What hard training requires from your sleep

Eleven players on the Stanford men's varsity basketball team slept on their usual schedule for two to four weeks, then spent five to seven weeks trying to stay in bed at least 10 hours a night. Their measured sleep rose by an average of 110.9 minutes. Their timed sprint fell from 16.2 to 15.5 seconds, free throw percentage rose 9%, and 3-point percentage rose 9.2% (Mah et al., 2011, Sleep). Reaction time, daytime sleepiness and mood all improved as well.

The study is small and had no control group, and the players knew they were sleeping more. It is still the cleanest demonstration in sport that athletes who think they sleep enough often do not, and that the gap costs measurable performance. The rest of the evidence fills in why. A watch can measure four things a good night delivers. They are enough hours, the right mix of stages, a stable schedule and a quiet nervous system the next morning. This article covers each in turn, then shows exactly how a Sleep score turns those measurements into one number, using the weights Titan publishes in its help center.

01What a good night buys a hard-training body

The population baseline comes from a National Sleep Foundation panel of 18 experts who reviewed the sleep literature with the RAND/UCLA Appropriateness Method (Hirshkowitz et al., 2015, Sleep Health). Their ranges are the source of the "7 to 9 hours" figure quoted almost everywhere.

The panel wrote that sleep need "var[ies] across the lifespan and from person to person," and the ranges describe healthy people without sleep disorders. They say nothing about training load. The 2021 expert consensus on sleep and the athlete, written by 19 authors from sport science and sleep medicine, reached a similar position from the other direction (Walsh et al., 2021, British Journal of Sports Medicine). Elite athletes commonly sleep under 7 hours a night with poor quality, and the authors recommend individual sleep targets built from each athlete's perceived need in place of a single number for everyone.

For most people who train hard, the practical answer sits in the upper half of the adult range or above it. The Stanford players gained performance well past the top of it.

Why hard training pushes the need toward the top of the range

Training adds work that has to be done during sleep. Halson (2014, Sports Medicine) notes in a review of sleep in elite athletes that sleep deprivation hits submaximal, prolonged exercise hardest. The same review describes changes in glucose metabolism, neuroendocrine function and protein synthesis under chronic partial sleep deprivation, all of which bear on how well a hard week converts into adaptation.

The most direct measurement of that conversion comes from Lamon et al. (2021, Physiological Reports). Thirteen healthy young adults went through one night of total sleep deprivation and one normal night in random order. After the lost night, muscle protein synthesis was 18% lower, plasma cortisol was 21% higher and testosterone was 24% lower. One night without sleep is a harsher stimulus than a short night, so the size of the effect should not be carried over to a 6 hour night. The direction is the useful part. Sleep loss pushes the hormonal environment toward breakdown at the exact time training asks for repair.

Athletes also get less out of their time in bed than they assume. Leeder et al. (2012, Journal of Sports Sciences) put wrist actigraphy on 47 Olympic athletes and 20 matched non-athletes. Total time asleep did not differ between the groups. Sleep efficiency did, at 80.6% for the athletes against 88.7% for the controls, and the athletes' sleep was more fragmented. An athlete who needs 8 hours asleep at that efficiency needs about 10 hours in bed, which is the Stanford protocol almost exactly.

People also judge their own shortfall badly. Simpson et al. (2017, Scandinavian Journal of Medicine and Science in Sports) note that healthy adults are "notoriously poor" at self-assessing the effect of sleep loss. Van Dongen et al. (2003, Sleep) showed the same thing in the lab. Participants restricted to 6 or 4 hours in bed for 14 nights built up cognitive deficits equal to as much as two nights of total sleep deprivation, while their own sleepiness ratings rose only slightly after the first day. This is the strongest argument for measuring sleep with a device instead of trusting how rested you feel.

02What deep sleep and REM sleep each do

A night runs in cycles of about 90 to 120 minutes, four or five of them across eight hours. Each cycle passes through the stages of non-REM sleep and ends in REM. Cleveland Clinic gives the typical adult split.

Apple Watch and Apple Health group stages 1 and 2 as Core, stage 3 as Deep, and REM as REM, so the table maps directly onto what your watch reports.

The cycles are not identical. Deep sleep is concentrated in the first half of the night. REM periods start short, around 10 minutes in the first cycle, and grow to as long as an hour by the last one. That asymmetry decides what a short night costs. Going to bed late and waking on time trims some of each stage. Waking 90 minutes early removes a disproportionate share of REM, since the longest REM periods sit in the last cycles.

