The running app that adapts to your recovery
Most apps show your HRV and recovery but never change the plan. Here is how an app that actually adjusts training to sleep, resting heart rate, and HRV works.
The 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 it anyway, swap to something easy, or rest?
Most training apps leave that decision entirely to you.
What HRV, resting heart rate and sleep actually tell you
HRV measures the variation between your heartbeats and reflects how your autonomic nervous system is doing. High variation usually means you're recovered. A clear dip can mean your body is still working through load, lack of sleep, stress or an infection on the way.
A single morning tells you very little. What matters is the trend against your own baseline over days and weeks, and the numbers are individual enough that your normal HRV can't be compared to anyone else's.
HRV, resting heart rate and sleep usually point the same way. When all three dip together the signal is far 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 measures sleep and readiness. They're good at measuring and displaying.
That's usually where it ends. You get a number, and your session sits there exactly as planned.
The interpretation is yours. You connect the data to today's workout and decide whether to ease the pace, swap the session or add a rest day. It's a small decision every day, and it's easy to either push too hard or become overcautious.
What it means for the plan to actually adapt
An app that adapts to recovery makes the difference 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 look bad. That an extra rest day appears when the trend points the wrong way several days running. Or that weekly volume comes down when load is climbing faster than recovery can keep up.
The point isn't to react to every noisy reading, but to catch the actual trend and adjust before a small signal turns into a long break.
How Coach Fartlek does it
Coach Fartlek reads both your workouts and your recovery data through Intervals.icu, meaning HRV, resting heart rate and sleep alongside the training itself. It keeps a baseline for you and looks at the trend rather than 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.
If the numbers look fine but you still feel worn down, you can say so in your own words and it gets taken into account.
It's deliberately built around trends 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. Measure at the same time, ideally first thing in the morning, and in the same position every time. Lying down one day and standing the next just measures noise.
And look at the week, not yesterday's single value.
If you have a Garmin, Coros, Suunto or Polar, the data is already being collected. Connecting your watch to Intervals.icu gives Coach Fartlek access to both your workouts and your recovery.
For the bigger picture on how the coach thinks, see what makes Coach Fartlek different.
Questions and answers
Can you guide running training with HRV?
Yes, but not slavishly. HRV works best as a trend against your own baseline — a clear dip over several days is a signal to back off, while a single low morning rarely means much. Coach Fartlek weighs HRV together with resting heart rate and sleep.
Which app adapts training to recovery?
Most apps (Garmin, Whoop, Oura) show your recovery but don't change the plan. Coach Fartlek reads HRV, resting heart rate, and sleep via Intervals.icu and adjusts upcoming sessions automatically based on your trend.
Is HRV reliable?
HRV is useful if you measure consistently — same time, same position, every morning — and look at the trend over a week rather than single values. Individual days are noisy.
Meet your coach
Coach Fartlek builds your plan from your Intervals.icu history — and keeps adjusting it, every single day.