The quest for an advantage in high performance sports starts well beyond the baseball diamond, basketball court or football field. In fact, performance advantages in professional sports leagues like the NFL, NBA, EPL and MLB are often a product of knowledge first gleaned from military research.

Much like professional sports teams but with significantly higher stakes, the military, particularly the most elite units, take deep stock of human performance, timing and measuring everything, from strength to endurance to cognition. Among the most important factors? Using technology to measure and predict sleep and fatigue, a practice increasingly finding its way into high performance sports.

Neglecting sleep, or even slightly changing established patterns, particularly before a big game, can have predictable, far reaching effects on the human body. In fact, fatigue caused by a lack of sleep has similar effects to drugs and alcohol, significantly impairing cognitive function. But unlike drugs and alcohol it’s been almost impossible to accurately screen for fatigue impairment. A soldier or an athlete or anybody, can be significantly fatigued with almost no outward signs whatsoever. However, as wearable sleep technology leaps from military labs and into locker rooms, the performance advantages of sleep and fatigue measurement are having an indelible mark on high performance athletics.

Sleep plays a key role getting athletes ready to compete and has a direct, measurable, and in fact highly predictable effect on player performance. Understanding this can help with daily decisions around training, peak performance periods and in identifying sudden or chronic sleep issues.     

SAFTE: From the Department of Defence to the Major League Champions  

Tasked with understanding the effect of disrupted sleep on critical operations, the US military’s brightest minds devised a biomathematical model that simulates the effects of sleep loss on mental effectiveness. This model, called SAFTE (Sleep, Activity, Fatigue, Task, Effectiveness), is the result of millions of dollars in investment and 25+ years of applied research. Today, SAFTE remains the working fatigue model for the US Department of Defence. In combination with wearable technology it’s also a part of the winning formula for the Super Bowl Champion Seattle Seahawks and the MLB World Series Champions the Chicago Cubs.


Mental vs. physical fatigue

Fatigue is about reduced alertness, reaction time, and effectiveness—all of which manifest in the form of sub-optimal athletic performance. Cognitive fatigue happens when activities fall outside of specific, biological needs to consistently sleep at night and be active in the day. This is not the same as fatigue resulting from physical exertion.

Cognitive fatigue and physical fatigue are very different but can co-exist. While there’s very little evidence that bursts of physical exertion impact judgment or reaction time, research does support the influence of the psychological over the physical.

Those who routinely obtain less than 7-9 hours of sleep per 24-hour period will have a high homeostatic drive for sleep as the body struggles to restore balance. In professional sports, scheduling inconsistencies often compel athletes to sleep at the wrong times of day, which can lead to sleep-initiation problems at night.

When athletes lose sleep, when they’re unable to stick to consistent schedules due to travel or social engagements, and when they have to train in a new time zone, they’ll be faced with both a high homeostatic and a high circadian drive for sleep. This results in impaired judgment, reaction time, and situational awareness—the hallmarks of poor mental effectiveness. And at the highest levels of sport, it’s no secret that winning is at least as much mental as it is physical.

Unfortunately, athletes can’t train homeostatic and circadian requirements to tolerate stress like they can train cardiovascular organs, the respiratory system, and muscle groups. Sleep deprivation or circadian desynchronization cuts into the cognition and effectiveness of every human being, whether they’re physically tired or not. And when athletes are deprived of sleep, performance suffers.

Athlete alertness is influenced by three main sleep factors

Sleep debt (quantity of sleep)

To function in top form, athletes must clock 8-9 hours of sleep every 24 hours. Consistently coming up short (an hour here or there), creates sleep debt, and the more of a deficit, the harder it is to recover, balance, and excel. In elite team environments, creating adequate opportunity for players to get optimal sleep is difficult due to travel, training and game schedules, not to mention media, promotional and social activities. The science is clear though—the more sleep debt, the less alert athletes will be.

