Steps toward developing a comprehensive fatigue monitoring and mitigation solution: perspectives from a cohort of United States Naval Surface Force officers.

Study Objectives: This study analyzed fatigue and its management in US Naval Surface Force warships, focusing on understanding current practices and barriers, and examining the influence of organizational and individual factors on managing chronic fatigue. Furthermore, this study explored the impact of organizational and individual factors on fatigue management. Methods: As part of a larger study, 154 naval officers (mean ±â€…standard deviation; 31.5 ±â€…7.0 years; 8.8 ±â€…6.8 years of service; 125 male, and 29 female) completed a fatigue survey. The survey addressed (1) self-reported fatigue, (2) fatigue observed in others, (3) fatigue monitoring strategies, (4) fatigue mitigation strategies, and (5) barriers to fatigue mitigation. Logistic and ordinal regressions were performed to examine the effect of individual (i.e. sleep quality and years in military service) and organizational (i.e. ship-class) factors on fatigue outcomes. Results: Fatigue was frequently experienced and observed by 23% and 54% of officers, respectively. Of note, officers often monitored fatigue reactively (i.e. 65% observed others nodding off and 55% observed behavioral impairments). Still, officers did not frequently implement fatigue mitigation strategies, citing few operationally feasible mitigation strategies (62.3%), being too busy (61.7%), and not having clear thresholds for action (48.7%). Fatigue management varies across organizational factors, which must be considered when further developing fatigue management strategies. Conclusions: Fatigue remains a critical concern aboard surface force ships and it may be better addressed through development of objective sleep and fatigue monitoring tools that could inform leadership decision-making.

Dawn of a New Dawn: Advances in Sleep Health to Optimize Performance.

Optimal sleep health is a critical component to high-level performance. In populations such as the military, public service (eg, firefighters), and health care, achieving optimal sleep health is difficult and subsequently deficiencies in sleep health may lead to performance decrements. However, advances in sleep monitoring technologies and mitigation strategies for poor sleep health show promise for further ecological scientific investigation within these populations. The current review briefly outlines the relationship between sleep health and performance as well as current advances in behavioral and technological approaches to improving sleep health for performance.

Natural Oscillatory Frequency Slowing in the Premotor Cortex of Early-Course Schizophrenia Patients: A TMS-EEG Study.

Despite the heavy burden of schizophrenia, research on biomarkers associated with its early course is still ongoing. Single-pulse Transcranial Magnetic Stimulation coupled with electroencephalography (TMS-EEG) has revealed that the main oscillatory frequency (or "natural frequency") is reduced in several frontal brain areas, including the premotor cortex, of chronic patients with schizophrenia. However, no study has explored the natural frequency at the beginning of illness. Here, we used TMS-EEG to probe the intrinsic oscillatory properties of the left premotor cortex in early-course schizophrenia patients (<2 years from onset) and age/gender-matched healthy comparison subjects (HCs). State-of-the-art real-time monitoring of EEG responses to TMS and noise-masking procedures were employed to ensure data quality. We found that the natural frequency of the premotor cortex was significantly reduced in early-course schizophrenia compared to HCs. No correlation was found between the natural frequency and age, clinical symptom severity, or dose of antipsychotic medications at the time of TMS-EEG. This finding extends to early-course schizophrenia previous evidence in chronic patients and supports the hypothesis of a deficit in frontal cortical synchronization as a core mechanism underlying this disorder. Future work should further explore the putative role of frontal natural frequencies as early pathophysiological biomarkers for schizophrenia.

Shared and distinct abnormalities in sleep-wake patterns and their relationship with the negative symptoms of Schizophrenia Spectrum Disorder patients.

