If you do a search on hear rate zones you'll get a large selection of HR zones with different values and number of zones. Enough to get really confused. It seems that everyone has a different opinion on the matter. As we are regularly coaching cyclists that just want to get on and train right without having to get a degree in medical science we keep our zones simple. I've found that these zones are very effective for the training required for cycling. They are slightly different to the ones that normally come as default with the polar heart rate monitors. At the end of the day no one HR zone system is better than another. The important thing is to decide on one and then stick to it. In the table below and the descriptions that follow I describe the HR Zones that we use for our own personal training as well as the Remote Coaching program that we offer. This is one of the most effective ways of using your heart rate monitor to improve your cycling.
 

Description	Intensity	Code	Zone
VO2 MAX Boosting	Very Hard – Can’t speak	O2	92	-	100	%
Anaerobic Threshold Endurance	Hard – Difficult to speak at all	E3	85	-	91	%
General Aerobic Endurance	Moderate – Talk in short sentences	E2	75	-	84	%
Base Aerobic Endurance	Easy – Able to carry out conversation	E1	65	-	74	%
Recovery	Easy – Able to carry out conversation	REC	50	-	64	%

Cycling Australia official Heart Rate Zones

Rest <50% MHR
Any training done lower that 50% MHR is rest. This zone is not really training at all and is normally associated with very light exercise such as walking. This zone can be used during the transition phase of the training year.

Zone REC (Recovery) 50-64%MHR
This zone can be used for recovery rides on the bike. It takes discipline to ride at this pace though!

Zone E1 (Aerobic Endurance) 65-74%MHR
This is the zone you will spend most of your time in. It is the zone used for base training and to build your aerobic base and your foundation for the season ahead. In practice you'll be training in this zone throughout the year as it builds aerobic power throughout the season. Training in this zone allows you to ride with a good average speed but without a great deal of perceived effort. If you're riding fast but not hard you'll most likely be in this zone. You should be able to maintain a conversation without taking deep or extended breaths. For this reason, this training is very effective when done with one or two training partners and whilst having a sociable chat on the bike.

Zone E2. (General Aerobic Endurance) 75-84%MHR
Be careful with this zone. Because this zone is still just below your lactate threshold, it will do little to increase your V02 Max or increase your lactate threshold. This zone is sometimes called the "no-man's land" training since it is too fast for an endurance ride and too slow to improve your maximum aerobic power or threshold. It is an important zone to train in but it's even more important that you manage the amount of time and how you train in this zone. This is because it is at the top end of the endurance zone and this it will tire you out if you train in it without proper control! Interestingly, it is the zone that you usually end up riding in when riding in a group! It's ok though in the specialization period before the start of racing and can be used as an introduction to interval training.

Zone E3. (Anaerobic Threshold Endurance) 85-91%MHR
This zone is critical to your success in bike racing. Training in this zone develops your ability to ride at lactate threshold. Train in this zone and you will be able to tolerate lactic acid in your muscles whilst maintaining the muscle contractions necessary to produce sustainable power on the bike. Use this zone to train for bridging across to a break, working in a break or climbing for an extended period of time. Training in this zone is hard! Train in this zone to increase V02 Max and Maximum Aerobic Power.

Zone O2. (VO2 MAX Boosting) 92-100% MHR
In this zone you are riding flat out. These intervals are probably best done on a trainer. If you do them on the road take care to keep your head up and in control of the bike! Typically you will only last seconds in this zone as your muscles fill with lactic acid and force you to recover. Use this zone to train for sprinting.