Three Minute Step test

The three minute step test (3MST) is performed in the lung function unit, it is a type of exercise test that 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.

Do I need to bring anything?

You should receive a letter with the instructions and location of the lung function unit or you can find the details on your child’s MyGOSH. Please ensure your child wears suitable clothing and shoes for performing the exercise test.

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

Children with respiratory disease should continue their medication as per their daily routine.

Make sure your child is well rested before doing the test.

What happens before the 3 Minute Step test?

The physiologist will explain the test in more detail. 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.

What does it involve?

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

Before the test starts, we will ask a couple of questions about their breathing and leg tiredness using a visual analogue scoring system – this is simply a scale to show assess the severity 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 metronome beat. 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 may be stopped early. This test can be challenging for some 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 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 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 test results 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 Unit in collaboration with the Child and Family Information Group
Last review date:
November 2022