Sleep restriction and cognitive load affect performance on a simulated marksmanship task

Psychological endurance: how grit, resilience, and related factors contribute to sustained effort despite adversity

Many concepts describe how individuals sustain effort despite challenging circumstances. For example, scholars and practitioners may incorporate discussions of grit, hardiness, self-control, and resilience into their ideas of performance under adversity. Although there are nuanced points underlying each construct capable of generating empirically sound propositions, the shared attributes make them difficult to differentiate. As a result, substantial confusion arises when debating how these related factors concomitantly contribute to success, especially when practitioners attempt to communicate these ideas in applied settings. The model proposed here-psychological endurance-is a unified theory to explore how multiple concepts contribute to sustained goal-directed behaviors and individual success. Central to this model is the metaphor of a psychological battery, which potentiates and sustains optimal performance despite adversity. Grit and hardiness are associated with the maximum charge of the psychological battery, or how long an individual could sustain effort. Self-control modulates energy management that augments effort required to sustain endurance, whereas resilience represents the ability to recharge. These factors are constrained by both psychological and physiological stressors in the environment that drain the psychology battery. Taken together, these ideas form a novel framework to discuss related psychological concepts, and ideally, optimize intervention to enhance psychological endurance.

From trenches to technology: a narrative review of sleep medicine in the military

Diagnoses of military-relevant sleep disorders have increased substantially since the terrorist attacks of September 11, 2001. The cause of this increase appears to be complicated and multifactorial, with military and civilian populations clearly differing with respect to both the nature and distribution of sleep disorders diagnoses. In part, these differences may be attributable to the fact that a majority of service members are chronically sleep-restricted-an unavoidable consequence of continuous and sustained military operations that "set the stage" for development of specific sleep disorders. The purpose of this narrative review is to describe the military relevance of several common sleep disorders, assess the extent to which these disorders currently constitute a burden on the military health care system, and suggest strategies to alleviate that burden. The military health care system does not have enough sleep medicine providers to address the immediate and long-term consequences of sleep disorders in military personnel. Digital technologies and education packages can be leveraged to improve access to care.

CITATION

Thomas CL, Carr K, Yang F, et al. From trenches to technology: a narrative review of sleep medicine in the military. J Clin Sleep Med. 2024;20(6):973-981.

Insufficient Sleep and Behavioral Health in the Military: A 5-Country Perspective

PURPOSE OF REVIEW

The goal of this paper was to highlight the degree to which sleep, behavioral health, and leader involvement were interrelated using data from militaries in five English-speaking countries: Australia, Canada, New Zealand, the UK, and the United States.

RECENT FINDINGS

Many service members reported sleeping fewer than the recommended 7 h/night: 34.9%, 67.2%, and 77.2% of respondents from New Zealand, Canada, and the United States, respectively. Countries reporting shorter sleep duration also reported fewer insomnia-related difficulties, likely reflecting higher sleep pressure from chronic sleep loss. Across all countries, sleep problems were positively correlated with behavioral health symptoms. Importantly, leader promotion of healthy sleep was positively correlated with more sleep and negatively correlated with sleep problems and behavioral health symptoms. Insufficient sleep in the military is ubiquitous, with serious implications for the behavioral health and functioning of service members. Leaders should attend to these risks and examine ways to promote healthy sleep in service members.

Recovery of Cognitive Performance Following Multi-Stressor Military Training

OBJECTIVE

This project aimed to assess the impact of an 8-day military training exercise on cognitive performance, and track its recovery in periods of reduced training load and partially restored sleep.

BACKGROUND

Military personnel often work in challenging multi-stressor environments, where sleep loss is inevitable. Sleep loss can impair multiple cognitive domains, which can have disastrous consequences in military contexts.

METHOD

A total of 57 male and female soldiers undergoing the Australian Army combat engineer Initial Employment Training course were recruited and tracked over a 16-day study period which included an 8-day field-based military training exercise. Cognitive performance was assessed via a computerised battery at seven time points across four sequential study periods; 1) baseline (PRE), 2) military field training exercise which included total sleep deprivation (EX-FIELD), 3) training exercise at simulated base with restricted sleep opportunities (EX-BASE), and 4) a 3-day recovery period (REC). Subjective load, fatigue, and sleep were evaluated continuously via questionnaire and actigraphy.

RESULTS

Psychomotor speed, reaction time, visual tracking and vigilance were impaired following the EX-FIELD period (p < 0.05). The majority of affected measures recovered 2 days following EX-FIELD, being no different in EX-BASE compared to PRE.

CONCLUSION

The sensitivity of the cognitive tests to sleep restriction, and recovery, indicates they can help assess operational readiness in military personnel. Future studies should explore other indicators of, and strategies to preserve, operational readiness in military personnel.

