The orange blocks indicate estimated time asleep as well as when you fell asleep and awoke. The gaps between them suggest awakenings.
The vertical grey lines represent wrist movement. The taller the line, the more active your wrist was.
With the Readiband, an awakening is defined as any period of more than 5 continuous minutes where the movement of your wrist suggests you may be awake. Most people don't sleep right through the night, and are agitated awake due to things like noise, a full bladder, stress, or the movement of a partner, pet or small child.
Significance of awakenings
Generally speaking, continuous sleep with few awakenings is more efficient, and therefore more restorative. On the other hand, a high number of awakenings suggests that sleep is broken up and less restorative, and so more total sleep will be necessary to have the same health and alertness benefits than less fragmented sleep. For example, 7 hours of sleep with 2 awakenings will boost your Alertness Score more than 7 hours of sleep with 6 awakenings.
It’s one of many possible indicators of the quality of your sleep.
Awakenings per hour
This is a better relative measure of the fragmentation of your sleep over time compared to total awakenings. For example, 4 awakenings over 8 hours of sleep (0.5/hr) is very different than 4 awakenings over 4 hours of sleep (1/hr).
Rules of thumb
- Less than 0.37 is one indicator of good sleep quality
- More than 0.68 may indicate poor sleep quality
Fatigue view: the Alertness (or Effectiveness) Score
The Alertness Score is a scientific measure of the effects your body experiences with a lack of good and consistent sleep. It’s powered by the SAFTE™ Fatigue Model.
- Note: If you’re an athlete, you’ll see this referred to as an Effectiveness Score in your app.
Consider the impact alcohol consumption has on one’s ability to perform tasks efficiently and safely (or in sports, to perform at the highest level). It affects things like their judgment and reaction time.
A lack of sleep has a similar influence, and your Alertness Score quantifies the extent of that fatigue, sort of like a breathalyzer does for any alcohol in your system.
For example, at a score of 70, the effects of fatigue are scientifically equivalent to the effects of having a Blood Alcohol Concentration of 0.08—the legal limit for operating a vehicle in many countries.
Alertness Score influencers
Your score is directly informed by the quantity and quality of your sleep, as well as how consistently you go to sleep and wake daily. In other words, good sleep habits will result in a higher score.
And, it’s not just last night’s sleep that matters, but the influence of each of these factors over the past week and beyond.
3 days required before Alertness Score is generated
Because fatigue is a product of your cumulative sleep history, at least 3 days of sleep information is required to calculate an accurate SAFTE™ Alertness Score.
Scores dip and rise throughout the day due to your circadian rhythm
If you tend to feel energized or drowsy around the same times each day, that’s your circadian rhythm at play. What is it? It’s a 24-hour internal body clock that’s running in the background of your brain and cycles between sleepiness and alertness at regular intervals.
It dips and rises through the day, and is influenced by lightness and darkness. We’re designed to be awake during the day and asleep at night. So, when things like travel across time zones or shift work are at play, your circadian rhythm can be disrupted. This causes you to feel out of sorts and struggle to stay alert or perform at a high level.
While the dips and rises occur naturally and predictably every day, the intensity of the dips will be more pronounced when you’ve not had enough sleep.
Impact of travel on Alertness Scores
Your score is calculated based on your home time zone, and doesn’t accommodate for the impact a change in sunrise and sunset has on your body when traveling across zones, unless you've enabled the optional feature, Smart Time Zone.
However, if you’re travelling, your sleep and fatigue reports will always display in your local time.
The science behind the Alertness Score
It’s powered by the SAFTE™ (Sleep, Activity, Fatigue, and Task Effectiveness) Fatigue Model, which was developed by the US Army Research Lab through 25 years of applied research. The Model has been validated by the US Department of Transportation and shows a direct relationship between one’s SAFTE Alertness Score and the likelihood they’ll experience a mental lapse. More about the SAFTE Fatigue Model