When are you most productive?
Are you an early bird, a night owl, or somewhere in between? Your prime productivity window each day may be different from mine, and it may even shift during your lifetime. For example, my current prime productivity period is from roughly 9am to 12pm each day, but ten years ago as a college student I was most productive from 9pm to midnight. What happened?
Having worked at Arcascope for a while, I now know that in college I was likely working during my “wake maintenance zone”— the burst of energy and focus most of us experience a few hours before sleep. Now that I’m older, it’s likely that my rhythms have shifted so morning hours better align with the signals from my circadian clock to wake up and start my day. This means I’m feeling the most alert 12 hours out of sync from when I used to.
Knowing when one is most productive can be the first step to understanding one’s circadian rhythms. These rhythms shift with biological age, life-changing milestones, work environments, work hours, long-haul travel, or just a one-off bad night. By doing routine check-ins with your rhythms of alertness and performance, you can track changes over time and learn to better understand your body’s circadian messages.
Two-process model: homeostatic sleep drive and circadian rhythm
Most humans function best when they are awake in the day and asleep at night. However, technological innovation has created the relatively novel concept of 24-hour societies and the natural wake/sleep pattern is becoming less universal. Studying how humans sleep in artificial scenarios, such as constant darkness, constant light, or in sleep deprivation experiments, has led to the creation of the two-process model. In sleep science, the two-process model consists of (1) the build-up of homeostatic sleep drive and (2) circadian rhythm.
These concepts can be difficult to grasp, but we’ll give them a shot.I invite you, if you will, to think of your body as a flashlight operating on two batteries. We’ll call these the alertness batteries. The first charges while you’re asleep and discharges while you’re awake, almost like a normal battery. This battery captures how “full” you are of the restorative power of sleep. The second battery is a special type of battery called the “circadian rhythm.” Unlike standard batteries, this battery has a cutting-edge feature that enables the self-generation of energy, but it comes at the expense of periodic discharges; this battery is also sensitive to sources such as light, caffeine and exercise. When both batteries are in sync, they work together to produce the brightest light possible so that your surroundings are highly visible and as a result, you are highly alert. However, things are less bright when these two batteries fall out of sync. Either battery is capable of producing light solo, but the suboptimal amount of light produced is often not enough to adequately illuminate your surroundings, and as a result, your alertness is likely to be less than ideal. Your goal is to synchronize the charge and discharge of these alertness batteries, so that your light can shine at its brightest when you are awake and dim steadily as you prepare to sleep.
We all glance at the battery levels on our mobile devices several times each day. We should also take care to gauge the levels of our internal batteries. Fortunately, scientists have devised quick and easy tools to assess your body’s battery, such as sleepiness scales and psychomotor vigilance tests (PVTs).
In the next three sections, we will explore three different ways to assess how full your batteries are, including:
- Good: subjective sleepiness scales
- Better: objective psychomotor vigilance tests
- Best: predictive algorithms in Arcascope’s Shift application
Good: sleepiness scales
A subjective measure of sleepiness can be derived from scales like the Karolinska Sleepiness Scale (KSS) and Stanford Sleepiness Scale (SSS). Both scales ask users to self-report their feelings of alertness and fatigue, but the SSS extends its ratings into the state of sleep. For those who experience excessive daytime sleepiness, you may find value in exploring the Epworth Sleepiness Scale (ESS), which is commonly employed by sleep specialists as a prescreening for potential sleep disorders.
The advantages of sleepiness scales are that they put numbers to things that would otherwise be hard to talk about in systematic ways. The big disadvantages are that they’re subjective, and people’s subjective experiences of how sleepy they are often don’t track with how alert they actually are.
