Understanding Sleep Debt: Impact on Performance and Recovery

‘Sleep debt’ is more than a term for feeling fatigued after getting a poor night’s sleep a couple days in a row. It describes the real phenomenon of consistently not getting enough sleep on a nightly basis, and the negative impact it can have on overall health. 

The CDC reports that at least ⅓ of adults don’t meet ideal recommendations for nightly sleep. When balancing a busy schedule, rest is often sacrificed to make time for other pursuits. The effects of sleep deprivation are compounded when poor sleep habits become the norm. Forgoing rest on a long-term basis can negatively impact both physical and mental health. The toll sleep debt takes on the body can make achieving peak performance and promoting proper recovery much more difficult. Data from WHOOP research can lend further insight into the relationship between sleep debt and various performance metrics. 

Defining Sleep Debt

Every individual has an optimal number of hours of nightly sleep they should aim to get on a regular basis. The ideal number of hours can vary based on factors such as lifestyle, activity level, and health conditions. This ideal number is how much nightly rest your body needs to recover and function properly during the waking hours. 

When you get less sleep than you ideally need, you begin to accumulate a sleep debt. Think of sleep debt as the difference between how much sleep your body needs and how much sleep you actually get. If your optimal sleep amount is 7 hours a night but you only sleep for 3 hours, you’ll have a sleep debt of 4 hours for that one night. It’s important to note that sleep debt is cumulative.

Sleep expert Dr. Allison Brager uses this analogy to explain sleep debt: “We think of sleep as a bank account: The more you take out, the more you have to repay.” If you continue to get less sleep than you need, you’ll continue adding hours to your total sleep debt — and make it that much harder to catch up on your total sleep need.

Common Causes of Sleep Debt

Getting enough sleep on a nightly basis is challenging. There are several factors that can make it even more difficult, and contribute to the accrual of sleep debt. These include:

• Sleep disorders — There are multiple sleep disorders that can result in sleep deprivation. Sleep apnea, narcolepsy, insomnia, and restless leg syndrome are all examples of conditions that can get in the way of sleeping through the night and getting enough quality sleep.
• Stress — High stress levels are notorious for disrupting a good night’s sleep. If you’re having trouble managing your worry and stress, it’s more likely to keep you up at night. Racing thoughts and anxiety are common obstacles to restful sleep. Sleep deprivation can also increase stress levels, indicating a bidirectional relationship between stress and lack of sleep.
• Poor nightly routine — Poor sleep hygiene and a suboptimal nightly routine can contribute to sleep deprivation. Factors such as sleeping in a warm, uncomfortable environment, consuming alcohol or caffeine close to bedtime, scrolling on your phone or computer before going to sleep, and a lack of exercise during the day are all examples of lifestyle choices that can cause sleep debt.
• Health conditions — Certain medical issues and health conditions are associated with sleep difficulties. For example, pregnancy, chronic pain, diabetes, thyroid conditions, heartburn, cancer, head injuries, and Alzheimer’s disease have all been linked to trouble sleeping. Individuals with mental health conditions including depression, schizophrenia, and anxiety disorders also commonly report sleep problems. 

Sleep Debt Demographics

While sleep debt can affect anyone who fails to get enough nightly sleep, research has examined whether certain demographic groups are more likely to deal with sleep deprivation. Women are more likely to deal with sleep deprivation than men, and are more likely to have sleep disorders. Older adults can find sleeping more difficult due to increased prevalence of medical issues, as well as a general trend of declining sleep efficiency and duration. 

Work and daily responsibilities can also impact the likelihood of experiencing sleep debt. Individuals who complete shift work, like working nights, early opening schedules, or alternating between varying shifts, are more likely to be sleep deprived.

These atypical work schedules can lead to disruptions in the sleep-wake cycle and disturb the body’s natural circadian rhythm, making it tough to meet daily sleep requirements. Caregiving responsibilities, such as parenting or caring for the elderly, can also get in the way of regular uninterrupted sleep and increase the incidence of sleep deprivation. 

The Effects of Sleep Debt on Performance

Sleep has a major impact on both physical and mental performance. On the WHOOP Podcast, VP of Performance Kristen Holmes and SVP of Data Science & Research Emily Capodilupo dove into this topic, stating that, “A lot of people have no idea how sleep deprived they are and they have no idea how it’s affecting things because it becomes so normal. You lose that self awareness.”

Sleep deprivation is a serious issue when it comes to performance, but this widespread phenomenon is often overlooked because not getting enough sleep is just accepted as the status quo. 

WHOOP data focusing on chronic sleep deprivation has found a link between sleep debt and an overall reduction in HRV. With regular sleep deprivation, the sympathetic nervous system becomes hyper-activated and a global stress response is triggered throughout the body. There is a resulting imbalance between the sympathetic and parasympathetic branches of the autonomic nervous system, leading to a drop in HRV. 