Sleep and rest-activity-rhythm (RAR) abnormalities are commonly reported in schizophrenia spectrum disorder (SSD) patients. However, an in-depth characterization of sleep/RAR alterations in SSD, including patients in different treatment settings, and the relationship between these alterations and SSD clinical features (e.g., negative symptoms) is lacking. SSD (N = 137 altogether, N = 79 residential and N = 58 outpatients) and healthy control (HC) subjects (N = 113) were recruited for the DiAPAson project. Participants wore an ActiGraph for seven consecutive days to monitor habitual sleep-RAR patterns. Sleep/rest duration, activity (i.e., M10, calculated on the 10 most active hours), rhythm fragmentation within days (i.e., intra-daily variability, IV; beta, steepness of rest-active changes), and rhythm regularity across days (i.e., inter-daily stability, IS) were computed in each study participant. Negative symptoms were assessed in SSD patients with the Brief Negative Symptom Scale (BNSS). Both SSD groups showed lower M10 and longer sleep/rest duration vs. HC, while only residential patients had more fragmented and irregular rhythms than HC. Compared to outpatients, residential patients had lower M10 and higher beta, IV and IS. Furthermore, residential patients had worse BNSS scores relative to outpatients, and higher IS contributed to between-group differences in BNSS score severity. Altogether, residentials and outpatients SSD had both shared and unique abnormalities in Sleep/RAR measures vs. HC and relative to one another, which also contributed to the patients' negative symptom severity. Future work will help establish whether improving some of these measures may ameliorate the quality of life and clinical symptoms of SSD patients.

Military tactical adaptive decision making during simulated military operational stress is influenced by personality, resilience, aerobic fitness, and neurocognitive function.

Laboratory-based studies designed to mimic combat or military field training have consistently demonstrated deleterious effects on warfighter's physical, cognitive, and emotional performance during simulated military operational stress (SMOS). Purpose: The present investigation sought to determine the impact of a 48-h simulated military operational stress (SMOS) on military tactical adaptive decision making, and the influence of select psychological, physical performance, cognitive, and physiological outcome measures on decision making performance. Methods: Male (n = 48, 26.2 ± 5.5 years, 177.7 ± 6.6 cm, 84.7 ± 14.1 kg.) subjects currently serving in the U.S. military were eligible to participate in this study. Eligible subjects completed a 96-h protocol that occurred over five consecutive days and four nights. Day 2 (D2) and day 3 (D3) consisted of 48-h of SMOS wherein sleep opportunity and caloric needs were reduced to 50%. Differences in SPEAR total block score from baseline to peak stress (D3 minus D1) were calculated to assess change in military tactical adaptive decision making and groups were stratified based on increase (high adaptors) or decrease (low adaptors) of the SPEAR change score. Results: Overall, military tactical decision-making declined 1.7% from D1 to D3 (p < 0.001). High adaptors reported significantly higher scores of aerobic capacity (p < 0.001), self-report resilience (p = 0.020), extroversion (p < 0.001), and conscientiousness (p < 0.001). at baseline compared to low adaptors, while low adaptors reported greater scores in Neuroticism (p < 0.001). Conclusion: The present findings suggest that service members whose adaptive decision making abilities improved throughout SMOS (i.e., high adaptors) demonstrated better baseline psychological/self-reported resilience and aerobic capacity. Further, changes in adaptive decision-making were distinct from those of lower order cognitive functions throughout SMOS exposure. With the transition of future military conflicts placing higher priority on enhancing and sustaining cognitive readiness and resiliency, data presented here demonstrates the importance of measuring and categorizing baseline measures inherent to military personnel, in order to change and train one's ability to suffer less of a decline during high stress conditions.

Less daytime sleepiness and slow wave activity during sleep predict better physical readiness in military personnel.

