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M:We all know that exercise is good for us,but sometimes it seems too hard to leave the sofa.W:I can see that you seldom do exercise.M:Plus having the doctor tell us to get 2.5 hours of exercise a week doesn't really help our motivation much.W:Don't be discouraged.Now,a new study suggests getting benefits from exercise doesn't have to be that demanding.Jacob Saddle from Harvard University has done a study into how much exercise is needed to lower the risk of heart attacks.M:Um Interesting.W:The study showed that people who put in 300 minutes a week of exercise had a 20% lower risk of death due to heart disease.Still,the people who exercised 150 minutes a week did pretty well too lowering their death risk by 14%.M:And what about the people who exercise half as much as that?Like what I'd probably do,does that help?W:Of course,even 15 minutes would help.