220 minus your age gives you your maximum heart rate?
You can often hear or read that ones maximum heart rate can be determined by the above stated "rule". That rule was made up by a cardiologist who used this math to limit his patients during their heart testing on a bike. If the limit was reached, he stopped the testing as a precaution, this was purely for security reasons. Whether this was really safe is highly doubtful if you ask me. How this rule later evolved into the current rule is unknown to me, but that may be so because it so simple and easy to recollect. I know that this rule is fairly pointless in practice and often misses the real maximum quite a bit. Heart rates that deviate from this rule with 10/20 strokes are no exception, both above and below this limit.What also makes the heart rate stroke frequency, is the position of your body, the more vertical the body is the higher the rate. In a vertical position the heart has to pump the blood against gravity, this takes effort, so therefore a higher heart rate. Now the test, to do this you must be fresh and well rested, also use the main sport that you practice or the sport which comes most closely. For many sports, that will be running and not cycling. (cycling is often used because it works so easy in a test situation). You need a good hart rate monitor. Do a good warm up take a short rest and start the test. Choose a constant speed that you approximately can sustain for about 15/20 minutes. The moment you feel you almost have to reduce speed you start pushing the pace with a final sprint for 1 minute, until you really have to stop. The heart rate you'll see at this point will be very close to your personalized Maximum.
Having a high maximum heart rate also says little or nothing about your condition or talent. For that not only your heart rate is important, but both frequency and heart stroke volume do matter. It is after all how much blood cans your heart pump around, it's not about how fast your heart can beat. Often the maximum heart rate of a well-trained person is lower than the average heart rate of less trained individuals, that's because the stroke volume of the heart is larger and it takes more time to empty this larger amount of blood from the heart. Giving a somewhat lower rate.
The only real way to determine your maximum heart rate is by doing an exhaustion test, you should only do this if you're otherwise healthy, but only under a sports physician supervision.
Your maximum heart rate is also not a fixed number, so fat the rule is correct, it is also different for different kinds of exercise and over time it will get's lower. But often not as low as the 220 rule says. A runner for example, on a bike will see a lower maximum heart rate. This is because during an exercise in which a body is not especially trained the muscles will give out before the maximum oxygen uptake level is reached. The heart and lungs still provide enough oxygen to the muscles, but muscle can not process it well enough. This makes sense of course because training is specific, to be a good cyclist you have to train cycling and not running.
Of course there are sports that come close and work well together. For example, skating and cycling both uses the legs muscles in a similar way, although skating requires a lot more technique. On the other hand, look at swimming, lots of the swimming power comes from the torso and upper body, a swimmer will therefore not be really good at running or cycling. He is there simply not trained that way.
If you're with a group and would do this test, you will see that rule 220 minus your age will often be wrong. Although there will be exceptions of course.