Page 106 - JSOM Winter 2022

FIGURE 1 The stages of normal sleep. and activity data from these devices with sleep logs from
subjective recall yields sleep duration and sleep-efficiency
measures that generally agree with those obtained from poly-
somnography, the gold standard sleep-assessment technique.
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Studies are also needed that obtain clinically diagnosed MSI
(rather than self-reports), and these can be obtained from the
Defense Medical Surveillance System. 50, 51

Sleep and MSI in Civilian Athlete Populations
Before moving into the potential mechanisms that might ex-
plain the association between suboptimal sleep and MSI risk,
it is useful to review two other systematic reviews in civilian
athletes examining poor sleep and sports/physical training in-
juries. 34, 35 In one systematic review, studies were included if
These are characterized from electroencephalographic (EEG) record- they 1) contained original data, 2) involved adults (aged >18
ings involving placing electrodes on the head and tracing the electrical
patterns of brain activity during sleep and arousal. years), 3) reported measures of sleep quantity or quality, 4)
REM = rapid eye movement sleep prospectively tracked participants for training-related MSI or
Figure modified from https://teachmephysiology.com/nervous-system/ concussions, and 5) reported associations between injuries and
34
sensory-system/consciousness-and-sleep. sleep. Twelve studies met the review criterion. Six of the 12
studies reported an association between markers of poor sleep
was a significant relationship with traumatic injuries. Two of quality or quantity and risk of sport or physical training re-
39
the most recent studies used the well-validated Pittsburg Sleep lated injuries. However, one of studies with the highest meth-
Quality Index to measure sleep quality. 44,45 The Pittsburg Sleep odological quality found no association between sleep and MSI
Quality Index is a 19-item questionnaire that assesses sleep after controlling for running mileage and prior injury. Other
quality over the last 30 days. Scores range from 0–21, with studies that found significant relationships between poor sleep
≥5 indicating poor sleepers, although ≥7 may be more valid in and injury were deemed of low methodological quality for a
Chinese participants, as in the study by Ruan et al. 44,46,47 Both variety of reasons. The authors concluded that there was cur-
studies using the Pittsburg Sleep Quality Index found that rently insufficient evidence supporting an association between
lower sleep quality was associated with a higher risk of MSI sleep quality or quantity and risk of sport or physical training-
(Table 3, Figure 2). 44,45 related injuries. 34
Three studies examined sleep duration in relation to MSI or Another systematic review examined the association between
35
musculoskeletal symptoms. On the one hand, Shattuck et al. sleep quantity and sports injuries in adolescents. Studies were
found shorter self-reported sleep duration was associated with included if 1) they reported on individuals <19 years of age, 2)
adverse musculoskeletal symptoms among Navy personnel had measures of sleep quantity, and 3) reported on musculo-
after adjusting for age, gender, body mass index, and other skeletal sport-related injuries. Seven studies met the inclusion
factors. As shown in Figure 3, Grier et al. found that self- criteria. The authors found that adolescents who had chronic
41
reported MSI was associated with shorter self-reported sleep sleep problems were more likely to suffer musculoskeletal in-
duration in a dose-response manner (i.e., as sleep duration de- juries than those who slept well (odds ratio = 1.6, 95% confi-
creased MSI risk increased); this relationship was maintained dence interval 1.1–2.4, p = 0.03). 35
13
after adjustment for demographic and lifestyle factors. Com-
pared to those that slept eight hours or more, Soldiers were Potential Mechanisms Whereby Sleep
progressively more likely to report an MSI the less they slept. May Influence MSI Risk
On the other hand, Ritland et al. found that Army Rangers
with and without a current self-reported MSI had similar There are potential mechanisms whereby suboptimal sleep
self-reported sleep durations, although the authors cautioned quality or duration may make physically active SMs more sus-
that both groups averaged less than the recommended amounts ceptible to MSIs. While going into depth on these potential
of sleep (see Table 3). 45 mechanisms is beyond the scope of this manuscript, briefly
some of them include: 1) increased muscle catabolic processes,
In summary, there appears to be some evidence that higher risk 2) increased inflammation, and 3) decreased bone formation.
of MSI and adverse musculoskeletal symptoms are associated Testosterone, growth hormone (GH), and insulin-like growth
with lower sleep quality and shorter sleep duration in SMs. hormone factor-1 (IGF1) are anabolic hormones known to in-
There are limitations associated with the studies from which crease protein synthesis; corticosterone/cortisol are involved in
these conclusions are drawn. First, most studies involved protein catabolic pathways. During normal sleep, plasma GH
convenience samples, not samples randomly drawn from the reaches a peak 90 minutes after sleep onset, plasma cortisol
larger population of SMs. 13,39,41,43–45 Second, different methods levels become minimal, and testosterone rises progressively,
were used to measure sleep quality and duration with most peaking at the first occurrence of REM sleep. When sleep is
involving self-reports. 13,39–41,43–45 Finally, most studies used disrupted, GH, testosterone, and IGF1 levels can be reduced
self-reports of musculoskeletal symptoms or MSI rather than while cortisol secretions increase, thus moving the usual ana-
conditions diagnosed by medical providers. 13,40,41,43,45 Studies bolic sleep profile to one more catabolic. 52–55 Besides the more
are needed that assess more objective measures of sleep du- catabolic environment, markers of inflammation (mainly tu-
ration and sleep quality using devices such as wrist actigraph mor necrosis factor-α) and post-exercise markers of muscle
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devices. Studies have shown that combining the sleep, wake, damage are increased. 56–58 In addition to effects on muscle
104 | JSOM Volume 22, Edition 4 / Winter 2022