A further modification is the Karvonen formula, [(Max HR - Resting HR) x % intensity] + Resting HR.
Combining a gender-specific estimate of MPHR with the Karvonen formula gives the most accurate results--but even the best formulas are based on estimates from population studies.
An alternative to the two HRmax equations mentioned above to estimate the high-intensity effort, you could use the Heart Rate Reserve (HRR) method, also known as the Karvonen formula
The Karvonen formula
 was used to determine the cardiovascular intensity (i.e., % of HRR) during bouts of walking.
Target heart rate can be calculated by using the Karvonen formula
. To use this, you must first determine your resting heart rate.
This item assessed how program directors determine the training zone whereby participants were asked to select all response options that applied to their program(s) including use of "Karvonen formula," "direct percentage of maximum heart rate," (12) "trial and error," "other," and "do not know."
The most widely accepted method of determining training zone for the purpose of inducing an aerobic endurance training effect in CR appears to be utilization of heart rate, either using the Karvonen formula or percent of maximum heart rate.
The training zone obtained from HR data can be formulated using either a percent of maximum HR (%HRmax) or HR reserve method (Karvonen formula).
(1) Karvonen Formula
220 -Age = Maximum Heart Rate Max Heart Rate--Resting Heart Rate x Intensity + Resting Heart Rate = Training Heart Rate
We monitored cardiac safety and initially ensured that subjects did not exceed 10 to 20 min at 40 to 50 percent of maximal HR reserve, as calculated by the Karvonen formula :
We described use of the Karvonen formula to determine peak exercise capacity in our previous work with stroke patients [10-11].