Sleep/ wake timing (consistency of sleeping and waking relative to diurnal pressures)

It’s not just how much sleep athletes get but the consistency of when sleep is obtained. When humans cooperate with diurnal nature to sleep at night and be active during the day, the restorative value of sleep is maximized, and the quality of waking performance is optimized. From a homeostatic standpoint, the longer someone is awake, the greater the pressure to sleep. But when an athlete’s opportunity to stick to a sleep/wake routine is disrupted by travel, late games or other commitments, it’s not only waking performance that will be affected—nighttime sleep will be impacted as well.

Time of day (the influence of our circadian rhythm)

Assuming an athlete sleeps well for eight hours from 11pm to 7am, throughout the coming day, their reaction time will vary up to 10% as they experience troughs and peaks in alertness. These natural troughs and peaks are a well-rested daytime baseline—an ebb and flow of cognitive effectiveness based mostly on circadian factors. Circadian factors influence athletic performance to such a degree that, based on 40 years of win-loss data, west coast NFL teams have proven dominant when playing evening games on the east coast.

It’s tough to influence the time games are played, but to some degree, athletes and trainers can influence and take advantage of the timing of daily circadian peaks. When viewed as an ecosystem of either preparedness or unpreparedness, it becomes clear that sleep loss and circadian disruptions significantly impact competitive edge.

What else is sleep influencing in athlete performance?

Sleep deprivation doesn’t just reduce reaction time and decision-making ability. It impairs immune functions, physical and psychological performance, motivation, memory consolidation, and increases risk of injury, anxiety, stress, and a rise in ammatory markers. Sleep loss also affects appetite regulation, predisposing people to weight gain and increased body fat.

Even though physical fatigue has little to no impact on mental alertness, the reverse is true—mental fatigue has a great deal of impact on physical performance. An athlete who sleeps consistently well will demonstrate high cognitive effectiveness even when physical energy has been temporarily depleted.

Athletes with insufficient sleep will still be able to run, lift weights, and perform with basic capacity and resilience. But their time to physical exhaustion will be shorter, their perception of exertion and endurance distorted, and their motivation, judgment, alertness, decision-making, and situational awareness impaired. And all of that is very difficult to detect, with coaches and athletes often completely in the dark about their fatigue levels. This is what more than 25 years’ of military research tells us: although mental and physical fatigue are not directly linked in a mechanical or biological way, the two are intertwined.

Methods for measuring and monitoring sleep

To begin to understand sleep’s influence on team performance, it needs to be measured, which is not as easy as many claim. In sleep and fatigue research, there are three common ways to measure sleep:

Polysomnography (PSG)

The gold standard, PSG is the most comprehensive, most reliable form of sleep measurement. It involves subjects sleeping in a lab where various physiological functions are monitored. 100% accurate


By capturing body movement via a wrist-worn device, actigraphy is a non-invasive method of measuring sleep/wake patterns. 93% accurate when using the scientifically validated Fatigue Science Readiband.


A low-tech substitute is diary-keeping. This strategy relies on an individual’s ability to estimate or recall their own sleep patterns. 50-60% accurate—most respondents overestimate their sleep by as much as 70 minutes/night.

Consumer sleep devices
Recently a flood of consumer-grade wearables have sprung up claiming to accurately measure sleep. And while many serve valuable functions, experts agree that most are not accurate at all for measuring sleep.

While Polysomnography is the most accurate way to measure actual sleep obtained, it’s not practical in an elite team environment. Self reporting and consumer grade wearables are not reliable enough. Actigraphy, on the other hand, is simple, cost-effective, and practical. What’s more is that recent developments in the use of wearable technology allow large teams outside the military to seamlessly monitor fatigue. That means accurately measuring and predicting in real time when athletes will be fatigue impaired and at their worst or when they’re sharp and ready to perform their best.

From US Army special operations to NFL wide receivers, fatigue impacts everyone. With clients in the NFL, MLB, NBA, NCAA, NHL and in elite sports around the world, Fatigue Science is committed to working with researchers, athletes and coaches to further open new frontiers in human performance.