Page 105 - JSOM Winter 2022

TABLE 1 Definition of Sleep Quality Variables Developed by the While the effects of sleep loss on performance and illnesses
National Sleep Foundation’s Expert Panel 10 have been well documented, the effects on MSI have received
Type of less attention and will be a major focus of this article. This
Measure Variable Measurement and Definition article will briefly discuss the stages of normal sleep, then ex-
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Sleep Sleep Efficiency Percent (%) of total sleep time amine in detail another systematic review on the association
Continuity to time in bed (i.e., sleep time/ between sleep and MSI in military populations, while also con-
bed time × 100%) sidering reviews on the associations between sleep and injuries
Sleep Latency Minutes in transition from in athletes. 34–36 Finally, ways of optimizing sleep and mitigating
wake to sleep the effects of sleep loss will be discussed.
Wake after Sleep Minutes spent awake after
Onset sleep initiated and before final
awakening Sleep Stages
Awakenings >5 Number of times awake for
Minutes >5 minutes It is helpful to understand the stages of normal sleep to appre-
Napping Naps Number of naps in 24 hours ciate how disruptions of sleep may alter normal sleep patterns.
Variables Nap Duration Average minutes of each nap Sleep stages are categorized by variations in polysomnographic
Nap Frequency Number of days in the past 7 (PSG) recordings that identify electrical patterns of brain activ-
ity, muscle activity, and eye movements monitored from elec-
that a nap occurred
Sleep Rapid Eye Percent of total sleep time spent trodes placed on the head, face, and chin. Two types of sleep
Architecture a Movement (REM) in REM sleep are non-rapid eye movement (NREM) sleep and rapid eye
Sleep movement (REM) sleep. In traditional nomenclature, NREM
Stage N1 Sleep Percent of total sleep time spent sleep has four stages, although a recent update combines stages
in non-REM Stage 1 light sleep 3 and 4. Each progressive stage associated with increasingly
Stage N2 Sleep Percent of total sleep time spent deeper sleep (Figure 1). Stage 1 is light sleep from which an
in non-REM Stage 2 sleep individual can easily be awoken. Stage 2 is often considered the
Stage N3/4 Sleep Percent of total sleep time spent first true stage of sleep. In stage 2, brain activity slows, rolling
in slow wave deep sleep eye movements occur, and muscle activity is reduced. Stages 3
Arousals Number per hour of abrupt and 4 are deep sleep characterized by large, slow-wave brain
changes from deep non-REM activity and further reductions in muscle tension. NREM sleep
sleep to lighter sleep or from makes up about 75% of total sleep time and is considered re-
REM sleep to awakening storative and recuperative for the brain and the body. REM
a These are measures obtained by electroencephalography (EEG) which sleep is associated with dreaming and makes up about 25% of
involves placing electrodes on the head and tracing the electrical pat-
terns of brain activity during sleep and arousal. the total sleep time. REM sleep consists of remarkably active
brain activity along with rapid eye movements, but muscles are
deployed or just recently (two months) redeployed in support paralyzed to prevent acting out the dreams. There are usually
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of the wars in Iraq and Afghanistan. Inadequate sleep or 4–6 sleep cycles during the night and as the night progresses the
trouble sleeping prior to deployment also increases the risk REM periods tend to lengthen. There are many theories about
for new-onset mental health problems such as post-traumatic the biological function of REM sleep, and among these are that
stress disorders and anxiety. Problems may persist after de- REM sleep is involved in learning, memory consolidation, re-
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ployment as indicated by the fact that among redeployed SMs, cuperation, and possibly stress reduction. 37,38
72% reported ≤six hours of sleep between 90 and 180 days
after leaving the combat environment. 19
Sleep and MSI in Military Populations
The adverse effects of sleep deprivation (no sleep for extended A recent systematic review examined the association between
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periods) or sleep restriction (limited sleep per night) on perfor- sleep and MSI in military personnel. Studies were selected for
mance have been well documented. Studies have shown that this review if they had 1) original data, 2) examined military
sleep deprivation affects various aspects of cognitive function- personnel (foreign or US), 3) reported measures of sleep qual-
ing, especially vigilance, alertness, problem solving, learning, ity or quantity, 3) reported the incidence of MSI, and 4) had
situational awareness, and mood states. 7, 20–23 Many of these some measure of association between sleep and MSI (e.g., cor-
adverse effects are seen in military field training exercises that relations, risk ratio, hazard ratio, odds ratio). Eight articles
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involve factors besides sleep loss, such as continuous physical met the review criteria. 13,39–45 Table 2 shows the participants,
activity, dehydration, nutritional deficiencies, and environ- methods, and results of these studies. Only three studies were
mental and psychological stressors. 20,24–28 Measures of physical specifically focused on sleep and MSI, with the other five ex-
performance to include aerobic performance, anaerobic capac- amining sleep as a secondary covariate. 13, 44, 45
ity, and muscular endurance can also be affected. Important
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military tasks have also been shown to be degraded by sleep Most studies indicated that lower sleep quality, assessed by
loss. For example, measures of marksmanship such as number a variety of measures, was associated with higher MSI in-
of target hits, accuracy, sighting time, and shot group tightness jury risk. 13, 39–42, 44, 45 One exception was the study by Kovcan
were degraded after sleep deprivation or sleep restriction. 27,30–32 et al. which measured “current musculoskeletal complaints”
During continuous military operations, the number of field ar- in relation to a poorly described measure of sleep quality.
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tillery rounds accurately delivered on target decreased roughly The study did not provide the actual numeric data on the re-
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in proportion to the decrease in the hours of sleep per night. lationship and just noted the lack of relationship in the text
Lack of sleep has been implicated in US military friendly fire of the article. Another exception was the study by Gregg et
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incidents and has been identified as a common contributing al. which found no relationship between self-reported “trou-
factor to US fratricide incident rates. 20,33 ble falling/staying asleep” and overuse injuries, although there
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