I found this at cptips.com/hrmntr.htm and felt it was something that was a terrific piece of info for me to keep in mind:

HEART RATE TRAINING ZONES
There are 5 training "zones" or heart rate ranges. These are arbitrary divisions and can differ from article to article or coach to coach. They are based on the increase in heart rate (and cardiac output) as the oxygen consumption of the exercising muscle increases, and the concept of the benefits of variable stress in developing the exercising muscle (heart or skeletal). As one moves up the hierarchy of training zones, exercise intensity increases and there is a shift from the use of fat as an energy source for the muscle cell to carbohydrate (below 70% MHR fat is burned preferentially). And as the MHR is reached, there is a shift in the muscle cell towards anaerobic (without oxygen) metabolism with increased lactic acid production.

The Heart Rate Intensity Zones are divided as follows:

* Zone 1 65% of MHR (recovery rides) [111]*
* Zone 2 65-72% of MHR (endurance events) [111-123]
* Zone 3 73-80% of MHR (high level aerobic activity) [125-137]
* Zone 4 84-90% of MHR (lactate threshold(LT,AT); time trialing) [144-154]
* Zone 5 91-100% of MHR (sprints and anaerobic training) [156-171]

If you always train at low heart rates, you will develop endurance with no top end speed. Conversely if you train hard most of the time, you'll never recover completely and chronic fatigue will poison your performance. The solution is to mix hard training with easy pedaling in the proper proportions.

The best approach is to stay below 80% of maximum heart rate (zones 1 to 3) on your easy days to build an aerobic base while allowing day to day recovery, and then push above 85% when it's time to go hard to improve your high level performance. But avoid training in the no man's land or mediocre middle at 80-85% of MHR where it's too difficult to maintain the pace for the long rides needed to build endurance and allow some recovery time, but not hard enough to significantly improve your aerobic performance and increase your lactate threshold.

Training programs should be individualized, but once a good base is developed early in the season with Zones 1 and 2 exertion, most programs contain the following elements.

TRAINING TIPS USING A HEART RATE MONITOR
Tips for a training week: (see also mileage tips and training options)

* one long recovery ride - zone 1 or 2 [111] or [111-123]
* one long day (event distance + 10 to 20%) - maxhr = to that planned for the event
* three high intensity days - zone 4 [144-154]
* one or two interval workout days which are counted as one of the three zone 4 days. For example:
o warm up - zone 1 [111]
o 20 min - zone 3 [125-137]
o 5 min - zone 4 [144-154]
o 7 intervals - hit 90% max, recover to 60 - 65% max [154]; [103-111]
o 5 min - zone 4 [144-154]
o 20 min - zone 3 [125-137]
o warm down - zone 1 [111]
* the sixth and seventh days of the week can be rest days off the bike or slow recovery rides at zone 1 or 2 exertion to stretch out your muscles. [111] or [111-123]

* All amounts are for a 51 year old female