BACKGROUND: Military personnel must maintain physical performance despite exposure to operational stressors such as sleep loss, caloric restriction and high cognitive load. Habitual sleep and specific sleep features are positively associated with fitness and may contribute to physical performance in operational settings. Further, by affecting muscle recovery, sleep may contribute to the ability to maintain performance across multiple days of exposure to operational stressors. OBJECTIVES: We examined the role of individual differences in baseline sleep on baseline physical performance and on change in physical performance throughout exposure to simulated military operational stress (SMOS). METHODS: Military personnel (36 male, 9 female, 26.3 ± 5.3 years) completed a 5-day SMOS protocol during which they completed a tactical mobility test daily. Sleep questionnaires were administered at intake and sleep was monitored each night with polysomnography. Lasso regressions were used to identify meaningful predictors of physical performance at baseline and of change in physical performance across SMOS. RESULTS: Better aerobic fitness, lower daytime sleepiness (Epworth Sleepiness Scale), and lower absolute slow wave activity (0.5-4 Hz) predicted better physical performance at baseline (66.1% of variance explained), but did not relate to changes in performance. CONCLUSIONS: Collectively, higher daytime sleepiness and slow wave activity may reflect more chronic exposure to insufficient sleep and higher baseline sleep drive, which in turn led to compromised physical performance. The findings suggest that low self-report sleepiness and low objective slow wave activity may reflect two quantifiable markers of healthy sleep behaviors that have implications for operational performance.

Prevention of Lower Extremity Musculoskeletal Injuries in Tactical and First Responder Populations: A Systematic Review and Meta-Analysis of Randomized Trials From 1955 to 2020.

ABSTRACT: Sinnott, AM, Krajewski, KT, LaGoy, AD, Beckner, ME, Proessl, F, Canino, MC, Nindl, BC, Turner, RL, Lovalekar, MT, Connaboy, C, and Flanagan, SD. Prevention of lower extremity musculoskeletal injuries in tactical and first responder populations: A systematic review and meta-analysis of randomized trials from 1955 to 2020. J Strength Cond Res 37(1): 239-252, 2023-Lower extremity musculoskeletal injuries (LEMSIs) impose a significant burden on tactical and first responder populations. To determine the effectiveness of LEMSI prevention strategies, we performed a systematic review and meta-analysis of randomized controlled trials published in English from 1955 to 2020 (PROSPERO: CRD42018081799). MEDLINE, EMBASE, Cochrane, CINAHL, ProQuest, and DTIC databases were searched for trials that assigned military service members, police, firefighters, or paramedics to LEMSI prevention interventions with a minimum surveillance period of 12 weeks. Evidence was synthesized as odds ratios (OR) for LEMSI occurrence between individuals assigned to interventions and those assigned to standard activities. Risk of bias was assessed with the Cochrane Risk of Bias tool 2.0. Random-effects meta-analyses were conducted for (a) physical training and (b) footwear modifications to reduce LEMSI and (c) footwear modifications to reduce stress fractures specifically. Certainty in the body of evidence was determined with the GRADE approach. Of 28,499 records, 18 trials comprised of more than 11,000 subjects were synthesized. Interventions included physical training (8, N = 6,838), footwear modifications (8, N = 3,792), nutritional supplementation (1, N = 324), and training modifications (1, N = 350). Overall risk of bias was generally moderate ( N = 7 of 18) or high ( N = 9 of 18). Physical training (OR = 0.87, 95% CI [0.71, 1.08], p = 0.22, I 2 = 58.4%) and footwear modification (OR = 1.13, 95% CI [0.85, 1.49], p = 0.42, I 2 = 0.0%) did not reduce LEMSI or stress fractures (OR = 0.76, 95% CI [0.45, 1.28], p = 0.30, I 2 = 70.7%). Our results indicate that there is weak evidence to support current LEMSI prevention strategies. Future efforts will benefit from longer surveillance periods, assessment of women and nonmilitary populations, improved methodological rigor, and a greater breadth of approaches.

Relationships between rest-activity rhythms, sleep, and clinical symptoms in individuals at clinical high risk for psychosis and healthy comparison subjects.

