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Papers by rachel markwald

Journal of Biological Rhythms, 2021

Measuring individual circadian phase is important to diagnose and treat circadian rhythm sleep-wa... more Measuring individual circadian phase is important to diagnose and treat circadian rhythm sleep-wake disorders and circadian misalignment, inform chronotherapy, and advance circadian science. Initial findings using blood transcriptomics to predict the circadian phase marker dim-light melatonin onset (DLMO) show promise. Alternatively, there are limited attempts using metabolomics to predict DLMO and no known omics-based biomarkers predict dim-light melatonin offset (DLMOff). We analyzed the human plasma metabolome during adequate and insufficient sleep to predict DLMO and DLMOff using one blood sample. Sixteen (8 male/8 female) healthy participants aged 22.4 ± 4.8 years (mean ± SD) completed an in-laboratory study with 3 baseline days (9 h sleep opportunity/night), followed by a randomized cross-over protocol with 9-h adequate sleep and 5-h insufficient sleep conditions, each lasting 5 days. Blood was collected hourly during the final 24 h of each condition to independently determine...

Journal of defense analytics and logistics, May 18, 2023

Purpose-Marksmanship data is a staple of military and law enforcement evaluations. This ubiquitou... more Purpose-Marksmanship data is a staple of military and law enforcement evaluations. This ubiquitous nature creates a critical need to use all relevant information and to convey outcomes in a meaningful way for the end users. The purpose of this study is to demonstrate how simple simulation techniques can improve interpretations of marksmanship data. Design/methodology/approach-This study uses three simulations to demonstrate the advantages of small arms combat modeling, including (1) the benefits of incorporating a Markov Chain into Monte Carlo shooting simulations; (2) how small arms combat modeling is superior to point-based evaluations; and (3) why continuous-time chains better capture performance than discrete-time chains. Findings-The proposed method reduces ambiguity in low-accuracy scenarios while also incorporating a more holistic view of performance as outcomes simultaneously incorporate speed and accuracy rather than holding one constant. Practical implications-This process determines the probability of winning an engagement against a given opponent while circumventing arbitrary discussions of speed and accuracy trade-offs. Someone wins 70% of combat engagements against a given opponent rather than scoring 15 more points. Moreover, risk exposure is quantified by determining the likely casualties suffered to achieve victory. This combination makes the practical consequences of human performance differences tangible to the end users. Taken together, this approach advances the operations research analyses of squad-level combat engagements. Originality/value-For more than a century, marksmanship evaluations have used point-based systems to classify shooters. However, these scoring methods were developed for competitive integrity rather than lethality as points do not adequately capture combat capabilities. The proposed method thus represents a major shift in the marksmanship scoring paradigm.

Sleep Health, Dec 1, 2022

F1000Research, Nov 7, 2022

In 2017, USS Fitzgerald and USS John S. McCain, both guided-missile destroyers, experienced under... more In 2017, USS Fitzgerald and USS John S. McCain, both guided-missile destroyers, experienced underway collisions that resulted in the deaths of 17 Sailors and degradation of national defense as two warships were removed from the frontline. This incident garnered Congress' attention leading to numerous fatigue management policies and working groups instituted at various levels across the Department of Defense. One policy of the Department of the Navy (3120.2A; Dec 11, 2020) specifically addressed risk mitigation factors for maritime operations occurring in the overnight and early morning hours around the circadian nadir or trough in alertness and vigilance. Despite these circadian challenges that come with mission demands of military service, there are many opportunities as outlined in the Department of Navy policy to reduce and/or eliminate the performance-related risks associated with circadian misalignment. In regard to actionable systems and processes aligned with these policies, the first step is to perform a risk assessment to identify circadian-related problems that could arise in response to conducting the military training exercise or operation. The second step is to integrate a means to monitor 24-hour physiology, mitigate performance risk through fatigue countermeasures, and/or realign the circadian timing system of military personnel to enhance sleep, manage fatigue, and optimize performance. Most importantly, the approach is not a one size fits all. Each military operation will require unique adaption (re-alignment) to the environment and each military operation may require a unique countermeasure(s).