APPLICATION

This study highlights the impact of work-induced fatigue on cognitive performance, and would interest authorities seeking to preserve operational readiness.

Effects of 36-hour recovery on marksmanship and hormone concentrations during strenuous winter military survival training

OBJECTIVES

Survival training can provide a unique setting for scientific examination of human stress responses and physical performance in a realistic operational military context. The aim of the present study was to observe effects of a 36-h recovery period on serum hormone concentrations, salivary cortisol, and marksmanship during 10-day winter military survival training in north of the Arctic Circle.

DESIGN AND METHODS

Sixty-eight male soldiers were randomly divided into two groups; EXP (n = 26) and CON (n = 42). While CON performed the whole exercise phase in the field, EXP had 36-h recovery period between days 6 and 8. Several hormones were measured during the study to investigate recovery.

RESULTS

Subjective physical and mental demand as well as catabolic hormone levels increased and anabolic hormones decreased in CON (p < 0.05), whereas in EXP, recovery period attenuated negative effects of survival training. Prone shooting performance decreased (87.5 ± 6.5 vs. 76.3 ± 8.8, points out of 100, p < 0.05) between days 6 and 8 in CON while EXP was able to maintain shooting performance throughout the study.

CONCLUSION

A short recovery during a strenuous training can prevent the degradation in psychophysiological state and shooting performance in soldiers, which can be crucial for survival in demanding operational winter environment. In the present study, 36-h rest period during the field training seems to enhance recovery but the duration of the period was inadequate for full recovery from the accumulated operative stress. In conclusion, appropriate recovery periods should be implemented in order to optimize occupational performance during high operative stress.

The relationship between sleep, pain,and musculoskeletal injuries in US Army Soldiers

INTRODUCTION

The purpose of this study was to investigate the relationship between sleep and pain in military personnel and to determine if metrics of sleep and pain intensity differ between the injured and uninjured in this population.

METHODS

Active-duty US Army Soldiers (n=308; 26.8±6.5 years, 82% male) from the 2nd Infantry Division, Joint Base Lewis-McChord, Washington, and 101st Airborne Division, Fort Campbell, Kentucky, completed the Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and questionnaires about current musculoskeletal injuries and pain intensity (0=no pain to 10=worst imaginable pain). Pearson correlation coefficients were used to assess the association between pain and sleep. Differences in sleep and pain between injured and uninjured participants were determined using an analysis of covariance.

RESULTS

Pain intensity was positively correlated with sleep quality (global PSQI score, r=0.337, p<0.001) and daytime sleepiness (ESS score, r=0.163, p=0.005), and negatively associated with sleep duration (r=-0.118, p=0.039). Injured participants accounted for 37.7% (n=116) of the study population. Injured participants reported greater pain intensity (3.7±2.5 vs 1.3±1.9, p<0.001), were older (28.5±7.4 years vs 25.8±5.7 years, p=0.001) and in the service longer (6.3±6.3 years vs 4.6±4.7 years, p=0.013) than uninjured participants. Injured participants had higher global PSQI scores (9.0±4.1 vs 6.4±3.4, p<0.001), including each of the seven PSQI components (all p<0.050), and reported sleeping less per night than uninjured participants (5.7±1.3 hours vs 6.1±1.2 hours, p=0.026).

CONCLUSION

These data demonstrate that pain intensity is associated with sleep in active-duty US Army Soldiers and that those who report a musculoskeletal injury, regardless of age and time in service, report poorer sleep quality, shorter sleep durations, and greater levels of pain than uninjured Soldiers.

Intraocular pressure responses to a virtual reality shooting simulation in active-duty members of the Spanish Army: The influence of task complexity

Ocular physiology is sensitive to cognitively demanding tasks. However, it is unknown whether the intraocular pressure is also affected by the cognitive demands of military operations. The main objective was to determine the impact of a virtual reality shooting simulation with two levels of complexity on intraocular pressure levels in military personnel. Eighteen active-duty members of the Spanish Army and eighteen civilians performed two 4 min simulated shooting tasks with two levels of complexity using a virtual reality. In the "easy" task participants performed a simulated shoot when the stimulus (military with a rifle) appeared, while in the "difficult" task the stimulus randomly was a military with a rifle or with his hands on the air and participants were instructed to respond only when the military with a rifle appeared. Intraocular pressure was measured with a rebound tonometer before and immediately after each task. Complementarily, perceived levels of mental load and shooting performance (reaction time) were assessed. Intraocular pressure was greater after completing the more complex task in both military personnel (p-value < 0.01, Cohen´s d = 1.19) and civilians (p-value < 0.01, Cohen´s d = 1.16). Also, perceived levels of task load and reaction time were higher in the difficult compared to the easy shooting tasks (both p < 0.001). The rise in intraocular pressure is positively associated with the cognitive demands of simulated military operations. The potential application of this finding is the development of objective tools based on intraocular pressure for the evaluation of the mental state in real-world contexts, permitting to improve soldiers´ safety and performance.

