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The impact of sleep loss on total fitness

A significant factor that Warfighters have to face in attempting to achieve total fitness is getting enough sleep to prevent dangerous fatigue, which can impact many aspects of fitness.


Sleep affects almost every aspect of Total Force Fitness and is an important factor for total fitness. No one can do without sleep, and many Warfighters have trouble getting enough, especially when deployed. Sleep affects cognitive skills, ability to handle stress, relationships with others, and physical and nutritional conditioning.


Most individuals need seven to eight hours of sleep at night to function optimally for maximum alertness.10,11 The body cannot be trained to need less sleep than the normal. Although there are individual differences in sleep needs, there are no “superheroes” who can get by on no sleep at all, and everyone who sleeps only four to five hours of sleep each night will experience some loss of performance.

HPRC has already examined the basic sleep needs of Warfighters in “How Much Sleep Does a Warfighter Need?” Additional background information can be found there. However, the focus of that earlier article is on cognitive alertness, operational strategies and how to compensate for lack of sleep. The intent here is to examine how sleep loss affects aspects of Total Force Fitness.


Misconceptions about sleep are covered elsewhere on the HPRC website, but in short, despite claims to the contrary:

  • You can’t go without sleep or with very little sleep for long without serious detriment to your physical and mental performance.
  • You can’t train your body to need less sleep over time.

Nevertheless, the warrior myth sometimes persists that one can function on little sleep, plenty of caffeine, and self-sustained hyper-vigilance.1


Some individuals can function reasonably well on little sleep for short durations (i.e., one night of restricted sleep), particularly with the aid of caffeine or other stimulants, but even their performance is impacted to a measurable extent. Although the generally detrimental effects of sleep loss on cognitive and work performance are widely appreciated, the specific effects of sleep loss are less commonly widely known.  These include the following:

Mind Tactics: Not getting enough sleep certainly has serious impact on how and what you think including decreased working memory, ability to concentrate, situational/battlefield awareness, focus, slowing of responses and response time.2,3 Moreover, sleep loss reduces your ability to make good decisions2 and increases the tendency to be distracted by emotional stimuli.4 Specifically, it severely compromises the ability to think positively and problem solve.

Stress Management: Sleep loss has been found to reduce the ability to control one’s impulses, delay gratification, and make mature and sound moral decisions.5 These are key factors in managing stress well, because one’s ability to make good decisions that could reduce one’s stress over the long term can be compromised in times of stress.

Relationships: Sleep loss hinders one’s ability to accurately interpret the emotions of others and identify what one is feeling—specifically, the ability to interpret anger and happy facial expressions.6 It also lowers the ability to interact effectively with those around you and to communicate effectively.2 Therefore, sleep loss can decrease one’s ability to understand where others are coming from (i.e., to empathize and comprehend what they are expressing) and reduce one’s ability to maintain good relationships.7

Exercise: It is commonly thought that exercise could help prevent the effects of sleep loss, however it only decreases the perception of sleepiness and fatigue for one hour after exercise and does not seem to mitigate actual performance losses throughout the day.8 Although regular exercise (both strength training and high-intensity endurance) does improve sleep quality9, it is not an antidote to replace the sleep debt incurred from sleep loss—only sleep and napping strategies will do that. Sleep loss reduces physical performance primarily by reducing the motivation to engage in physical exercise as the effects of sleep loss on strength and endurance are relatively minimal.

Dietary Supplements: Caffeine. Since sleep loss causes decrements in performance, some turn to products containing caffeine and other sleep aid dietary supplements. It is well recognized that caffeine increases alertness and may delay some aspects of fatigue during extended operations. However, the effective dose may vary, depending on habitual caffeine intake and sensitivity to caffeine. Caffeine is less effective for those who routinely consume large amounts. Caffeine-rich beverages and foods are among the most popular forms of nutrition to help Warfighters maintain alertness at night. However, most products containing caffeine do not list amounts of caffeine on Nutrition Facts Labels. It is important to find out the benefits and risks associated with any dietary supplement. For more detailed information, the HPRC has monographs on Caffeine and Energy Drinks & Energy Shots.

Environment: When to sleep is dictated by circadian rhythms regulated by the brain on a 24-hour basis.10-12 Circadian rhythms are linked to core body temperature, so nightly sleep should include the optimal sleep hours between 0300 and 0500, when core body temperature is lowest, sleepiness is greatest, and performance abilities are minimal.  Also, one’s individual circadian schedule is on local time because environmental cues such as sun and social patterns drive the rhythm. When crossing time zones, the circadian clock needs time to adjust, which can take from several days. Factors that influence this adaptation are how many time zones are crossed and whether flying eastbound or westbound; taking an eastward flight takes longer to acclimate than a westbound flight. For example, maximum sleepiness is 0300 to 0500 and from 1300 to 1500. If sleep needs to be made up or circadian rhythms adjusted due to travel, sleeping or napping during these key hours is optimal.


No one can function on just a few hours of sleep a night over time. With total sleep deprivation, performance typically declines by 25 percent every 24 hours (depending on the type of performance) being measured.19 Sleep loss impacts multiple performance areas, as described above; therefore, an understanding of its overall impact is important for total fitness.