Nature and Science of Sleep, Mar 1, 2022

Commercial wearable sleep-tracking devices are growing in popularity and in recent studies have p... more Commercial wearable sleep-tracking devices are growing in popularity and in recent studies have performed well against gold standard sleep measurement techniques. However, most studies were conducted in controlled laboratory conditions. We therefore aimed to test the performance of devices under naturalistic unrestricted home sleep conditions. Participants and Methods: Healthy young adults (n = 21; 12 women, 9 men; 29.0 ± 5.0 years, mean ± SD) slept at home under unrestricted conditions for 1 week using a set of commercial wearable sleep-tracking devices and completed daily sleep diaries. Devices included the Fatigue Science Readiband, Fitbit Inspire HR, Oura ring, and Polar Vantage V Titan. Participants also wore a research-grade actigraphy watch (Philips Respironics Actiwatch 2) for comparison. To assess performance, all devices were compared with a high performing mobile sleep electroencephalography headband device (Dreem 2). Analyses included epoch-by-epoch and sleep summary agreement comparisons. Results: Devices accurately tracked sleep-wake summary metrics (ie, time in bed, total sleep time, sleep efficiency, sleep latency, wake after sleep onset) on most nights but performed best on nights with higher sleep efficiency. Epoch-by-epoch sensitivity (for sleep) and specificity (for wake), respectively, were as follows: Actiwatch (0.95, 0.35), Fatigue Science (0.94, 0.40), Fitbit (0.93, 0.45), Oura (0.94, 0.41), and Polar (0.96, 0.35). Sleep stage-tracking performance was mixed, with high variability. Conclusion: As in previous studies, all devices were better at detecting sleep than wake, and most devices compared favorably to actigraphy in wake detection. Devices performed best on nights with more consolidated sleep patterns. Unrestricted sleep TIB differences were accurately tracked on most nights. High variability in sleep stage-tracking performance suggests that these devices, in their current form, are still best utilized for tracking sleep-wake outcomes and not sleep stages. Most commercial wearables exhibited promising performance for tracking sleep-wake in real-world conditions, further supporting their consideration as an alternative to actigraphy.

The Journal of Physiology, Jun 25, 2007

Muscle sympathetic vasoconstrictor nerve activity increases with advancing age, but does not resu... more Muscle sympathetic vasoconstrictor nerve activity increases with advancing age, but does not result in elevated forearm vasoconstrictor tone because of a selective reduction in α1-adrenoceptor responsiveness. In contrast, the leg circulation of older adults is under greater tonic sympathetic vasoconstriction, but it is unclear whether α-adrenoceptor responsiveness is altered with age. In the present study, we tested the hypothesis that postjunctional α-adrenergic vasoconstrictor responsiveness is reduced in the leg circulation with age. We measured femoral blood flow (Doppler ultrasound) and calculated the femoral vascular conductance (FVC) responses to α-adrenoceptor stimulation during local blockade of β-adrenoceptors in 12 young (24 ± 1 year) and seven healthy older men (62 ± 2 year). Whole-leg vasoconstrictor responses to local intrafemoral artery infusions of tyramine (evokes noradrenaline (NA) release), phenylephrine (α1-agonist) and dexmedetomidine (α2-agonist) were assessed. Consistent with previous data, resting femoral blood flow and FVC were ∼30% lower in older compared with young men (P < 0.05). Maximal vasoconstrictor responses to tyramine (−30 ± 3 versus−41 ± 3%), phenylephrine (−25 ± 4 versus−45 ± 5%), and dexmedetomidine (−22 ± 4 versus−44 ± 3%) were all significantly lower in older compared with young men (all P < 0.05). Our results indicate that human ageing is associated with a reduction in leg postjunctional α-adrenoceptor responsiveness to endogenous NA release, and this reduction is evident for both α1- and α2-adrenoceptors. However, given that basal leg vascular conductance is reduced with age and is primarily mediated by sympathetic vasoconstriction, impaired α-adrenoceptor responsiveness does not negate the ability of the sympathetic nervous system to evoke greater tonic vasoconstriction in the leg vasculature of older men.