HRV is a key metric in determining the body’s readiness to perform. Thus, low HRV indicates that the body will struggle to perform at a high level. Sleep debt makes tapping into vital training skills like endurance and strength more difficult, and makes it harder to sustain gains in these areas. In addition, sleep deprivation increases injury risk. 

Sleep debt isn’t just detrimental to physical performance. Not getting enough sleep on a regular basis will also impact cognitive function. In a 2021 WHOOP study, participants exhibited a 5-10% decline in both executive function and cognitive control after accruing just 45 minutes of sleep debt. Sleep deprivation impairs decision-making abilities, general cognition, and reaction time. 

WHOOP research also found that for every additional 30 minutes of slow wave or deep sleep, individuals experience a gain of 5-10% in mental control the following day. This indicates that while sleep debt can seriously impact mental performance, increasing sleep duration can improve cognitive function. Small changes in sleep duration can affect mental acuity and key cognitive skills, like making decisions and focusing on tasks.

Understanding Sleep Debt in Recovery

According to findings from WHOOP research, chronic sleep deprivation results in poorer recovery. This is not surprising, given the wealth of research into how sleep supports physiological recovery and repair processes throughout the body. During sleep, muscles are repaired, growth hormones are released, key proteins are produced, and tissue growth occurs. Experts theorize that sleep plays an important role in restoring physiological stores that allow essential biological processes to unfold during the waking hours. 

Studies have demonstrated that sleep deprivation impedes muscle repair after muscular injury and hormonal and inflammatory processes associated with recovery following exercise. Research has also consistently found a link between sleep deprivation and muscular injuries in athletes. 

During training and physical exertion, natural wear occurs in the muscles in the form of microscopic tears. Ideally, this muscular damage is repaired during sleep as tissue repair and regeneration occurs in order to facilitate proper recovery.

When sleep duration or quality declines, recovery processes are slowed or disrupted, leading to reductions in overall healing and muscle growth. Sleep debt increases vulnerability to new muscular injuries, and makes recovering from existing ones much harder. 

Mitigating Sleep Debt

Ignoring the consequences of sleep debt might be tempting in the short-run, but the harmful effects of not getting enough nightly sleep will quickly catch up with you. The best way to get out ahead of these negative effects is to take a hard look at your relationship with sleep and start to incorporate healthy sleep hygiene strategies into your routine. Here are some practices that can be beneficial in mitigating sleep debt:

• Aim for Sleep Consistency — Recent research into sleep habits indicates that sleep consistency may be even more beneficial than efforts to increase total sleep duration. To capitalize on the benefits of sleep consistency, try to go to bed and wake up at the same time every day. That means keeping sleep and wake times consistent throughout the weekend too.
• Avoid Sleep-Disrupting Habits — There are a variety of lifestyle habits that can disrupt sleep. For example, long afternoon naps, large meals close to bedtime, evening alcohol and caffeine consumption, and screen time before closing your eyes are all known to negatively impact sleep. Try replacing these habits with more sleep-friendly practices, like yoga, meditating, taking a bath, reading, journaling, or listening to your favorite calming music.
• Optimize Sleep Environment — A poor sleep environment can easily lead to sleep problems. An ideal sleep environment is cool, dark, and free of loud, distracting noises. Investing in a comfortable mattress and bedding can also be helpful. Keeping your room clean and free of extra clutter is also a good idea.
• Prioritize Sleep — This strategy is simple: make sleep a priority. If you’re searching for health resolutions, add “prioritize sleep” to the top of the list. Setting aside extra time for sleep can be a daunting task when you’re trying to fit in time for work, family, and training, but there’s no way around it: sleep is important. If you really want to make a difference in your performance in all areas of your life, avoiding sleep debt is a must.

Track Your Sleep Habits with WHOOP

Sleep debt impedes optimal mental and physical performance, and compromises the body’s ability to recover from exertion and daily activities. Sleep debt is linked to lower HRV and poorer recovery metrics. Cumulative sleep debt can take days or weeks to recover from with adjustments to sleep duration, sleep consistency, and sleep hygiene habits. The best way to avoid the lingering effects of sleep debt is to prioritize sleep and meet your optimal sleep needs in the first place.

The amount of sleep an individual needs varies. Fortunately, WHOOP makes calculating your individual sleep need and tracking your sleep habits simple. WHOOP determines how much sleep your body needs in order to support peak performance by drawing on several factors, including sleep baseline, daily strain, and sleep debt.

With the WHOOP Journal, you can also keep a record of healthy sleep habits, like keeping your sleep/wake times consistent or trying different relaxing activities before bed. You can rely on WHOOP to better understand and manage your individual sleep habits to unlock improvements in performance and recovery.