Deep sleep and growth hormone

The link between deep sleep and anabolic hormones is one of the better established findings in sleep physiology. Van Cauter et al. (2000, JAMA) pooled polysomnography and 24 hour hormone profiles from 149 healthy men aged 16 to 83. Deep slow wave sleep fell from 18.9% of the night between ages 16 and 25 to 3.4% between 36 and 50, replaced by lighter sleep. Growth hormone secretion fell in parallel, by 372 micrograms per decade across the same span, and the amount of growth hormone a man secreted was tied to his slow wave sleep independent of age.

Two practical points follow. The textbook 25% deep sleep figure describes a young adult, and a 45 year old athlete should expect far less without concluding anything is wrong. Compare your deep sleep with your own recent nights and not with a population table. The second point concerns what a short night takes. Deep sleep sits early in the night, so an early alarm removes little of it. The stage most exposed to lost hours is REM.

Light sleep and REM sleep carry the skill work

Stage 2 sleep is often treated as filler between the stages that matter. Walker et al. (2002, Neuron) found that it does real work in motor learning. A night of sleep after practicing a motor sequence task produced a 20% gain in speed with no loss of accuracy, while the same number of hours awake produced no significant gain. The size of the overnight gain correlated with stage 2 sleep, particularly late in the night. For any sport with a technical skill component, the late cycles of the night are where practice turns into performance.

REM sleep has a large laboratory literature on memory and emotional processing, but the direct evidence tying REM to sport outcomes is thinner than for deep sleep or total sleep. What is clear is the timing. REM lives in the last third of the night, so REM is what an early alarm, a dawn training slot or a red-eye flight takes away.

Why the balance between deep and REM counts

Two nights with the same total can have very different contents. A night heavy in deep sleep and nearly empty of REM is what you get after alcohol, which increases slow wave sleep in the first half of the night and delays REM (Ebrahim et al., 2013, Alcoholism: Clinical and Experimental Research). A night with plenty of REM and very little deep sleep is normal for many athletes past their mid-thirties, as the Van Cauter data show. Each has lost something the other kept. A score that rewards only the combined total of deep and REM would rate both nights the same. Titan's Sleep score adds a separate credit for an even split between the two, covered in the section on the score below.

03Sleep regularity is its own signal

Phillips et al. (2017, Scientific Reports) followed 61 undergraduates for 30 days with sleep diaries and introduced the Sleep Regularity Index, which measures how likely you are to be in the same state, asleep or awake, at any two moments 24 hours apart. A person who sleeps 11:00 PM to 7:00 AM every night scores near the top. A person who sleeps the same 8 hours at shifting clock times scores low.

The irregular sleepers in that study had later circadian clocks. Dim-light melatonin onset, the standard marker of circadian phase, came at 00:08 on average in the least regular fifth against 21:32 in the most regular fifth, a gap of more than two and a half hours. Their daily peak in sleep propensity came at 06:33 against 04:45, and their light exposure had a flatter daily rhythm, 102 against 179 lux in amplitude. A model of the circadian pacemaker attributed most of the difference to their light exposure patterns. Irregular sleep and irregular light kept their clocks late.

Windred et al. (2024, Sleep) took the index to 60,977 UK Biobank participants with more than 10 million hours of wrist accelerometer data, then followed them for a mean of 6.3 years. Compared with the least regular fifth, the more regular fifths had a 20% to 48% lower risk of all-cause mortality, a 16% to 39% lower risk of cancer mortality and a 22% to 57% lower risk of cardiometabolic mortality after adjustment for age, sex, lifestyle and health factors. Regularity predicted all-cause mortality more strongly than sleep duration did.

The cohort averaged 63 years old and the outcome was death, so the study says nothing direct about next week's intervals. What it does establish is that the timing of sleep carries information that total hours miss, in a sample large enough that the finding is unlikely to be noise. Almost no athlete sleep advice mentions it yet.

What a stable wake time protects

The circadian clock is set mostly by light. The Sleep Foundation calls light the most powerful influence on circadian rhythm, and the Phillips model traced the late clocks of irregular sleepers to their light exposure. A fixed wake time puts your first light of the day at the same clock time every morning and keeps the clock anchored. A wake time that drifts by two hours between weekdays and weekends moves that light exposure around, and the Phillips data show what follows, a later clock, later sleepiness and a harder time falling asleep on the nights that matter.

