“Sleeping for less than 8 hours per night increases your risk of injury by 70%”

Written by Georgina

Fizzy Lemon Physiotherapy

Did you know that sleep deprivation may cause an individual to perform poorly when they are working out and also lead them to crave unhealthy foods that can promote weight gain?

This blog looks into how sleep deprivation can affect our injury risk, recovery time, our perception of pain and much more.

The stages of sleep:
There are 4 stages in a sleep cycle and each stage can vary significantly between nights andindividuals. During an ideal night’s sleep, your body has enough time to go through 4 to 5 90-minute cycles.
In general, your body goes through a routine sequentially through each of the 4 stages of sleep:

1. Wake – this is the time spent in bed before and after you go to sleep.  You will wake up naturally during the night whether you are conscious of this or not.

2. Light sleep – this is where your muscles may twitch and jerk and you spend about 50% of your time in light sleep.

3. Deep sleep – this is the stage where muscle repair and growth happens and the one we are most interested in exploring during this blog post. It has been shown that blood flow increases to muscles, growth hormone is release and the stage where tissue growth and
cell repair occur (Oura, 2023).

4. REM sleep – this is where dreams occur and your body becomes immobile to stop you from acting out.

Image by Oura Ring

Cycles earlier in the night tend to have more deep sleep whilst later cycles have a higher proportion of REM.

All stages of sleep are important and your body naturally regulates your sleep cycles to make sure you get what you need. The average amount of time each adult needs to sleep is between 7-9 hours. 

Elite athletes vs non-elite/ Performers vs non-performers

on socials makes
us go oooooooh
and ahhhhhh and
wow I wish I was
like them, but,
did you know
that elite
athletes get on
average 1.5 hours
less sleep
than us?

In a study by Lastella et al (2015) and Leeder et al (2012), it was shown that elite athletes get less total sleep than non elite, with elite being reported to only sleep 6.5 hours per night.

Furthermore, when they do obtain an adequate sleep time of at least 8 hours they found itharder than non-elite to fall asleep and had a lower quality of sleep. This can be due to several reasons:

  • Athletes often have rigorous and strict training schedules
  • Travel obligations
  • Time zone changes
  •  Athletes may downplay the importance of sleep and may consider it less important to
    other aspects of their mandatory training
  • Stress/anxiety in the lead up to a big event

A small section of super nerdy stuff

Effects of lack of sleep

Lack of sleep can affect a huge variety of factors.  There is well documented evidence that lack of sleep can have an impact on:

  • Brain function – this includes judgement and/or decision making.
  • Food – sleep deprived individuals often crave unhealthy foods. A study by Morselli et al
    (2012) noted that there is also impaired glycogen repletion and protein synthesis. Sleep deprivation shows an increase in pro-inflammatory cytokines (these are molecules that are secreted from immune cells to regulate growth, cell activation, differentiation and homing of the immune cells to sites of infection) … basically this means that you’re more prone to risk of developing an illness.
  • Impedes muscle recovery and repair from damage.
  • Stimulates overtraining symptoms.
  • Alters pain perception.
  • Results in slower/less accurate cognitive performance
    Vitale et al (2019).

Effects of sleep on accuracy and reaction times

Sleep deprivation/restriction has been consistently shown to impair accuracy in athletic events
whereas accuracy has been found to improve after sleep extension.

  • A single night of 5 hours of sleep in tennis players was associated with a decrease in
    serving accuracy of up to 53% compared with a normal night’s sleep (Reyner and Horne,
    2013). Another study found that a sleep extension of 1.6hours improved serving
    accuracy between 36-41% (Schwartz, Simon, 2015).
  • A study of 29 adolescent student-athletes found decrease sleep time on weekdays than weekends, with accumulated sleep dept through the week was associated with worsening reaction times by the end of the week (Suppiah, Low, Chia, 2016)
  • A 2011 study on a male basketball team increased their sleep from 6.6 hours per night to 8.5 hours per night over a 5-7 week period and found an improvement in throwing accuracy of 9% in free throws and 9.2% in 3 point field goal, with significant improvement in psychomotor vigilance tasks (Mah et al, 2011)

Sleep is critical for your brain to focus and learn. Have you ever gone to class tired and been watching the instructor demonstrate, but, once they stop you have absolutely no retention of what they did?

Well, sleep actually helps you in 2 ways:

  • A sleep deprived person cannot focus attention optimally and therefore cannot learn efficiently.
  • Second is the ability to learn, memorise, retain and recall.

The ability to learn is broken down into 3 components:

1. Acquisition – this refers to the introduction of new information to the brain

2. Consolidation – this represents the process by which a memory becomes stable

3. Recall – this refers to the ability to access information after it has been stored.

Each of these steps are necessary for proper memory function (Division of Sleep at Harvard Medical School, 2007).

More super nerdy stuff!

When learning facts and information, most of what we learn is temporarily stored in a region of the brain called the hippocampus. Some scientists hypothesise that , like most storage centres, the hippocampus has limited storage capacity. This means, if the hippocampus is full, and we try to learn more information, we won’t be able to.

