If you like to use heart rates in your training as I do then this calculator will be of use. It will give you the old standard rate using a percentage of your max heart rate and also the Karvonen method using a percentage of your heart rate reserve which is more accurate and now the gold standard.
The idea behind training with heart rate monitors is to help you run at the level of effort you designate. Turns out that your heart rate is an excellent indicator of the efficiency with which your muscles are using oxygen. And this indicator is consistent over your lifetime. No matter how fit you become, a given range of heart rate will always indicate the same level of effort. As your conditioning improves, it takes a harder workout than when you started running to match the same level of effort and also, with an HRM, you can avoid running your recovery runs to fast.
If you're running mainly for performance and you want to squeeze the maximum conditioning out of each workout, you'd probably like an HRM. If you run mainly for fun and for recreation, you probably won't like it. It's up to you.
Training zones based on heart rates:
