I have read an article showing that slow run at a single speed is not so effective as running in a few speed. For example, you run 10km/hour for 1 hour may burn 500 calories, but if you mix it up with 2 session of 15km/hour for 5minutes, the calories will burn up 600++ at the same time, it's 20% increase. Now you know, you can exercise smarter as well. What is this going to do with Sex machine? Don't you know that stronger heart equals to better sex? Work hard now and you can have better sex as well.