MrCrassic 

Training by heart rate monitor can be pretty useful to assess where you should concentrate the bulk of your training, but they are not as effective as training by power using a power monitor (which are much more expensive due to the equipment involved). There are many variables that control a person's heart rate at any given time; stress, other health conditions, sleep are just a few. Good people to ask about this are Enthalpic and umd.

If you are going to train by heart rate, you need a heart rate monitor. You really don't know how hard you're working until you get one. There are times where I feel like I'm fine, but my heart rate is really through the roof and other times where I'm struggling, but my heart is hardly working. You should also try to determine your maximum heart rate, which will calibrate all of your other training levels. You cannot increase your maximum heart rate, but training using a power meter can help you optimize your performance over your range. It takes or makes your experience as you see fit. I personally don't wear one when I'm riding for fun because, well, I don't want to think about that. When I'm training or doing a more serious ride, then I wear it.

Now, as far as determining where you should spend your time most, it really depends on the workout that you're doing. I recommend going to the Road Racing Forum or squatting here for more information on that. An important model to follow is the use of zones; Friel's is pretty popular. Look around for it. Having a structured workout helps you get better and more efficient on the bike, as well as get the most out of your workout.

Good luck!

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