A user sleeps 9 hours, wakes up feeling rested, and expects their health data to confirm they’re ready to go. But their Readiness Score is 55 — low. Why? Because they’ve been under-sleeping by 90 minutes a night for the past week, ran a personal best 10k two days ago, and their resting heart rate is still elevated 4 beats above their normal baseline. One good night didn’t clear the accumulated load. The body knows, even when the user doesn’t.
The Readiness Score measures how recovered and prepared the body is for the day’s demands. It doesn’t just look at last night — it compares today’s data against a shifting 30-day personal baseline that becomes more tuned to the individual over time. It factors in accumulated sleep debt, recent physical strain, and cardiovascular recovery signals. This is why it can feel decoupled from a single good night of sleep: it’s designed to flag hidden fatigue that hasn’t cleared the system yet.
Think of it less as a performance report and more as a personal weather forecast. It tells you whether to push harder or play it safe — before you feel the crash.
| State | What It Means |
|---|---|
| High (80–100) | Green light — the body is well-recovered and ready for intensity |
| Medium (60–79) | Normal routine — no need to hold back, but no need to push either |
| Low (40–59) | Keep it light — reduce intensity, prioritize lighter activity |
| Minimal (0–39) | Recovery is the priority — avoid heavy exertion, focus on rest |
Science: Every factor in the Readiness Score is grounded in peer-reviewed research. For the evidence behind each one, see The Science Behind the Readiness Score.
Readiness Score Factors
The Readiness Score draws from three domains — sleep recovery, activity strain, and cardiovascular signals — across eight factors. Each returns a value (what was measured), a sub-score (0 to 100), a state, and a goal (a static, evidence-based target).
Sleep Recovery
These factors measure whether the body got the sleep it needed to recover from the previous day’s demands.
Sleep Duration — Total time spent asleep. The same metric as the Sleep Score, but in a readiness context it answers a different question: did the user sleep enough to recover, not just enough in general? A demanding physical day raises the bar — the body needs more recovery time after high strain. Chronic short sleep is the single most common driver of persistently low readiness.
Goal: 8 hours (480 minutes) | Phone
Physical Recovery — Duration and timing of deep sleep (slow-wave sleep). Deep sleep is when the body does its most intensive physical repair — muscle recovery, tissue growth, immune strengthening. In the readiness context, this factor tells your product whether the body got the physical restoration it needed. A user who slept 8 hours but got only 40 minutes of deep sleep may not have recovered as well as someone who slept 7 hours with a full 90 minutes of deep sleep.
Goal: 90 minutes | Wearable
Mental Recovery — Duration and timing of REM sleep. REM sleep is critical for cognitive readiness — memory consolidation, emotional regulation, reaction time. A user preparing for a mentally demanding day (a presentation, an exam, complex decision-making) benefits from knowing whether they got adequate REM. Since REM periods are longest in the later sleep cycles, cutting sleep short disproportionately reduces mental recovery.
Goal: 120 minutes | Wearable
Sleep Debt — Accumulated shortfall between sleep need and sleep obtained over time. Sleep debt is the accumulator that explains why readiness can stay low for days. A user sleeping 6 hours when they need 8 builds 2 hours of debt per night. After five days, that’s 10 hours of accumulated deficit affecting cognitive performance, physical recovery, and stress tolerance. Debt clears gradually over several nights of adequate sleep — not in a single long night.
Goal: 0 hours | Phone
Activity Strain
These factors measure how much physical demand the body has been under and how well it’s coping.
Walking Strain Capacity — How well the body handles low-intensity daily activity based on recent patterns. This is compared against the user’s own 30-day baseline — not a population average. A sudden increase in daily walking (a vacation involving lots of sightseeing, a new commute pattern) will temporarily reduce walking strain capacity as the body adapts. Over time, as the baseline shifts, the same activity level becomes the new normal.
Goal: 1.0 (fully adapted) | Phone
Exercise Strain Capacity — How well the body copes with higher-intensity exertion based on recent training load. This is the “hidden fatigue” detector. Several consecutive days of hard training, a race, or an unusually intense workout will pull exercise strain capacity down — even if the user feels fine the next morning. The factor catches the accumulated load before the user feels the crash. It’s particularly valuable for fitness-oriented users who tend to push through fatigue.
Goal: 1.0 (fully adapted) | Phone
Cardiovascular Signals
These factors measure the body’s physiological recovery state directly, using signals from the autonomic nervous system.
Resting Heart Rate — Lower RHR generally indicates better cardiovascular recovery. What matters isn’t the absolute number — it’s the deviation from the user’s personal baseline. An RHR that’s 4–5 beats above normal often signals incomplete recovery, accumulated stress, or the early stages of illness — sometimes 1–2 days before the user notices symptoms. The 30-day baseline makes this comparison personal and meaningful.
