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Young people should aim to do 60 minutes of exercise a day but most young people are not hitting that target.

A recent study, published in The Lancet Child & Adolescent Health, claims that four in five 11 to 17 year are not doing enough physical exercise.

This is a problem which is effecting children from all different backgrounds.

Boys were more active than girls in all but four of the 146 countries studied.

When you physically start to move it gets your brain moving too.

As you exercise your heart beats faster and pumps more oxygen around your body, which means that there's more oxygen in your brain.

It also helps to release a load of hormones (chemicals that send messages to cells in your body) to your brain that provide a healthy environment for new cells to grow and develop.

When more cells grow in an area of the brain called the hippocampus, which is responsible for learning and memory, this can help you perform better at school.

There's also evidence that happy hormones called endorphins are released through exercise, which can benefit your mental health and wellbeing.

So basically, exercise is good for you!

Anything that gets the heart and lungs working harder than usual.

It could include any of the following: running, cycling, swimming, football, hopping, skipping, gymnastics and many more.

Whatever way you choose to exercise, you need to make sure that it's vigorous exercise and not moderate.

Moderate exercise is when you're exercising and you can still have a chat with your friends whilst doing it.

Whereas, vigorous exercise is when you work harder and feel breathless at the end.

There are multiple reasons for this.

Leanne Riley, one of the report's authors says that 'young people in this age group are very encouraged to work hard, to study for exams'.

Researchers have also said that it's because roads are unsafe, and places to play sports are limited, expensive and far away from people's homes.

Another reason is that there's more "digital play" taking place on phones, tablets and gaming stations.

In the UK 75% of boys and 85% of girls weren't doing enough exercise.

But that isn't the case for girls in Tongo, Samoa, Afghanistan and Zambia - where girls are more active than boys.

Again, reasons for the difference between girls and boys vary from place to place.

Researchers say that the way sports is encouraged and shown in the media makes it appeal more to boys than girls.

Tell us what you think.

Why do you think children are less active and what can be done to get more people moving?