Scientists fear people already vulnerable to Covid-19 due to pre-existing conditions such as obesity are in a “no win” situation as they cut vital exercise in a bid to spend less time outdoors.

Research found adults with illnesses such as hypertension, lung disease and those who are overweight were disproportionately likely to cut activity levels at the beginning of the shutdown.

Their pre-existing conditions make them more vulnerable to the disease, but now scientists fear a long-term reduction in exercise could increase the overall number of people with these diseases.

A study led by University College London (UCL) in collaboration with the London School of Hygiene and Tropical Medicine (LSHTM) and the University of Bath found 25.4% of adults were doing less exercise at the beginning of the shutdown.

This group had a bigger proportion of people with a condition increasing their risk of suffering the most severe effects of Covid-19 if they were to contract it.

It also found that those who merely perceived themselves or others in their home to be at greater risk had also shifted to a more inactive lifestyle.

Senior author Dr Chrissy Roberts, associate professor at LSHTM, said: “We believe that the trade-off between being protected from Covid-19 and the health detriments of reduced physical activity could place already vulnerable populations in a potential ‘no-win’ situation.

“When we’re talking about vulnerable people, it’s not just those who already have underlying health problems, but those who perceive themselves to be at risk too.”

Dr Roberts said the UK could well experience season cycles of Covid-19 like flu.

She said those who had reduced physical activity in response to the first wave could develop the risk factors that would make them more vulnerable to complications if they were to catch the disease in a second wave.

Lead author Dr Nina Rogers, of UCL’s Department of Epidemiology & Public Health, said: “Low levels of physical activity put adults at increased risk of chronic diseases like obesity, cardiovascular disease and stroke which are also potential risk factors for more severe complications if someone develops Covid-19.

“It is concerning that in the mid to long-term, multiple lockdowns might lead to prolonged periods of low physical activity which could increase the size of the population that is most vulnerable to severe complications from Covid-19.”

The study was based on the results of an online survey of more that 5,800 adults aged 20 and over across the UK undertaken between April 6 and April 22.

The research has yet to be peer reviewed but is thought to be the first substantive work on the impact of the Covid-19 outbreak on exercise levels among UK adults, and was supported by the National Institute for Health Research.

A recent survey by Asthma UK and the British Lung Foundation found as many as two-thirds of people with lung conditions said they felt less fit since the start of the shutdown.

The Taskforce for Lung Health, of which both charities are members, said face-to-face pulmonary rehabilitation classes have had to be halted to prevent the spread of Covid-19.

Alison Cook, the taskforce’s chairwoman, said: “It is vital that people with lung conditions have the means to stay active at home during this difficult time.

“The Taskforce for Lung Health is calling for a roll-out of digital pulmonary rehabilitation services to people shielding or considered vulnerable to Covid-19.

“This will also help build resilience to later ‘waves’ of Covid-19 and winter respiratory infections. In the meantime, people can find online resources to help them exercise at home, for example on the British Lung Foundation website.”