Fortunately, many scientists also hypothesise that sleep plays a role in replenishing our ability to learn. In one study, a group of 44 participants underwent two rigorous sessions of learning, once at noon and again at 6:00 PM. Half of the group was allowed to nap between sessions, while the other half took part in standard activities. The researchers found that the group that napped between learning sessions learned just as easily at 6:00 PM as they did at noon. The group that didn’t nap, however, experienced a significant decrease in learning ability.

How is this relevant to circus skills!?

Errrrm don’t most of us either go to classes in the evening after work/attend whole day workshops such as MAC or flow festivals/ go on camps with multiple lessons per day?

This is totally relevant to you!

Now the controversial part! If you struggle with sleeping consistently through the night, it is recommended that you do not nap during the day. If you are a chronic nap goblin like my mother who can fall asleep anytime, anywhere, then theseare fun facts you might want to take forward in the future.

Now the juicy bit that you are here for!

Sleep, injury, and illness
Studies have shown that those who slept less than 8 hours per night were 70% more likely to get an injury compared to those who slept more than 8 hours! (Milewski et al, 2014 ; Watson,


It is also well documented that an increased risk of injury occurs when training load increases and sleep duration reduces simultaneously – this is often seen in competitive travel and training camps (von Rosen etal, 2017) and is really important information for performers who often are away from home for weeks on end doing huge corporate gigs late into the evening.

Interestingly, lots of research has also been carried out on sleep deprivation and illness:

  • When suffering with the common cold, those who slept for less than 7 hours over a 5
    day period were 3 times more likely to develop an infection compared to those who
    slept for 8 hours.
  • Those who slept for less than 5 hours over a 7 day period and has complaints of a common cold were 4.5 times more likely to develop an infection (Prather et al, 2015)

When you sleep, you’re giving your body time to repair and recover from the day’s activities. The first reason relates to blood flow. As you fall into the deeper stages of sleep, your muscles will see an increase in blood flow, which brings along oxygen and nutrients that help recover and repair muscles a regenerate cells.

Hormones pay a role too. When the body enters its deep sleep stage, the pituitary gland releases growth hormones that stimulate muscle repair and growth. When the body doesn’t get enough rest, the secretion of this growth hormone declines, and it can become harder for your body to recover from injury. The hormone prolactin, which helps regulate inflammation is also released while sleeping, meaning that if you don’t get enough sleep, you’re likely to have more inflammation in the body. (Gunning, 2001 ; Nadler et al, 2003 ; Basta et al, 2007).

We know that when we are unwell, generally we naturally tend to sleep more to allow the body
more time to recover from our illnesses, but we don’t consider this if we sustain an injury??

Is this something that should be considered more?

Sleep and pain

Having a niggly shoulder that won’t recover, maybe you should explore your sleeping habits?

Sleep complains are present in 67-88% of persistent pain disorders. Studies have shown that patients who experience acute pain post operation show shortened and fragmented sleep with reduced amounts of REM sleep (Rohers and Roth, 2005).

Studies have shown that individuals suffering with chronic pain have recurrent awakenings during the night and spent longer awake during these awakening than individuals without pain (Mathias et al, 2018). It has also been shown that sleep deprivation can increase a hyperalgesic response (an abnormal increase in sensitivity to pain) (Schuh-Hofer et al, 2013), with authors noting that shorter sleep duration and poorer quality of sleep predicted higher morning pain intensity. However, evening pain did not predict nighttime sleeping pattern, suggesting that sleep deficiency, as opposed to late night pain, is more related to next day pain (Lewandowski et al, 2017).

Overall sleep has a huge impact on a massive variety of factors in our lives, so what can we do to improve this?

Napping – Studies have show that athletes may benefit from sleep supplementation in the form of napping (Halson, 2008). Research has demonstrated that napping at lunch time for 30 minutes after experiencing partial sleep loss (4 hours less than usual), significantly improved performance in 20m spring performance, alertness and reduced the feeling of sleepiness (Waterhouse et al, 2007). From an athletic perspective, the authors suggest that napping is of potential benefit to athletes during training and in a competitive environment, especially in athletes experiencing sleep deprivation.

Sleep extension – A study conducted on the Stanford University men’s varsity basketball team, under the assumption that the majority of collegiate athletes carry a sizable sleep debt (sleep deprivation), had 11 players obtain extra sleep with a goal of 10 hours per day for a 5- to 7-week period. The players were found to have significantly enhanced basketball performance in all measures after habitual sleep extension. Total sleep times increased (110.9 ± 79.7 minutes), and the players demonstrated faster sprint times (282-ft sprint: 16.2 versus 15.5 seconds) and shooting accuracy in both free throws out of 10 (7.9 versus 8.8) and 3-point shots out of 15 (10.2 versus 11.6). Players also reported improved alertness and mood, and less sleepiness and fatigue, leading the investigators to conclude that optimizing sleep need through sleep extension has a positive impact on basketball athletic performance (Mah et al, 2011.


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