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The Role of Sleep In Recovery

Introduction:

First of all, some sleep facts regarding athletes.

Sleep is critically important for athletes as shown by research of 175 elite athletes performed by Swinbourne et al. 2016. The study found 50% of the athletes investigated presented as "poor sleepers". In addition 28% of these athletes also reported clinically significant daytime sleepiness. Furthermore injury is strongly associated with lesser hours of sleep per night, this will be discussed later in the post.

Secondary, for athletes, recovery is a critical part of the training adaptation cycle known as 'super-compensation' or general adaptation syndrome. This process defines training adaptation to occur in a phases in which the training stimulus induces fatigue to which reduces performance below the pre-established level. The up-side however comes through the recovery process enabling a dramatic 'super-compensation' in ability by stimulating the appropriate changes to our physiology to take us to a greater level of performance than previously experienced (This process is highlighted below).

 Image 1 - The General Adaptation Syndrome (Super-compensation cycle).

Image 1 - The General Adaptation Syndrome (Super-compensation cycle).

Given that recovery is a critical part of this process, it is in endurance athlete's best interest to maximise the methods responsible for enhancing the recovery process. The number 1 contributor to the recovery process is sleep. 

The Science of Sleep:

To master sleep we need first need to understand the science behind it and there is no better place to start than with the Circadian Rhythm.

Otherwise known as the "Body Clock" the Circadian Rhythm is the natural fluctuation of hormones within the body reacting to our external environment to create a sensation of feeling sleepy. This feeling then places us into a state of repair and recovery we call sleep. This natural sleeping pattern is based upon how much light enters a sensory receptor in the brain called the Suprachiasmic Nucleus.

When a high amount of light is sensed the "Circadian Drive" or "Wake Drive" initiates to cause us to awake or stay awake. It is when the amount of light sensed is lowered and or the stimulus is removed the body begins to initiate the "Sleep Drive" or "Adenosine" mechanism involving in which the hormone Melatonin is released. Melatonin causes us to feel sleepy and ultimately higher doses of melatonin will drive us into a sleep state. However this process then reverses and our wake drive re-initiates allowing us to wake up. No surprises that the wake drive peaks just after sunrise when the Suprachiasmic Nucleus senses a high amount of light.

 Image 2 - The Suprachiasmic Nucleus (Source: Science for Sport)

Image 2 - The Suprachiasmic Nucleus (Source: Science for Sport)

 Image 3 - The Melatonin response to light source throughout the day. (Source: Science for Sport)

Image 3 - The Melatonin response to light source throughout the day. (Source: Science for Sport)

 Image 4 - The Circadian and Adenosine Drive patterns. (Source: Science for Sport)

Image 4 - The Circadian and Adenosine Drive patterns. (Source: Science for Sport)

We must remember that this is a natural process and that humans have evolved with this rhythm ingrained within our physiology. Over the duration of a 24-hour period we experience the fluctuating sleep and wake drives as a process called the 'Recycle Rate'. This is the natural rate at which we sleep and are awake over a each 24-hour cycle. Approximately 8 hours of the day are spent sleeping as a result of the natural Circadian Rhythm. This is the natural amount of sleep we require on a daily basis to match up with our body clock's demand. 16 hours of the day are therefore left as wake hours. However, athletes must be careful with this estimated number of hours as it is critical that athletes accumulate additional hours of sleep to compensate for the heightened stressors applied through intense and/or high volume training bouts.

Sleep Is Individualised:

Given sleep is highly regulated by the Circadian Rhythm, everyone is going to have a slightly different preference of how and when to accumulate those precious hours of shut eye. A key contributor to this is our genetic chronotype. Essentially most people will fall into 1 of 2 categories.

1. Morning Lark - Early riser and Early to bed.

2. Night Owl - Late riser and Late to bed.

Regardless of which side of the spectrum you sit, it is the accumulation of hours that is the critical component. Adjusting your day as much as possible around your preferred sleeping pattern is optimal for gaining a greater amount of sleep each 24 hour period. As mentioned previously, 8 hours is the recommended dosage for most people, athletes need more than this. Optimising your sleep structure to suit your chronotype is going to go a long way towards a good nights sleep.

Furthermore, not everyone may be able to accumulate 1 large block of sleep per day and may need to break up and accumulate "sleep periods" over the course of the 24 hour period. A useful tool to combat this is the use of "Power Naps". These are chunks of short sleep periods aimed to provide a "booster" to get you through a day or to assist in accumulation of ideal sleep hours per day. The aim of having a short nap is to restore alertness, restore the hormonal impact of a poor nightly sleep, reduce stress and reduce mental fatigue. Although not the ideal situation for recovery, having a power nap pre-training session (if training later in the day) may be beneficial to improving the output during the following session.

