How much cardio you actually need

Cardio occupies a strange position. It is simultaneously the thing most people reach for first when they want to lose fat, and one of the less efficient tools for that job. Meanwhile the thing it is genuinely excellent at — keeping you alive longer — is barely mentioned.

Let us separate the two.

For health: do it, and the dose is known

Cardiovascular fitness is among the strongest predictors of all-cause mortality that we can measure. Not body fat, not strength — aerobic capacity. The association is large and consistent across populations.

The standard guidance, which is well supported:

150 minutes a week of moderate-intensity activity, or 75 minutes of vigorous, or a combination. Plus muscle-strengthening activity on two or more days.

Moderate means you can talk but not sing — brisk walking, easy cycling, gardening. Vigorous means you can manage a few words at a time.

That is the health dose. If you do nothing else in this article, do that. The largest health returns come from moving from zero to something, not from optimising an already-active routine.

For fat loss: less impressive than it feels

Here is where expectations go wrong.

A 30-minute run at moderate pace burns somewhere around 300 to 400 calories for an average adult. That is roughly a large flapjack. Forty-five minutes on a cross-trainer might be 350. An hour of moderate cycling, perhaps 500.

Meanwhile the diet side of the equation moves in units of 500 to 700 calories a day without any time cost at all.

Worse, the effect is partly self-cancelling. Structured cardio reliably increases appetite in many people, and it tends to reduce spontaneous movement for the rest of the day — you sit more after a hard session. The net deficit created is frequently much smaller than the number on the machine suggests.

None of this means cardio is useless for fat loss. It means it is a supplement to a dietary deficit, not a substitute for one.

What to do instead, first

Steps. Non-exercise activity — walking, standing, moving about your day — accounts for a far larger share of daily energy expenditure than most people's exercise does, and it does not trigger the same appetite response.

Eight to ten thousand steps a day is, for most people, 300 to 500 calories that structured cardio would have taken 45 minutes to produce. It does not interfere with recovery from lifting, and it does not leave you ravenous.

If you are choosing between adding three cardio sessions and adding 4,000 daily steps, take the steps.

When cardio earns its place

Later in a fat-loss phase, and for a specific reason.

As you get leaner, maintenance falls. Eventually you reach a point where cutting calories further would compromise protein intake, training quality or basic satisfaction with your food. At that point, adding activity is a better way to widen the deficit than removing more food.

That is the moment for structured cardio. Typically:

Two sessions a week, 20 to 30 minutes, moderate intensity, added in the final third of a diet.

Adding it at the start means you have used the tool before you needed it, and you have nowhere to go when progress slows.

HIIT versus steady state

HIIT — short, very hard intervals with recovery — burns more calories per minute and produces a modest elevation in metabolic rate afterwards, the so-called afterburn. That afterburn is real and considerably smaller than the marketing suggests, typically in the region of 6 to 15 per cent of the session's own cost.

Steady state burns fewer calories per minute but is far less fatiguing, so you can do more of it and it interferes less with lifting.

For someone lifting three times a week, steady state is usually the better choice. Hard intervals compete directly with resistance training for recovery, and legs that are trashed from sprint intervals do not squat well two days later.

Use intervals if you enjoy them, if you are short on time, or if you have a specific fitness goal. Do not use them because you think the afterburn is doing heavy lifting.

Does cardio kill your gains?

The interference effect is real but heavily overstated for normal training volumes.

What matters is dose, mode and proximity. Large volumes of running create the most interference with lower-body strength — impact plus overlapping muscle groups. Cycling interferes less. Upper-body-limited work like rowing interferes differently again.

Practical rules that resolve nearly all of it:

• Keep hard cardio and heavy lower-body sessions on different days, or at least six hours apart
• If they must be on the same day, lift first
• Keep cardio volume modest while trying to build muscle — two to three moderate sessions a week will not cost you anything meaningful

At the volumes most people actually do, this is not a problem worth planning around.

Choosing the type

The best cardio is the one you will keep doing. Genuinely — adherence dominates every other consideration.

Walking is underrated, joint-friendly, and can be done while doing something else. Cycling is low-impact and easy to scale. Rowing is efficient and works more of the body. Swimming is excellent if you can already swim well. Running is free and effective but the highest-impact option and the one most likely to produce injury in people carrying extra weight.

If you hate all of them, walk. It counts, and it is the one you will still be doing in a year.

Zone 2, and whether it matters

Zone 2 training — sustained work at an intensity where you can hold a conversation, typically around 60 to 70 per cent of maximum heart rate — has become the subject of a great deal of attention.

The underlying claim is reasonable: prolonged moderate-intensity work drives mitochondrial adaptations and improves fat oxidation and aerobic base. That is well established in endurance physiology and is why endurance athletes spend most of their training hours there.

Where the discussion has run ahead of the evidence is in the specificity. The idea that there is a narrow, precisely defined zone which must be hit exactly, and that training slightly above or below it forfeits the benefit, is not well supported. Moderate steady work is beneficial across a fairly broad band.

For most people the practical version is simply: do some of your cardio at an easy, conversational pace, for thirty to sixty minutes, once or twice a week. You do not need a lactate meter. The talk test is adequate.

Cardio and appetite

One reason cardio disappoints as a fat-loss tool is that the appetite response varies enormously between individuals.

Some people experience little or no compensatory increase in hunger after exercise. Others reliably eat back most of what they burned, without any conscious decision. Both responses are normal, and which one you have is largely outside your control.

The way to find out is to observe. If you add three cardio sessions a week and your weekly weight average does not change over a month with everything else held constant, you are compensating — and adding more cardio will not help. Steps and dietary structure will.

The summary

For health: 150 minutes a week of moderate activity, non-negotiable, and it is one of the highest-value things you can do for your lifespan.

For fat loss: get your steps up first. Add two moderate sessions a week in the later stages of a diet, when cutting food further stops being sensible. Do not open with it, and do not expect it to substitute for the deficit.

The heart argument is much stronger than the fat argument. Do it for the heart.