Understanding Heart Rate Zones.
I would encourage people training for a specific event to incorporate heart rate based training into their regime. Without it, your training will tend to become one dimensional, you may train at a similar speed each run and never actually improve.
Without your heart giving feedback you run the risk of training with too high a heart rate on easy days, and too low a heart rate on hard days. A number of runners therefore land up in a fairly narrow range of heart beats per minute -somewhere in zone 3. Most athletes normally sit at between 86% to 89% of max heart rate. 
You have two main energy systems, your aerobic system and your anaerobic system.
Aerobic – your body uses oxygen to burn up stored fat and convert it into energy. The mix of oxygen and fat will give you an almost endless supply of energy.
Anaerobic – this system uses glycogen to power you. Your body stores sugar in relatively small quantities.
Your body will rely on both systems to different degrees when you exercise. At higher speeds you will rely more on your anaerobic system and at lower speeds, more on your aerobic system. Knowing your heart rate will help you understand which system you are using more. 
A good training regime will have you training at all 4 zones. This means that when you work hard, you will work really hard, and when you take it easy, you will really take it easy. Taking it easy on some of the workouts will leave you fresher for those all out efforts.
There are two main ways of estimating your maximum heart rate:
- Run a 5 km race and push as hard as possible. You will need a watch that records your heart rate. At the end of the run, go over your figures and record your highest heart rate moment.
- Slightly less accurate is to subtract your age from 220. So, a 35 year old would have a maximum heart rate of 185 b/m.
Now get a calculator and do the following – fill in the run column first. Leave the cycling column for a moment. ( where mhr= maximum heart rate)
Zone Run Ride
Zone 4 90-95% of mhr (Anerobic training) __-__ __-__
Zone 3 86-89% of mhr (Middle) __-__ __-__
Zone 2 75-85% of mhr (Higher end aerobic) __-__ __-__
Zone 1 61-75% of mhr (Lower end aerobic) __-__ __-__
Now it is time to fill in your cycling figures. Because cycling stresses the body less than running, you can subtract 5% off of your running figures. The calculator sequence will look like this for 160 beats per minute: 160 – 160 x 5/100 = 152.
We are able to write programs for people wanting to participate in triathlons etc. They rely fairly heavily on heart rate based training. Let me know if I can help.
Regards,
Mike Roscoe.
Kinesiologist.
