MHR = 220 – age
The standard formula for maximum heart rate (MHR) and its derivatives is MHR = 220 – age. It’s so commonly used in the training world one would think the scientific foundation for the statement was solid and profound and absolutely the last word. It’s none of the above. The equation was derived in the 1960’s from an observation of data Dr. William Haskell had collected and graphed from a study about heart disease. The subjects were male, under fifty, not in particularly good shape, and many smoked. The original goal of his study was to determine just how hard heart disease patients could push themselves and was not designed at all to evaluate healthy individuals or conditioned athletes. So, how did it become "law"? It wasn’t the study, but the timing of its release. Cardiovascular training was just becoming popular in gyms and on the streets (I can still remember neighbors teasing me, yelling “Hey, what are you running from?” when running in 1968!). Doctors and trainers were hungry for an answer to the question “How hard should I run?”. The formula stuck. Not very scientific when it comes to training perhaps, but whole industries grew up around it so it’s probably going to be in people’s repertoire for a while.
For training purposes we like to manipulate different physiological responses within the body which we know are related to how oxygen is exchanged, which can be roughly related to percentages of the maximum heart rate. Therefore, a Target Maximum Heart Rate formula (TMHR - a percentage of the MHR) is used to target these changes.
For example:
A 40 year old woman is instructed to run at an intensity of 75 to 80% of her maximum heart rate.
TMHR(lower limit) = (220 – 40).75 = (180).75 = 135bpm (or about 23b/10sec)
TMHR(upper limit) = (220 – 40).80 = (180).80 = 144bpm (or about 24b/10sec)
Now for my money, if we are going to use a set formula like this, we need to be looking for the percent of change between the minimum heart rate (resting heart rate, RHR) and maximum heart rate. We can then add in the resting heart rate at the end to provide us with a real countable beats per minute number.
Therefore, that same 40 year old female athlete with a resting heart rate of 60 beats per minute would be:
TMHR(lower limit) = (180 – 60).75 + 60 = 150bpm (or 25b/10sec)
TMHR(upper limit) = (180 – 60).80 + 60 = 156bpm (or 26b/10sec)
One of the reasons this formula has stuck around is that it is relatively safe for the average person. For general conditioning purposes, however, it has been suggested that rate of decrease in heart rate from maximum heart rate to resting heart rate after exercise might be a better indicator of when to increase the intensity of an aerobic workout. That is, in general, how long does it take your system to recover is a better indicator of your health and conditioning. In training athletes, perceived exertion levels are often used instead of specific heart rates, which really does make sense, especially with elite athletes whose heart rates often don’t fit the MHR format at all.
One final note – don’t trust the built-in heart rate monitors in the cardio equipment at the gym. The accuracy varies wildly – depends on the machine and the gym maintaining them. Check it yourself. Yes, your calculations are correct – the machine is wrong.
In future blogs, we will examine the specific changes cardiovascular training promotes in the body.
References Utilized:
1. Ultimate Fitness
Kolata, Gina Farrar, Straus and Giroux 2003 NY, NY
2. Essentials of Strength and Conditioning, 2nd Edition
Baechle, Thomas R., Earl, Roger W. Human Kinetics 2000 Champaign, IL
