different between the injured and uninjured limb of the injured group (I, 111.6° ± 9.4°; U, 114.4° ± 9.3°; P = .008). The back injury analysis found no significant strength differences between the healthy and injured groups. Conclusion Few physical differences existed between operators with prior knee or back injury. However, operators with a previous history of shoulder injury demonstrated significantly less shoulder strength than uninjured operators as well as decreased shoulder flexibility on the injured side. All operators, regardless of prior injury, must perform the same tasks; therefore, a targeted injury rehabilitation/human performance training specifically focused on internal rotation strength and tightness of the posterior capsule may help reduce the risk for recurrence of injury. Operators presenting with musculoskeletal asymmetries and/or insufficient strength ratios may be predisposed to musculoskeletal injury. Clinical Relevance Specific fitness programs to compensate for deficiencies in strength and flexibility need to be designed that may reduce the risk of injuries in Special Forces Operators.

Greater ankle strength, anaerobic and aerobic capacity, and agility predict Ground Combat Military Occupational School graduation in female Marines

Women can serve in all military occupational specialties (MOS); however, musculoskeletal and physiological characteristics that predict successful completion of ground combat MOS schools by female Marines are unknown. OBJECTIVES To determine which demographic, musculoskeletal, and physiological characteristics predict graduation from infantry and vehicle ground combat MOS schools in female Marines. DESIGN Prospective cohort study. METHODS Prior to MOS school, the following were assessed in 62 female Marines (22.0±3.0yrs, 163.9±5.8cm, 63.4±7.2kg): isokinetic shoulder, trunk, and knee and isometric ankle strength; body composition; anaerobic power (AP)/capacity (AC); maximal oxygen uptake (VO2max); and field-based fitness tests (broad jump, medicine ball throw, pro-agility). Both absolute and normalized (%body mass: %BM) values were utilized for strength, AP, AC, and VO2max. Select tests from each Marines most recent Physical Fitness Test (PFT: abdominal crunches, 3-mile run time) and Combat Fitness Test (CFT: Maneuver Under Fire, Movement to Contact) were recorded. Participants were classified as graduated (N=46) or did not graduate (N=16). Simple logistic regression was performed to determine predictors of MOS school graduation. Statistical significance was set a priori at α=0.05. RESULTS Absolute and normalized ankle inversion and eversion strength, normalized anaerobic capacity, absolute and normalized VO2max, right pro-agility, and PFT 3-mile run time significantly predicted MOS school graduation (p<0.05). CONCLUSIONS Greater ankle strength, better agility, and greater anaerobic and aerobic capacity are important for successful completion of ground combat MOS school in female Marines. Prior to entering ground combat MOS school, it is recommended that female Marines should train to optimize these mobility-centric characteristics.

Epidemiology of musculoskeletal injuries sustained by Naval Special Forces Operators and students

OBJECTIVES The aim of this analysis was to describe the incidence and common types of medical chart-reviewed musculoskeletal injuries, among four distinct groups of Naval Special Warfare (NSW) personnel: Sea, Air, and Land (SEAL) Operators, SEAL Qualification Training (SQT) students, Special Warfare Combatant-craft Crewman (SWCC) Operators, and Crewman Qualification Training (CQT) students. DESIGN Descriptive cross-sectional study. METHODS Medical records were reviewed for 920 NSW personnel. MSI were described and classified by frequency and incidence; anatomic location; injury type and cause; activity during injury; and potential for prevention. RESULTS The frequency of MSI was 23.1, 46.5, 31.6, and 17.0 per 100 participants per year among SEAL, SQT, SWCC, and CQT, respectively. Upper extremity MSI were the most common in SEAL, lower extremity MSI were common in the other groups. The most frequent MSI anatomic sub-locations varied across groups (SEAL: shoulder, 21.6% of MSI; SQT: foot and toes, 17.0%; SWCC: lumbopelvic spine, 21.7%; and CQT: knee, 30.3%). Pain/spasm/ache were the most common MSI type in SEAL (29.7%) and SWCC (21.7%), tendonitis/tenosynovitis/tendinopathy was the most common MSI type in SQT (21.0%), and tendonitis/tenosynovitis/tendinopathy and fracture were the most common in CQT (15.2% each). A considerable proportion of MSI were classified as potentially preventable-SEAL: 35.1%, SQT: 53.0%, SWCC: 36.7%, and CQT: 21.2%. CONCLUSIONS MSI cause considerable morbidity among NSW Operators and students, with distinct patterns of distribution by anatomic location and injury type. Since many injuries may be preventable, targeted interventions may be able to mitigate MSI risk.