Titan measures two separate things here, and the distinction is worth getting right. Sleep consistency scores how close each night's time asleep is to the median of the nights with data in the 7 days ending that night. Titan divides the gap in hours by 2 and subtracts it from 100%, so a night 30 minutes from the median scores 75% and a night 2 hours or more away scores 0%. It needs at least 3 nights with data in the window. Consistency is built from hours asleep only. Bedtime and wake clock times do not enter it.

The clock time lives in a second number, target wake time, which is the median time your sleep ended over the last 14 days. Waking within 30 minutes of it counts as aligned. Titan pairs last night's wake time with your latest consistency value to choose a coaching message on the Sleep screen.

Consider two 8 hour nights, one from 11:00 PM to 7:00 AM and one from 1:00 AM to 9:00 AM, in a week where your median is 8 hours and your target wake time is 7:00. Both score 100% consistency, because the hours match. Only the second one shows up as a problem, as a wake time two hours past target. The Sleep Regularity Index would penalize the second night, and so should you. Read consistency and target wake time together. Sleep consistency also feeds Titan Age as one of its Recovery signals, averaged across the week.

04A short night does not average out

Van Dongen's participants did not adapt to 6 hours. Their performance kept sliding for two weeks, and lapses in alertness rose almost linearly with cumulative time awake beyond about 15.8 hours a day. That is the physiological sense of sleep debt. The cost of lost sleep builds across nights, and one long night does not restore performance that took a week to lose.

Titan's sleep debt reports the shortfall one night at a time against your sleep need, which is the Sleep Debt Threshold setting, 7.5 hours by default and adjustable from 5 to 12 hours in half-hour steps. Sleep 6 hours against a 7.5 hour need and that night carries 1.5 hours of debt. Sleep 9 hours the next night and that night carries 0. Titan does not keep a running total and does not let the long night pay back the short one. A night with no sleep data has no debt value at all, neither 0 nor a full night short.

The per-night design keeps each bar honest, and it leaves the accumulation for you to read. Four bars of 1 hour across a hard week is the pattern the Van Dongen data warn about, even though no single bar looks alarming. The Debt tab on the Sleep screen charts 7, 30 or 60 days, and the week view is the one to check. For how to read those bars, when a weekend lie-in helps and when it only moves your clock, see sleep debt explained.

One setting deserves attention during a heavy block. The Training Goal does not change your sleep need in the current app. If you move into peak training and want a higher need, raise the Sleep Debt Threshold yourself at Settings > Recovery & Sleep.

05Why a rough night shows up in HRV and resting heart rate

Heart rate variability at rest is mostly a readout of parasympathetic, or vagal, activity. Sleep loss shifts the autonomic balance toward sympathetic drive. Fullagar et al. (2015, Sports Medicine) concluded in their review that reduced sleep quality and quantity could produce an autonomic imbalance that mimics the symptoms of overtraining syndrome, along with a rise in pro-inflammatory cytokines. A 2025 meta-analysis of 11 randomized trials with 549 participants found that sleep deprivation significantly lowered RMSSD, the short-term vagal index most wearables report, and raised the LF/HF ratio, a marker of relative sympathetic activity (Zhang et al., 2025, Frontiers in Neurology).

That is why a short or broken night so often greets you with a low HRV and a raised resting heart rate the next morning. Training causes the same pattern, which is the problem. A low morning HRV after a short night and a low morning HRV after three hard days look identical on the watch. The sleep data is how you tell them apart.

Titan's Recovery score reads one HRV value and one resting heart rate value per day. By default the HRV comes from a Mindfulness session recorded before noon if there is one, then from the average HRV during your night's sleep. Titan compares each input with the median of your baseline window, 7, 30 or 60 days, in units of your own median absolute deviation, which is your normal day-to-day spread. Baselines covers how each window behaves. Five weighted signals go through a logistic curve, and the result is placed against your last 60 Recovery calculations, with your 10th percentile mapped to 0 and your 90th to 100. The score is personal by construction. A 5 ms drop means a lot for someone whose HRV rarely moves and little for someone whose HRV swings every day.