Be aware of additional factors that can impact sleep, such as sleep apnea or PTSD. Also, there is evidence that not getting enough sleep could be linked to weight gain.13

Finally, although regular exercise can help a person sleep, it is important not to exercise vigorously too close to bedtime. Try not to work out within three hours of when you want to fall asleep for the night.

Summary of Military Relevance

A 2009 survey14 reported that not getting enough sleep was the number one concern among deployed Warfighters—expressed by roughly one-third of those surveyed. It also revealed that sleep loss remains a challenge, as these levels have not improved since previous surveys from 2006-2009.15-17 In addition, deployment has an impact on sleep quality; Warfighters who have experienced combat have more trouble sleeping—during and after deployment—than those who have not deployed.18 Clearly, it is an issue that needs serious consideration. Note that many studies report that the performance decrements resulting from sleep loss disappear once sleep is recovered.6 Additionally, emerging research suggests that it might be possible to bank sleep ahead of time prior to sleep loss. Banking sleep prior to sleep loss may mitigate some of the performance decrements caused by sleep loss, help with alertness and speed recovery – all important factors for operational environments.20 The main strategy for banking sleep ahead of time is to protect sleep time -i.e., make it a priority.  Sleep experts do NOT recommend that individuals try to bank sleep by using sleep-inducing agents since that strategy has not been tried. Of note is that naps also contribute to daily total sleep time so long as the individual actually sleeps (as opposed to just "rests") during the nap period. Finally, most important is to simply avoid accumulating a sleep debt that will have to be paid off.  Obtaining sufficient time asleep on a daily basis is the BEST way to maintain long-term optimal operational readiness.

Sleep is so important to Warfighter fitness that HPRC has dedicated an entire section of its website to Sleep Optimization. It includes extensive resources to help Warfighters get the sleep they need to pursue total fitness. Check it out.


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  6. vanderHelm E, Gujar N, Walker MP. Sleep Deprivation Impairs the Accurate Recognition of Human Emotions. Sleep. 2010;33(3):335-42.
  7. Killgore W, Kahn-Greene E, Lipizzi E, Newman R, et al. Sleep deprivation reduces perceived emotional intelligence and constructive thinking skills. Sleep Medicine. 2008;9:517-26.
  8. LeDuc PA, John A. Caldwell J, Ruyak PS, Prazinko B, et al. The Effects of Exercie as a Countermeasure for Fatigue in Sleep Deprived Aviators. Fort Rucker, Alabama: U.S. Army Aeormedical Research Laboratory; August 1998 1998.
  9. Roveda E, Sciolla C, Montaruli A, Calogiuri G, et al. Effects of endurance and strength acute exeercise on night sleep quality. Internaional SportMed Journal. 2011;12(3):113-24.
  10. Rosekind MR, Boyd JN, Gregory KB, Glotzbach SF, et al. Alertness Management in 24/7 Settings, Lessons from Aviation. Occupational Medicine: State of the Art Reviews. 2002;17(2):247-59.
  11. Rosekind MR, Gander PH, Gregory KB, Smith RM, et al. Managing Fatigue in Operational Settings 1: Physiological Considerations and Countermeasures. Behavioral Medicine. 1996;21(4):157-65.
  12. Rosekind MR, Gregory KB, Mallis MM. Alertness Management in Aviation Operations: Enhancing Performance and Sleep. Aviation, Space, and Environmental Medicine. 2006;77(12):1256-65.
  13. St-Onge M-P, Roberts AL, Chen J, Kelleman M, et al. Short sleep duration increases energy intakes but does not change energy expenditure in normal-weight individuals. American Journal of Clinical Nutrition. 2011;94(2):410-6.
  14. Office of the Command Surgeon U.S. Forces Afghanistan (USFOR-A), Office of the Surgeon General United States Army Medical Command. Mental Health Advisory Team (MHAT) 6, Operation Enduring Freedom 2009 Afghanistan 6 November.
  15. Office of the Command Surgeon, Office of the surgeon General United States Army Medical Command. Mental Health Advisory Team (MHAT) V, Operation Iraqi Freedom 06-08: Iraq, Opration Enduring Freedom 8: Afghanistan. 2008:223.
  16. Office of the Surgeon Multi-National Corps-Iraq, Office of the surgeon General United States Army Medical Command. Mental Health Advisory Team (MHAT) VI, Operation Iraqi Freedom 07-09. 2009:92.
  17. Office of the Surgeon Multinational Force - Iraq, Office of the Surgeon General United States Army Medical Command. Mental Health Advisory Team (MHAT) IV, Operation Iraqi Freedom 05-07 Final Report 17 November 2006.
  18. Seelig AD, Jacobson IG, Smith B, Hooper TI, et al. Sleep Patterns Before, During, and After Deployment to Iraq and Afghanistan. Sleep. 2010;33(12):1615-22; S1-S4.
  19. Belenky G, Wesensten NJ, Thorne DR, Thomas ML, et al. Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose-response study. J Sleep Res. 2003;12(1):1-12. PMID: 12603781
  20. Rupp, T., Wesensten, N., Bliese, P., & Balkin, T. (2009). Banking sleep: Realization of benefits during subsequent sleep restriction and recovery. Sleep, 32(3), 311-321.


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