Karolinska Sleepiness Scale
The KSS employs numerical ratings from 1-9, with 1 as most alert and 9 as most sleepy. A common variation employs odd numbers only. The full Karolinska Scale is displayed below, with odd numbers in bold.
| 1 | Extremely alert |
| 2 | Very alert |
| 3 | Alert |
| 4 | Fairly alert |
| 5 | Neither alert nor sleepy |
| 6 | Some signs of sleepiness |
| 7 | Sleepy, but no effort to keep alert |
| 8 | Sleepy, some effort to keep alert |
| 9 | Very sleepy, great effort to keep alert, fighting sleep |
Stanford Sleepiness Scale
The SSS employs numerical ratings of 1 to 7 and an alphabetical rating of X, with 1 as most alert and X as asleep.
| 1 | Feeling active, vital, alert, or wide awake |
| 2 | Functioning at high levels, but not at peak, able to concentrate |
| 3 | Awake, but relaxed; responsive but not fully alert |
| 4 | Somewhat foggy, let down |
| 5 | Foggy; losing interest in remaining awake, slowed down |
| 6 | Sleepy, woozy, fighting sleep; prefer to lie down |
| 7 | No longer fighting sleep, sleep onset soon; having dream-like thoughts |
| X | Asleep |
Epworth Sleepiness Scale
Reflect on your chance of dozing in each situation from 0 to 3: 0: no chance of dozing, 1: slight chance of dozing, 2: moderate chance of dozing, and 3: high chance of dozing.
| Situation | ||||
| Sitting and reading | 0 | 1 | 2 | 3 |
| Watching TV | 0 | 1 | 2 | 3 |
| Sitting inactive in a public place (movie theater or meeting) | 0 | 1 | 2 | 3 |
| As a passenger in a car for an hour without a break | 0 | 1 | 2 | 3 |
| Lying down to rest in the afternoon when circumstances permit | 0 | 1 | 2 | 3 |
| Sitting and talking to someone | 0 | 1 | 2 | 3 |
| Sitting quietly after lunch without alcohol | 0 | 1 | 2 | 3 |
| In a car, while stopped for a few minutes in traffic | 0 | 1 | 2 | 3 |
Better: Objective Psychomotor Vigilance Tests
As an alternative to sleepiness scales, one may opt for a psychomotor vigilance test, which objectively measures alertness. Many variations exist, but the most common version measures how quickly a person responds to text appearing on a black screen. The gold-standard is 10 minutes in duration but shorter variations are available. If interested, you may download “NASA PVT” on your mobile device, or opt for an in-browser two-minute PVT from Sleep Disorders Florida.
The advantage of the PVT is that it gives you an actual measure of how likely someone was, in that time period, to miss a stimulus—which could be critical for operations in which overlooking something can be fatal. One downside is that it can take a long time to have robust confidence in the score (e.g. 10 minutes), and it can’t help you look forward to project how sleepy you’ll be in the future.
Best: Arcascope launches “Shift” application
Both sleepiness scales and PVTs have been critical to building our understanding of sleep and performance. But there’s no reason to stop there: mathematical modeling can help us estimate performance without the need for a time-consuming PVT and help us project forward into the future to predict future fatigue.
That’s where we come in. Arcascope’s Shift application fuses the latest in combining physiological modeling with machine learning to predict alertness as accurately as possible.
And we’re not just predicting: we can also help you shift your future alertness to better meet your needs. By inputting your work schedule and desired wake time, our app can help to optimize your body’s batteries, bringing your circadian rhythms and homeostatic sleep drive into alignment through interventions, such as:
- Bright light exposure
- Times to avoid light
- Meal timing
- Melatonin timing
- Caffeine timing
- Activity timing
You need (and deserve) a customized solution
In modern 24-hour societies, people are waking and sleeping at vastly different hours. As a result, researchers see greater diversity in people’s homeostatic sleep drives and circadian processes than ever before, which can make fatigue hard to predict. Since your lifestyle and habits are unique, your circadian management tool should be personalized too. Arcascope can help you move past self-reporting fatigue, and show you the path to shift you into the best, balanced version of yourself. Paying attention to your alertness batteries will help you shine your absolute brightest.
