The results suggest that poor air quality can cancel out exercise benefits and demonstrate the health impacts of even short-term exposure to air pollution.
The report calls for stricter air quality limits, better traffic control measures and greater access to green spaces. They also occur among healthy people, the study found.
A separate study published in The BMJ suggested that pregnant mothers exposed to higher levels of air pollution are more likely to have a baby born at lower birth weights. Average day and night-time road traffic noise levels were also estimated.
An analysis of the data found that increases in traffic-related air pollutants were associated with 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age.
But the researchers, from Imperial College London and Duke University in the U.S., also discovered that air pollution is very localised - so leaving a busy street and exercising in a park instead was enough to reverse the trend. "We need to reduce pollution so that everyone can enjoy the benefits of physical activity in any urban environment".
The study was funded by the British Heart Foundation, whose chief executive Simon Gillespie said: 'Exercise is crucial in reducing the risk of a heart attack or stroke, but it seems risky levels of air pollution could be erasing these benefits in older adults.
The project was again led by researchers from Imperial College London alongside Duke University.
The scientists tested 119 over-60s as they walked for two hours in central London.
Physical measurements were taken before and after the walks to show the effects of the exercise on cardiovascular health, including measurements of lung volume exhaled, blood pressure, and the degree to which the blood vessels could expand.
Brooke Havlik, communications director for the New York-based nonprofit organization WE ACT for Environmental Justice, said that far from improving the situation, the U.S.is going backward at a federal level when it comes to combatting air pollution.
All the participants who walked around the park benefitted from increased lung capacity after the first hour, but very little difference was seen for those who walked around Oxford Street.
In healthy participants the walk in Hyde Park led to a 7.5 per cent improvement in the amount of air they could expel in one breath and improvements in blood flow which persisted up to 26 hours after exercise.
On the other hand, people who walked for two hours in a large city park - away from direct exposure to street-side traffic fumes - reduced arterial stiffness by more than 24 per cent in healthy and COPD volunteers and more than 19 per cent in heart disease patients.
The study added: "These beneficial responses were attenuated after walking on Oxford Street". "But for those living in inner cities, this may be hard to do, and there may be a cost associated with it as they have to travel further away from where they live or work".
"For many people, such as the elderly or those with chronic disease, the only exercise they very often can do is to walk", Chung said.
'Our research suggests that we might advise older adults to walk in green spaces, away from built-up areas and pollution from traffic'.
'However, telling joggers to avoid polluted streets is not a solution to the problem.