Sleep-wake disturbances in individuals at clinical high risk (CHR) of psychosis may relate to increased symptom severity and contribute to disease progression. Here, we examined differences in rest-activity rhythms (RAR) measures, derived from actigraphy, and objective sleep outcomes, derived from electroencephalography (EEG), between 12 CHR and 16 healthy comparison (HC) individuals. Further, we examined the relationships between RAR disturbances, objective sleep outcomes and clinical psychosis symptoms (i.e., negative, positive, disorganized, general symptoms). Sleep-wake behaviors were monitored via actigraphy for 3-7 days (CHR: 5.7 ± 1.7 days; HC: 6.3 ± 1.2 days) prior to participants spending a night in the sleep laboratory, which was monitored with EEG. Separate regressions were used to examine the effect of clinical group on RAR measures and objective sleep outcomes after controlling for age and gender. CHR participants were found to be less active, specifically during the evening (17:00-20:00; ß = 1.145, SE = 0.362, p = .004) and nighttime (21:00-24:00; ß = 1.152, SE = 0.326, p = .002) relative to HC. Further, CHR participants had more fragmented sleep (wake after sleep onset: ß = 0.888, SE = 0.395, p = .034) and more hyperarousal during sleep (NREM gamma activity: ß = 1.087, SE = 0.348, p = .005), but these sleep disturbances were not related to reduced activity or clinical symptoms, whereas lower nighttime activity was related to more disorganized symptoms (ρ = -.640, p = .025). Thus, increasing activity through behavioral interventions may have additional beneficial effects on CHR clinical symptoms.

Combined effects of time-of-day and simulated military operational stress on perception-action coupling performance.

Perception-action coupling, the ability to 'read and react' to the environment, is essential for military personnel to operate within complex and unpredictable environments. Exposure to military operational stressors (e.g., caloric restriction, sleep loss, physical exertion), including around-the-clock operations, may compromise perception-action coupling, thereby impacting performance and safety. We examined the combined effects of simulated military operational stress (SMOS) and time-of-day on perception-action coupling. Fifty-seven active duty and reservist military personnel (45 M; 26.4 ± 5.6 years) completed a 5-day SMOS protocol that included two consecutive days of caloric restriction, and sleep restriction, and disruption. Participants completed a tablet-based perception-action coupling task (PACT) that involves perceiving whether virtual balls fit through virtual apertures. Familiarization occurred on day 0. Eight trials across day 1 (18:00, 22:00), 2 (04:00, 18:00, 22:00) and 3 (04:00, 18:00, 22:00) were analyzed. Mixed models were run to examine the interactive and main effects of day, and time-of-day on PACT response speed and accuracy outcomes. PACT response speed and accuracy outcomes improved at 18:00 and 22:00, whereas performance at 04:00 deteriorated across days. Perception-action coupling performance was resilient to SMOS, except in the early morning when the circadian drive for sleep is high, and the effects of sleep loss are more prominent.

Sleep spindle alterations relate to working memory deficits in individuals at clinical high-risk for psychosis.

STUDY OBJECTIVES: Sleep spindles are waxing and waning EEG waves exemplifying the main fast oscillatory activity occurring during NREM sleep. Several recent studies have established that sleep spindle abnormalities are present in schizophrenia spectrum disorders, including in early-course and first-episode patients, and those spindle deficits are associated with some of the cognitive impairments commonly observed in these patients. Cognitive deficits are often observed before the onset of psychosis and seem to predict poor functional outcomes in individuals at clinical high-risk for psychosis (CHR). Yet, the presence of spindle abnormalities and their relationship with cognitive dysfunction has not been investigated in CHR. METHODS: In this study, overnight high-density (hd)-EEG recordings were collected in 24 CHR and 24 healthy control (HC) subjects. Spindle density, duration, amplitude, and frequency were computed and compared between CHR and HC. Furthermore, WM was assessed for both HC and CHR, and its relationship with spindle parameters was examined. RESULTS: CHR had reduced spindle duration in centro-parietal and prefrontal regions, with the largest decrease in the right prefrontal area. Moderation analysis showed that the relation between spindle duration and spindle frequency was altered in CHR relative to HC. Furthermore, CHR had reduced WM performance compared to HC, which was predicted by spindle frequency, whereas in HC spindle frequency, duration, and density all predicted working memory performance. CONCLUSION: Altogether, these findings indicate that sleep spindles are altered in CHR individuals, and spindle alterations are associated with their cognitive deficits, thus representing a sleep-specific putative neurophysiological biomarker of cognitive dysfunction in psychosis risk.

