Examination of Sleep and Injury Among College Football Athletes.

Burke, TM, Lisman, PJ, Maguire, K, Skeiky, L, Choynowski, JJ, CapaldiII, VF, Wilder, JN, Brager, AJ, and Dobrosielski, DA. Examination of sleep and injury among college football athletes. J Strength Cond Res 34(3): 609-616, 2020-The purpose of this study was to characterize subjective sleep metrics in collegiate football players at the start of the season, determine the relationship between preseason subjective sleep measures and in-season objective sleep characteristics, and examine the association between subjective and objective sleep metrics and incidence of time-loss injury during the competitive season. Ninety-four Division I football players completed 5 validated sleep-related questionnaires to assess sleep quality, insomnia severity, daytime sleepiness, sleep apnea risk, and circadian preference before the start of the season. Clinical thresholds for sleep questionnaires were used to determine risk of sleep disorders. Continuous wrist actigraphy was collected throughout the season to generalize sleep behaviors. Time-loss injury incidence data were recorded and used for analysis. Results indicated that 67.4% (60 of 89) of athletes scored above clinical threshold in at least 1 questionnaire to indicate sleep disorder risk. At the start of the season, players subjectively reported an average sleep duration of 7:16 ± 1:18 hours:minutes, which was in contrast to the 6:04 ± 0:41 hours:minutes measured through actigraphy during the season. Logistic regression models adjusted for age and body mass index revealed no significant associations between injury and subjective (odds ratio [OR] = 1.00; 95% confidence interval [CI] = 0.99-1.01) and objective (OR = 1.01; 95% CI = 0.99-1.02) sleep duration or measures attained from sleep questionnaires (ORs ranged from 1.01 to 2.87). Sleep metrics (quantity and quality) were not associated with increased risk of injury in this cohort of collegiate football players.

Impact of sleep inertia on visual selective attention for rare targets and the influence of chronotype.

Sleep inertia is affected by circadian phase, with worse performance upon awakening from sleep during the biological night than biological day. Visual search/selective visual attention performance is known to be sensitive to sleep inertia and circadian phase. Individual differences exist in the circadian timing of habitual wake time, which may contribute to individual differences in sleep inertia. Because later chronotypes awaken at an earlier circadian phase, we hypothesized that later chronotypes would have worse visual search performance during sleep inertia than earlier chronotypes if awakened at habitual wake time. We analysed performance from 18 healthy participants [five females (22.1 ± 3.7 years; mean ± SD)] at ~1, 10, 20, 30, 40 and 60 min following electroencephalogram-verified awakening from an 8 h in-laboratory sleep opportunity. Cognitive throughput and reaction times of correct responses were impaired by sleep inertia and took ~10-30 min to improve after awakening. Regardless whether chronotype was defined by dim light melatonin onset or mid-sleep clock hour on free days, derived from the Munich ChronoType Questionnaire, the duration of sleep inertia for cognitive throughput and reaction times was longer for later chronotypes (n = 7) compared with earlier chronotypes (n = 7). Specifically, performance for earlier chronotypes showed significant improvement within ~10-20 min after awakening, whereas performance for later chronotypes took ~30 min or longer to show significant improvement (P < 0.05). Findings have implications for decision making immediately upon awakening from sleep, and are consistent with circadian theory suggesting that sleep inertia contributes to longer-lasting impairments in morning performance in later chronotypes.

Sleep inertia, sleep homeostatic and circadian influences on higher-order cognitive functions.

Sleep inertia, sleep homeostatic and circadian processes modulate cognition, including reaction time, memory, mood and alertness. How these processes influence higher-order cognitive functions is not well known. Six participants completed a 73-day-long study that included two 14-day-long 28-h forced desynchrony protocols to examine separate and interacting influences of sleep inertia, sleep homeostasis and circadian phase on higher-order cognitive functions of inhibitory control and selective visual attention. Cognitive performance for most measures was impaired immediately after scheduled awakening and improved during the first ~2-4 h of wakefulness (decreasing sleep inertia); worsened thereafter until scheduled bedtime (increasing sleep homeostasis); and was worst at ~60° and best at ~240° (circadian modulation, with worst and best phases corresponding to ~09:00 and ~21:00 hours, respectively, in individuals with a habitual wake time of 07:00 hours). The relative influences of sleep inertia, sleep homeostasis and circadian phase depended on the specific higher-order cognitive function task examined. Inhibitory control appeared to be modulated most strongly by circadian phase, whereas selective visual attention for a spatial-configuration search task was modulated most strongly by sleep inertia. These findings demonstrate that some higher-order cognitive processes are differentially sensitive to different sleep-wake regulatory processes. Differential modulation of cognitive functions by different sleep-wake regulatory processes has important implications for understanding mechanisms contributing to performance impairments during adverse circadian phases, sleep deprivation and/or upon awakening from sleep.

