Warfighter Performance Research Articles

The Effect of a Powered Lower-Body Exoskeleton on Physical and Cognitive Warfighter Performance

This study analyzed the performance of twelve military members in a simulated, fatigue-inducing patrol task under three conditions: wearing a powered exoskeleton, wearing an unpowered exoskeleton, and without wearing an exoskeleton. While walking with weight at a prescribed pace over obstacles while following a confederate, participants were subject to a dual-task cognitive test in which they answered radio calls and visually scanned for lighted targets. Cognitive load was varied through a secondary radio task and measured with a visual reaction time test. Physical load and cognitive load were varied throughout the test. For this paper, the dependent measures of interest were reaction time for the visual task and lag time behind the confederate. Significant differences and interactions were found in the visual reaction time among the exoskeleton conditions, physical loads, and cognitive loads. Significant differences and interactions were also found for the lag time of the subject behind their prescribed pace, and the variability of this lag time. Both measures had significant interactions with subject. Future work should examine what design features of the exoskeleton and capability of the human are related to these variabilities. An understanding of subject variability can lead to improvements in integrated exoskeleton design.

Cognitive Training for Military Application: a Review of the Literature and Practical Guide

In recent years, the potential to improve cognitive skills through training has captured the attention of academic researchers, the commercial market, and the general public. Numerous clinical and healthy populations have been identified as targets for cognitive training, and military personnel are one particular group that may be able to uniquely benefit from cognitive training interventions. Military operations involve a wide range of human performance skills, many of which are cognitive in nature. Use of cognitive training to improve these critical everyday skills for service members represents an untapped potential resource by which to improve operational readiness and warfighter performance. While much of the cognitive training research to date has been circumscribed within basic science pursuits, here we propose ways in which this research may start to be applied in a military setting. In the current review, we examine instances of military operations that may readily lend themselves to cognitive training. Further, we examine the existing literature from academic endeavors and pinpoint areas of exemplary efforts that can serve as a guide for military research to follow, as well as pitfalls to avoid. In particular, we identify and review evidence from the video game, working memory, and executive function training literatures. Finally, the goals of basic and applied science often differ, and that is certainly the case when comparing outcome-based research in a military context with mechanism-based research in an academic context. Therefore, we provide a guide for best practices when conducting cognitive training research specifically in a military setting. While cognitive training has attracted much controversy in both academia and commercial markets, we argue that utilizing near transfer effects in a targeted, outcome-based approach may represent a powerful tool to improve human performance in a number of military-relevant scenarios.

Update: Efficacy of Military Fluid Intake Guidance.

Fluid intake during military training is prescribed based on the interactions among work rates, environmental conditions, and uniform configurations. The efficacy of this guidance has not been empirically assessed in over a decade. To determine the acceptability of the fluid intake guidance, sweat losses were measured in a variety of conditions with modern uniform/body armor configurations and were then compared to prescribed fluid intakes for each condition (workload, environment, clothing). Whole body sweat losses of 324 Soldiers and 14 model simulations were measured under a variety of work intensities ((Watts) easy, moderate, hard), work durations (2-25 h), environmental conditions (White-Black flag), and uniform configurations (including Army Combat Uniform and body armor). Whole body sweat losses were then calculated relative to 4 h drinking guidance and in accordance with TB MED 507 recommended work/rest ratios. The differences between the prescribed fluid intake and sweat loss were calculated and expressed as a percent loss or gain of body weight. Values within a threshold of ±2% body water flux (BWF) were deemed an acceptable conservative starting point for performance and health concerns. Values within ±2% BWF numbered 309/338; 25 of 338 observations exceeded the +2% BWF while 4 of 338 observations exceeded the -2% BWF. When total fluid restriction was simulated, all experienced body weight loss with 151 of 338 observations exceeding the -2% BWF. When calculated using actual measured sweating rates from the laboratory and model simulations, current fluid intake guidance appears to predict with 91.4% accuracy the volume of fluid required to maintain a proper euhydrated state (±2%) during 4 h of exercise. Simulations of total fluid restriction support the necessity for fluid intake guidance so that the Warfighter's performance does not degrade. It is recommended that the current military fluid intake guidance focuses on methods for accurately tracking fluid intakes.

