Three-Minute Step test

Children and young people may be referred for a test called the 3-Minute Step test (3MST). The test is a type of exercise test and can be used to assess your child’s exercise tolerance. This page from Great Ormond Street Hospital (GOSH) describes what to expect when your child is booked for a 3MST test.The 3MST is an exercise test that is used to assess the body’s response to exercise. It is used to work out your child’s exercise capacity.

At GOSH, the 3MST is performed by a respiratory physiologist in the Lung Function Lab.

Do I need to bring anything?

You should receive a letter with the instructions on where to come for the test. Please ensure your child wears suitable, comfortable shoes to walk in and loose fitting clothing.

If your child uses supplemental oxygen (continuously or sometimes during the day), please bring this with you.

Children with respiratory disease should use all regular medications on their daily schedule.

Make sure your child is well rested before doing the test. For example, if required, please use your child’s wheelchair to move around the hospital and from the waiting room to the Lung Function Lab.

What happens before the 3MST?

The physiologist will explain about the test in more detail on the day if required. We will ask for your permission (consent) to perform the test.


The person bringing your child for the test should have ‘Parental Responsibility’ for them. Parental Responsibility refers to the individual who has legal rights, responsibilities, duties, power and authority to make decisions for a child. If the person bringing your child does not have Parental Responsibility, we may have to cancel the test.

This test is unsuitable for pre-school age children due to the difficulty co-ordinating the stepping.

What does it involve?

We will put a pulse oximeter sensor on their finger or forehead to measure oxygen saturations and heart rate.

Before the test starts, we will ask some questions about their breathing and leg tiredness using a visual analogue scoring system – this is simply a scale to show the severity of their breathing and tiredness.

A 15 breath count is also carried out. The Physiologist will ask your child to take a big breath and count out loud to 15, we will assess if they can do this in one breath or if they need additional breaths.

The physiologist will ask your child to step on and off a step to a beat of a metronome for as long as they can. The test is timed at three minutes but if your child is unable to complete this or keep with the rhythm of the metronome, the test maybe stopped early. This test can be difficult so the physiologist will ensure your child is given lots of encouragement throughout.

Please note, children of a younger age (around six years and under) may not be able to perform the test due to co-ordination of stepping to the beat.

Your child’s heart rate and oxygen levels will be monitored before and during the test. If your child’s oxygen levels decrease below a certain level, we may stop the test before the 3 minutes.

Once the test has stopped, your child (or you) will be asked to complete the visual analogue score again. They will also repeat the 15 second breath count.

Your child will be allowed to rest for as long as they need to after the test.

Are there any risks?

3MSTs carried out in hospital are very safe – the Physiologists are experienced in carrying out the test and safety equipment is available and will be used if necessary.

Your child’s baseline oxygen saturations and heart rate will be assessed and, in some circumstances checked with a respiratory Consultant prior to the 3MST. If your child uses supplemental oxygen, the decision to perform on or off oxygen will be made by their Consultant beforehand.

Your child will be monitored throughout the test and for a while afterwards.

Sometimes, children find the stepping hard to co-ordinate and in these circumstances, the test may not go ahead due to risk of fall.

Getting the results

The results for you test will be uploaded onto our electronic patient record system for your doctor to view. If you are seeing your doctor in clinic or later that day, they will go through the results with you.

If you are not seeing the doctor that day, they will still be able to view your test results and contact you if there is anything your child needs to do before their next appointment.

Compiled by:
The Lung Function Laboratory in collaboration with the Child and Family Information Group
Last review date:
April 2020