Distribution of dim light melatonin offset (DLMOff) and phase relationship to waketime in healthy adults and associations with chronotype.

OBJECTIVES: Dim light melatonin onset, or the rise in melatonin levels representing the beginning of the biological night, is the gold standard indicator of circadian phase. Considerably less is known about dim light melatonin offset, or the decrease in melatonin to low daytime levels representing the end of the biological night. In the context of insufficient sleep, morning circadian misalignment, or energy intake after waketime but before dim light melatonin offset, is linked to impaired insulin sensitivity, suggesting the need to characterize dim light melatonin offset and identify risk for morning circadian misalignment. METHODS: We examined the distributions of dim light melatonin offset clock hour and the phase relationship between dim light melatonin offset and waketime, and associations between dim light melatonin offset, phase relationship, and chronotype in healthy adults (N = 62) who completed baseline protocols measuring components of the circadian melatonin rhythm and chronotype. RESULTS: 74.4% demonstrated dim light melatonin offset after waketime, indicating most healthy adults wake up before the end of biological night. Later chronotype (morningness-eveningness, mid-sleep on free days corrected, and average mid-sleep) was associated with later dim light melatonin offset clock hour. Later chronotype was also associated with a larger, positive phase relationship between dim light melatonin offset and waketime, except for morningness-eveningness. CONCLUSIONS: These findings suggest morning circadian misalignment risk among healthy adults, which would not be detected if only dim light melatonin onset were assessed. Chronotype measured by sleep timing may better predict this risk in healthy adults keeping a consistent sleep schedule than morningness-eveningness preferences. Additional research is needed to develop circadian biomarkers to predict dim light melatonin offset and evaluate appropriate dim light melatonin offset timing to promote health.

The Association Between Sleep and Musculoskeletal Injuries in Military Personnel: A Systematic Review.

INTRODUCTION: Musculoskeletal injuries (MSKIs) are a significant health problem in the military. Accordingly, identifying risk factors associated with MSKI to develop targeted strategies that attenuate injury risk remains a top priority within the military. Insufficient sleep has garnered increased attention as a potential risk factor for MSKI in both civilians and military personnel. Yet, there are no systematic evaluations of the potential association between sleep and MSKI in the military. The purpose of this review is to examine the relationship between sleep and injury in military personnel. MATERIALS AND METHODS: Literature searches were performed in multiple electronic databases using keywords relevant to sleep quantity and quality, MSKI, and military populations. Two investigators independently assessed the methodological quality of each study using the Newcastle-Ottawa Scale for cohort studies or an adapted form of this scale for cross-sectional studies. RESULTS: The search yielded 2402 total citations, with 8 studies (3 cohort and 5 cross-sectional) fitting the inclusion criteria. Overall, the systematic review found 5 of the 8 reviewed studies supporting an association between sleep (quality and duration) and MSKI in military personnel. Specifically, poor sleep was associated with increased injury incidence in 2 cohort and 3 cross-sectional studies. CONCLUSION: This is the first systematic review to evaluate the published literature on the association between sleep and MSKI risk in military populations. Although there is currently limited research on this topic, findings suggest that sleep is associated with MSKI and should be considered when designing strategies aimed at reducing MSKI risk in military personnel.

Association Between Self-Reported Sleep Quality and Musculoskeletal Injury in Male Army Rangers.