The relationship between physical fitness and military operational obstacle course performance times

Introduction: Defence research organizations across the world use the Load Effects Assessment Program (LEAP), a military mission obstacle course, to assess the impact of clothing and individual equipment on warfighter performance. However, there is interest in understanding the impact of a participant's physical characteristics on performance. This study investigated the role of strength on obstacle course completion times with a variety of loads.

Performance nutrition: An international perspective

The maintenance of nutritional status is essential for the optimization of Warfighter physical and cognitive performance; diminished nutritional status has been linked to degraded performance, injury, and poor health outcomes. The objective of the Thematic Session titled “Performance Nutrition: An International Perspective” is to outline and summarize nutrition perspectives and primary research from a series of nations exploring nutritional requirements for the optimization of Warfighter performance. Speakers will detail observational and interventional studies conducted in laboratory, field, and operational environments contributing to the development of Warfighter nutritional standards. The impact of nutritional interventions, including the use of dietary supplements and sustainable approaches, on physical and cognitive performance will be highlighted. Speakers will conclude by providing examples by which nutrition research studies were utilized to develop national or international nutrition requirements and the optimization of military feeding platforms, to include snacks, rations, and garrison feeding policies.

Method for Estimating Three-Dimensional Knee Rotations Using Two Inertial Measurement Units: Validation with a Coordinate Measurement Machine.

Three-dimensional rotations across the human knee serve as important markers of knee health and performance in multiple contexts including human mobility, worker safety and health, athletic performance, and warfighter performance. While knee rotations can be estimated using optical motion capture, that method is largely limited to the laboratory and small capture volumes. These limitations may be overcome by deploying wearable inertial measurement units (IMUs). The objective of this study is to present a new IMU-based method for estimating 3D knee rotations and to benchmark the accuracy of the results using an instrumented mechanical linkage. The method employs data from shank- and thigh-mounted IMUs and a vector constraint for the medial-lateral axis of the knee during periods when the knee joint functions predominantly as a hinge. The method is carefully validated using data from high precision optical encoders in a mechanism that replicates 3D knee rotations spanning (1) pure flexion/extension, (2) pure internal/external rotation, (3) pure abduction/adduction, and (4) combinations of all three rotations. Regardless of the movement type, the IMU-derived estimates of 3D knee rotations replicate the truth data with high confidence (RMS error and correlation coefficient).

Performance of Intravenous Insertion is Impaired Following Cold Water Immersion in Military Medical Providers

Accidental cold water immersion or unprepared exposure to extreme cold temperatures can negatively impact warfighter performance and mission outcomes by hindering hands and feet use due to numbness. Skin or extremity temperature has been identified as a relevant variable that predicts impairment in manual dexterity and tactile sensitivity, yet no data have been presented showing performance of medically-specific tasks, such as intravenous (IV) insertion following a cold water immersion. PURPOSE: To determine the influence of cold water immersion and rewarming on IV insertion performance among military medical providers. METHODS: Thirty-eight military personnel (mean ± SD age: 25.8 ± 5.4 yrs, height: 179.5 ± 9.9 cm, weight: 83.2 ± 10.9 kg), trained in the technique of IV insertion, participated in a Cold Weather Medicine course. During the training exercise, students completed six stations: baseline in a classroom (5 min, 23° C), pre-immersion (pre) outdoors (5 min, -4.6° C), immersion in cold water (10 min, 0.2° C), post-immersion (post) (5 min, wet clothing, -4.6° C), transition (5 min, change into dry clothing), and rewarming (60 min, using various techniques). An IV insertion task was performed upon arrival at baseline, pre- and post-immersion, and after rewarming. The IV insertion task required students to insert an IV using a manikin arm. Students were assessed for time to insert IV and success of administering fluid. RESULTS: Assessment revealed a significant increase in IV insertion time (p<0.001) and a decrease in IV insertion success rate following cold water immersion. IV insertion times (seconds) for each station were: baseline 82 ± 17, pre 70 ± 12, post 168 ± 45, and rewarm 73 ± 14. IV insertion success rates were similar among baseline (76%), pre (71%), and rewarm (84%) stations; however, post-immersion, IV success trended downward (47%). CONCLUSION: Results were consistent with the expected loss of manual dexterity following cold water immersion. When given one hour of rewarming, performance returned to baseline. It is essential that military personnel are educated and trained on the effects of accidental cold exposure, the impact it may have on their performance as medical providers, and appropriate extremity rewarming techniques.