Outside the app, use one rule of thumb. A morning HRV more than one median absolute deviation below your baseline median for two or more consecutive days, with resting heart rate above baseline, is a signal to pull intensity. One low morning after one short night is a data point. Two in a row with a raised resting heart rate is a pattern, and if the sleep bars show the same two nights short, you know the cause. For the full treatment of HRV-guided training, see the HRV training readiness guide.

06Sleep and injury risk

Milewski et al. (2014, Journal of Pediatric Orthopaedics) surveyed 112 athletes in grades 7 through 12 and checked their injury records. Athletes who slept under 8 hours a night on average were 1.7 times as likely to have had an injury as those who slept 8 hours or more. Eight hours is the bottom of the teenage range in the National Sleep Foundation table, so the short sleepers in that sample were below their own age norm. The study is observational, relied on self-reported sleep and covered adolescents, so the 1.7 figure should not be applied to adult athletes as a precise estimate. It remains the most cited number in the field because it points the same way as everything else.

The mechanism is plausible and measurable. Vitale et al. (2019, International Journal of Sports Medicine), in a review of sleep hygiene for athletes, list the effects of sleep deprivation that the lab literature agrees on, slower reaction time, lower accuracy, reduced submaximal strength and endurance, and worse judgment and decision-making. A defender who reacts late, a lifter whose bar path drifts in the last rep, or a runner who misjudges footing at the end of a long run is at higher risk for the same reason. Charest and Grandner (2020, Sleep Medicine Clinics) and the Walsh consensus both treat sleep as a modifiable factor in injury prevention, one that costs nothing to change.

07Napping without wrecking your next night

The Sleep Foundation's guidance for adults is a nap of about 20 minutes and no longer than 30, taken eight or more hours before bedtime, which for most people means before 3:00 PM. Short naps stay in light sleep. Grogginess after a nap usually comes from waking out of deep sleep, which longer naps reach. A nap of around 90 minutes can cover a full cycle and avoid that, at the risk of taking sleep pressure away from the night if it comes too late in the day.

For athletes, naps have two legitimate jobs. The first is repair on a day when the night fell short, with a 20 minute nap before an afternoon session. The second is planned. Vitale et al. (2019) describe sleep banking, extending sleep on the nights before a known deficit such as an early race start, an overnight event or a travel day. A few nights of longer sleep before the deficit appear to blunt its effect, a small idea with a large practical return for anyone who races early in the morning.

Titan's sleep detection rules decide what happens to a nap in your data. A session counts for the calendar day it ends on, and it must end after midnight and no later than noon. An afternoon nap ends after noon, so Titan ignores it. It adds nothing to your time asleep, your Sleep score or your sleep debt, and on a day you napped for an hour after a short night the debt bar will overstate how far short you actually came up.

A morning nap follows two other rules. Samples join one session when each starts within 2 hours of the previous one ending, so going back to sleep at 8:30 after waking at 7:00 folds into the night. The gap shows on the timeline and adds nothing, and the extra sleep counts toward the night's total. A nap that starts more than 2 hours after you woke forms a separate session, and when two sessions end before noon on the same day, Titan keeps the one with more time asleep and drops the other.

08Travel, jet lag and training camps

The Sleep Foundation puts jet lag at 1 to 1.5 days per time zone crossed, with wide individual variation, and about 75% of people find eastward travel harder than westward. A six-zone trip east can take six to nine days to clear completely. An athlete who arrives two days before a race is racing on a clock that is still several hours out of place, and the plan should expect it.

Light is the strongest tool for shifting the clock, and the Sleep Foundation is blunt that the timing is easy to get wrong. Light at the wrong time of the circadian day pushes the clock the wrong way. For a short trip of a day or two, many athletes are better served by holding home-time sleep and training as closely as the schedule allows. For a training camp or a long stay, the goal is to move the clock quickly, and the Phillips findings describe what helps, regular sleep and regular daylight exposure at the new local wake time.

Travel also produces the nights your data handles worst. Titan assigns each session to the day it ends on in your phone's local time, so the noon cutoff moves with the phone when it changes zones. A long recovery sleep after arrival that ends at 1:00 PM counts for no day. A jet-lagged night with a 3 hour stretch awake in the middle splits into two sessions, and only the one with more time asleep counts toward the day. If a travel night looks missing or short, the missing sleep article walks through the checks in order. Expect Recovery to read low for a few days after a long trip as well. Disrupted sleep lowers HRV, as the Zhang meta-analysis showed, and a travel week supplies plenty of it. A low score in that week says little about your fitness.

