The biggest hurdles are discipline,want to, and commitment. If you want to be active, you will find a way to be active. President Obama the busiest man in America wakes up early everyday to exercise. A lot of people workout once,twice, or for a week and then stop due to lacked commitment. Working out is like brushing your teeth, or changing a babys diaper. You may not always want to do it, but you need to it. I am in great shape, and even I do not always want to go to the gym, change, and exercise. When you workout enough though it eventually becomes a routine that you want to do, before you get to this point though you will have to be disciplined and keep working out, even when you do not feel like it.
This is another reason to pay attention to professional athletes. They are the epitome of fitness, dedication, and discipline. For example- Kobe Bryant used to work out in the gym for 7 hours every day. That is part of his job so he does have the time to be in the gym for 7 hours. However do you think he always wanted to do that. Or did he do it because he knew it needed to be done.