Finding a rhythm: Relating ultra-short-term heart rate variability measures in healthy young adults during rest, exercise, and recovery.

Ultra-short-term (UST; <5 min) heart rate variability (HRV) is increasingly used to indirectly assess autonomic nervous system modulation and physical health. However, UST HRV estimates may vary with measurement technique, physiological state, and data preprocessing. The purpose of this investigation was to assess the information content of UST HRV and its sensitivity to different physiological states and preprocessing techniques. 26 time, frequency, and non-linear HRV measures were determined in 80 healthy men (age: 22.1 ± 3.7 yr) and 25 women (age: 19.4 ± 2.8 yr) from 2-min ECG recordings during seated and standing rest, low-intensity exercise, and seated recovery after maximal exercise. For men, HRV measures obtained during each condition were further analyzed with principal component analysis, k-means clustering, and one-way ANCOVAs. Backward stepwise regression was used to determine the ability of UST HRV to predict aerobic fitness. The sensitivity of UST HRV estimates to different artifact correction procedures was determined with intraclass correlation coefficients. Compared with men, women displayed HRV characteristics suggestive of greater vagal modulation. Nearly 80% of HRV information content was distilled into three principal components comprised of similar measures across conditions. K-means clusters varied in composition and HRV characteristics but not aerobic fitness, which was best predicted by HRV during standing rest. HRV estimates differed depending on artifact correction procedures but were generally similar after individualized correction. Our results indicate that UST HRV measures display redundancy but convey state-specific information and do not strongly predict aerobic fitness in healthy men. Most UST HRV measures are robust to slight differences in artifact correction procedures.

A trait of mind: stability and robustness of sleep across sleep opportunity manipulations during simulated military operational stress.

STUDY OBJECTIVES: Within-subject stability of certain sleep features across multiple nights is thought to reflect the trait-like behavior of sleep. However, to be considered a trait, a parameter must be both stable and robust. Here, we examined the stability (i.e. across the same sleep opportunity periods) and robustness (i.e. across sleep opportunity periods that varied in duration and timing) of different sleep parameters. METHODS: Sixty-eight military personnel (14 W) spent 5 nights in the sleep laboratory during a simulated military operational stress protocol. After an adaptation night, participants had an 8-hour sleep opportunity (23:00-07:00) followed by 2 consecutive nights of sleep restriction and disruption which included two 2-hour sleep opportunities (01:00-03:00; 05:00-07:00) and, lastly, another 8-hour sleep opportunity (23:00-07:00). Intra-class correlation coefficients were calculated to examine differences in stability and robustness across different sleep parameters. RESULTS: Sleep architecture parameters were less stable and robust than absolute and relative spectral activity parameters. Further, relative spectral activity parameters were less robust than absolute spectral activity. Absolute alpha and sigma activity demonstrated the highest levels of stability that were also robust across sleep opportunities of varying duration and timing. CONCLUSIONS: Stability and robustness varied across different sleep parameters, but absolute NREM alpha and sigma activity demonstrated robust trait-like behavior across variable sleep opportunities. Reduced stability of other sleep architecture and spectral parameters during shorter sleep episodes as well as across different sleep opportunities has important implications for study design and interpretation.

Individuals with and without military-related PTSD differ in subjective sleepiness and alertness but not objective sleepiness.

