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The Importance of Sleep
Our understanding of the science of sleep mirrors
our understanding of the human brain: we are only just scratching the surface
in what we currently know. Yet we know enough to know “how we sleep” affects
every aspect of our lives and performance on the sporting field.
It took for me to have children (who didn’t sleep
at night!!), to really appreciate the impact of poor quality sleep on cognitive
function, immune ability and physical performance! This article will examine
the impact that sleep deficit has on performance and injury, with a future
article discussing how to improve sleep.
Why
do we sleep?
It was once thought that the brain simply “shuts-down” during sleep, yet we now know that there are much more complex activities happening. One way to explain what occurs is “brain housekeeping”: the brain performs checks, repairs and cleaning toxins (beta-amyloid amongst others) [1] that build up during the day. In addition to this, good sleep promotes tissue repair, immune function and hormonal and metabolic rebalancing [2, 3].
How
do we measure sleep?
There are continued advancements in technology for
quantifying sleep quality. Currently the gold standard is a sleep study
conducted in the lab via polysomnography which measures multiple variables including
brain waves (EEG), breathing, heart rate and rhythm, muscle activity, eye
movement and blood oxygen saturation.
One could argue, however, that sleeping in a lab
connected to multiple machines might not give an accurate result when compared
to the individuals “natural” environment [4]. Enter the
portable sleep monitoring devices. With the rise of popularity in these devices
(FitBit, Oura ring, ReadiBand) and phone apps, the question has to be raised on
their accuracy. Most devices are similar in that they are based on the same
type of sensor (accelerometer and/or noise). Ultimately, sleep is best tracked
through polysomnography, but these devices offer much more accessible and
convenient options for casual users to track their activity. Multiple studies [5-8] conclude
that wrist monitors can be quite accurate when it comes to estimating
information such as total time asleep, sleep percentage, and how long after
sleep waking occurs.
It has been my personal experience with sleep monitoring
on both myself and my patients, that if you wake in the morning and you feel
tired, you haven’t had ideal sleep quality/quantity. Whilst it’s nice to be
able to put an objective measure on everything, sometimes subjective measures
can be just as useful, as previously discussed in Saw et al’s study on training
response [9]. At a
basic level, recording when you went to bed, when you woke, and subjectively
measuring how rested you feel in the morning can give you a good indication of
your sleep quality.
How
much is normal?
The National
Sleep Foundation’s recommendation for young adults (18-25 years) and adults
(26-64 years) is between 7-9 hours. From the research, we see that athletes
commonly average below 7 hours [10]. A recent
questionnaire based study found that 50% of highly trained and elite athletes
were identified as “poor” sleepers, with 28% experiencing daytime sleepiness [11].
For
athletic individuals, sleep is paramount when considering the training
response, which requires a balance between stress, fatigue and recovery[12]. Therefore
athletes should look to promote recovery which would then decrease their
stress/fatigue state. Sleep is surprisingly often overlooked by athletes
themselves as a cause of fatigue [13]. Poor
sleep quantity and/or poor quality appears to exist in many athletic
populations, which can be due to a combination of scheduling of training
sessions and competition, travel fatigue, and impaired sleep-onset due to increased
arousal post competition.
Effects on
injury and performance
We previously briefly mentioned the benefits of sleep, but what about
the detrimental effects of decreased sleep?
Injury
- Milewski et al’s study on adolescent athletes found
those who sleep on average less than 8 hours per night have 1.7 times greater
risk of being injured than those who slept more than 8 hours [14]. - In another study on elite adolescent athletes, von
Rosen et al found that sleeping more than 8 hours during a week reduced risk of
injury by 61% [15].
Illness
- A range of metabolic and immunologic process are negatively affected
by poor sleep [16]. - Reduced sleep quantity was associated with increased incidence of
illness within the next 7 days in competitive male AFL players [17] - Those who sleep less than 5 hours are 4.5 times more likely to
suffer a cold vs those who sleep 7 hours [18].
Performance
- Reductions in motor and cognitive performance, reaction times, and
mood state/emotional stability are often observed in sleep-deprived athletes [19]. - Poor sleep quality, particularly during high training loads and
competition periods, has been identified as a marker of under recovery and an
early sign of overreaching [20]. - Brandt et al’s study on Brazilian athletes revealed a relationship
between poor sleep quality and lost matches during a competition[21]. - Silva et al found a correlation between sleep duration and competition
performance in elite gymnasts [22]. - Napping improves running performance in those endurance runners
that had less than 7 hours sleep [23].
This
information should hopefully highlight to you the reader on the importance of
sleep, and get you starting the conversation (if you haven’t already) with your
athletes about their sleep habits. In our next instalment, we will discuss what
can be done in those with suboptimal sleeping habits.
References
5. Martin,
J.L. and A.D. Hakim, Wrist actigraphy.
Chest, 2011. 139(6): p. 1514-1527.