For me it is slow start. After i came back to work from my 2nd baby, i went the gym with my coworker. I could not even walk for 10 mins. Graduately, I increased the time/resistance/speed on the treadmill & ecliptical, now I can run/walk do interval for 40 mins with no problem. It is not only for losing weight, cardio gives the heart good excise, the chemical released during work makes me happy and i see that my body is getting solid & healthy, and every time i challenge myself to do just 1 minute more, or just one more situp or pushup...