Preventive Effects of a Single Bout of Exercise on Memory and Attention following One Night of Sleep Loss in Sports Students: Results of a Randomized Controlled Study

Sleep loss is a severe problem in night-shift workers. It causes fatigue and a decrease in awareness that may be counter-acted by exercise. This randomized controlled study of 22 university students investigated the effects of exercise to prevent loss of cognitive and physical performance following sleep deprivation. We compared a single bout of 20 min circuit training to control in an experimental setting of overnight sleep loss. Outcomes included memory, cognitive tasks, and physical parameters. The occurrence of false memories was considered the main outcome. Exercise did not exert significant effects on false memories (p = 0.456). We could detect a trend to significance (p < 0.01) assessing cognitive dimensions, i.e., selective and sustained attention, and visual scanning speed. This revealed strong effects of exercise on attention (p = 0.091; Cohen’s d = 0.76; ∆14%), cognitive performance, performance speed, and perceived sleepiness (p = 0.008; d = 0.60; ∆2.4 cm VAS). This study failed to show the effects of exercise on memory function. Still, the observed effects on attention and consciousness could be considered clinically relevant, as these results encourage further research to determine its practicability and meaningfulness among night-shift workers.

Sleep Deprivation Influences Trial-to-Trial Transfer but Not Task Performance

Previous research has shown that sleep deprivation can affect emotions and some cognitive functions. However, research on how sleep deprivation influences the visuomotor memory have rarely been reported. In the current study, a Fitts’ Law task was used to investigate how movement and the visuomotor memory are affected under the condition of sleep deprivation. Experiment 1 had 36 participants (15 males, mean age = 21.61 years) complete the same Fitts’ Law task 10 days apart under standard conditions. Experiment 2 had five participants (three males, mean age = 27.2 years) complete the task after 7 days of sleep deprivation, then complete it again after 10 days without sleep deprivation. Experiment 1 demonstrated the stability of the trial-to-trial effects. Experiment 2 showed that the previous trial (n) exerted no effect on the current trial (n + 1) under the conditions of sleep deprivation (p = 0.672). However, the effect was observed after 10 days without sleep deprivation (p = 0.013). This suggests that sleep deprivation did not affect task performance but influenced the transfer of the trial history. Future studies are required to investigate the effect of sleep deprivation with more participants.

Anthropometrics and body composition predict performance during a simulated direct-fire engagement

This study determined anthropometric and body composition predictors of performance during a simulated direct-fire engagement. Healthy subjects (N = 33, age = 25.7 ± 7.0 yr) underwent anthropometric and body composition assessments before completing a simulated direct-fire engagement - consisting of marksmanship with cognitive workload assessment and a fire-and-move drill (16 × 6-m sprints) while wearing combat load. Susceptibility to enemy fire was modelled on sprint duration. Partial correlations and multiple linear regressions established the relationships between predictors and performance outcomes, controlling for age and sex. Significance was p ≤ 0.05. Higher percent body fat, fat mass, fight load index predicted greater susceptibility to enemy fire (r = 0.40 to 0.42) and lower cognitive performance (r= -0.45 to -0.49). Higher BMI also predicted lower cognitive performance (r= -0.49). Shorter stature/hand length predicted higher marksmanship accuracy (r= -0.40), while higher fat-free mass/fat-free mass index predicted slower reaction times (r = 0.36-0.41). These data suggest anthropometric and body composition measures modulate combat effectiveness and reinforce body composition standards in military organisations. Practitioner summary: This study identified field-expedient anthropometric and body composition predictors of a simulated direct-fire engagement that evaluated survivability (i.e. susceptibility to enemy fire) and lethality (i.e. marksmanship, cognitive performance) outcomes. Our findings suggest that anthropometric and body composition measures may play a role in soldier survivability and lethality during simulated direct-fire engagements.