09Alcohol and late training sessions

Alcohol is the most common reason a normal-length night scores badly. Ebrahim et al. (2013) reviewed the controlled studies. Alcohol shortens the time to fall asleep at every dose and consolidates the first half of the night, then disrupts the second half. It delays the first REM period at every dose, reduces total REM at higher doses and increases slow wave sleep in the first half. The result is exactly the unbalanced night described above, deep-heavy early and fragmented late.

The heart shows it too. Pietilä et al. (2018, JMIR Mental Health) analysed beat-to-beat heart data from the first 3 hours of sleep in 4,098 Finnish employees, comparing each person's nights with and without alcohol. The HRV-derived recovery state fell by an average of 9.3, 24.0 and 39.2 percentage points after low, moderate and high intake, with low defined as 0.25 g/kg or less. For a 70 kg adult that is up to about 17 grams of alcohol, a little more than one US standard drink. Physically active participants were not protected, and the effect was stronger in younger people. Since Titan's Recovery score reads your average overnight HRV by default, a drink with dinner lands directly on the next morning's number.

To see what alcohol does to your own data, tag it in the Journal. Journal Insights compares your Sleep score, sleep debt or Recovery score on tagged days against untagged days over 60 days. Titan compares a tag with the score stored for the same calendar day, and a Sleep score belongs to the morning you woke up. Put the tag on the date you woke up after drinking, using the date picker at the top of the Journal screen, so it lines up with the night alcohol could have affected.

Late training is less of a problem than most advice suggests. Stutz et al. (2019, Sports Medicine) pooled 23 studies of evening exercise and found that it did not impair sleep. Evening exercise slightly increased slow wave sleep and delayed REM onset by 7.7 minutes. The exception was vigorous exercise ending within an hour of bedtime, which may lengthen the time to fall asleep and reduce total sleep and sleep efficiency. Higher body temperature at bedtime and a session that was hard relative to the person's usual activity both predicted more time awake after sleep onset. A 9:00 PM interval session followed by lights out at 10:00 is the case to avoid. In score terms it shows up as awake time.

10How accurate the watch is at staging

Every number above depends on the watch getting the night right, and consumer sleep tracking is better at some parts of the night than others. Chinoy et al. (2021, Sleep) tested seven consumer sleep trackers against polysomnography in 34 healthy young adults over three nights, one of them deliberately disrupted. Epoch-by-epoch sensitivity for sleep was high on every device, 0.93 or above. Specificity, the ability to recognize wake, ran from 0.18 to 0.54. Stage agreement was mixed, and devices performed worse on disrupted nights. Apple Watch was not among the devices tested.

The general pattern is that wearables detect sleep well, undercount time awake and estimate stages with real error. That shapes how to use the numbers. Total time asleep is the most reliable. Deep and REM minutes are best compared with your own recent nights on the same device, since a consistent bias cancels out when you compare yourself with yourself. For the Apple Watch evidence specifically, see how accurate Apple Watch sleep tracking is.

If you wear two trackers, Titan merges their samples slice by slice and keeps the highest-priority stage in each slice, with Awake ranked above every sleep stage. A wake-up that one device catches and the other misses still counts as awake time. Choosing your sleep source explains how to set a preferred tracker and what happens on nights it misses.

11How a Sleep score gets built from Apple Watch data

Most wearable makers explain what goes into their sleep score and stop there. Oura's own explainer names seven contributors, total sleep, efficiency, restfulness, REM sleep, deep sleep, latency and timing, and does not publish how they are weighted. Titan publishes its weights, its exponents and a worked example in the Sleep score help article, which makes it possible to see what a sleep score actually is.

Three parts and their weights

Titan scores a night with stage data on three parts. Each part earns a result between 0 and 1. Titan multiplies each result by its weight, adds them, divides by the total weight of 0.68, and raises the result to the power 0.9.

Duration. Time asleep divided by your target, raised to the power 0.82. Meeting the target earns full credit, and sleeping past it adds nothing. The power below 1 means the first hours of shortfall cost less than a strict ratio would. Seven hours against an 8 hour target is 87.5% of the target and earns 0.90. Time in bed spent awake does not count.

