Your maximum sustainable heart rate varies depending on your overall fitness level. A physically fit person can sustain a high heart rate longer than a beginning or intermediate cyclist. The reason is because physically fit people have lower resting heart rates, meaning their heart is much more efficient at pumping blood throughout the body, including to the muscles during strenuous activity like cycling. By figuring out your target heart rate, you can make a relatively accurate determination of your maximum sustainable heart rate.
The American Heart Association (AHA) offers a basic formula for determining your maximum heart rate. It has a error rate of plus/minus 12 beats per minute, or bpm, according to Dario Fredrick, an exercise physiologist and the director of Whole Athlete Performance Center. The deviation may be even higher for professional cyclists. So this method is best for beginners. Start by subtracting your age in years from 220 to determine your maximum heart rate, or MHR. The AHA suggests not exceeding 85 percent of your MHR. Based on these recommendations, a 30-year-old would have a maximum sustainable heart rate of about 162 bpm.
A more accurate depiction of your own personal max sustainable heart rate can be found using what's called a VO2 max test. This test is conducted at a training facility, a rehab center or a doctor's office with the necessary equipment. It consists of having you ride a stationary bike starting a slow pace and gradually working up the intensity while the computer records your oxygen intake and heart rate levels. The test continues for a pre-determined length of time or until exhaustion.
You can also road test to calculate your maximum sustainable heart rate, which Fredrick refers to as your maximal steady state, or MSS. This is a 30-minute outdoor trial that requires a heart rate monitor. After warming up, begin cycling a moderate uphill gradient for a total of 30 minutes. Push yourself to get more accurate results. At the end of 30 minutes, determine your average heart rate during your ride -- many heart monitors will display this information for you.
Exceeding your maximum sustainable heart rate -- 85 percent of your MHR -- does not increase the effectiveness of your workout and may even lead to heart problems, according to the Cleveland Clinic. In addition to cardiovascular problems, exceeding your target heart rate zone can also have orthopedic consequences, such as damaged joints, ligaments and muscles. In addition, exceeding your MHR can lead to premature muscle fatigue, which can shortens your cycling time significantly in some cases.