The running app that adapts to your recovery

Your plan says intervals tomorrow. But you slept badly, your resting heart rate is five beats high, and your HRV is below normal. Do you run anyway, swap it for an easy session, or rest? Most training apps leave that decision entirely to you.

This is about the difference between an app that shows your recovery and one that actually does something about it.

What HRV, resting heart rate, and sleep actually tell you

HRV (heart rate variability) measures the variation between your heartbeats and reflects how your autonomic nervous system is coping. More variation usually means you're recovered; a clear dip can mean your body is still dealing with training load, poor sleep, stress, or a coming infection.

Three things worth keeping in mind:

• A single morning tells you little. What matters is the trend against your own baseline over days and weeks.
• The numbers are individual. Your normal HRV can't be compared with anyone else's.
• HRV, resting heart rate, and sleep usually point the same way. When all three drop together, the signal is stronger than when only one does.

Most apps show recovery — but don't change the plan

Garmin has Body Battery and Training Readiness. Whoop gives you a recovery percentage every morning. Oura tracks sleep and readiness. They're good at measuring and displaying.

But that's usually where it ends. You get a number — and your workout stays exactly as planned. It's on you to interpret the data, connect it to today's session, and decide whether to ease off, swap the workout, or add a rest day. It's a small decision every day, and it's easy to either push too hard or get overly cautious.

What it means for a plan to actually adapt

An app that adapts to recovery closes the loop at the other end: the plan changes. In practice that can mean

• an interval session becomes an easy run on a day when the signals are poor,
• an extra rest day when the trend points the wrong way several days in a row,
• the week's volume comes down when load is climbing faster than your recovery can keep up.

The point isn't to react to every noisy reading, but to catch the real trend and adjust training before a small signal turns into a longer break.

How Coach Fartlek does it

Coach Fartlek reads both your workouts and your recovery data through Intervals.icu — HRV, resting heart rate, and sleep alongside the training itself. It keeps a baseline for you and looks at the trend, not a single day.

When the signals suggest you're heading toward too much, the coach reaches out on its own and adjusts the sessions ahead. You don't have to open the app and ask. And if the numbers look fine but you still feel worn down, you can just say so in your own words and it's taken into account.

It's deliberately built around trends and baselines rather than knee-jerk reactions. One low morning isn't enough to rewrite the week — a clear trend is.

Measure so the numbers are worth trusting

HRV is only useful if you measure consistently. A few simple habits:

• Measure at the same time, ideally first thing in the morning.
• Measure in the same position (lying or sitting), not standing one day and lying the next.
• Look at the trend over a week, not yesterday's single value.

If you have a Garmin, Coros, Suunto, or Polar, the data is already being collected. By connecting your watch to Intervals.icu, Coach Fartlek gets access to both your workouts and your recovery.

Want the bigger picture on how the coach thinks? See what makes Coach Fartlek different.