Posttraumatic stress disorder-related sleep disturbances may increase daytime sleepiness and compromise performance in individuals with posttraumatic stress disorder. We investigated nighttime sleep predictors of sleepiness in Veterans with and without posttraumatic stress disorder. Thirty-seven post-9/11 Veterans with posttraumatic stress disorder and 47 without posttraumatic stress disorder (Control) completed a 48-h lab stay. Nighttime quantitative EEG and sleep architecture parameters were collected with polysomnography. Data from daytime sleepiness batteries assessing subjective sleepiness (global vigor questionnaire), objective sleepiness (Multiple Sleep Latency Tests) and alertness (psychomotor vigilance task) were included in analyses. Independent samples t-tests and linear regressions were performed to identify group differences in sleepiness and nighttime sleep predictors of sleepiness in the overall sample and within each group. Participants with posttraumatic stress disorder had higher subjective sleepiness (t = 4.20; p < .001) and lower alertness (psychomotor vigilance task reaction time (t = -3.70; p < .001) and lapses: t = -2.13; p = .04) than the control group. Objective daytime sleepiness did not differ between groups (t = -0.79, p = .43). In the whole sample, higher rapid eye movement delta power predicted lower alertness quantified by psychomotor vigilance task reaction time (ß = 0.372, p = .013) and lapses (ß = 0.388, p = .013). More fragmented sleep predicted higher objective sleepiness in the posttraumatic stress disorder group (ß = -.467, p = .005) but no other nighttime sleep measures influenced the relationship between group and sleepiness. Objective measures of sleep and sleepiness were not associated with the increased subjective sleepiness and reduced alertness of the posttraumatic stress disorder group.

Impact of simulated military operational stress on executive function relative to trait resilience, aerobic fitness, and neuroendocrine biomarkers.

PURPOSE: To study the impact of 48 h of simulated military operational stress (SMOS) on executive function, in addition to the role of trait resilience (RES) and aerobic fitness (FIT) on executive function performance. Associations between executive function and neuropeptide-Y (NPY), brain-derived neurotropic factor (BDNF), insulin-like growth factor-I (IGF-I), oxytocin, and α-klotho (klotho) were assessed to elucidate potential biomarkers that may contribute to cognitive performance during a multi-factorial stress scenario. METHODS: Fifty-four service members (SM) (26.4 ± 5.4 years, 178.0 ± 6.5 cm, 85.2 ± 14.0 kg) completed the 5-day protocol, including daily physical exertion and 48 h of restricted sleep and caloric intake. Each morning subjects completed a fasted blood draw followed by Cognition, a 10-part cognitive test battery assessing executive function. SMs were grouped into tertiles [low (L-), moderate (M-), high (H-)] based on Connor Davidson Resilience Score (RES) and V˙O2peak (FIT). Repeated measures ANOVA were run to analyze the effect of day on cognitive performance and biomarker concentration. Separate two-way mixed ANOVAs were run to determine the interaction of group by day on cognitive function. Friedman test with Bonferroni-corrected pairwise comparisons were used if assumptions for ANOVA were not met. Associations between changes in biomarkers and cognitive performance were analyzed using parametric and non-parametric correlation coefficients. RESULTS: SMOS reduced SM vigilance -11.3% (p < 0.001) and working memory -5.6% (p = 0.015), and increased risk propensity +9.5% (p = 0.005). H-RES and H-FIT SMs demonstrated stable vigilance across SMOS (p > 0.05). Vigilance was compromised during SMOS in L- and M-RES (p = 0.007 and p = 0.001, respectively) as well as L- and M-FIT (p = 0.001 and p = 0.031, respectively). SMOS reduced circulating concentrations of α-klotho -7.2% (p = 0.004), NPY -6.4% (p = 0.001), and IGF-I -8.1% (p < 0.001) from baseline through the end of the protocol. BDNF declined -19.2% after the onset of sleep and caloric restriction (p = 0.005) with subsequent recovery within 48 h. Oxytocin remained stable (p > 0.05). Several modest associations between neuroendocrine biomarkers and cognitive performance were identified. CONCLUSION: This study demonstrates H-FIT and H-RES may buffer the impact of SMOS on vigilance. SMOS negatively impacted circulating neuroendocrine biomarkers. While BDNF returned to baseline concentrations by the end of the 5 d protocol, NPY, IGF-I, and α-klotho may require a longer recovery period. These data suggest that the military may benefit by training and/or selection processes targeting at augmenting trait resilience and aerobic fitness for increased readiness.