Sleep and Infantry Battle Drill Performance in Special Operations Soldiers

BACKGROUND: Although multiple studies have documented the impact of insufficient sleep on soldier performance, most studies have done so using artificial measures of performance (e.g., tablet or simulator tests). The current study sought to test the relationship between sleep and soldier performance during infantry battle drill training, a more naturalistic measure of performance.METHODS: Subjects in the study were 15 junior Special Operations infantry soldiers. Soldiers wore an actigraph and reported their subjective sleep duration and quality prior to close quarter battle (CQB) drills. Experienced leaders monitored each iteration of the CQB exercise and recorded the number of errors committed.RESULTS: The number of errors committed during the live ammunition iterations was negatively correlated with subjective number of hours slept and subjective sleep efficiency/quality during the month prior. Soldiers with subjective sleep duration ≥7 h had a significantly lower number of errors than soldiers with subjective sleep duration <7 h (1.71 vs. 0.63 errors), and soldiers with sleep quality <85% committed more errors than those with sleep quality ≥85% (1.50 vs. 0.40 errors).DISCUSSION: These data preliminarily suggest that sleep quality and duration may influence subsequent performance on infantry battle drill training, particularly for soldiers with limited experience in battle drill conduction who have not yet perfected battle drill techniques. Future studies should enact sleep augmentation to determine the causal influence of sleep on performance in this setting.Mantua J, Shevchik JD, Chaudhury S, Eldringhoff HP, Mickelson CA, McKeon AB. Sleep and infantry battle drill performance in Special Operations soldiers. Aerosp Med Hum Perform. 2022; 93(7):557–561.

Changes in sleep quality among Chinese active service personnel: A cross-temporal meta-analysis, 2003-2019

Military personnel live in operating environments in which poor sleep is common. In this cross-temporal meta-analysis (CTMA), 100 studies (144 data sets, N = 75,998) were identified to examine changes in sleep quality among Chinese active service personnel from 2003 to 2019. Participants were divided into three groups: the navy, the non-navy, and the unknown service. The Pittsburgh Sleep Quality Index (PSQI) was used as the measure of sleep quality; it contains a global score and seven component scores, with higher scores indicative of poorer sleep. Among all active military personnel, the PSQI global and seven component scores decreased from 2003 to 2019. In examining the results by military type, the PSQI global and seven component scores increased in the navy group. Conversely, both the non-navy and unknown-service groups showed decreased PSQI global scores over time. Similarly, all PSQI component scores decreased over time for both the non-navy and unknown service groups, except for the use of sleeping medication (USM), which increased in the non-navy group. In conclusion, the sleep quality of Chinese active service personnel showed a positive trend. Further research should focus on improving the navy's sleep quality.

Effects of Sleep Restriction on Self-Reported Putting Performance in Golf

In the present study, we aimed to explore the effects of sleep restriction (SR) on self-reported golf putting skills. Eleven collegiate golfers participated in a self-reported, counterbalanced experimental study under two conditions: (a) a SR condition in which sleep on the night prior to putting was restricted to 4-5 hours, and (b) a habitual normal sleep (NS) condition on the night before the putting test. Following each sleep condition, participants engaged in ten consecutive putting tests at 7 am, 11 am, and 3 pm. Participants reported their subjective sleepiness before each time frame, and their chronotype, defined as their individual circadian preference, was scored based on a morningness-eveningness questionnaire (MEQ). Participants restricted sleep to an average period of 267.6 minutes/night (SD = 51.2) in the SR condition and 426.2 (SD =38.0) minutes/night in the NS condition. A two-way analysis of variance revealed a significant main effect of the sleep condition on the lateral displacement of putts from the target (lateral misalignment) (p = 0.002). In addition, there was a significant main effect of time on distance from the target (distance misalignment) (p = 0.017), indicating less accuracy of putting in the SR condition. In the SR condition, the MEQ score was positively correlated with distance misalignment at 3 pm (ρ = 0.650, p = 0.030), suggesting that morningness types are susceptible to the effects of SR on putting performance. Our findings suggest that golfers should obtain sufficient sleep to optimize putting performance.

The Development, Implementation, and Feasibility of a Circadian, Light, and Sleep Skills Program for Shipboard Military Personnel (CLASS-SM)

Service members face unique barriers to sufficient and high quality sleep. In the present study, a circadian, light, and sleep skills program for shipboard military personnel (CLASS-SM) was designed to encourage and inform strategies that support optimal sleep and circadian health in the context of those barriers. Phase 1 included program development and refinement via an iterative formative evaluation, including structured interviews with service members and feedback from veterans and experts, resulting in further tailoring to the population. In Phase 2, the highly tailored program was administered to shipboard personnel (n = 55), and acceptability indicators were measured. Sleep- and circadian-related knowledge (pre- and post-program) and the perceived relevance of, and satisfaction with, program content (post-program) were assessed. Before the intervention, most individuals were unaware that 7−9 h of sleep is recommended (72%) and had little understanding of the physiological effects of light; however, knowledge scores increased significantly post-program, from 51% to 88% correct (p < 0.0001). Reception was positive, with high reported satisfaction and relevance. Most individuals reported that they learned something new (89%), planned to use one or more learned strategies (100%), and intended to share learned information with others (85%); the physiological effects of light and circadian rhythms were the content areas most frequently reported as new and useful. The results demonstrate the need for, and feasibility of, the delivery of this program in operational environments.

