The key influencers of fatigue

The key influencers of fatigue come down to how much one sleeps, the quality of that sleep and the timing consistency of when that sleep occurs. 

Each metric has a range that’s considered normal, fair, or poor. Those details can be found here.


Sleep quantity is the most straightforward influencer of fatigue. Most adults require 7-9 hours of sleep daily to function optimally. 



Sleep quality is the most complicated influencer of fatigue. There are many metrics that could suggest someone’s sleep quality, but several of them can only be measured with in-lab sleep testing (Polysomnography). On Analyze, metrics like Wake after sleep onset, Awakenings, Sleep latency, and Sleep efficiency may give you an idea of sleep quality.  

Wake after sleep onset is a measure of sleep quality, helping you understand how fragmented someone's sleep is. It's the total number of awake minutes between the sleep onset and wake time.  

Awakenings are any period of more than 5 continuous minutes where the movement of your wrist suggests you may be awake. 

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.

Analyze also shows you 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).

Sleep latency is the average amount of time it takes for someone to transition from wakefulness to sleep. Take this metric with a grain of salt. It can be inflated on occasions where someone is motionless reading a book or watching a movie.  

Sleep efficiency is another metric that could be influenced by someone lying in bed but not sleeping (i.e. reading a book or watching a movie). It’s the percentage of time spent in bed sleeping. 

Both Sleep latency and Sleep efficiency are helpful hints as to someone’s sleep quality if looked at from a macro perspective and in conjunction with other metrics.


Going to bed and waking up at the same time every day makes everything to do with sleep easier. Inconsistent sleepers will find it more difficult to fall asleep and wake, and to regularly obtain a sufficient amount of sleep. This is due to the 24-hour internal body clock (the circadian rhythm) which cycles between sleepiness and alertness at regular intervals. When we deviate daily from the natural signals of our body clock, our natural biology gets out of alignment.

Metrics like Sleep onset, Wake time, Onset variance, and Wake variance are the key metrics here. Sleep onset is the time of transition from wakefulness to sleep for the major sleep period or the moment one falls asleep, and Wake time marks the end of the major sleep period or when one wakes up. 

The Onset and Wake variances are measures of consistency. Onset variance tells you how much difference there is between a particular night’s Sleep onset and the average sleep onset for the date range you’ve selected. Wake variance is calculated in the same way using Wake times.


Using Analyze

To learn what each metric is, how it’s calculated, and what the normal range is, hover over the name. What values show up as red, orange, or green are dependent on the normal range for that particular metric. 

Sort the table by a metric by clicking the name. You can also choose to hide or show particular metrics using the dropdown menu just above the table on the right. This helps you focus on the metrics you want, and not the ones you don’t. 

Trend, while not a sleep metric itself, is a great way to understand whose sleep is improving, and whose may not be. Here's a whole article on it. 

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