Fitness trends

What to expect

Three measures of how your body is responding to training, taken from the sessions you already record.

Estimated VO2 max. How much oxygen you can use at full effort, the standard single number for aerobic fitness. Estimated from the relationship between your heart rate and the work you are doing, so it improves as you train rather than sitting where a one-off test left it.

Heart rate variability. The variation in time between beats, which reflects how recovered and how stressed you are. Measured from the same chest strap signal that drives your zones.

Recovery speed. How quickly your heart rate falls once you ease off. One of the clearest markers of aerobic fitness, and one that changes noticeably within weeks of starting to train.

Watching them move

A single reading of any of these is close to meaningless. Bodies vary day to day with sleep, heat, caffeine and stress, and a VO2 max estimate from one session carries real uncertainty.

So these are shown as trends, over months, with the noise smoothed out and the honest spread visible rather than hidden behind a confident-looking number. Alongside them sits how much you actually trained in the same period, because that is the context that makes a change mean anything: fitness drifting down through a month of missed weeks is a different story from the same drop during a heavy block.

Estimates get better with more data. Early on you will see a wide range rather than a precise figure, and it will narrow as you record more.

What this is not

These are estimates from a chest strap, not laboratory measurements, and we will not dress them up as more than that. A proper VO2 max test involves a mask and a treadmill.

Nor is any of it medical. Heart rate variability in particular is easy to over-read: it is genuinely useful for spotting your own trend, and not a diagnosis of anything.

Why we're building it

Zone points measure what you did. They cannot tell you whether it is working.

Two people can put in identical weeks and adapt at completely different rates, and the only way to know which one you are is to watch your own numbers over time. Recovery speed in particular improves early and visibly, which makes it the most encouraging thing an app can show someone in their first couple of months.

When it's ready

No date yet. Use Vote for this feature at the top of this page and you'll get one email the day it ships.