You're ready to jump into that heart-pumping activity and intensive cardiovascular exercise session, but are you doing more harm than good? Most people don't realize how important it is to keep your heart rate at a certain level while exercising, and you need to maintain a specific heart rate when you want to lose weight or improve your fitness level. If you're not increasing your heart rate enough -- or pushing yourself too hard and getting it too high -- you won't be getting the most ...