Cardio and heart-rate zones

Cardio is not the enemy of muscle. Done in sensible amounts, it strengthens your heart, improves your work capacity in the gym and helps with fat loss. This guide covers how much to do, how hard to go, and how to use heart-rate zones without overthinking them.

How much you need

The WHO’s physical activity guidelines for adults recommend, every week:

• 150-300 minutes of moderate aerobic activity, or
• 75-150 minutes of vigorous activity, or an equivalent mix of the two
• Muscle-strengthening activity on 2 or more days

Moderate means you can talk but not sing. Vigorous means you can only say a few words before needing a breath. The WHO also stresses that any activity is better than none, and that cutting down long periods of sitting helps on its own.

For someone who lifts, a practical target is 2-3 cardio sessions of 20-40 minutes a week, plus plenty of daily walking.

Finding your maximum heart rate

Heart-rate zones are percentages of your maximum heart rate. Testing a true maximum is hard and not advisable for most people, so it is estimated from age.

The app uses the Tanaka formula, which tracks real maximums across adult ages more closely than the old 220 minus age:

Maximum heart rate = 208 - 0.7 x age

For a 30-year-old, that is 208 - 21 = 187 beats per minute.

Any formula is an average; your real maximum can be 10 or more beats higher or lower. Treat zones as a guide, and cross-check with how the effort feels.

The Karvonen method

If you know your resting heart rate, the Karvonen method gives more personal zones. It works on your heart-rate reserve, the gap between resting and maximum:

Target = resting + (maximum - resting) x intensity

Measure resting heart rate in the morning, before getting out of bed, for a few days and take the average. A fitness watch will also estimate it.

Worked example

A 30-year-old with a resting heart rate of 60:

• Maximum: 187
• Reserve: 187 - 60 = 127
• 60% intensity: 60 + 127 x 0.6 = about 136

Without a resting heart rate, the app falls back to plain percentages of maximum, the right-hand column. Get your own numbers from the heart-rate zones calculator.

What each zone is for

Zone 1: recovery

Very easy movement such as a gentle walk or easy cycling. It helps blood flow and recovery without adding fatigue.

Zone 2: endurance

Steady, conversational effort: brisk walking, easy jogging, cycling or swimming. This is where most of your cardio should be. It builds your aerobic base and heart health, and it is easy to recover from, so it does not interfere much with lifting.

Zone 3: tempo

Comfortably hard. Useful for runners and sport players, but easy to overdo; many people drift into this zone on every run and end up tired without getting much fitter.

Zones 4 and 5: threshold and max

Hard intervals, sprints, and the hardest moments of a match. These build top-end fitness but are costly to recover from. For lifters, one short session a week is plenty, and it should be kept away from heavy leg days.

A simple split

Keep roughly 80% of your cardio easy (zones 1-2) and 20% hard (zones 4-5), a pattern long used by endurance athletes. If you only do cardio for health, almost all of it can be zone 2 and brisk walking.

Walking deserves more credit

Walking is the most underrated form of cardio.

• It counts towards the WHO’s moderate minutes when done briskly.
• It burns meaningful energy without hurting recovery: a 70 kg person burns about 150 kcal in 30 minutes of brisk walking.
• A 10-15 minute walk after meals helps blood sugar control, which matters for South Asians, who are at high risk of type 2 diabetes.
• It needs no equipment, no gym and no recovery days.

Aim for about 7,000-10,000 steps a day. Easy ways to get there:

• A walk after lunch and after dinner
• Taking calls on foot
• Using the stairs and getting off the auto or metro one stop early
• An evening walk in the park with family

Estimate what any activity costs with the calories-burned calculator. It multiplies the activity’s metabolic equivalent by your weight and time; running at 10 km/h for 30 minutes, for example, burns about 340 kcal for a 70 kg person.

Fitting cardio around lifting

• Separate them where possible: different days, or lifting first if they share a session.
• Keep hard cardio away from heavy leg days.
• Prefer low-impact options such as cycling, swimming or incline walking when your legs are already working hard.
• On a fat-loss phase, raise steps first and add cardio second. See fat loss.

If you play a sport, see training with sports.

Safety

Start gently if you are new to exercise, and build up over a few weeks. Stop and get medical help if you feel chest pain or pressure, unusual breathlessness, dizziness or palpitations. Some medicines, such as beta blockers, lower your heart rate, which makes zone formulas unreliable; ask your doctor how hard to train.

This is general information, not medical advice; see a doctor before starting vigorous exercise if you have heart disease, high blood pressure, diabetes or any symptoms during activity.