Engineering out the noise

The US Navy, through an Office of Naval Research (ONR) lead effort on Noise Induced Hearing Loss (NIHL), is investigating methods and techniques to mitigate hearing loss for the crews and warfighters. Hearing protection is a viable and increasingly popular method of reducing hearing exposure for many ship crew members; however, it has limitations on comfort and low frequency effectiveness. Furthermore, Personal Hearing Protection (PHP) is often used improperly. Proper vessel planning, programmatic changes and advances in noise control engineering can also have significant impacts by inherently reducing noise exposure through ship design and use of noise control treatments. These impacts go beyond hearing loss mitigation since they can improve quality of life onboard vessels and provide enhanced warfighter performance. Such approaches also can be made to work in the lower frequency range where hearing protection is not as effective. This paper describes non-hearing protection methods being implemented to mitigate and control noise within the US Navy and US Marine Corps. These approaches reflect the latest changes to Mil-Std 1474E, Appendix F.

Quantifying warfighter performance in a target acquisition and aiming task using wireless inertial sensors

An array of inertial measurement units (IMUS) was experimentally employed to analyze warfighter performance on a target acquisition task pre/post fatigue. Eleven participants (5M/6F) repeated an exercise circuit carrying 20 kg of equipment until fatigued. IMUs secured to the sacrum, sternum, and a rifle quantified peak angular velocity magnitude (PAVM) and turn time (TT) on a target acquisition task (three aiming events with two 180° turns) within the exercise circuit. Turning performance of two turns was evaluated pre/post fatigue. Turning performance decreased with fatigue. PAVMs decreased during both turns for the sternum (p < 0.001), sacrum (p = 0.007) and rifle (p = 0.002). TT increased for the sternum (p = 0.001), sacrum (p = 0.003), and rifle (p = 0.02) during turn 1, and for the rifle (p = 0.04) during turn 2. IMUs detected and quantified changes in warfighter aiming performance after fatigue. Similar methodologies can be applied to many movement tasks, including quantifying movement performance for load, fatigue, and equipment conditions.

The Effects of Military Body Armor on Isometric and Isokinetic Knee Behaviors

OCCUPATIONAL APPLICATIONSDespite the proven effectiveness of new-generation body armor against ballistic threats, small arms, and improvised explosive devices, such body armor has become a source of concern for warfighters' performance and musculoskeletal injuries. Prolonged periods of performing physical activities, with versus without body armor, were found to alter knee neuromuscular behavior. With body armor, the maximum strength of the knee flexors and the extensor-to-flexor strength ratio were found, respectively, to reduce and increase than in conditions without body armor. Such changes in knee neuromuscular behavior are known to adversely affect physical performance and risk of knee injury. Quantitative information related to changes in knee neuromuscular behavior induced by body armor can be used in the design of injury risk assessment tools, physical training programs that decrease or correct a particular imbalance, and to establish return to service (i.e., post injury) standards for dismounted warfighters.TECHNICAL ABSTRACT Background: Knee injuries among military service members have a substantially high prevalence. Dismounted warfighters often must navigate diverse environments while wearing body armor. Purpose: Given the suggested role of body armor mass on a warfighter's performance and risk of injury, the immediate and prolonged effects of body armor on the neuromuscular behavior of knee flexors and extensors were investigated. Methods: Body armor-induced changes in selected measures related to isometric and isokinetic behaviors of the knee were quantified using a commercial dynamometer. This was done in two testing sessions, with and without body armor, by assessing neuromuscular behaviors of the knee before and after participants completed a battery of basic and military-inspired tests, as well as a 45-minute brisk walking protocol. Results: Completing tests with body armor versus no armor was found to cause a greater change (i.e., reduction of ∼10 N·m) in maximum isometric strength of the knee flexors. It also was found to be associated with a significant increase in conventional/functional strength ratios. While there was no significant difference in maximum isometric knee extensor strength between genders at baseline, females demonstrated a significant reduction (∼16 N·m) following completion of tests regardless of the body armor condition. Conclusion: In general, the prolonged duration of wearing body armor was found to cause changes in the neuromuscular behavior of knee flexors and extensors that have been suggested in the literature to be associated with a higher risk of injury and reduced warfighter performance.