INTRODUCTION: Musculoskeletal injuries and insufficient sleep are common among U.S. Army Rangers. There has been limited research into whether indices of sleep differ between injured and uninjured Rangers. The purpose of this study was to investigate the association between self-reported sleep and musculoskeletal injury in Rangers. MATERIALS AND METHODS: A total of 82 Army Rangers (male, 25.4 ± 4.0 years) were asked if they currently have any musculoskeletal injuries; completed the Pittsburgh Sleep Quality Index (PSQI), the Insomnia Severity Index (ISI), and the Stanford Sleepiness Scale; and were asked about their average sleep quality/sleep duration over the preceding week. Rangers were then dichotomized into groups, one that reported a current musculoskeletal injury and another that did not. RESULTS: The reported musculoskeletal injury prevalence was 15.9% (n = 13). The Rangers that reported an injury, compared to those that did not, had a significantly higher Global PSQI score (6.7 ± 3.7 versus 4.5 ± 2.7, P = .012) and ISI score (10.9 ± 3.7 versus 7.2 ± 4.1, P = .003), both indicative of poorer sleep. The group reporting an injury rated their average sleep quality over the preceding week significantly lower compared to those that did not report an injury (50.8 ± 17.5 versus 68.9 ± 18.3, P = .001). There was no significant group difference in the average nightly sleep duration (6.1 ± 1.0 hours versus 6.5 ± 0.9 hours, P = .099). CONCLUSION: In this cohort of male Army Rangers, In this cohort of male Army Rangers, those with a musculoskeletal injury reported poorer sleep quality than uninjured Rangers. Sleep duration was not associated with reported injuries; however, both the injured group and uninjured group averaged less than the recommended amounts of sleep. Further investigation into the relationship between musculoskeletal injury and sleep in military personnel is warranted.

Sleep and occupational well-being in active duty special operations soldiers: A replication and expansion.

OBJECTIVE: To assess the relationship between sleep quality and occupational well-being in active duty military Service Members. DESIGN: Longitudinal prospective analysis. SETTING: An annual military training event. PARTICIPANTS: US Army special operations Soldiers (n = 60; 100% male; age 25.41 ± 3.74). INTERVENTION: None. MEASUREMENTS: The Pittsburgh Sleep Quality Index (PSQI) was administered prior to the training event, and the Emotional Exhaustion Scale, the Role Overload Scale, the Walter Reed Army Institute of Research Soldier-Specific Functional Impairment Scale, and the Perceived Stress Scale were administered after the event. Linear regression models were used to assess the relationship between sleep and occupational wellness measures, and the outcome measures of "good" and "poor" sleepers (per the PSQI scoring criteria) were compared with Student's t tests. RESULTS: Higher (poorer) PSQI Global Scores predicted poorer occupational wellness of all measures (emotional exhaustion: B = 1.60, P < .001, R2 = 0.25; functional impairment: B = 0.29, P = .03, R2 = 0.14; role overload: B = 0.28, P = .008, R2 = 0.12; and perceived stress: B = 0.34, P = .004, R2 = 0.20). There were additional relationships between specific PSQI component scores and occupational wellness measures, which is a replication of This team's previous work. Furthermore, emotional exhaustion (t(58) = -4.18, P < .001), functional impairment (t(59)= -3.68, P = .001), role overload (t(58) = -3.20, P = .002), and perceived stress (t(58) = -2.43, P = .02) were all higher in poor sleepers. CONCLUSIONS: The findings of this study suggest that US Army special operations Soldiers who have poorer sleep quality may be at increased risk for having poorer occupational well-being.

Sleep and high-risk behavior in military service members: a mega-analysis of four diverse U.S. Army units.

Experimental sleep restriction and deprivation lead to risky decision-making. Further, in naturalistic settings, short sleep duration and poor sleep quality have been linked to real-world high-risk behaviors (HRB), such as reckless driving or substance use. Military populations, in general, tend to sleep less and have poorer sleep quality than nonmilitary populations due to a number of occupational, cultural, and psychosocial factors (e.g. continuous operations, stress, and trauma). Consequently, it is possible that insufficient sleep in this population is linked to HRB. To investigate this question, we combined data from four diverse United States Army samples and conducted a mega-analysis by aggregating raw, individual-level data (n = 2,296, age 24.7 ± 5.3). A negative binomial regression and a logistic regression were used to determine whether subjective sleep quality (Pittsburgh Sleep Quality Index [PSQI], Insomnia Severity Index [ISI], and duration [h]) predicted instances of military-specific HRB and the commission of any HRB (yes/no), respectively. Poor sleep quality slightly elevated the risk for committing HRBs (PSQI Exp(B): 1.12 and ISI Exp(B): 1.07), and longer duration reduced the risk for HRBs to a greater extent (Exp(B): 0.78), even when controlling for a number of relevant demographic factors. Longer sleep duration also predicted a decreased risk for commission of any HRB behaviors (Exp(B): 0.71). These findings demonstrate that sleep quality and duration (the latter factor, in particular) could be targets for reducing excessive HRB in military populations. These findings could therefore lead to unit-wide or military-wide policy changes regarding sleep and HRB.