Overnight Sleep Parameter Increases in Frontoparietal Areas Predict Working Memory Improvements in Healthy Participants But Not in Individuals With Posttraumatic Stress Disorder.

BACKGROUND: Preliminary evidence indicates that non-rapid eye movement (NREM) sleep is implicated in enhancing working memory (WM) performance across days in healthy individuals. While REM sleep has been implicated in other forms of memory, its role in WM remains unclear. Further, the relationship between sleep changes and WM improvement is largely unknown in posttraumatic stress disorder (PTSD). Examining the relationship between changes in sleep and WM improvement in healthy participants and participants with PTSD may inform cognitive enhancement strategies and intervention targets. METHODS: Repeated assessments of WM and overnight measurement of NREM and REM sleep parameters were performed in 79 participants (participants with PTSD: n = 33) during a 48-hour laboratory stay. Relationships between sleep parameter changes, WM performance changes, and clinical characteristics were analyzed in PTSD and healthy groups. RESULTS: A between-night enhancement in both NREM and REM sleep parameters in frontoparietal areas predicted across-day better WM performance in healthy participants, particularly in those with improved performance. In contrast, in participants with PTSD, an enhancement of these sleep parameters predicted a worse WM performance and was also associated with more PTSD-related sleep disturbances. CONCLUSIONS: This study shows that higher sleep activity in frontoparietal areas leads to enhanced WM performance in healthy individuals, whereas in individuals with PTSD, it likely reflects the presence of sleep disturbances that interfere with WM improvement. Interventions focused on addressing sleep disturbances could therefore ameliorate cognitive impairments in individuals with PTSD.

You Snooze, You Win? An Ecological Dynamics Framework Approach to Understanding the Relationships Between Sleep and Sensorimotor Performance in Sport.

Sleep has a widespread impact across different domains of performance, including sensorimotor function. From an ecological dynamics perspective, sensorimotor function involves the continuous and dynamic coupling between perception and action. Sport performance relies on sensorimotor function as successful movement behaviors require accurate and efficient coupling between perceptions and actions. Compromised sleep impairs different aspects of sensorimotor performance, including perceptual attunement and motor execution. Changes in sensorimotor performance can be related to specific features of sleep, notably sleep spindles and slow waves. One unaddressed area of study is the extent to which specific sleep features contribute to overall sport-specific performance.

Compromised Dynamic Postural Stability Under Increased Load Carriage Magnitudes.

Warfighter performance may be compromised through the impact of load carriage on dynamic postural stability. Men and women may experience this impact to differing extents due to postural stability differences. Therefore, the authors investigated the effect of load magnitude on dynamic postural stability in men and women during a landing and stabilization task. Dynamic postural stability of 32 subjects (16 women) was assessed during the unilateral landing of submaximal jumps under 3 load conditions: +0%, +20%, and +30% body weight. Dynamic postural stability was measured using the dynamic postural stability index, which is calculated from ground reaction force data sampled at 1200 Hz. Two-way mixed-measures analysis of variance compared dynamic postural stability index scores between sexes and loads. Dynamic postural stability index scores were significantly affected by load (P = .001) but not by sex or by the sex by load interaction (P > .05). Dynamic postural stability index scores increased between the 0% (0.359 ± 0.041), 20% (0.396 ± 0.034), and 30% (0.420 ± 0.028) body weight conditions. Increased load negatively affects dynamic postural stability with similar performance decrements displayed by men and women. Men and women warfighters may experience similar performance decrements under load carriage conditions of similar relative magnitudes.