Sensors, Dec 25, 2020

Traditional measures of sleep or commercial wearables may not be ideal for use in operational env... more Traditional measures of sleep or commercial wearables may not be ideal for use in operational environments. The Zulu watch is a commercial sleep-tracking device designed to collect longitudinal sleep data in real-world environments. Laboratory testing is the initial step towards validating a device for real-world sleep evaluation; therefore, the Zulu watch was tested against the gold-standard polysomnography (PSG) and actigraphy. Eight healthy, young adult participants wore a Zulu watch and Actiwatch simultaneously over a 3-day laboratory PSG sleep study. The accuracy, sensitivity, and specificity of epoch-by-epoch data were tested against PSG and actigraphy. Sleep summary statistics were compared using paired samples t-tests, intraclass correlation coefficients, and Bland-Altman plots. Compared with either PSG or actigraphy, both the accuracy and sensitivity for Zulu watch Sleep-Wake determination were >90%, while the specificity was low (~26% vs. PSG,~33% vs. actigraphy). The accuracy for sleep scoring vs. PSG was~87% for interrupted sleep,~52% for light sleep, and~49% for deep sleep. The Zulu watch showed mixed results but performed well in determining total sleep time, sleep efficiency, sleep onset, and final awakening in healthy adults compared with PSG or actigraphy. The next step will be to test the Zulu watch's ability to evaluate sleep in industrial operations.

Nature and Science of Sleep, Apr 1, 2023

Previous studies have found that many commercial wearable devices can accurately track sleep-wake... more Previous studies have found that many commercial wearable devices can accurately track sleep-wake patterns in laboratory or home settings. However, nearly all previous studies tested devices under conditions with fixed time in bed (TIB) and during nighttime sleep episodes only. Despite its relevance to shift workers and others with irregular sleep schedules, it is largely unknown how devices track daytime sleep. Therefore, we tested the sleep-tracking performance of four commercial wearable devices during unrestricted home daytime sleep. Participants and Methods: Participants were 16 healthy young adults (6 men, 10 women; 26.6 ± 4.6 years, mean ± SD) with habitual daytime sleep schedules. Participants slept at home for 1 week under unrestricted conditions (ie, self-selecting TIB) using a set of four commercial wearable devices and completed reference sleep logs. Wearables included the Fatigue Science ReadiBand, Fitbit Inspire HR, Oura Ring, and Polar Vantage V Titan. Daytime sleep episode TIB biases and frequencies of missed and falsepositive daytime sleep episodes were examined. Results: TIB bias was low in general for all devices on most daytime sleep episodes, but some exhibited large biases (eg, >1 h). Total missed daytime sleep episodes were as follows: Fatigue Science: 3.6%; Fitbit: 4.8%; Oura: 6.0%; Polar: 37.3%. Missed episodes occurred most often when TIB was short (eg, naps <4 h). Conclusion: When daytime sleep episodes were recorded, the devices generally exhibited similar performance for tracking TIB (ie, most episodes had low bias). However, the devices failed to detect some daytime episodes, which occurred most often when TIB was short, but varied across devices (especially Polar, which missed over one-third of episodes). Findings suggest that accurate daytime sleep tracking is largely achievable with commercial wearable devices. However, performance differences for missed recordings suggest that some devices vary in reliability (especially for naps), but improvements could likely be made with changes to algorithm sensitivities.

Journal of Science and Medicine in Sport, May 1, 2022

Military Medicine, Apr 27, 2023

The U.S. military invests substantial resources to vaccinate all personnel, including recruits, a... more The U.S. military invests substantial resources to vaccinate all personnel, including recruits, against operationally important infectious disease threats. However, research suggests that vaccine immune response and, therefore, vaccine effectiveness may be inadvertently reduced because of chronic and/or acute sleep deficiency experienced by recipients around the time of vaccination. Because sleep deficiency is expected and even necessary in deployed and training contexts, research investigations of the impacts of sleep and related physiological systems such as circadian rhythms on vaccine effectiveness in military settings are needed. Specifically, research should be aimed at understanding the effects of sleep deficiency, as well as vaccine administration schedules, on response to vaccination and clinical protection. Furthermore, knowledge gaps among military medical leadership on sleep, vaccines, and immune health should be assessed. This area of research may benefit the health and readiness of service members while also decreasing health care utilization and associated costs from illness.

