The people involved with the Olympics are determined to make athletes of us all. Bradley Wiggins's win has inspired fans to get on their bikes; meanwhile Transport for London is encouraging passengers to walk between venues during the Games. But before we start doing Usain Bolt impressions through the city, scientists and campaigners are suggesting that we ought to think about the quality of air we are inhaling first.
Days before the opening ceremony, there were warnings that Olympic athletes could underperform, and even risk their health, because of London's summer smog. Although there have been several smogs already this year, last week's was the worst since 2006, according to Simon Birkett from campaigning group Clean Air in London. Pollution has caused problems at the Olympics before – at the 1984 Los Angeles Games, Steve Ovett blamed air pollution when he collapsed after the 800m final, with exercise- induced asthma. China used cloud seeding to clear the air before Beijing.
Luckily, good old British weather – in the form of last week's rain and wind – helped to dispel the smog, which builds in still conditions. But Birkett warns it could be back in time for the closing ceremony if the sun returns as forecast.
Smog, explains Dr Keith Prowse, medical adviser for the British Lung Foundation, is made of a particularly high concentration of fumes, particles and ground-level ozone. At high levels, this causes irritation to the respiratory tract, from the nose down to the lungs, leading to coughing, wheeziness or breathlessness. Of the particles in smog, the smallest are thought to do most harm, as they can be inhaled deepest into the lungs, although all cause problems.
It is not just athletes who are at risk. London's air is the worst in the UK – and in Europe, according to campaigners. The UK is also facing fines over the levels of pollution in 12 cities and urban areas (including Birkenhead and South Wales), which have high levels of exhaust emissions. Birkett says, exposure to air pollution is the biggest public health risk after smoking in the UK; government figures suggest 29,000 deaths a year could be attributed to it.
On high-pollution days, the advice for older people and those with lung problems is to reduce strenuous physical exercise. But even healthy people can experience discomfort such as sore eyes, a cough or sore throat, and are warned to consider decreasing outdoor exercise if they do. On days with very high levels of pollution – such as we experienced last month – everyone is advised to cut down their physical exertions.
So is this the excuse we have been looking for to stay on the sofa instead of pounding the streets? Definitely not, says Prowse. "The health benefits of exercise are generally greater than the health risks posed by pollution, certainly at normal UK levels. Most people in this country are unlikely to be affected by pollution when exercising."
"The most important thing is that people take note if they start to feel breathless or wheezy, or if they are coughing more during periods of high pollution. In these instances, they should visit a doctor in case it is the result of any undiagnosed condition, and minimise the impact of pollution on their bodies."
Air-quality expert Dr Gary Fuller, of King's College London, says he would encourage joggers, cyclists and walkers to "be a bit smarter and think about where they are doing their exercise", for instance choosing quieter routes away from heavy traffic. "If you are out taking exercise in an urban area, then it's sensible to think about the risks around you. You should think about minimising your exposure to air pollution," he says. Fuller and his colleagues have created a free app that allows people in London to check real-time air pollution levels where they are. Defra's website also provides air-quality readings and advice on when it is necessary to be careful.
Prowse says exercising in an air-conditioned gym or sports hall can help if you stay inside long enough for your breathing to return to normal. Avoid mid- to late-afternoon exercise as this is when ground-level ozone is highest. On really bad days, this is true for those living in rural areas too. Commuting before or after rush hour can help cyclists, joggers and walkers.
But there is no need to buy a mask because there is little evidence they work, according to Prowse. "Some people report that they make breathing and exercise more difficult. A lot of masks cannot filter out many of the smallest particles that are thought to cause the greatest harm."
But as Birkett points out, it's just as important that we all try to improve air quality, by reducing our own emissions and lobbying the government to take action. "People need the government to stop looking for loopholes to avoid complying with the law. Instead they should be proposing bold solutions such as banning the oldest diesel vehicles, as Germany has done." That, he says, really would be a breath of fresh air.