Calories burned

See Calories Burned After Every Session

The session summary now shows an estimated calorie burn for every workout, along with two facts to put it in context: how much extra your metabolism burns in the hours afterward (the "afterburn" effect), and how many sessions like this one add up to 1 kg of fat loss.

The Afterburn Effect (EPOC)

Intense cardio keeps your metabolism elevated long after you stop. This is called EPOC — Excess Post-exercise Oxygen Consumption. Crucially, EPOC is not a fixed percentage of calories burned: it scales non-linearly with intensity. Research (Børsheim & Bahr, 2003; LaForgia et al., 2006) puts afterburn at roughly 7% for easy Zone 1 effort and up to 19% for maximal Zone 5 effort, with moderate zones in between.

ZonePoints uses the time you spent in each zone — already tracked for your zone points score — to compute a weighted afterburn that reflects exactly how hard each part of the session was. A session spent mostly in Zone 4 and 5 will show a proportionally larger afterburn than the same total calories at Zone 1 and 2.

Fat-Loss Context

One kilogram of body fat stores approximately 7,700 kcal. ZonePoints shows how many sessions at your current intensity — workout plus afterburn — add up to that milestone, so you have a concrete number to work toward.

Personalise Your Estimate

By default the app assumes a body weight of 70 kg. For a more accurate number, open Settings → Calorie estimation and enter your weight and sex. Weight scales calorie output directly, and sex adjusts the aerobic capacity coefficient to reflect documented differences at equivalent training status. All details are stored on-device only.

How It Works

The estimate is built directly on your zone points — no extra data needed. Zone points accumulate as speed × minutes, where speed encodes your heart-rate reserve (%HRR) at each moment. This means total zone points are mathematically equal to the sum of %HRR × minutes across your session — exactly the workload integral exercise physiologists use to measure cardiovascular effort. Dividing by training time recovers your average %HRR in a single step.

From there, the app applies the standard Karvonen VO₂ model — established by Swain et al. (1994, 1997), who showed that %HRR and %VO₂max are essentially interchangeable:

VO₂ = VO₂rest + %HRR × (VO₂max − VO₂rest)

VO₂max is estimated from your stored max and resting heart rates using the Uth–Sørensen–Overgaard–Pedersen formula (2004): VO₂max ≈ 15.3 × HRmax / HRrest. Fitter people have a lower resting rate relative to their max and automatically receive a higher VO₂max. Finally, one litre of O₂ releases roughly 5 kcal, giving a calories-per-minute figure multiplied by training time.