Association of prospective lower extremity musculoskeletal injury and musculoskeletal, balance, and physiological characteristics in Special Operations Forces

OBJECTIVES Previous research has examined lower extremity (LE) musculoskeletal injury (MSI) patterns and risk factors in Special Operations Forces (SOF) trainees, conventional military personnel, and athletes; however, it is unclear if SOF have the same patterns/risk factors. This study aimed to determine the association of musculoskeletal, balance, and physiological characteristics with LE MSI in SOF. DESIGN Cohort study. METHODS A total of 726 Air Force (N=140), Navy Sea, Air, and Land (N=301), and Special Warfare Combatant Crewmen (N=285) SOF (age=25.72±4.77years, height=178.34±6.63cm, weight=84.28±9.03kg) participated in laboratory testing, including: LE muscular strength and flexibility; balance; body composition; anaerobic power/capacity; and aerobic capacity. Medical charts were reviewed for LE MSI 365days following laboratory testing. Participants were assigned by injury status and laboratory data stratified by tertile. Chi-square statistics were calculated to determine the frequency of LE MSI across tertiles for each characteristic. RESULTS There was a significant association between LE MSI and: ankle inversion strength (weaker side: Χ(2)=17.703; stronger side: Χ(2)=18.911; p≤0.001); ankle eversion/inversion strength ratio (lower side: Χ(2)=13.456; higher side: Χ(2)=16.885; p≤0.001); hamstring flexibility (less flexible: Χ(2)=19.930; more flexible Χ(2)=15.185; p≤0.001); gastrocnemius-soleus flexibility (less flexible: Χ(2)=7.889, p=0.019); dynamic balance asymmetry (Χ(2)=7.444, p=0.024); Vestibular and Preference ratios (Χ(2)=9.124, p=0.010 and Χ(2)=6.572, p=0.037, respectively); and aerobic capacity (Χ(2)=13.935, p=0.001). CONCLUSIONS Characteristics associated with LE MSI are unique in SOF. Human performance program initiatives should include efforts to optimize ankle strength and flexibility, maintain moderate hamstring flexibility, expand dynamic balance strategies, and maximize aerobic capacity to reduce LE MSI risk.

Using the capture–recapture method to estimate the incidence of musculoskeletal injuries among U.S. Army soldiers

Musculoskeletal injury (MSI) data typically are obtained from medical chart-review (MCR) or injury self-reports (ISR). MSI incidence may be under-counted if only one source is utilized, as MCR will not capture MSI for which medical care was not sought, and ISR may be affected by issues with recall. OBJECTIVES The purposes of this study were to determine MSI incidence from two sources (MCR, ISR) and to estimate the incidence, after accounting for the under-counting in both sources, among a sample of U.S. Army soldiers. DESIGN Descriptive cross-sectional study. METHODS The estimated cumulative incidence during a one-year period was calculated from the two sources of MSI data using a novel statistical analysis (capture-recapture-CRC). RESULTS MSI data were available for 287 soldiers (age: 27.5±6.3years (mean±standard deviation)). The one-year cumulative incidence of MSI was 17.8% (MCR), 19.5% (ISR), and 54.0% (CRC). CRC analysis showed that there was under-counting from both sources of data and the percent of CRC estimated MSI observed were 32.9% (MCR), 36.1% (ISR), and 57.4% (MCR and ISR combined). When analyzed by MSI type, percent of CRC estimated MSI counted from both sources was highest (75.0%) for fracture, followed by sprain (53.8%), strain (43.8%), and pain/spasm/ache (35.8%). CONCLUSIONS There was under-counting of MSI from both sources of data, and the under-counting varied by MSI type. There is a need for further investigation of the relative benefits of various sources of MSI data and the application of the capture-recapture analysis in military populations.