Journal of Sleep Research, Apr 5, 2023

SummarySubmariners face many environmental and operational challenges to maintaining good sleep, ... more SummarySubmariners face many environmental and operational challenges to maintaining good sleep, including suboptimal lighting, shift work, and frequent interruptions. Anecdotally, many Sailors consume caffeine to alleviate the effects of poor sleep on alertness, mood, and performance; however, caffeine itself may also degrade sleep quantity and/or quality. This study provides the first exploration of the potential relationship between caffeine use and sleep onboard submarines. Objective measures (wrist actigraphy, available from 45 participants), self‐report sleep metrics, and self‐reported caffeine consumption were collected from 58 US Navy Sailors before and during a routine submarine underway at sea lasting 30 days. Contrary to expectations, less caffeine was reportedly consumed at sea (232.8 ± 241.1 mg) than on land prior to the underway (M = 284.4 ± 251.7 mg; X2(1) = 7.43, p = 0.006), positive rather than negative relationships were observed between caffeine consumption and sleep efficiency (F = 6.11, p = 0.02), and negative relationships were observed between caffeine consumption and wake after sleep onset (F = 9.36, p = 0.004) and sleep fragmentation (F = 24.73, p < 0.0001). However, in contrast, higher caffeine consumption was also negatively related to self‐reported sleep duration while at sea (F = 4.73, p = 0.03). This observational study is the first to measure relationships between caffeine consumption and sleep quantity and/or quality in a submarine environment. We propose that the unique submarine environment and the unique caffeine consumption patterns of submariners should be considered in the development of potential countermeasures for sleepiness.

Applied Ergonomics, Oct 1, 2023

The Journal of Defense Modeling and Simulation, Jun 2, 2023

Military performance must be evaluated, and one of the most critical concepts to measure involves... more Military performance must be evaluated, and one of the most critical concepts to measure involves the lethal capabilities of a military force. However, there are multiple challenges that complicate any accurate performance assessment, including theoretical issues of measurement due to statistical irregularities and practical limitations due to the military context. Here, we describe the lethality paradox, which states that measuring lethality could be a self-defeating exercise despite its necessity. Specifically, the value of any collected metric may be inherently reduced by the act of measurement while, also, creating operational vulnerabilities for a military force. This paradox is conceived as an extension of Goodhart’s Law and incorporates the same challenges of a personnel gaming a set standard rather than developing the skill set supposedly measured by this standard. Our discussion identifies the limitations and applications of Goodhart’s Law to lethality while also concluding with several proposed solutions to different paradoxical challenges.

Journal of Strength and Conditioning Research, May 26, 2023

Jensen, AE, Bernards, JR, Hamilton, JA, Markwald, RR, Kelly, KR, and Biggs, AT. Do not shoot me: ... more Jensen, AE, Bernards, JR, Hamilton, JA, Markwald, RR, Kelly, KR, and Biggs, AT. Do not shoot me: potential consequences of force-on-force training modulate the human stress response. J Strength Cond Res 37(9): 1761–1769, 2023—Close-quarters combat (CQC) engagements trigger the “fight-or-flight” response, activating the sympathetic nervous system and hypothalamic-pituitary-adrenal axis in response to perceived threats. However, it has yet to be shown if a force-on-force (FoF) CQC training environment will lead to adaptations in the physiological stress response or performance. United States Marines and Army infantry personnel participated in a 15-day CQC training program. The CQC program focused heavily on FoF training with the use of nonlethal training ammunition (NLTA). Data collections occurred on training days 1 and 15, during a simulated FoF-hostage rescue (HR) scenario and photorealistic target drill. For the FoF-HR, subjects were instructed to clear the shoot house, rescue the hostage, and only shoot hostile threat(s) with NLTA. The photorealistic target drills were similar, but replaced the role players in the FoF-HR with paper targets. Salivary alpha-amylase (sAA) and salivary cortisol were obtained immediately before entering and exiting the shoot house. Time to completion significantly decreased, between days 1 and 15, for both the FoF-HR and the photorealistic drills by 67.7 and 54.4%, respectively (p < 0.05). Analyses revealed that the change in sAA, nonsignificantly, doubled from day 1 to 15 during FoF-HR (p > 0.05), whereas the change in sAA decreased during the photorealistic drills across days (p < 0.05). Cortisol was significantly higher during the FoF-HR in comparison to the photorealistic drills (p < 0.05). These data suggest that potential consequences of FoF training heighten the stress response in conjunction with enhanced performance.

