This article is from the Aerobics Fitness FAQ, by firstname.lastname@example.org (Robles) with numerous contributions by others.
The general formula for the average person is 220-age X 60%
and X 90% of HRmax. For example, a 30-year old would calculate
his target zone using the above formula: 220-30=190.
190x.60=114 and 190x.90=171. This individual would try to
keep his heartrate between 114 (low end) and 171 (high end)
beats per minute.
(from Evelyn Mitchell <email@example.com>)
The Karvonen Formula calculates your heartrate reserve
range. To calculate it, take your pulse for one minute on
three successive mornings upon waking up. (We will be using
the case of a 30-year old male whose resting pulse was 69,70
and 71 for an average of 70 over the 3 days.)
Calculate target heartrate by subtracting your age from 220
Subtract your average resting heart rate from target heartrate
The lower boundary of the percentage range is 50% of this
plus your resting heart rate [(120 x .5) + 70 = 130]. The
higher boundary is 85% plus your RHR [(120 x .85) + 70
=172]. Using the Karvonen Formula for percentage of heartrate
reserve, this 30-year old man should be working between 130
and 172 BPM.
Like the maximum heartrate formula, the Karvonen formula
can vary from individual to individual. Not every
individual is "average", and there can be large differences
among people. Therefore heartrate alone may not be the best
indicator of how hard or how well you are working.
It is important to note that the deviation in both the
age-specific formula and the Karvonen formula is due to the
estimation of HRmax. If you have an actual HRmax from a
graded exercise test, it will be more accurate. ACSM lists
two formulas for estimating HRmax, each one with
a standard deviation of +/- 10-12 BPM:
HRmax = 220 - age (low estimate)
HRmax = 210 - (0.5 * age) (high estimate)
HR = exercise intensity * HRmax * 1.15
Source, ACSM's Guidelines for Exercise Testing and
Prescription, 5th Edition, p. 274, Williams and Wilkins