Effects of the melatonin MT-1/MT-2 agonist ramelteon on daytime body temperature and sleep.

STUDY OBJECTIVES: A reduction in core temperature and an increase in the distal-proximal skin gradient (DPG) are reported to be associated with shorter sleep onset latencies (SOL) and better sleep quality. Ramelteon is a melatonin MT-1/MT-2 agonist approved for the treatment of insomnia. At night, ramelteon has been reported to shorten SOL. In the present study we tested the hypothesis that ramelteon would reduce core temperature, increase the DPG, as well as shorten SOL, reduce wakefulness after sleep onset (WASO), and increase total sleep time (TST) during a daytime sleep opportunity. DESIGN: Randomized, double-blind, placebo-controlled, cross-over design. Eight mg ramelteon or placebo was administered 2 h prior to a 4-h daytime sleep opportunity. SETTING: Sleep and chronobiology laboratory. PARTICIPANTS: Fourteen healthy adults (5 females), aged (23.2 +/- 4.2 y). MEASUREMENTS AND RESULTS: Primary outcome measures included core body temperature, the DPG and sleep physiology (minutes of total sleep time [TST], wake after sleep onset [WASO], and SOL). We also assessed as secondary outcomes, proximal and distal skin temperatures, sleep staging and subjective TST. Repeated measures ANOVA revealed ramelteon significantly reduced core temperature and increased the DPG (both P < 0.05). Furthermore, ramelteon reduced WASO and increased TST, and stages 1 and 2 sleep (all P < 0.05). The change in the DPG was negatively correlated with SOL in the ramelteon condition. CONCLUSIONS: Ramelteon improved daytime sleep, perhaps mechanistically in part by reducing core temperature and modulating skin temperature. These findings suggest that ramelteon may have promise for the treatment of insomnia associated with circadian misalignment due to circadian sleep disorders.

Sleep problems and functioning during initial training for a high-risk occupation.

OBJECTIVES: The current study sought to characterize the sleep problems of soldiers entering Basic Combat Training and to identify the link between sleep problems and subsequent performance, psychological distress, anger reactions, and attention. DESIGN: Soldiers were surveyed at 4 time points throughout the standard 10 weeks of Basic Combat Training. Surveys were administered at weeks 1, 3, 6, and 9. Sleep problems were identified as either present or absent at each time point using a sleep problem screening questionnaire. Four sleep patterns were identified and then used to evaluate outcomes throughout training (n = 1577). RESULTS: When compared to those who never had a sleep problem ("healthy "; 60.6%), those who recovered from their initial sleep problem ("recovered"; 12.8%) started training with higher psychological distress and anger reactions and lower attention but steadily improved throughout training. Those who developed a sleep problem during training ("new onset"; 20.0%) and those who had a sleep problem throughout training ("chronic"; 6.6%) also started off significantly worse than the healthy group. The new-onset and chronic groups saw slower psychological distress improvement and a decline in attention throughout the course compared to the healthy group. The chronic group also significantly increased their anger reactions throughout training compared to the healthy group. CONCLUSION: Sleep problems during Basic Combat Training may be an indicator for difficulties managing entry into the military. These findings highlight the importance of improving sleep health for soldiers throughout Basic Combat Training and for others with similar training in high-risk occupations.

Objective changes in activity levels following sleep extension as measured by wrist actigraphy.