The role of death anxiety on marksmanship performance: a virtual reality simulator study

Despite the well-established relationship between state anxiety and marksmanship performance, few efforts have examined the individual differences that affect the extent to which individuals experience state anxiety in combat situations. Thus, further studies are needed to increase the probability of mission accomplishment, which could ultimately serve to safely bring soldiers home. The present study examined how death anxiety, a trait-based difference affects state anxiety, which in turn affects shooting performance on a battlefield. In particular, we used a virtual reality simulator to create a realistic engagement setting in which simulated death anxiety is salient. On a sample of 99 active-duty enlisted men in the Republic of Korea Army, we found that death anxiety, and not trait anxiety, increased state anxiety, which in turn decreased marksmanship performance. Overall, the current findings highlight the role of death anxiety in combat situations. The practical implications and avenues for future research are also discussed.

The effect of sleep restriction on cognitive performance in elite cognitive performers: a systematic review

STUDY OBJECTIVES

To synthesize original articles exploring the effects of sleep restriction on cognitive performance specifically for Elite Cognitive Performers, i.e. those who engage in cognitively demanding tasks with critical or safety-critical outcomes in their occupation or area of expertise.

METHODS

Backward snowballing techniques, gray literature searches, and traditional database searches (Embase, MEDLINE, Web of Science, Google Scholar, PSYCinfo, and SportDiscus) were used to obtain relevant articles. A quality assessment was performed, and the risk of training effects was considered. Results were narratively synthesized. Fourteen articles fit the criteria. Cognitive outcomes were divided into three categories defined by whether cognitive demands were "low-salience," "high-salience stable," or "high-salience flexible."

RESULTS

Low-salience tests (i.e. psychomotor vigilance tasks & serial reaction tests), mainly requiring vigilance and rudimentary attentional capacities, were sensitive to sleep restriction, however, this did not necessarily translate to significant performance deficits on low-salience occupation-specific task performance. High-salience cognitive outcomes were typically unaffected unless when cognitive flexibility was required.

CONCLUSIONS

Sleep restriction is of particular concern to occupations whereby individuals perform (1) simple, low-salience tasks or (2) high-salience tasks with demands on the flexible allocation of attention and working memory, with critical or safety-critical outcomes.

The First-Night Effect in Elite Sports: An Initial Glance on Polysomnography in Home-Based Settings

Self-applied portable polysomnography is considered a promising tool to assess sleep architecture in field studies. However, no findings have been published regarding the appearance of a first-night effect within a sport-specific setting. Its absence, however, would allow for a single night sleep monitoring and hence minimize the burden on athletes while still obtaining the most important variables. For this reason, the aim of the study was to assess whether the effect appears in home-based sleep monitoring of elite athletes. The study sample included eight male and 12 female German elite athletes from five different sports. Participants slept with a portable polysomnography for two nights, which they self-applied at night before going to bed. Time in bed and wake-up time in the morning were freely chosen by each individual athlete without any restrictions regarding time or sleeping environment. Participants were asked to keep the same location and time frame during the two days of monitoring and stick to their usual sleeping schedules. Sleep stages were manually scored using 30-s epochs. Sleep parameters and stages were later compared with the help of linear mixed models to investigate the factor time. Significant differences between the two nights were found for percentage of Non-REM sleep [T(19) = -2,10, p < 0.05, d = -0.47, 95%-CI (-7.23, -0.01)] with small effect size, Total Wake Time [T(19) = 2.30, p = 0.03, d = 0.51, 95%-CI (1.66, 35.17)], Sleep Efficiency [T(19) = -2.48, p = 0.02, d = -0.55, 95%-CI (-7.43, -0.63)], and Wake percentage [T(19) = 2.47, p = 0.02, d = 0.55, 95%-CI (0.61, 7.43)] with moderate effect sizes, and N3 Sleep Onset Latency [T(19) = 3.37, p < 0.01, d = 0.75, 95%-CI (7.15, 30.54)] with large effect size. Confidence Intervals for all other indices range from negative to positive values and hence specify, that parameters were not systematically negatively affected in the first night. Findings suggest that some individuals are more affected by the first-night effect than others. Yet, in order to keep the measurement uncertainties to a minimum, a more conservative approach with at least two monitoring nights should be used whenever possible, if no other supporting information on the athletes says otherwise.