The effects of military body armour on the lower back and knee mechanics during toe-touch and two-legged squat tasks

While effective in the prevention of otherwise lethal injuries, military body armour (BA) has been suggested to reduce warfighter's performance and increase injury-related musculoskeletal conditions. Providing the significant role of joint biomechanics in both performance and risk of injury, the immediate and prolonged effects of wearing BA on biomechanics of the lower back and knee during toe-touch (TT) and two-legged squat (TLS) tasks were investigated. The immediate effects of BA were an increase of >40 ms (p ≤ 0.02) in flexion duration of the dominant joint and an ∼1 s (p ≤ 0.02) increase in overall task duration as well as an ∼18% (p = 0.03) decrease in the lumbopelvic rhythm ratio near the mid-range of trunk flexion. In general the prolonged duration of wearing BA (i.e. 45 min of walking) was not found to cause more changes in our measures than walking without BA.

Relationship between Variations in Single-nucleotide Polymorphisms and Warfighter Performance

Previous research has demonstrated potential links between variations in single-nucleotide polymorphisms (SNPs) and performance on various cognitive tasks. This study replicated the methods previously used to investigate such relationships and attempted to extend the methods to comparing genetic variations and operational warfighter performance during naval training tasks. The goal was to determine if such methods could be applied to operational performance metrics and, if so, could the results of such investigations be utilized to enhance warfighter training programs and system designs. The study investigated the relationship between various SNPs in the brain-derived neurotrophic factor (BDNF) (rs6265) and catechol-O-methyltransferase (COMT) (rs4680) genes and performance on working memory, cued visual-spatial attention, and surface warfare combat tasks. Study results showed no significant effects with respect to cued visual-spatial attention but did indicate significant effects for BDNF allele “A” carriers regarding working memory accuracy. Finally, due to the limited types of training metrics that could be collected, statistical analysis of the link between genetic variation and warfighter performance could not be performed. However, the lessons learned from this study may provide guidance for future studies in such comparisons.

Noise induced hearing loss mitigation via planning and engineering

The US Navy, through an ONR lead effort, is investigating methods and techniques to mitigate hearing loss for the crews and warfighters. Hearing protection is a viable and increasingly popular method of reducing hearing exposure for many ship crew members; however, it has limitations on comfort and low frequency effectiveness, and is often used improperly. Proper naval vessel planning, programmatic changes, and advances in noise control engineering can also have significant impacts by inherently reducing noise exposure through ship design along with the use of passive noise control treatments. These impacts go beyond hearing loss mitigation since they can improve quality of life onboard vessels and provide enhanced warfighter performance. Such approaches also can be made to work in the lower frequency range where hearing protection is not as effective. This paper describes the programmatic and noise control methods being pursued to mitigate and control noise within the US Navy and US Marine Corps. Methodologies to assess the cost impact are also discussed.

The enhanced warfighter

Modern technological warfare requires a level of cognitive ability and discipline unique in the history of armed conflict. Recent advances in physiology, nutrition, neuroscience, and engineering offer a significant potential to prevent or reduce the degradation of a warfighter’s mental or physical capabilities in this demanding environment. The authors explore four categories for potential enhancement of military personnel: genetic or computational-mechanical alteration of the human body; physiological monitoring and tighter coupling between man and machine; pharmaceuticals; and nutrition and supplementation. None of these types of enhancements is without controversy; in particular, genetic intervention would require morally intolerable experimentation. In the foreseeable future, the military enhancement technologies most likely to see use will be akin to those seen in elite athletics. Physiological monitoring and feedback, changes in nutrition, and careful pharmaceutical interventions all could improve warfighter performance, and, the authors assert, such enhancements are not morally problematic if their effects are candidly assessed and revealed. In choosing whether and how to enhance military personnel, the government must balance long-term health hazards with a reduced risk of near-term injury or death. If physiological monitoring and feedback (and regulation, through drugs or other means) can decrease large, immediate, or long-term risks to the life or well-being of service personnel, the authors write, there appears to be a moral obligation to provide those enhancements to warfighters.

