A) Recovery zone or easy zone (60% - 70% of MHR).
This zone is used from serious fitness enthusiasts during recovery days and between intense workouts.
Training in this zone is actually an active recovery. You can lose fat while recovering. Permanently training at lower intensities is like you are losing your time.
B) Aerobic or Endurance zone
Use this zone to develop your cardiovascular system and aerobic capacity. The big volume of your aerobic training – unless you are a professional athlete – should be within this zone.
C) Anaerobic zone (80% - 90% MHR)
Somewhere in here you will find your anaerobic threshold (or lactate threshold).
Lactate will begin to accumulate in blood and muscles and cause fatigue.
So this zone can be divided in two sub-zones.
In the first subzone training can be just below A.T.
In the second subzone the A.T. should be challenged. It is advisable to challenge your anaerobic threshold once a week for at least five consecutive minutes.
D) Speed zone or red line zone
This is a zone in which one can train only for short periods. This zone is used for H.I.I.T. (High Intensity Interval Training) or sprinting.
If you are quite fit, it’s highly beneficial to have one H.I.I.T. activity/per week.
Choose your heart rate training zones wisely and you will reap the maximum benefits from your aerobic training.