It was only a month ago that Boris Johnson was in intensive care with coronavirus. But on Tuesday, the Prime Minister, a keen jogger and cyclist, was spotted on Downing Street in exercise gear for the first time since his Covid-19 battle, which he blamed on being overweight. Yesterday, he embarked on another early morning run in his signature Bermuda shorts.

Like 55-year-old Johnson – who reportedly weighed 17-and-a-half stone before he was hospitalised – many people will be returning slowly to an exercise regime after fighting off the virus. Follow our guide on how to get your strength back.

If you’ve been hospitalised by Covid-19…

Those hit hardest by Covid-19 – namely, those with severe symptoms that confined them to a hospital bed – will have experienced a serious loss in strength, says James Turgis, physiotherapist and owner of London’s Excellence Physiotherapy. Turgis coached his 70-year-old father back to health after he developed Covid-19 and was placed on a respirator.

“If you are in bed for more than two weeks, you lose a lot of muscle and might struggle to stand,” says Turgis.

Start with working the legs, which will give you the strength to get out and about. With his own father, Turgis started him off with exercises that he could do while in bed. “He tried things like squeezing a pillow or pushing the bed with his heel,” he says.

Turgis recommends that when you are strong enough to sit without assistance, perform gentle exercises on the edge of the hospital bed or in an armchair, such as lifting and lowering the legs. Once you have the strength to stand unaided, hold onto the rail of the bed and try gentle squats, but limiting how far you lower yourself until your are stronger.

But do begin an exercise routine as soon as you feel able: “Start as soon as possible,” says Turgis. “don’t wait and let yourself get worse. It’s so important psychologically, too.”

As your lung function may have been compromised by the infection, some breathing exercises could help develop those, he says. “Blowing bubbles into a glass of water through a straw is a very good exercise: when you push and blow, the water makes resistance, which strengthens your diaphragm.”

Recovering from this loss of fitness is achievable, but may take longer than you’d imagine. If it was a short hospital stay, you could be back to normal fitness in six weeks. Any longer may require six months’ or more recuperative exercise.

Initially, after leaving hospital, Boris Johnson chose walking – not running – as his exercise of choice

If you’ve had a moderate case of Covid-19…

For those who recuperated at home in bed, you may still have lost strength: even a week of bedrest leads to a remarkable loss of muscle mass.

Once you can get up, try a few strengthening exercises. To work your legs, Anna Clayton, who specialises in pilates at BuryPhysio in Bury St Edmunds, Suffolk, recommends the Chair Challenge – getting up from the seated position without using your arms – then lifting yourself onto one leg before extended your other foot, heel first, out in front, before a round of marching on the spot.

To improve core strength, she suggests carrying around a weighted rucksack around the house and up the stairs, which will work your muscles all the while you remain upright. Tins of food might be suitable weights.

If you’ve been immobile for a while, you will also have lost some cardiovascular fitness. Whatever level of fitness you were before you became ill, start with walking, says Clayton. “Gradually increase your walking distance and use a garden or field where you can see how far you’re going each time,” she says.

Unfortunately, many people who have caught coronavirus complain of extreme and lasting fatigue, which may hinder your desire to do the gentle exercise that will help you return to full fitness. Clayton suggests getting other family members involved in your routine and to do it with you, to keep up your willpower. Alternatively, download the Relive app (relive.cc) to your phone, which will monitor your speed over the course of your walk, including your fastest moments, and, when completed, create a shareable video of your route.

If you’ve had a mild case of Covid-19…

Even if you feel you got off lightly – eight out of ten people who contract coronavirus likely experience only mild symptoms – it can still leave you tired and breathless and feeling less fit than you were before. Your heart rate often rises when the body is fighting an infection, and things might generally feel like more effort than before.

It is difficult to know exactly the right time to return to exercising, says Laura Williams, a personal trainer based in London. One way to see how stressed your body is is to monitor your heart rate throughout a workout, something she does in video sessions for one client who has had coronavirus. If it spikes higher than you are used to, it’s time to take your training down a notch.

In this case, Clayton recommends starting with bodyweight exercises rather than hardcore cardio. “Do five shallow lunges to start your workout, holding onto a chair if you need to. If you feel extra heaviness in your legs, then park that a day or two.” She also recommends squats and stepping up onto a chair, as well as climbing the stairs, as good strength-builders.

If your fever settled within a few days and you felt significantly better after a week with Covid-19, you won’t have to worry too much about the fitness you’ve lost in recovery, says Clayton: “It should only be a matter of days and weeks, rather than months, before you’re back to normal.”