This strategy is unbelievably effective and when the nap is kept to 15-20mins and caffeine is consumed immediately before the nap, you'll find you wake up refreshed and ready to go again. YES I said CAFFEINE BEFORE A NAP! The premise being you'll almost can a double kick out the caffeine hit by napping immediately after consumption. However important to note the timing of this process. Leaving too large a gap between the caffeine ingestion and the nap may lead to disruption to the power nap by keeping you awake and alert. 

Sleep & Injury:

Time and time again the literature has shown sleep and injury are closely related with nearly all studies suggesting an increase in the likelihood of injury as a result of lesser total sleep hours per night.

A key finding by Milewski et al. 2014 when studying the likelihood of injury over a 21 month period uncovered athletes who slept less then 8 hours (average) per night were 1.7 x more likely to become injured than those who gained more than 8 hours (average) per night. (A summary of results is below). With increasing average sleep hours the likelihood of becoming injured drastically began to reduce showing a clear connection with the quantity of sleep and injury risk.

 Image 5 - Likelihood of injury based on average hours of sleep per night. (Source: YLM Sport Science)

Image 5 - Likelihood of injury based on average hours of sleep per night. (Source: YLM Sport Science)

Another contributor to injury risk is the quality of sleep. The psychological impact of poor sleep on alertness and mental fatigue is critical. Poorer sleep quality may lead to a reduction in concentration and ability to coordinate movements and react to external stimuli, thus resulting in increased risk of injury due to external factors (i.e. crashing off the bike, ankle sprain running on an uneven surface due to slower corrective ability).

Key Considerations For Quality Sleep:

First of all some non-negotiables when it comes to getting a good nights sleep. Ensure that the environment is quiet and dark with optimally no light source present. Remember if light is sensed by the brain we are initiating the "wake" response and will find it more difficult to fall asleep. A maintained and comfortable room temperature is also a key consideration (~18 degrees is ideal). The final environmental consideration for great sleep quality is to ensure that your clothing and bedding choices don't create an environment that is too hot, thereby exceeding the optimal environmental temperature. 

If utilising power naps as part of your daily routine ensure that the nap occurs no later than mid-afternoon and although caffeine is useful when conducting a power nap, before your main bout of sleeping limit the consumption of food and fluid immediately before sleep. This includes caffeine. The benefits of the caffeine before nap strategy are most effective in a short dosage of sleep and will begin to limit your sleep ability when attempting to accumulate a full, ideal 8 hours. Of course ~8 hours is the optimal duration however as discussed earlier, athletes generally require more than this, so aim to achieve 8 hours as a minimum.

A reasonably obvious consideration is a consistent routine. Establishing a routine sleep time and wake time will enable the adaptation of the body clock to work in around your typical day. Obviously not every day will be identically structured. You may have extra work, social activities etc. The important note here is that if your normal routine is consistent most of the time, your sleep patterns will become far more consistent. No surprise that when we set a dedicated "bedtime" and wake time and stick to it over multiple weeks we end up feeling far more energetic and refreshed due to the enhanced sleeping quality and consistency of sleep hours gained.

Finally limiting the amount of computer, phone and TV use before sleeping will also help you to gain that precious 8 hours. Screen-time prior to bed has been strongly linked to delayed and reduced sleep as a result of Melatonin suppression, therefore impacting our Circadian Rhythm. The body is unable to release the higher dosage of Melatonin due to a high amount of light being sensed within the brain and we extend the "wake drive" response. The reason being the light source sensed by the brain from a technological device (i.e. smartphone) is regarded as "Blue Light" which is interpreted in the brain as the same light source as sunlight. using the "night-shift" mode on smart devices does reduce the impact however will not completely eliminate the blue light effect. Aim to minimise screen time overall in the lead up to bedtime.

Summary:

+ We need 8 hours of sleep for our natural cycle (Circadian Rhythm), athletes generally need MORE SLEEP!

+ Lack of sleep plays a significant role in the likelihood of injury for athletes.

+ Find out your ideal way to accumulate sleep based on your chronotype and preferences. Listen to your body here!

+ There are a number of considerations to maximise sleep hours and quality. Nailing these key components will improve your sleep dramatically.

 

If you wish to learn more about sleep for endurance athletes you can contact me (Nick Jankovskis) at: nick@metsperformance.com

Or check out my instagram page for all things endurance performance at: @nj_sportscience