Restorative sleep. Titan treats Deep plus REM at 40% of time asleep as a typical night. Reaching 40% earns full credit on the first piece, which makes up 82% of this part. The remaining 18% rewards an even split between Deep and REM. Equal amounts earn full balance credit, and a night with REM and no Deep earns none. This is the mechanic that separates the alcohol night from a normal one.

Awake time. Awake time divided by time in bed, compared against a cap of 20%. Credit falls as the awake share rises. At 5% awake the part keeps about 80% of its credit, and at 20% or more it scores zero.

The final power of 0.9 lifts middle scores slightly. A combined result of 50 becomes about 54.

The worked example, and two variations

The help article's example uses an 8 hour target and a night with 7 hours asleep, 7.5 hours in bed, 30 minutes awake, 1 hour of Deep and 1.5 hours of REM. Deep plus REM is 2.5 hours, or 36% of time asleep, a little under the 40% reference, and the split leans toward REM.

Dividing 0.583 by 0.68 gives 0.857, and 0.857 raised to the power 0.9 gives 0.87. The night scores 87, in the Excellent band.

Change only the stages. Keep 7 hours asleep and 30 minutes awake, and suppose the night had 1.4 hours of Deep and 1.4 hours of REM. That is 40% of time asleep with an exact even split, so restorative sleep earns full credit, 1.0. The weighted sum becomes 0.270 plus 0.240 plus 0.102, or 0.612. Divided by 0.68 that is 0.90, and after the 0.9 power the night scores 91.

Now go back to the original stages and add awake time. Keep 7 hours asleep, but spend 8.75 hours in bed, so 1.75 hours awake. That is 20% of time in bed, and the awake part drops to zero. The weighted sum is 0.270 plus 0.211, or 0.481. Divided by 0.68 that is 0.71, and the score falls to 73, in the Good band. The same 7 hours of sleep and the same stages lost 14 points to a night of lying awake, which is what a late hard session or a second-half alcohol night looks like in the data.

The three versions show which part moves the score most. Duration carries 44% of the score and caps at the target, so for a night well short of the target, more sleep moves the score fastest. For a night near the target, awake time is the part that swings hardest, because its credit falls to zero over a narrow range.

Nights with duration only

Some trackers record time asleep without stages. For those nights Titan scores duration alone, applies the same 0.9 power, and leaves the restorative sleep figure blank. Meeting the target scores 100.

Nothing counts against a duration-only night for low Deep and REM or for time awake, so 7 hours from a stage-less tracker scores 91 while the staged 7 hour night in the worked example scores 87. If your scores jump after you change trackers, check whether the new one records stages before concluding you sleep better.

Two targets, and which one each screen uses

Titan keeps two sleep settings. Today and the Sleep screen score against your Sleep Goal, 8 hours by default, set in your profile under Daily Targets with a range of 4 to 12 hours. When Trends recalculates your sleep history, it scores those nights against the Sleep Debt Threshold, 7.5 hours by default, the same number that defines your sleep need. A duration-only 7 hour night scores 91 against 8 hours and 95 against 7.5 hours. Both screens write to the same score history, so when the two targets differ, a past night's score depends on which screen last recalculated it. Set both to the same value. During a hard training block, 8 hours for both is a reasonable place to start, and the Stanford data argue for going higher if your schedule allows it.

What the headline score leaves out

Interruptions, sleep stress, breathing rate and blood oxygen do not change the headline Sleep score. Titan puts them in a separate Sleep Quality calculation, alongside restorative sleep and awake time, that scores wake-ups per hour, overnight stress, distance from your median breathing rate and blood oxygen between 93% and 97%. The Sleep screen does not display this score today. The headline number stays a measure of how much you slept, how much of it was restorative and how much of the night you spent awake.

Score bands

12The Sleep screen in Titan

Everything in this article resolves on one screen. Tap the Sleep card on Today to open the Sleep screen. The ring shows last night's score and its band, with time asleep, the restorative sleep percentage, the distance from your target and the device that tracked the night underneath. The Sleep target section shows Target, your Sleep Goal, next to Need, your Sleep Debt Threshold, and holds your Target Wake Time, which expands to show its coaching message when tapped. The Sleep history chart switches between views over 7, 30 or 60 days, including Debt for the nightly shortfall and Consistency for night-to-night regularity. Each morning, check the score, then the week of debt bars, then whether you woke within 30 minutes of your target. The Sleep score help article documents every number on the screen.

13References

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