Transitioning from daytime to nighttime operations in military training has a temporary negative impact on dynamic balance and jump performance in U.S. Army Rangers

OBJECTIVES

Explore the impact transitioning from daytime to nighttime operations has on performance in U.S. Army Rangers.

METHODS

Fifty-four male Rangers (age 26.1±4.0 years) completed the Y-Balance Test (YBT), a vertical jump assessment, and a grip strength test at three time points. Baseline testing occurred while the Rangers were on daytime operations; post-test occurred after the first night into the nighttime operation training (after full night of sleep loss), and follow-up testing occurred six days later (end of nighttime training).

RESULTS

On the YBT, performance was significantly worse at post-test compared to baseline during right posteromedial reach (104.1±7.2cm vs 106.5±6.7cm, p=.014), left posteromedial reach (105.4±7.5cm vs 108.5±6.6cm, p=.003), right composite score (274.8±19.3cm vs 279.7±18.1cm, p=.043), left composite score (277.9±18.1cm vs 283.3±16.7cm, p=.016), and leg asymmetry was significantly worse in the posterolateral direction (4.8±4.0cm vs 3.7±3.1cm, p=.030) and the anterior direction (5.0±4.0cm vs 3.6±2.6cm, p=.040). The average vertical jump height was significantly lower at post-test compared to baseline (20.6±3.4 in vs 21.8±3.0 in, p=.004). Baseline performance on YBT and vertical jump did not differ from follow-up.

CONCLUSIONS

Army Rangers experienced an immediate, but temporary, drop in dynamic balance and vertical jump performance when transitioning from daytime to nighttime operations. When feasible, Rangers should consider adjusting their sleep cycles prior to anticipating nighttime operations in order to maintain their performance levels. Investigating strategies that may limit impairments during this transition is warranted.

The Association Between Poor Sleep and the Incidence of Sport and Physical Training-Related Injuries in Adult Athletic Populations: A Systematic Review

BACKGROUND

The importance of achieving an adequate amount of sleep to optimize health and athletic performance is well recognized. Yet, a systematic evidence compilation of the risk for sport-related injury in adult athletic populations due to poor sleep does not exist.

OBJECTIVE

To examine the association between poor sleep and sport and physical training-related injuries in adult athletic populations.

DATA SOURCES

Electronic databases were searched using keywords relevant to sleep quantity and quality, and musculoskeletal injury and sport-related concussion (SRC).

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies were included in this systematic review if they were comprised of adult athletic populations, reported measures of sleep quantity or quality, followed participants prospectively for injury, and reported an association between sleep and incidence of sport or physical training-related injury.

STUDY APPRAISAL

The methodological quality of each study was assessed using the Newcastle-Ottawa Scale for Cohort Studies.

RESULTS

From our review of 12 prospective cohort studies, we found limited evidence supporting an association between poor sleep and injury in adult athletic populations. Specifically, there is (a) insufficient evidence supporting the associations between poor sleep and increased risk of injury in specific groups of athletic adults, including professional or elite athletes, collegiate athletes, elite or collegiate dancers, and endurance sport athletes; and (b) limited evidence of an association between poor sleep and increased risk of SRC in collegiate athletes.

CONCLUSIONS

The current evidence does not support poor sleep as an independent risk factor for increased risk of sport or physical training-related injuries in adult athletic populations. Given the methodological heterogeneity and limitations across previous studies, more prospective studies are required to determine the association between sleep and injury in this population.

When the response does not match the threat: The relationship between threat assessment and behavioural response in ambiguous lethal force decision-making

Deciding when to use lethal force inherently depends on assessing threat, a process that itself incorporates numerous perceptual factors. This study assessed this relationship between perception-based threat assessment and behaviour-based threat response. Specifically, participants completed multiple tasks designed to elicit either a threat rating (e.g., perception-informed threat assessment) or a binary behavioural response (e.g., shoot/don't-shoot). Actor posture and weapon presence significantly affected the threat assessment, which was an extremely powerful omnibus predictor of threat response. However, for ambiguous threat stimuli, perceived threat became a poor predictor for threat response relative to the omnibus test. Participants appeared to adopt additional rules to inform behaviour independent of the threat assessment when faced with an ambiguous situation. These results demonstrate an intriguing disparity between subjective threat assessment and the behavioural response to use force that does not apply well to ambiguous cases or adequately explain errors in lethal force decisions.

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

OBJECTIVE

To examine the sleep health of incoming Army trainees and how it is impacted during basic combat training (BCT).

DESIGN

Prospective.

SETTING

BCT site (Fort Jackson, SC).

PARTICIPANTS

A total of 1349 trainees (936 = male, 413 = female, 20.73 ± 3.67 years).

MEASUREMENTS

Participants 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.

RESULTS

At 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]).

