And now to bed: Sleep and Human Performance (Part 1)

Dr Martin I Jones
5 min read
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Most of us spend around 1/3 of our lives in bed, yet for many people, the requirement for adequate sleep is frequently underestimated and often ignored. Numerous world leaders and celebrity CEOs boast about their need for less than 5 hours of sleep per night, inferring that sleeping less makes them tougher or harder working than their well-slept counterparts. In doing so, they are wearing their restricted sleep as a badge of honour and surreptitiously encouraging their followers and fans to do the same.

The consequences of sleep debt are far-ranging, but broadly speaking, we can conclude that inadequate sleep significantly influences individual performance and health. The data is clear and consistent. Sleep is a fundamental pillar of health and performance (alongside nutrition and exercise). Burning the candle at both ends will not improve your performance.

What happens when we get insufficient sleep?

First and foremost, insufficient sleep results in sleepiness and the propensity to fall asleep unintentionally. Falling asleep while sitting on the sofa is not a problem (unless you are in the middle of a conversation with someone!). However, falling asleep behind the wheel of a car or while operating potentially dangerous machinery can be hazardous for both the inadvertent sleeper and everyone in their proximity.

People who are sleep deprived cannot recognise how impaired they are, and they overestimate their ability to remain alert - the combination of the two can be catastrophic. Being sleep deprived is like drunk driving in many ways. Much as the driver who has consumed a couple of pints will claim to be safe to drive (i.e., they do not recognise their incapacity), the sleep-deprived driver will also believe that they are safe. Unfortunately, subtle cognitive and motor functions, such as reaction time and coordination, are significantly impaired by relatively small amounts of alcohol and sleep deprivation.

From Central Queensland University in Australia, Professor Drew Dawson conducted a series of experiments on sleep deprivation and individual performance. Professor Dawson and his team revealed that relatively moderate levels of sleep-related fatigue impaired performance to an extent equivalent to or greater than is currently acceptable for alcohol intoxication. After 17 hours of sustained wakefulness, individual performance (i.e., hand-eye coordination) decreased to a level comparable to the performance impairment observed at a blood alcohol concentration of 0.05%, the drink-drive level in many western industrialised countries. After 24 hours of sustained wakefulness, performance decreased to a level equivalent to the performance deficit observed at a blood alcohol concentration of roughly 0.10%.

Other short-term sleep deprivation effects include reduced short term and working memory, negative mood, decreased vigilance, and degraded attention. Physically, sleep deprivation appears to exert a more negligible impact when compared to cognitive degradation. Interestingly, the perception of effort is influenced by sleep deprivation, which can manifest when participating in endurance exercise. Simply put, poor sleep might not affect your ability to run or cycle that much; however, the activity will feel harder sooner. Consequently, you will likely slow down or quit before you would have done after adequate sleep. If you are running a half-marathon or a triathlon, make sure you get a good night’s sleep the night before!

If people are habitually sleep-deprived (over many years), they increase their risk of longer-term memory issues, metabolic disorders, and chronic disease (i.e., diabetes, heart disease and some cancers). The mechanism of this effect is not entirely clear. Some suggestions include changes in stress hormone secretion, changes in blood pressure, or the body’s inability to “clear out” waste materials adequately.

What is adequate sleep?

You may have come across a golden figure of eight hours per night. Many people believe that they must get eight hours, and some worry about not getting eight hours. It is essential to recognise that this number (i.e., eight hours) is a population-based average, and consequently, some people will need more, and some will need less. A more useful concept is the range of sleep. Most people will require somewhere between 7-9 hours per night, and this requirement might change on a day-to-day basis because of things like the previous day’s sleep or exercise. People will fall outside of this range, but these “outliers” are in the minority in terms of the population. As an illustration, for most people, five hours per night will be insufficient. It is potentially more valuable to consider how you feel the following day rather than stressing over the exact number of hours (or minutes) that you get. Following adequate sleep, you should feel awake, dynamic, and energetic all day long. Clear signs of inadequate sleep include:

  • Needing an alarm clock to wake you up (and the desire to snooze the clock)
  • Yawning
  • Loss of interest in surroundings
  • Falling asleep unintentionally or microsleeps
  • Slumped posture
  • Vacant stare
  • Clumsiness
  • Irritability
  • Reduced communication
  • Visual illusions and hallucinations
  • Slurred speech
  • Blood-shot eyes
  • Pale skin tone
  • Body sway on standing
  • Failure to complete routine tasks

Some of these signs of poor sleep are extreme. For example, most people will not hallucinate after one poor night. However, it is worth recording the time you go to bed and the time you wake in combination with some of these signs to see whether you are getting the sleep you need. Pay attention to the timings of the signals. You might need more sleep if you are yawning at 1000 after waking at 0700. If you are yawning at 2200, it probably just indicates the need to retire to bed. You can use wearable sleep trackers but keep in mind that these devices only estimate sleep duration. They are not perfect (and, in many cases, not very accurate either). They cannot tell you much about your sleep architecture (i.e., the time spent in different sleep stages) no matter what the advertisements tell you. Take this data with a large pinch of salt!

For the best research based 'top tips' of how to actually how get better sleep, look out for part two in the coming days.

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Dr Martin I Jones