Today's article comes from the journal of Life. The authors are Bouzouraa et al., from the University of Jendouba, in Tunisia. In this study they're asking if getting just a single extra hour of sleep can significantly affect your cognitive and physical performance.
DOI: 10.3390/life15081178
Think about the last time that you got a terrible night's sleep. Maybe it was too hot in your bedroom, or maybe you were too worried about something. Maybe your upstairs neighbors were training their horse to tapdance again. Either way, do you remember how you felt the next morning?
Sluggish, maybe even nauseous. Difficulty concentrating. Slower reaction time. A lot of staring off into the abyss. Your morning workout probably felt like torture, and complex tasks at work felt far more demanding than usual.
But what happens when you do the opposite? When you intentionally get more sleep than usual/ Do all the effects flip? Can you actually boost your performance by extending your sleep? And is that a tactic someone could deploy? That is: if you're an athlete, or a student, or an executive, or anyone who needs to perform at your best at a specific day and time, is strategic sleep extension a viable performance enhancement tool?
Today we're looking at a study that tackled this question. The authors wanted to know whether a single night of extended sleep could improve both physical and cognitive performance. But they didn't just measure performance once. They tested the participants (24 students) at three different times of day to see how sleep extension interacted with their natural circadian rhythms. On today's episode, we're going to see what they did, and what they found. Let's dive in.
As a whole, this study used what's called a 'within-subjects', 'counterbalanced crossover' design. In other words: each participant completed both a normal sleep condition (a control) and a sleep extension condition (an experiment). For the experiment, the participants went to bed a little earlier but kept their normal wake time. This added close to an extra hour of time in bed compared to their normal schedule. The goal wasn't to dramatically change their total sleep pattern, just to inject one extra hour on one particular day. On all the other days, they maintained their schedule.
To take measurements, the authors used wrist actigraphy devices. These work like activity trackers. They continuously monitor movement patterns to determine when someone is asleep versus awake. It uses accelerometers to detect the movements that occur during different sleep stages, then applies algorithms to translate movement data into sleep metrics. These measurements are designed (in theory) to eliminate the reliability issues that come with self-reported sleep data. Though it's worth noting that actigraphy can sometimes misclassify quiet wakefulness as sleep. That is: the device might not know the difference between zoning-out watching TV or actually taking a nap.
The actigraphy devices were really just to validate that sleep was occurring at the times the authors had asked. The larger idea was that researchers would measure the participants' performance several times a day during both the control and the experiment, and compare the results. Here's what the tests looked like:
The first of the tests was for "explosive power". They used both squat jumps and countermovement jumps, measured with photoelectric cells. These systems work by creating light beams that detect when someone breaks the plane during takeoff and landing. The squat jump required participants to hold a deep knee bend before jumping, eliminating the stretch-shortening cycle contribution that occurs when muscles are pre-stretched. The countermovement jump allowed a rapid downward movement followed by maximum vertical propulsion. This comparison helps researchers understand whether sleep affects different types of muscle contractions differently.
Dynamic balance was evaluated using the Y-Balance test, which measures how far someone can reach in three directions while balancing on one leg. This test challenges the integration of visual, vestibular, and proprioceptive systems that maintain postural control. After a few practice trials, participants performed multiple attempts for each leg. The composite score represents overall dynamic balance capability normalized to leg length, but balance performance can be influenced by factors like ankle flexibility and hip mobility that aren't necessarily related to sleep quality.
Upper body power was assessed through standing backward overhead medicine ball throws. This test evaluates the power of the posterior chain muscles and the ability to coordinate multiple muscle groups in a ballistic movement pattern. But, the throwing motion is somewhat artificial compared to most sports movements, which may limit its generalizability.
The most complex physical assessment was the shuttle run: Six high-intensity sprints separated by brief recoveries. For this, the authors calculated multiple performance indices: best distance covered in any single sprint, total distance across all sprints, and a fatigue index that quantifies performance decline across repeated efforts. This provided insight into both peak anaerobic capacity and fatigue resistance, though manual distance recording does introduce some measurement error.
For the cognitive assessment, participants sat at a laptop and had their reaction time tested. This used specialized software to measure both simple and choice reaction responses.