The Influence of Agility Training on Physiological and Cognitive Performance

Agility training (AT) has recently been instituted in several military communities in hopes of improving combat performance and general fitness. The purpose of this study was to determine how substituting AT for traditional military physical training (PT) influences physical and cognitive performance. Forty-one subjects undergoing military technical training were divided randomly into 2 groups for 6 weeks of training. One group participated in standard military PT consisting of calisthenics and running. A second group duplicated the amount of exercise of the first group but used AT as their primary mode of training. Before and after training, subjects completed a physical and cognitive battery of tests including V[Combining Dot Above]O2max, reaction time, Illinois Agility Test, body composition, visual vigilance, dichotic listening, and working memory tests. There were significant improvements within the AT group in V[Combining Dot Above]O2max, Illinois Agility Test, visual vigilance, and continuous memory. There was a significant increase in time-to-exhaustion for the traditional group. We conclude that AT is as effective or more effective as PT in enhancing physical fitness. Further, it is potentially more effective than PT in enhancing specific measures of physical and cognitive performance, such as physical agility, memory, and vigilance. Consequently, we suggest that AT be incorporated into existing military PT programs as a way to improve war-fighter performance. Further, it seems likely that the benefits of AT observed here occur in various other populations.

Returning Service Members to Duty Following Mild Traumatic Brain Injury: Exploring the Use of Dual-Task and Multitask Assessment Methods

Within the last decade, more than 220,000 service members have sustained traumatic brain injury (TBI) in support of military operations in Iraq and Afghanistan. Mild TBI may result in subtle cognitive and sensorimotor deficits that adversely affect warfighter performance, creating significant challenges for service members, commanders, and clinicians. In recent conflicts, physical therapists and occupational therapists have played an important role in evaluating service member readiness to return to duty (RTD), incorporating research and best practices from the sports concussion literature. Because premorbid (baseline) performance metrics are not typically available for deployed service members as for athletes, clinicians commonly determine duty readiness based upon the absence of postconcussive symptoms and return to "normal" performance on clinical assessments not yet validated in the military population. Although practices described in the sports concussion literature guide "return-to-play" determinations, resolution of symptoms or improvement of isolated impairments may be inadequate to predict readiness in a military operational environment. Existing clinical metrics informing RTD decision making are limited because they fail to emphasize functional, warrior task demands and they lack versatility to assess the effects of comorbid deficits. Recently, a number of complex task-oriented RTD approaches have emerged from Department of Defense laboratory and clinical settings to address this gap. Immersive virtual reality environments, field-based scenario-driven assessment programs, and militarized dual-task and multitask-based approaches have all been proposed for the evaluation of sensorimotor and cognitive function following TBI. There remains a need for clinically feasible assessment methods that can be used to verify functional performance and operational competence in a variety of practice settings. Complex and ecologically valid assessment techniques incorporating dual-task and multitask methods may prove useful in validating return-to-activity requirements in civilian and military populations.

Transforming Training: A Perspective on the Need for and Payoffs From Common Standards

Standards today position the research community on the eve of scientific breakthrough. Efficiency and warfighter competency are likely to improve greatly as a result of the feedback and research studies enabled by the use of common standards for defining competencies, assessing performance, and enabling technologies to collect data. Such standards make it possible to evaluate warfighter performance across sites and across time. Standards also make it possible to do rigorous comparisons in the lab, operational simulator settings, and even live exercises. The standardized methods and leveraging of common data will yield unprecedented scientific power and opportunity to rapidly transform training.

