You’re probably familiar with the phrase, ‘no pain, no gain’.

But when it comes to burning fat and getting fitter, experts now say that advice could be wrong.

A growing number of fitness specialists are urging ‘Zone 2’ training to boost health – a lower-intensity workout such as a brisk walk, light jog or steady cycle where you can still hold a conversation – over a high-intensity, maximum-effort workout. 

The heart works across five heart rate zones, ranging from very light effort — Zone 1 — to maximum intensity — Zone 5.

Zone 2 sits firmly in the middle, at about 60 to 70 percent effort, and experts say it may be the key to unlocking the most fat loss and fitness gains.

Dr Christopher Travers, an exercise physiologist at the Cleveland Clinic, said: ‘You’re not going to feel like you’re pushing it if you’re exercising in zone 2.

‘It should feel like a comfortable workout effort and something that you can do for a longer period of time’.

To calculate heart rate zones, you must first establish your maxiumum heartrate, which can be calculated by subtracting your age from 220.

Using this measure, a 50-year-old has a maximum heart rate of 170 beats per minute (bpm), while a 60-year-old has a maximum heart rate of 160 bpm.

Zone 2 is equivalent to 60 to 70 percent of maximum heart rate. For a 50-year-old, it is from 100 to 120bpm, while for a 60-year-old, it is from 96 to 112bpm.

Experts say it is difficult to judge whether someone is in Zone 2 based on breathing or effort alone, and recommend using a smartwatch or fitness tracker to stay in the right range.

Zone 2 exercises also include slow running, cycling, swimming, rowing machines or the stair stepper.

While many assume that running faster will help them to burn fat and lose more calories, some experts say this may not be correct.

Fat burning relies on a steady supply of oxygen, but, as the heart rate surges, there is less available, prompting the body to turn to other sources of fuel such as carbohydrates and proteins.

At Zone 2, however, this does not happen because the oxygen supply remains plentiful, potentially leading to greater fat burn.

Travers said: ‘When your heart rate increases, you’re not taking in as much oxygen. You can’t burn fat fast enough when you have less oxygen, so your body turns to other readily available energy sources.’

Some experts also say that Zone 2 exercise can help to boost fitness gains.

High-intensity workouts often lead to rapid exhaustion, forcing people to stop earlier. But, in Zone 2 workouts, individuals can keep going for longer periods — providing, in some cases, that they don’t mind being overtaken by others.

Experts say that this added time helps to strengthen the heart muscle and boost mitochondria, the energy factory in cells, further boosting fitness.

Zone 2 training started to trend in 2025 after research emerged from University of Colorado exercise physiologist Dr Inigo San Millan, which suggested that cyclists who spent longer training at Zone 2 levels could go faster for longer.

Observations since then, however, have been less clear-cut on the benefits of Zone 2 cardio.

A 2023 meta-analysis that tracked nearly 6,000 individuals who followed exercise plans found that those who did high-intensity interval training (HIIT) or sprint interval training (SIT) for at least four weeks had up to 3.9 times greater improvements in a key fitness measure than those who did endurance training (ET).

The paper defined ET as continuous exercise at a moderate intensity. Exercises that fell under this may have included light running or moderate cycling.

Another meta-analysis, also from 2023, found there was no greater improvement in body fat percentage among people who did HIIT exercise compared to those who did continuous aerobic training (CAT).

Some experts have warned that, by over-emphasizing Zone 2, people may end up exercising at lower intensities and receiving no benefit.

But others have said that it may boost fitness by encouraging more people to exercise or stick to an exercise routine that they can manage.

Further research has shown that top athletes train across a variety of heart rate zones, often following an 80/20 split — with 80 percent of their time spent at low effort intensities, while the other 20 percent is spent at higher intensity.

Dr Millan agrees with this split, telling the New York Times: ‘Zone 2 is part of it [for fat loss and fitness gains]

‘But you need to do other intensities as well.’