Watching the Olympics probably made some peoplefeel a little guilty about not exercising.The truth is, if physical inactivity were a sport,a lot of us could give a gold-medal performance.Or should we say non-performance?To mark the London Olympics, the Lancet,a British medical journal,published a series of papers about this problem.Public health experts say physical inactivityis the world's fourth leading cause of death.They estimate that inactivity plays a major partin six to ten percent of deaths from non-communicable diseases.These include conditions like heart disease,diabetes, and colon and breast cancer.I. Min Lee at the Harvard School of Public Healthworked with a team that studied inactivity.She says the findings are conservativeand may even underestimate the problem.I. MIN LEE: "Physical inactivity is harmful to health,as harmful as far as deaths are concerned as smoking."The researchers compared data on physical inactivitywith disease rates in one hundred twenty-two countries.I. MIN LEE: "So when we did our analysis,we looked at increased risk of diseaseafter taking into account other health habitsthat might be associated with physical activity.For example, we know that if you are active,you probably smoke less.Additionally we factored out obesity, independent of the factthat active people also tend to weigh less."Harold Kohl from the University of Texas Schoolof Public Health also worked on the special report.He says physical inactivity should be recognizedas a global epidemic.HAROLD KOHL: "We have to realize that high income countriesare the most inactive around the world,but low to middle income countriesare not going to be far behind as things change,as their economies improve and their peoplerely more on the improvementsthat basically engineer physical activity out of our daily lives."Harold Kohl points to campaigns that continueto reduce smoking and alcohol use.He says the time has come to target physical inactivityas a major threat to public health.HAROLD KOHL: "It is not just telling someone to go outand be physically active, but how we rely on the transportation sectoror how our cities or neighborhoods are designed,how crime can be minimized to help peoplebecome more physically active in their neighborhoods,simply walking to the store or walking downand being outside with friends and family and so forth.These broader environmental issues are becoming much clearerin terms of their effects."I. Min Lee agrees -- and she challenges people to doone hundred fifty minutes a week of moderately intense exercise.I. MIN LEE: "Anything you can do is great!Even if you don't reach that 150 minutes a week,a little is better than none and more is better than a little."She plans to return every four years -- just like the Olympics-- to tell us how the world is doing.And that's the VOA Special English Health Report.How much physical activity do you get?Are you a couch potato or a gym rat,someone who just sits and watches TVor someone who continually works out at the gym?Tell us at 51voa.com. And if you listen to music when you exercise,give us your nominations for the best workout songs.