Sleep and performance: a one-night wonder

While it’s generally understood that sleep loss is ‘bad’, it’s not always clear how bad, particularly in acute situations. The reality is that most athletes will experience a night of poor sleep, sometimes in the lead up to critical training sessions or competitions.  With all the concern about poor sleep, it’s easy to perceive that any loss of sleep is a catastrophic event that can ruin a preparation.  However, that may not necessarily be the case.

While the importance of sleep is appreciated by most, the specific impact of sleep deprivation on short-term performance has not been sufficiently studied.  Nor has the effect of sleep recovery during the following night on the ability to restore performance and function.  There are many questions to be answered.  How long does it take for performance to recover following a bad night’s sleep, or even worse, no sleep?  And since lack of sleep is going to have negative psychological and physiological effects, what can be said about performance is being compromised?  These are all questions that need answers, and fortunately a recent study sought to provide them. 

The study

An international group of researchers conceived of a study to test the impact of one night of sleep deprivation and the subsequent impact of sleep recovery during the following evening(1).  26 subjects were recruited, all male cyclists and triathletes with an extensive cycling background.  The average VO2max of the subjects was 55.3 ml/kg/min, so while not fantastically fit, they were no slouches.  It was also required that they had been performing at least 3 hours per week of purposeful and challenging cycling training in the lead up to the study.  The researchers also screened out individuals who had extreme chronotypes, such as very early risers or very late risers, as well as those with sleep challenges.  They did so to avoid extreme measures compromising and skewing the data.

Here’s how the study was set up.  Baseline testing, which we’ll cover shortly, was performed for all subjects.  After baseline testing was performed the subjects were randomized into one of two groups.  The control group continued with their normal sleeping schedules and behaviors.  In contrast, the experimental group was to perform a night of complete sleep deprivation and then sleep normally the following night.  The night with the return to normal sleeping pattern was call recovery sleep.  To ensure that subjects remained awake, they were asked to stay overnight at the laboratory where all the testing took place.  Food and behavioral choices were controlled as much as possible to reduce the influence of potentially disruptive factors.  

Testing

To gain insight into the specific impact of sleep deprivation on endurance performance, numerous tests were performed.  Each subject performed the following tests three times.  A baseline, following a normal night of sleep or no sleep, and then following a normal night of sleep.  This allowed the researchers to determine what happens after no sleep, and what happens after sleep is restored.

The included tests were complementary in that the provided similar information that helped to paint a more nuanced picture as to what was occurring.  First, the subjects completed the Brunel Mood Scale and the Karolinska Sleepiness Scale.  These tests provided subjective measures of how the subjects perceived their mood and their level of sleepiness.  These tests were performed prior to any exercise during each experimental session.

Beyond these subjective psychological measures, objective measures were also taken.  The researchers performed what’s known as a 12-minute Alpha Attenuation Test using EEG technology.  EEG stands for electroencephalography, which allows for the measurement of the electrical activity of the brain, much like an EKG allows for the measurement of the electrical activity of the heart.  In this specific test, the subjects performed alternating two-minute periods where their eyes were open and closed, while looking at a fixed point.  This test allowed the researchers to understand how sleeping conditions impacted the baseline electrical activity of the brain. 

After the Alpha Attenuation Test, the subjects performed a psychomotor vigilance test.  This too is an objective measurement of brain function.  The test involves pressing a computer keyboard key in response to a visual stimulus.  The stimulus would appear randomly every 2-10 seconds.  If the subjects responded ‘too fast’ due to anticipation, it was considered an error, as were responses where no stimulus was given, no response was made to a stimulus, or the response was excessively delayed.  These responses were all defined based upon clear cutoff points. 

Just prior to the beginning of the physical testing, the subjects completed a motivation questionnaire to assess their current level of motivation.  Then, it was on to the testing.  For each day, the subjects performed two exercises bouts.  The first consisted of a 40-minute cycling bout performed at 60% of their VO2peak.  Their VO2peak was the highest amount of oxygen they consumed during a ramped exercise test, which was performed during a familiarization session prior to any of the sleep deprivation interventions.  The subjects had to simply maintain the assigned speed throughout the test.  This represented a moderate challenge, and the purpose was to assess the psychological and physiological response to moderate exercise.  The subjects then took a 5-minute break, after which the real fun started.  The subjects performed a 20-minute maximal effort cycling trial.  The goal was to do as much work as possible in 20 minutes.

Throughout the test itself multiple subjective and objective measures of intensity were taken.  Heart rate was monitored continuously to measure cardiovascular strain.  Blood samples were taken every 8 minutes during the 40-minute submaximal test.  They were also taken 60-seconds after the 20-minute all out trial.  Blood lactate was then measured to determine the degree of metabolic activation that occurred.   Rating of perceived exertion (RPE) and affect, a tendency toward pleasure or displeasure, were measured every 5 minutes throughout the tests.

At the conclusion of the test, three more questionnaires were given.  The Brunel Mood scale and the Karolinska sleepiness scale given again assess changes in subjective sleepiness.  The subjects were also given what’s known as the NASA-TLX multidimensional scale, which serves to measure the subject’s perceived workload.  It has multiple dimensions which all serve to measure the challenge of the exercise bout.

To measure performance during the 40-minute cycling test, the researchers took a clever approach.  Exercise has consistently been shown to terminate when RPE is 20, and RPE raises linearly over time. As RPE was slowly rising throughout the 40-minute trial, the authors could determine how long it would theoretically take for the RPE to hit 20.  They used this number as theoretical time to exhaustion.  A faster rising RPE indicates a shorter time to exhaustion as compared to a lower rising RPE.  Performance during the 20-minute bout was straightforward.  They just took the total workload that was accumulated as the measure of performance.