When you've finished your thirty minutes of aerobic exercise, the next thing you should do is slow down and cool down. Ah, blessed relief catching up with your breathing.

If you've been walking briskly or jogging, you should switch to a slow walk for about five minutes. This period of cooling down is important. It reduces muscle cramps and the possibility of muscle injury, and allows the muscles to get rid of any lactic acid that may have built up in your system when you were pushing hard.

And you should end up with another short period of stretching. You can use the same stretches that you started with. But again, don't hurt yourself. You should only stretch within your normal range of motion. Don't try to bend those joints much beyond where they usually go.