Action Boundary Proximity Effects on Perceptual-Motor Judgments.

INTRODUCTION: Designed as a more ecological measure of reaction times, the Perception-Action Coupling Task (PACT) has shown good reliability and within-subject stability. However, a lengthy testing period was required. Perceptual-motor judgments are known to be affected by proximity of the stimulus to the action boundary. The current study sought to determine the effects of action boundary proximity on PACT performance, and whether redundant levels of stimuli, eliciting similar responses, can be eliminated to shorten the PACT.METHODS: There were 9 men and 7 women who completed 4 testing sessions, consisting of 3 familiarization cycles and 6 testing cycles of the PACT. For the PACT, subjects made judgments on whether a series of balls presented on a tablet afford "posting" (can fit) through a series of apertures. There were 8 ratios of ball to aperture size (B-AR) presented, ranging from 0.2 to 1.8, with each ratio appearing 12 times (12 trials) per cycle. Reaction times and judgment accuracy were calculated, and averaged across all B-ARs. Ratios and individual trials within each B-AR were systematically eliminated. Variables were re-averaged, and intraclass correlation coefficients (ICC) and coefficients of variation (CVTE) were calculated in an iterative manner.RESULTS: With elimination of the 0.2 and 1.8 B-ARs, the PACT showed good reliability (ICC = 0.81-0.99) and consistent within-subject stability (CVTE = 2.2-14.7%). Reliability (ICC = 0.81-0.97) and stability (CVTE = 2.6-15.6%) were unaffected with elimination of up to 8 trials from each B-AR.DISCUSSION: The shortened PACT resulted in an almost 50% reduction in total familiarization/testing time required, significantly increasing usability.Johnson CD, LaGoy AD, Pepping G-J, Eagle SR, Beethe AZ, Bower JL, Alfano CA, Simpson RJ, Connaboy C. Action boundary proximity effects on perceptual-motor judgments. Aerosp Med Hum Perform. 2019; 90(12):1000-1008.

Intersession Reliability and Within-Session Stability of a Novel Perception-Action Coupling Task.

BACKGROUND: The perception-action coupling task (PACT) was designed as a more ecologically valid measure of alertness/reaction times compared to currently used measures by aerospace researchers. The purpose of this study was to assess the reliability, within-subject variability, and systematic bias associated with the PACT.METHODS: There were 16 subjects (men/women = 9 / 7; age = 27.8 ± 3.6 yr) who completed 4 identical testing sessions. The PACT requires subjects to make judgements on whether a virtual ball could fit into an aperture. For each session, subjects completed nine cycles of the PACT, with each cycle lasting 5 min. Judgement accuracy and reaction time parameters were calculated for each cycle. Systematic bias was assessed with repeated-measures ANOVA, reliability with intraclass correlation coefficients (ICC), and within-subject variability with coefficients of variation (CVTE).RESULTS: Initiation time (Mean = 0.1065 s) showed the largest systematic bias, requiring the elimination of three cycles to reduce bias, with all other variables requiring, at the most, one. All variables showed acceptable reliability (ICC > 0.70) and within-subject variability (CVTE < 20%) with only one cycle after elimination of the first three cycles.CONCLUSIONS: With a three-cycle familiarization period, the PACT was found to be reliable and stable.Connaboy C, Johnson CD, LaGoy AD, Pepping G-J, Simpson RJ, Deng Z, Ma L, Bower JL, Eagle SR, Flanagan SD, Alfano CA. Intersession reliability and within-session stability of a novel perception-action coupling task. Aerosp Med Hum Perform. 2019; 90(2):77-83.