United States Army Research Institute of Environmental Medicine: Warfighter research focusing on the past 25 years

The United States Army Research Institute of Environmental Medicine (USARIEM) celebrated its 50th anniversary on July 1, 2011. This article reviews its history, evolution, and transition of its research programs as well as its scientific and military accomplishments, emphasizing the past 25 yr. During the 1990s, USARIEM published a series of pocket guides providing guidance for sustaining Warfighter health and performance in Southwest Asia, Somalia, the former Republic of Yugoslavia, Rwanda, and Haiti. Issues identified during Operation Desert Storm elicited research that improved nutritional guidelines for protracted desert operations; safer use of nuclear, chemical, and biological protective clothing; equipment, development, and fielding of efficient microclimate cooling systems; and effective evaluation of pharmaceuticals to protect soldiers from chemical and biological threats. During the first decade of the 21st century, USARIEM and the Department of the Army published official medical/performance doctrines for operations in the heat and cold and at high altitude. The current Global War on Terrorism focused research to improve doctrines for hot, cold, and high-altitude operations, reduce musculoskeletal training injuries, provide improved field nutrition, more efficient planning for operational water requirements, and improve both military clothing and materiel. This article also describes the critically important interactions and communications between USARIEM and deployed units and the benefits to Warfighters from this association. This report presents USARIEM's unique and world-class facilities, organizational changes, scientific and support personnel, and major research accomplishments, including the publication of 2,200 scientific papers over the past 25 yr.

Acute Anxiety Among Marines After Recent Arrival at High Altitude: High Altitude Anxiety as a Distinct Diagnostic Entity

As United States and allied armed forces maintain a presence in high altitude regions such as eastern Afghanistan, a better understanding of the prevention, diagnosis, and treatment of altitude illness has become increasingly important. This preventable form of disease/nonbattle injury presents a significant issue to readiness for warfighter performance in the field. At the Marine Corps Mountain Warfare Training Center in Bridgeport, California (operational altitudes: 2061 to 3383 m), 1036 unacclimatized Marines participated in battalion-level mountain warfare exercises in July 2010. Several unexpected, clear-cut cases of severe anxiety were observed at the Battalion Aid Station (BAS), located at 2061 m, over the first 6 days after training proceeded above 2000 m. These cases occurred among otherwise healthy Marines, some having had no prior history of psychiatric illness, and others having had a history of well-controlled panic disorders or combat stress-related psychiatric illness. All patients presented with similar symptoms of mild to moderate tachycardia, tachypnea, and diaphoresis; some presented with extremity numbness and tingling. Acute cardiopulmonary events could not be decisively ruled out by electrocardiogram, chest radiograph, or lab studies (given the equipment limitation of the BAS); however, patients were monitored clinically with vital signs, pulse oximetry, and chest auscultation/palpation. All patients responded clinically to oxygen, rest, and benzodiazepine management; all returned to baseline psychiatric function within the same day. The near-simultaneous and unexpected onset of 7 cases of acute anxiety, coincident with new arrival at moderate to high altitude, represents a highly unusual incidence, prevalence, and temporal distribution suggestive of hypobaric hypoxemia as the proximal cause. Based upon the authors' extensive combined clinical experience and review of emerging peer-reviewed literature, High Altitude Anxiety is proposed as a diagnostic entity for consideration in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Further research is indicated.

Employing Human Performance Optimization Initiatives from Historically Black Colleges and Universities: The Case of the U.S. Military

Abstract To preemptively respond to the ever changing battlefield and in light of growing threats to national security, the U.S. Department of Defense (DoD) and by extension the U.S. military, have developed human performance optimization (HPO) initiatives to improve warfighter performance for increasing mission readiness. African American officers, by way of the Reserve Officer Training Corps (ROTC) at Historically Black Colleges and Universities (HBCUs), have long been and continue to be an important constituency for this strategy. Using the results of an online search via the Internet of HPO-like academic offerings at HBCUs, this paper proposes that the U.S. military could enhance its war fighting capability, and specifically that of its African American officers, for increased preparedness, increased performance and sustained and increased readiness by modeling HPO like programs at HBCUs. The authors examine similar efforts around the world, offer the potential benefits to be derived from expanded collaborations between the U.S. military and HBCUs and discuss the implications for the U.S. military and militaries within international communities, HBCUs and future research.