Goal: 58 bpm (varies by individual) | Wearable
Heart Rate Variability — Higher HRV typically signals better stress resilience and parasympathetic recovery. HRV is one of the most sensitive indicators of the autonomic nervous system’s state. A sudden drop in HRV — even with adequate sleep and low strain — can indicate that the body is fighting something (infection, high psychological stress, overtraining). Like RHR, HRV is most meaningful as a deviation from the individual’s baseline, not as an absolute number.
Goal: 55 ms (varies by individual) | Wearable
How Factors Interact
The three domains of readiness — sleep, strain, and cardiovascular signals — create a layered picture that no single domain can provide alone.
Sleep sets the foundation. Without adequate sleep, no amount of low strain or good cardiovascular numbers produces high readiness. Sleep duration and debt are the most common bottleneck — the majority of users with persistently low readiness are chronically under-sleeping.
Strain measures demand. Walking and exercise strain capacity reflect how much the body has been asked to do recently. High strain isn’t inherently bad — it’s how fitness improves. But strain without adequate recovery produces a deficit. The 30-day baseline comparison means the score adapts to the user’s training level: an avid runner and a sedentary desk worker aren’t measured against the same standard.
Cardiovascular signals measure the body’s response. RHR and HRV are the most objective, real-time indicators of recovery state. They’re also the earliest warning system — changes in HRV and RHR often precede noticeable fatigue, illness, or overtraining symptoms by 1–2 days. When sleep and strain look normal but cardiovascular signals are off, something else is going on.
The compound effect. Readiness stays low not because of one bad factor, but because multiple factors accumulate. A week of 6-hour nights (sleep debt building), two intense training sessions (strain capacity dropping), and an elevated resting heart rate (incomplete cardiovascular recovery) — each factor alone might produce a medium score, but together they drive readiness down to low or minimal. This is exactly the scenario the score is designed to catch: the user feels “a bit tired” but the data shows their recovery deficit is larger than they realize.
The 30-Day Baseline
Several readiness factors — particularly strain capacity, RHR, and HRV — are compared against a shifting 30-day personal baseline rather than fixed population norms. This means the score becomes more meaningful over time as it learns the user’s individual patterns. In the first few days, the baseline is rougher. After two weeks, it’s usable. After a month, it’s well-tuned to the individual.
This also means readiness naturally adapts as a user’s fitness changes. As someone trains consistently and becomes fitter, their baseline shifts: the same workout that once suppressed readiness for two days may barely register after months of adaptation.
Factor-to-Habit Guide
Readiness habits are mostly about not doing too much — recovery is the active ingredient.
| Factor | When Low, Suggest… |
|---|---|
| Sleep Duration | ”Get to bed 20-30 minutes earlier tonight” — sleep is the highest-leverage readiness input |
| Physical Recovery | ”Avoid intense exercise close to bedtime — it suppresses deep sleep” |
| Mental Recovery | ”Avoid cutting sleep short — REM is concentrated in the last 1-2 hours of sleep” |
| Sleep Debt | ”You’ve built up a sleep deficit — prioritize consistent 8-hour nights for the next few days” |
| Walking Strain | ”Your body is adapting to a recent increase in daily activity — it will adjust over time” |
| Exercise Strain | ”Swap today’s hard workout for a recovery session — walking, stretching, or yoga” |
| Resting Heart Rate | ”Your resting heart rate is elevated — prioritize rest and hydration today” |
| HRV | ”Your HRV has dropped — your body may be under more stress than you realize. Take it easy” |
Product tip: When readiness is low, the most trusted response is to tell users to rest — not to push them. “Your body is recovering — rest is the right call today” builds more long-term engagement than “you should be more active.” The apps that earn trust are the ones that tell users what they need to hear, not just what drives daily metrics.
Phone vs Wearable
The Readiness Score works with phone data alone — four of eight factors are available without a wearable. Phone factors cover sleep adequacy (duration, debt) and activity strain (walking and exercise capacity). This is enough for basic push-vs-rest guidance: if sleep debt is high and strain capacity is low, the user should take it easy.
Wearable data adds the physiological recovery layer: deep sleep and REM (physical and mental recovery), resting heart rate, and HRV. These are the most sensitive, objective indicators of recovery state — and they’re where wearable data makes the biggest difference across all Sahha scores. HRV and RHR, in particular, can detect recovery issues 1–2 days before the user notices symptoms.
For products targeting fitness-oriented users who are likely to own wearables, readiness is where that data investment pays off most. For broader consumer audiences, the phone-only strain and sleep factors still produce actionable guidance.
Further Reading
- The Science Behind the Readiness Score — peer-reviewed evidence for each contributing factor
- What are Health Scores and Score Factors — foundational guide to the scoring model
- Readiness Score — Docs — API reference, schemas, permissions, and integration details
- Sleep Score Explained — the sleep quality measure that feeds into readiness
- Activity Score Explained — daily activity measurement that complements readiness tracking