CONCLUSIONS

Army 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.

Predicting Cognitive Load and Operational Performance in a Simulated Marksmanship Task

Modern operational environments can place significant demands on a service member's cognitive resources, increasing the risk of errors or mishaps due to overburden. The ability to monitor cognitive burden and associated performance within operational environments is critical to improving mission readiness. As a key step toward a field-ready system, we developed a simulated marksmanship scenario with an embedded working memory task in an immersive virtual reality environment. As participants performed the marksmanship task, they were instructed to remember numbered targets and recall the sequence of those targets at the end of the trial. Low and high cognitive load conditions were defined as the recall of three- and six-digit strings, respectively. Physiological and behavioral signals recorded included speech, heart rate, breathing rate, and body movement. These features were input into a random forest classifier that significantly discriminated between the low- and high-cognitive load conditions (AUC = 0.94). Behavioral features of gait were the most informative, followed by features of speech. We also showed the capability to predict performance on the digit recall (AUC = 0.71) and marksmanship (AUC = 0.58) tasks. The experimental framework can be leveraged in future studies to quantify the interaction of other types of stressors and their impact on operational cognitive and physical performance.

Trait-like vulnerability of higher-order cognition and ability to maintain wakefulness during combined sleep restriction and circadian misalignment

STUDY OBJECTIVES

Determine stability of individual differences in executive function, cognitive processing speed, selective visual attention, and maintenance of wakefulness during simulated sustained operations with combined sleep restriction and circadian misalignment.

METHODS

Twenty healthy adults (eight female), aged 25.7 (±4.2 SD), body mass index (BMI) 22.3 (±2.1) kg/m2 completed an 18-day protocol twice. Participants maintained habitual self-selected 8-hour sleep schedules for 2 weeks at home prior to a 4-day laboratory visit that included one sleep opportunity per day: 8 hours on night 1, 3 hours on night 2, and 3 hours on mornings 3 and 4. After 3 days of unscheduled sleep at home, participants repeated the entire protocol. Stability and task dependency of individual differences in performance were quantified by intra-class correlation coefficients (ICC) and Kendall's Tau, respectively.

RESULTS

Performance on Stroop, Visual Search, and the Maintenance of Wakefulness Test were highly consistent within individuals during combined sleep restriction and circadian misalignment. Individual differences were trait-like as indicated by ICCs (0.54-0.96) classified according to standard criteria as moderate to almost perfect. Individual differences on other performance tasks commonly reported in sleep studies showed fair to almost perfect ICCs (0.22-0.94). Kendall's rank correlations showed that individual vulnerability to sleep restriction and circadian misalignment varied by task and by metric within a task.

CONCLUSIONS

Consistent vulnerability of higher-order cognition and maintenance of wakefulness to combined sleep restriction and circadian misalignment has implications for the development of precision countermeasure strategies for workers performing safety-critical tasks, e.g. military, police, health care workers and emergency responders.

Effect of cognitive load and emotional valence of distractors on performance during sleep extension and subsequent sleep deprivation

Study Objectives

The purpose of the present study was to assess the extent to which sleep extension followed by sleep deprivation impacts performance on an attentional task with varying cognitive and attentional demands that influence decisions.

Methods

Task performance was assessed at baseline, after 1 week of sleep extension, and after 40 h of total sleep deprivation.

Results

One week of sleep extension resulted in improved performance, particularly for high cognitive load decisions regardless of the emotional salience of attentional distractors. Those who extended sleep the most relative to their habitual sleep duration showed the greatest improvement in general performance during sleep extension. However, a higher percentage of time spent in slow-wave sleep (SWS) on the last night of the sleep extension phase was negatively correlated with performance on more difficult high cognitive load items, possibly reflecting a relatively higher level of residual sleep need. Sleep deprivation generally resulted in impaired performance, with a nonsignificant trend toward greater performance decrements in the presence of emotionally salient distractors. Performance overall, but specifically for high cognitive load decisions, during total sleep deprivation was negatively correlated with longer sleep and higher SWS percentage during subsequent recovery sleep.

Conclusions

The present findings suggest two possibilities: those who performed relatively poorly during sleep deprivation were more vulnerable because (1) they utilized mental resources (i.e. accrued sleep debt) at a relatively faster rate during wakefulness, and/or (2) they failed to “pay down” pre-study sleep debt to the same extent as better-performing participants during the preceding sleep extension phase.