Journal of Sleep Research, Nov 27, 2022

SummaryThe United States Navy is a high‐reliability organization that must maintain optimum perfo... more SummaryThe United States Navy is a high‐reliability organization that must maintain optimum performance under challenging conditions. One key challenge for sailors is obtaining sufficient sleep, which can lead to fatigue and other outcomes that compromise operational readiness. Identifying sleep issues and their causes is critical for military leaders to care for their personnel, and to make informed, risk‐based operational decisions. Though previous studies in shipboard environments have implicated factors responsible for insufficient sleep (e.g. poor sleep environment and work demands), there has been less research into characterizing the complex interplay among such factors in relation to sleep and work‐related fatigue outcomes. This study seeks to address this gap. Data were drawn from the Afloat Safety Climate Assessment Survey of 7617 sailors from 73 ships. The survey included demographic characteristics and measures of crew endurance (e.g. sleep, occupational impairment due to fatigue). Descriptive analyses characterized the presence and severity of sleep issues across subpopulations and operational settings (e.g. the type of ship); structural equation modelling techniques characterized and quantified the statistical associations among factors. The results indicate that sleep deficits are widespread, holding across subpopulations and operational settings. Though sleep deficits varied across subpopulations, no group obtained an average of more than 7 hr of sleep per night. Fatigue‐induced occupational functional impairment was directly related to sleep deficiency, and sleep environment and job‐related factors were contributors to sleep deficiency. Moreover, job‐related factors emerged as potentially more consequential. Lastly, factors may exist aboard a ship that could help promote better sleep.

Journal of Sleep Research, Jun 29, 2021

Chronic insufficient sleep is known to lead to a broad range of negative consequences (e.g. poor ... more Chronic insufficient sleep is known to lead to a broad range of negative consequences (e.g. poor health and cognitive performance). While insufficient sleep and associated fatigue are present in many diverse populations, it is of special concern in high-risk military environments, where a mishap can result in catastrophic outcomes. Although many studies have been conducted to characterise sleep in general military populations, relatively few have been conducted using a large representative sample of sailors assigned to United States Naval warships. The present cross-sectional study characterises self-reported sleep parameters in sailors (N = 11,738) and explores the role of possible contributors to insufficient sleep. The results indicate that sailors, across a variety of different subgroups, do not obtain the amount of sleep that they report requiring for feeling well-rested. Of the many potential factors thwarting sleep, workload and an uncomfortable mattress are the most promising candidates to target for improvement.

Reference Module in Neuroscience and Biobehavioral Psychology, 2021

SLEEP

Introduction Insufficient sleep is pervasive in U.S. Navy (USN) sailors and has been associated w... more Introduction Insufficient sleep is pervasive in U.S. Navy (USN) sailors and has been associated with increased risk of injury and mood disturbances. As such, monitoring sleep and identifying modifiable targets that influence sleep in this population is essential. We examined the sleep of USN sailors during 9-months in port and explored the influence of different lifestyle behaviors on sleep. Methods Sailors (n = 101, 31 ± 7 years old [mean ± SD], 21% female) wore a commercial wearable sleep-tracking device (Oura Ring, Gen2) during a 9-month home port maintenance period (September 2021 – May 2022). During the study, the sailors slept at home and had periods working on the ship (on-hull; higher demands) and off the ship (off-hull; lower demands). Participants also completed 5 self-report surveys that assessed sleep quality (Pittsburgh Sleep Quality Index; PSQI) and multiple lifestyle behaviors including: hours of natural light exposure, hours of moderate/vigorous physical activity, an...

Sleep

Introduction Sleep quality is known to be negatively impacted during military operations at sea. ... more Introduction Sleep quality is known to be negatively impacted during military operations at sea. Yet, there are limited naval studies that explore measures of sleep disturbances and sleep-related impairment, especially in relation to different warship classes. This analysis compares sleep disturbances and sleep-related impairment across two warship classes during similar at-sea periods. Methods 432 sailors (77.6% male; 27.4±7.1 years) participated in a training evolution aboard either a destroyer (DDG; n=194) or an amphibious class ship (LHD; n=238). Participants completed a 7-day recall questionnaire assessing their sleep and health behavior prior to getting underway (baseline) and 1–2 days prior to completing a 2-week underway (underway). Primary outcomes included the PROMIS Sleep-Related Impairment scale (P-SRI) and the PROMIS Sleep Disturbance scale (P-SD). While underway, participants self-reported their diet quality, daily caffeine and nicotine intake, overall health, and dail...