Heart Rate Calculations

by Barry Stokes, USA Triathlon Level II and IRONMAN Certified Triathlon Coach

There are a number of different ways to calculate your maximum heart rate and heart rate zones. Here are how the calculations work for the different heart rate zones.

Max HR based on age

This is the one you'll most commonly see and is the easiest to calculate, but it's also the least accurate since people of the same age can have widely varying maximum heart rates. This is the recommended method for beginners and those who cannot reach high intensities in their workouts.

For men, subtract your age from 220. This is your max. For women, subtract your age from 226.

Max HR based on reality

This is the most accurate method to find your max, determined by actual testing. In the preferred activity, running for example, you should warm up, then run for at least 15 minutes at fairly high speeds. Towards the end, increase your speed as hard as you can and as long as you can, then check your monitor to see where your heart rate is. This is your maximum heart rate. Then calculate out your percentages as above. This test is very strenuous and only experienced exercisers in good shape should attempt it. I personally like to measure this in a race at the finish line. I always push more in a race that if I am by myself so the measurement is more accurate. It is also safer that way: if I was to require assistance the are plenty of knowledgeable people around.

Lactate Threshold HR

This is also an accurate heart rate zone calculation, based more on your fitness level than your max heart rate. Your lactate threshold is the point where you enter your anaerobic zone. It is determined by finding your marked point, most often done by the Conconi method of testing. As your fitness level increases, your marked point should rise accordingly.
The Conconi test is performed under a controlled environment where your speed is raised at periodic intervals until you can go no faster. What exercise physiologists have found is that your heart rate increases in direct proportion to your speed up until you hit your lactate threshold, when more lactic acid is introduced into your muscles than there is oxygen to carry it away. If you graph your speed versus your heart rate, you will see the point where your heart rate veers off in comparison to your speed. This is the point at which you enter the anaerobic zone.

Once you have determined this point, you calculate your zones from here instead of your max, using the following percentages:

% of Lactate Threshold	HR Zone
65-81	Low Intensity
82-88	Weight Control
89-93	Aerobic
94-102	Anearobic
103-106+	Maximal

Karvonen Method

The Karvonen method is also based on your fitness level. As your fitness level increases, your resting (minimum) heart rate drops. The heart rate reserve is your maximum heart rate minus your resting heart rate. The resting heart rate is determined by testing -- put your heart rate monitor on just after you wake up (and after you pee if you need to) and keep it on for about fifteen minutes. Your heart rate at its lowest during this period is your resting heart rate.

Taking your heart rate reserve figure (max-min) and multiply it by the percentages above for each zone. Then add your resting heart rate to those figures to get your zones.

For example, if your max is 200 and your resting HR is 50, then your reserve is 150. To find your aerobic zone, multiply 150 by 70%-80% (105-120) and then add 50 to those numbers: your aerobic zone would be 155-170.

HR target = HR rest + (HR max - HR rest) x Intensity %

This is not the same as applying a straight percentage to your HR max. In my case, with a HR max of 195 and an HR rest of 45, working at 80% intensity means reaching HR target = 45 + (195-45) x .8 = 165, not 195 x .8 = 156. The table below shows a few more landmark values and illustrates the different results depending on whether I use the simple % method or the Karnoven method.

Intensity(%HR)	Simple%	Karnoven
95	185	187
90	175	180
85	166	172
80	156	165
70	136	150
55	107	128