Assessment of the Relationship between Military Weapon Qualification Scores and Attributes of Simulated Marksmanship Mission Readiness

The U.S. military uses performance in standardized weapons qualification tests as one benchmark of mission readiness. However, validity concerns have risen about the current qualification model in regards to its suitability to measure marksmanship ability in realistic, battlefield conditions as well as its relevance with recent weapon technological advancements. The present analysis provides an initial look at the relationship between performance in a standard weapons qualification test (qualification score) and performance attributes of marksmanship recorded prior to a field training mission. Marksmanship performance was measured using a simulator and a combined static-dynamic methodology capable of assessing the entire marksmanship process of moving, locating, positioning, and engaging targets. Results indicate that qualification scores in the current qualification model are a poor predictor of slow, untimed static marksmanship and a good predictor of high-paced dynamic marksmanship timing and mobility performance attributes during a rested state, prior to embarking on a mission.

Untangling the genomics of noise-induced hearing loss and tinnitus: Contributions of Mus musculus and Homo sapiens

Acoustic trauma is a feature of the industrial age, in general, and mechanized warfare, in particular. Noise-induced hearing loss (NIHL) and tinnitus have been the number 1 and number 2 disabilities at U.S. Veterans hospitals since 2006. In a reversal of original protocols to identify candidate genes associated with monogenic deafness disorders, unbiased genome-wide association studies now direct animal experiments in order to explore genetic variants common in Homo sapiens. However, even these approaches must utilize animal studies for validation of function and understanding of mechanisms. Animal research currently focuses on genetic expression profiles since the majority of variants occur in non-coding regions, implying regulatory divergences. Moving forward, it will be important in both human and animal research to define the phenotypes of hearing loss and tinnitus, as well as exposure parameters, in order to extricate genes related to acoustic trauma versus those related to aging. It has become clear that common disorders like acoustic trauma are influenced by large numbers of genes, each with small effects, which cumulatively lead to susceptibility to a disorder. A polygenic risk score, which aggregates these small effect sizes of multiple genes, may offer a more accurate description of risk for NIHL and/or tinnitus.

The effects of caffeine on marksmanship accuracy and reaction time: a systematic review

Military and law enforcement personnel are required to maintain optimal marksman accuracy and reaction time during extended duty hours amidst environmental stressors. Although caffeine is commonly used to mitigate the consequences of fatigue, the effects of caffeine on marksmanship accuracy are inconclusive. The purpose of this review was to determine the effect of caffeine on marksman accuracy and reaction time. A literature search was conducted and 17 articles were selected for review based on relevance and methodological quality. Caffeine consistently improved marksman reaction time but did not improve marksmanship accuracy. However, there is some evidence that caffeine attenuates performance decrements in marksman accuracy caused by stress and fatigue if optimal dosing strategies are employed. Dosing strategies timed according to hours of wakefulness and time before testing could prevent performance deterioration. Doses of 100-200 mg every 2 hours may effectively improve accuracy during extended duty; however, further research is needed. Practitioner Summary: The purpose of this review was to determine the effect of caffeine on marksman accuracy and reaction time. A literature search was conducted and 17 articles were selected for review based on relevance and methodological quality. Caffeine consistently improved marksman reaction time but did not improve marksmanship accuracy.

Insomnia and daytime sleepiness: risk factors for sports-related concussion

OBJECTIVE/BACKGROUND

Poor quality and inadequate sleep are associated with impaired cognitive, motor, and behavioral components of sport performance and increased injury risk. While prior work identifies sports-related concussions as predisposing factors for poor sleep, the role of sleep as a sports-related concussion risk factor is unknown. The purpose of this study was to quantify the effect of poor sleep quality and insomnia symptoms on future sports-related concussion risk.

PATIENTS/METHODS

In this study, 190 NCAA Division-1 athletes completed a survey battery, including the Insomnia Severity Index (ISI) and National Health and Nutrition Examination Survey (NHANES) Sleep module. Univariate risk ratios for future sports-related concussions were computed with ISI and NHANES sleepiness scores as independent predictors. An additional multiple logistic regression model including sport, sports-related concussion history, and significant univariate predictors jointly assessed the odds of sustaining a concussion.

RESULTS

Clinically moderate-to-severe insomnia severity (RR = 3.13, 95% CI: 1.320-7.424, p = 0.015) and excessive daytime sleepiness two or more times per month (RR = 2.856, 95% CI: 0.681-11.977, p = 0.037) increased concussion risk. These variables remained significant and comparable in magnitude in a multivariate model adjusted for sport participation.

CONCLUSION

Insomnia and daytime sleepiness are independently associated with increased sports-related concussion risk. More completely identifying bidirectional relationships between concussions and sleep requires further research. Clinicians and athletes should be cognizant of this relationship and take proactive measures - including assessing and treating sleep-disordered breathing, limiting insomnia risk factors, improving sleep hygiene, and developing daytime sleepiness management strategies - to reduce sports-related concussion risk and support overall athletic performance.