What is Body Charge? Cora's 0-100 Recovery Score Explained

Every morning you face the same question: push hard, go easy, or rest? Most people answer based on feel, which leads to a predictable mismatch — hard days when recovery is needed, easy days when a harder session would have built fitness. Over months, this mismatch compounds into plateaus, minor injuries, and frustration. Body Charge exists to replace that guesswork with a single, data-grounded number.

What the 0–100 scale actually means

The score is not a percentage of some theoretical maximum — it is your current readiness relative to your own recent history. A 75 for you might represent better recovery than an 85 for someone who has a higher baseline. This personal calibration is intentional: it makes the score useful regardless of fitness level, age, or device.

• 70–100 (Green): Well-recovered. Ready for hard intervals, heavy lifting, long efforts, or competition.
• 40–69 (Yellow): Moderate readiness. Zone 2 cardio, moderate-weight strength work, and skill-based sessions are appropriate.
• 0–39 (Red): Accumulated fatigue. Active recovery, mobility, walking, or full rest is recommended.

The four inputs: how Body Charge is calculated

1. Sleep quality

Sleep is the primary driver of overnight recovery. Cora evaluates sleep duration, efficiency (percentage of time in bed actually asleep), and — when available from Apple Health — deep and REM sleep stages. A night of fragmented sleep or less than 6 hours reliably depresses the following day's score.

2. HRV trend

Heart rate variability reflects autonomic nervous system balance. Rather than using a single night's HRV reading (which can fluctuate 20–30% from noise alone), Body Charge tracks the 7-day trend relative to your 30-day rolling average. A sustained HRV decline — even mild — is a meaningful recovery signal. See what is HRV for a deeper explanation of the metric.

3. Resting heart rate

Resting heart rate (RHR) rises when the body is under physiological stress — illness, overtraining, poor sleep, or dehydration. An RHR reading 5+ bpm above your personal average consistently predicts impaired performance and recovery. Cora uses overnight RHR from your Apple Watch rather than a spot measurement, which gives a more stable signal.

4. Training load

Acute training load measures the stress applied over the last 7 days, while chronic training load reflects the last 28 days. The ratio between these — sometimes called the Acute:Chronic Workload Ratio (ACWR) — is one of the most validated predictors of overreaching risk in sports science. Body Charge incorporates this ratio so that a single brutal workout doesn't crater the score the same way a two-week overload block does.

Body Charge vs. Whoop Recovery vs. Garmin Body Battery

Why your score dropped even though you feel fine

This is the most common question new users have. The answer is almost always one of three things:

1. Sleep efficiency was low. You may have spent 8 hours in bed but only had 6 hours of quality sleep. Restlessness, waking in the night, or early-morning waking all reduce sleep efficiency without necessarily making you feel tired.
2. HRV has been trending down for several days. A single low HRV night doesn't move the score much. But a 5-day downward trend — even from mild accumulated stress — will lower the score noticeably.
3. Training load spiked. If last week's mileage or volume was significantly higher than your chronic average, the score captures that even if your legs feel okay. The body often feels fine right before overuse injuries manifest.

Feeling fine is a useful signal, but it is not a complete one. Body Charge is designed to catch the physiological signals that precede how you will feel tomorrow, not just today.

How to improve your Body Charge

Because four inputs feed the score, there are four levers to pull:

Sleep: the highest-leverage change

Consistent sleep timing matters more than duration alone. Studies consistently show that athletes with variable sleep schedules (shifting bedtime by more than 60 minutes) show worse recovery metrics than those sleeping the same total hours on a fixed schedule. Targeting 7–9 hours with consistent timing will move the sleep component of Body Charge more reliably than any supplement or recovery device.

HRV: manage stress, not just workouts

HRV responds to all stressors — not only training. Work stress, alcohol, travel, illness, and poor nutrition all suppress HRV. The most effective HRV interventions in the research literature are: consistent aerobic training at low intensity (Zone 2), regular breathing exercises (slow diaphragmatic breathing at 5–6 breaths/minute), and reducing alcohol consumption. See our full guide to HRV-guided training for implementation details.

Resting heart rate: address the basics

Elevated RHR is often a hydration or illness signal. Ensure you are drinking adequate water, particularly in the hours before sleep. For chronic RHR elevation, increasing Zone 2 cardio volume over 8–12 weeks is the most reliable intervention — trained aerobic systems maintain lower RHR at rest.

Training load: build a periodized structure

The most common training load error is monotony — doing the same weekly volume indefinitely. Periodization — alternating harder and easier weeks (typically a 3:1 ratio of loading to deload) — allows the score to recover and the fitness gains to consolidate. See the deload week guide for how to structure easier weeks without losing fitness.

How Cora uses Body Charge to adjust your training

Body Charge is not a standalone metric — it is the input to Cora's daily coaching decision. When your score is in the green zone, Cora will schedule or confirm harder sessions: interval work, strength training, long runs. In the yellow zone, the AI coach may suggest reducing intensity or swapping a hard session for a moderate one. In the red zone, Cora will actively recommend rest or active recovery and flag if you attempt to log a hard session.

This is the key difference from using a recovery app alongside a static training plan: the plan adapts based on your real-time physiological state rather than requiring you to manually decide whether to follow or ignore today's scheduled session.

Body Charge during planned hard training blocks

It is normal and expected for Body Charge to run below your baseline during intentional overload phases — pre-race build-up, a strength hypertrophy block, or a structured high-volume cycle. The score should suppress during these periods. What you are watching for is whether the score recovers during the planned taper or deload. If it does, the training was productive. If it does not recover after a deload week, that is a signal the training load was excessive relative to your recovery capacity.

For more on how to structure your workouts around Body Charge, see our guides on deload weeks and HRV-guided training. You can also use the heart rate recovery calculator and resting heart rate tool to track the individual inputs over time.