OBJECTIVE/BACKGROUND: It is widely established that insufficient sleep can lead to adverse health outcomes. Paradoxically, epidemiologic research suggests that individuals who report habitual nightly sleep greater than 9 h also are at risk for adverse health outcomes. Further, studies have shown that long sleepers have decreased activity levels, which may partially explain the relationship between long sleep duration and mortality. The influence of sleep extension (longer time in bed) on levels of daily activity has not yet been established. The current study examined whether a week of sleep extension altered activity levels within the subsequent daily waking active and sleep period in order to determine whether increased time in bed indeed is related to decreased activity levels. METHODS: A total of 26 healthy volunteers wore wrist accelerometer devices (Actiwatch 2.0, Philips) in order to objectively measure sleep and activity for six days during their normal schedules and for six days during a sleep extension (10 h time in bed) intervention. RESULTS: There were no significant or clinically-relevant differences in 24-h activity or activity during the active or sleep period between baseline and sleep extension conditions. There were no main or interaction effects of day and condition when daily activity counts were compared between baseline and sleep extension conditions for the 24 h period (Day: F(5, 21) = 1.92, p = 0.12; Condition: F(1,25) = 2.93, p = 0.09; Day by Condition: F(5,21) = 0.32, p = 0.83), Active Waking Period (Day: F(5,25) = 1.53, p = 0.18; Condition: F(1,25) = 0.26, p = 0.61; Day by Condition: F(5,21) = 0.55, p = 0.74) or Nightly Sleep (Day: F(5,21) = 0.86, p = 0.51; Condition: F(1,25) = 1.78, p = 0.19; Day by Condition: F(5,21) = 0.79, p = 0.56) periods. In contrast, there was a main effect of condition when examining sleep duration by day between conditions (Day: F(5,21) = 1.60, p = 0.16; Condition: F(1,25) = 167.31, p < 0.001; Day by Condition: F(5,21) = 2.31, p = 0.07), such that sleep duration was longer during the sleep extension condition. DISCUSSION: Sleep duration increased during six days of a sleep extension protocol but activity levels remained similar to their baseline (normal) sleep schedule. The current findings suggest that extending time in bed alone does not alter waking activity counts in young healthy adults. The link between extended sleep and adverse health outcomes may be attributable to other phenotypic factors, or other biological correlates of extended sleep and poor health.

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.

Effects of caffeine on the human circadian clock in vivo and in vitro.

Caffeine's wakefulness-promoting and sleep-disrupting effects are well established, yet whether caffeine affects human circadian timing is unknown. We show that evening caffeine consumption delays the human circadian melatonin rhythm in vivo and that chronic application of caffeine lengthens the circadian period of molecular oscillations in vitro, primarily with an adenosine receptor/cyclic adenosine monophosphate (AMP)-dependent mechanism. In a double-blind, placebo-controlled, ~49-day long, within-subject study, we found that consumption of a caffeine dose equivalent to that in a double espresso 3 hours before habitual bedtime induced a ~40-min phase delay of the circadian melatonin rhythm in humans. This magnitude of delay was nearly half of the magnitude of the phase-delaying response induced by exposure to 3 hours of evening bright light (~3000 lux, ~7 W/m(2)) that began at habitual bedtime. Furthermore, using human osteosarcoma U2OS cells expressing clock gene luciferase reporters, we found a dose-dependent lengthening of the circadian period by caffeine. By pharmacological dissection and small interfering RNA knockdown, we established that perturbation of adenosine receptor signaling, but not ryanodine receptor or phosphodiesterase activity, was sufficient to account for caffeine's effects on cellular timekeeping. We also used a cyclic AMP biosensor to show that caffeine increased cyclic AMP levels, indicating that caffeine influenced a core component of the cellular circadian clock. Together, our findings demonstrate that caffeine influences human circadian timing, showing one way that the world's most widely consumed psychoactive drug affects human physiology.

Combination of light and melatonin time cues for phase advancing the human circadian clock.

STUDY OBJECTIVES: Photic and non-photic stimuli have been shown to shift the phase of the human circadian clock. We examined how photic and non-photic time cues may be combined by the human circadian system by assessing the phase advancing effects of one evening dose of exogenous melatonin, alone and in combination with one session of morning bright light exposure. DESIGN: Randomized placebo-controlled double-blind circadian protocol. The effects of four conditions, dim light (∼1.9 lux, ∼0.6 Watts/m(2))-placebo, dim light-melatonin (5 mg), bright light (∼3000 lux, ∼7 Watts/m(2))-placebo, and bright light-melatonin on circadian phase was assessed by the change in the salivary dim light melatonin onset (DLMO) prior to and following treatment under constant routine conditions. Melatonin or placebo was administered 5.75 h prior to habitual bedtime and 3 h of bright light exposure started 1 h prior to habitual wake time. SETTING: Sleep and chronobiology laboratory environment free of time cues. PARTICIPANTS: Thirty-six healthy participants (18 females) aged 22 ± 4 y (mean ± SD). RESULTS: Morning bright light combined with early evening exogenous melatonin induced a greater phase advance of the DLMO than either treatment alone. Bright light alone and melatonin alone induced similar phase advances. CONCLUSION: Information from light and melatonin appear to be combined by the human circadian clock. The ability to combine circadian time cues has important implications for understanding fundamental physiological principles of the human circadian timing system. Knowledge of such principles is important for designing effective countermeasures for phase-shifting the human circadian clock to adapt to jet lag, shift work, and for designing effective treatments for circadian sleep-wakefulness disorders.