Heart rate
/ zones.

1. Set your age. The calculator estimates your max heart rate from it. If you have seen a real max on a chest strap or watch, choose "I know it" and enter that instead. It will be closer.
2. Add a resting heart rate if you have one. Take it lying down on waking, or read the overnight figure from a watch. With it, the zones are worked out from your heart rate reserve, which fits fitter people better.
3. Train by the rows. Tap any zone to see its range on the band. Easy days sit in zones 1 and 2, hard intervals in 4 and 5. Copy the link and the numbers come back exactly as you left them.

Formula maxes are rough. For any one person the real number can sit 10 to 20 beats above or below the estimate. If the zones feel wrong against how hard you are breathing, trust the breathing and find your real max (see below). This is a training guide, not medical advice.

Five zones is the common model used by most watches, bikes and coaches. The bands here are the standard 10% steps from 50 to 100%.

Zone 1, recovery (50 to 60%)

Barely working. Warm-ups, cool-downs, walking and easy spins on a rest day. It helps you recover without adding fatigue.

Zone 2, aerobic base (60 to 70%)

You can hold a full conversation. This is where the heart, lungs and muscles get better at using oxygen and burning fat, and it is the zone most athletes spend too little time in.

Zone 3, tempo (70 to 80%)

Comfortably hard, talking in short sentences. Steady runs and longer rows. Useful, but easy to drift into on every session so that nothing is truly easy or truly hard.

Zone 4, threshold (80 to 90%)

Hard, a few words at a time. Around the point where lactate builds faster than you clear it. Raising this ceiling is what lets you hold a faster pace for longer.

Zone 5, max (90 to 100%)

All out, sustainable for seconds to a couple of minutes. Sprints, short intervals and the last round of a workout. Heart rate lags behind effort, so in short bursts you may finish before the number catches up.

Endurance coaches have long had athletes do most of their volume easy, often around 80% of weekly time in zones 1 and 2, with the hard 20% done properly hard. Easy work builds the aerobic base cheaply: it recovers fast, so you can do a lot of it, and it makes every harder effort feel easier.

The honest problem is that zone 2 feels too easy. Most people creep into zone 3 because they want the session to feel like training. Use the number, and if you have to walk the hills or slow the rower to stay under it, that is the session working. The running pace calculator and rowing pace calculator help you plan what that pace looks like over a set distance.

Mixed-modal workouts, the ones with thrusters, burpees, wall balls and a rower, push heart rate high and keep it there. A 10 to 20 minute AMRAP will usually sit in zone 4 with spikes into 5, and short couplets like Fran live almost entirely at the top. That is by design. It is also why a program made only of metcons can leave the aerobic base underbuilt.

A simple fix is to add one or two easy zone 2 sessions a week, a long row, an easy run or a recovery spin, and keep the hard days hard. Set up your intervals on the WOD timer and watch where your heart rate lands in each round.

Age formulas describe a population, not you. Two 30-year-olds can have maxes of 175 and 205 and both be perfectly healthy. A higher max is not a sign of better fitness either, it is just how your heart is built.

• Check your history. If you train with a chest strap, the highest figure from your hardest sessions in the last few months is a good working max. Wrist sensors often spike or lag in intense workouts, so treat a single odd reading with suspicion.
• Run a field test. After a thorough warm-up, run or row hard for 3 minutes, recover for 3, then go all out for another 3, finishing with a sprint. The peak is close to your max. Only do this if you are healthy and used to hard efforts.
• Get it tested. A lab or clinic exercise test is the most accurate option and the right one if you have any health concerns.

Percentage of max is the simple version: zone 2 is 60 to 70% of your max heart rate. It is what most watches use by default.

The Karvonen method uses your heart rate reserve, the gap between your resting and maximum rates. Zone 2 becomes resting rate plus 60 to 70% of that gap. Because a fit athlete's resting rate is low, the reserve is large, and the zones shift upward to match how their heart actually behaves. For two people with the same max, the one with the lower resting rate gets higher easy zones.

If you know your resting heart rate, Karvonen is usually the better fit. If you don't, percentage of max is a sound starting point.