These tests probe different aspects of information processing, from basic sensorimotor speed to more complex decision-making processes. But it's worth noting that reaction time can be influenced by factors like caffeine intake, motivation, and familiarity with the testing equipment.
Finally, the digit cancellation test assessed selective attention and processing speed. They had to scan rows of numbers to identify and mark specific target digits, within a time limit. This task requires sustained attention, visual scanning, and the ability to maintain accuracy while working quickly. Your performance reflects both the speed and precision of your attentional processes. But to be fair, it's a fairly artificial task that may not translate directly to real-world attention demands.
The authors ran the tests, tabulated the data, and crunched the numbers. So what did they find?
Well, the most notable results came from the shuttle run test. They found significant effects of both sleep condition and time of day, plus interactions between these factors. During the morning assessment, participants who had extended their sleep the night before covered more distance in their best sprint effort compared to the normal sleep condition. Approximately a ten percent improvement in anaerobic performance. Total distance across all sprints showed similar patterns, with sleep extension yielding better performance at morning testing. The fatigue index also saw improvements, with participants showing better resistance to performance decline across repeated efforts. This suggests that sleep extension enhanced not just peak performance but also the ability to maintain high-intensity output over time.
The cognitive results also improved. Simple reaction time was faster after sleep extension, particularly during morning and afternoon testing sessions. At morning testing, reaction times were substantially faster. Afternoon testing also showed strong gains, reinforcing that the benefits extended beyond just the early hours. Choice reaction saw improvement in both speed and accuracy. This goes against the typical speed-accuracy trade-off, suggesting enhancement in information processing efficiency rather than just strategic changes in response bias. Meanwhile, the digit cancellation test showed that participants correctly identified more targets, improved their sustained attention and their visual processing speed.
The jumps didn't see as much of a gain. Both the squat jump and countermovement jump heights increase, but with smaller effects. Meanwhile, the balance test revealed improvements primarily in the afternoon, with composite scores increasing during late-day testing. This timing suggests an interaction between sleep extension benefits and circadian enhancement of postural control during afternoon hours when core body temperature and neuromuscular coordination typically peak.
The time-dependent nature of the benefits suggests homeostatic rather than circadian mechanisms. Extended sleep likely reduces baseline sleep pressure accumulation, providing greater reserves during morning hours when sleepiness is typically elevated. As homeostatic sleep pressure rebuilds throughout wakefulness, these benefits gradually diminish. This explains the smaller effect sizes in the afternoon, compared to the morning assessments.
During extended sleep, people typically get more of both slow-wave sleep and rapid eye movement sleep, the two deepest and most restorative sleep stages. Slow-wave sleep is when the brain clears metabolic waste products that accumulate during wakefulness, including adenosine, which builds up sleep pressure. More slow-wave sleep means better clearance of these fatigue-inducing compounds. Rapid eye movement sleep is crucial for memory consolidation and neural plasticity. Extended time in this stage may enhance the formation of new neural connections and the strengthening of existing ones. This could explain why complex cognitive tasks showed such pronounced improvements following sleep extension.
The interaction with circadian rhythms reveals something about how our internal clocks affect performance. Most people experience a natural dip in alertness and performance during the early morning hours, corresponding to the circadian trough in core body temperature. Sleep extension appears to provide a buffer against this natural low point, essentially giving people more cognitive and physical resources to draw upon during challenging morning hours. And this also highlights the difference between sleep quantity and sleep quality. While participants got more total sleep time through extension, they also showed only modest gains in efficiency, suggesting the main driver wasn't necessarily adding "better" sleep, just more of it.
From a practical standpoint: the magnitude of the improvement they saw for just one hour of additional sleep seems (to me) to be a notable return on investment. For athletes or anyone needing to perform at high levels, this research suggests that strategic sleep extension might be as effective as many other performance interventions, while being far simpler to implement.
If you want to see the authors' complete statistical breakdowns, the methodology for each performance test, or the correlational analyses between sleep architecture and specific performance domains, you'll definitely want to download the paper. The authors also provide a discussion of the neurophysiological mechanisms at play and more practical implementation strategies that any of us could use the next time we want to perform at our best.