Hi Slimdown,
Let's see if this will help you.
Your heart rate determines your work out intensity. It is important to work hard enough to strengthen your heart and burn those calories but you don't want to work so hard that you put yourself at risk. So with that said, you can check your heart rate easily by counting your carotid (neck) or radial (wrist) pulse.
Your target heart rate for any aerobic exercise should be between fifty and eighty percent of your maximum heart rate. Here is the formula I use for target heart rate:
220 minus Age = Maximum heart rate
times 50% to 80% = target heart rate
Example for a fifty year old (me

) in good health
220 - 50 = 170 (maxium heart rate) beats per minute
X 65% = 110 (Target heart rate) that's 110 beats per minute
If you are just beginning an exercise program it is recommended that you shoot for 50% of maximum heart rate. Take it slower if you are really out of condition.
Remember that the rate at which you exercise should be free of pain, if it is too exhausting and hurts then you must adjust things until you condition yourself. Also, ideally you should be able to exercise at your target heart rate and be able to talk without huffing and puffing.
I hope this helps and Good Luck!~~~~~~~Meg