Harnessing Heart Rate for Training

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Athletes training for endurance sports measure their effort through different means: some with time, some with distance and some with perceived exertion. Others monitor their heart rate to gain a better understanding of the intensity they put into a workout, and while heart rate monitoring has existed for quite some time, in recent years the method has become simpler with the integration of optical monitors into wearables, eliminating the need for chest straps.

Mio was the first to market with optical heart rate monitoring, though many other companies, including Garmin, Adidas, TomTom, FitBit and even Polar, long synonymous with heart rate tracking, have followed suit in some of their products, either using Mio’s technology in the case of Garmin, Adidas and TomTom, or a similar concept.

“Many people find the chest strap to be restrictive,” Dr. Mark Gorelick, director of product science and innovation for Mio, says. “It has to be tight, so you can’t move around too much. Particularly during heavy breathing and higher intensity stuff you feel constricted.”

Wrist-based optical heart rate monitoring also allows athletes to avoid chafing from a chest strap, makes it easier to share a device between individuals without the discomfort of putting on a chest strap made sweaty by another person and eliminates the need to lift up your shirt in order to put on the device.

Aside from location, optical heart rate monitoring also differs in its method of tracking the user’s heart rate. Instead of picking up the heart’s electrical impulses, optical heart rate monitoring uses a small but powerful LED light to track blood flow.

“Blood moves in wave form, so we’re driving through light [which allows us to] know how much blood is being pushed to the skin,” Gorelick says. “As a larger pulse wave comes through under the LED, more light is absorbed and less is reflected back through the optic sensor. We take the difference in light and relate that to a heartbeat.”

The technology, Gorelick says, mimics the technology hospitals use to monitor a patient’s heart rate through his or her finger, but works well while in motion.

When training by heart rate, an athlete tries to stay within one of five zones to achieve maximum benefits from any workout, from recovery days to high intensity training. Zones represent a particular percentage of a person’s maximum heart rate, which users can estimate through various formulas.

The standard equation for determining one’s maximum heart rate is to subtract his or her age from 220, but Gorelick says that that a person’s maximum heart rate could in fact be up to 12 beats faster or 12 beats slower per minute than the results the equation produces. An updated version of that formula, 220-(0.7 x age), produces slightly more accurate results, with a six to seven beats per minute margin of error. Using this maximum heart rate estimate, an athlete can determine how many times his or her heart should beat per minute in a particular zone, ranging from Zone 1, an easy workout where a person’s heart rate is 50-67 percent of his or her maximum heart rate, to Zone 5, a difficult workout that keeps the heart beating at no less than 85 percent of the maximum heart rate.

“On days you may be overtrained, you might run slower but stay within your [targeted] heart rate zone,” Gorelick says. “You can use it as a guide to stay within a safe threshold so that you’re not too low, making your workout inefficient, or too high, training too hard or overtraining.”

An athlete in good shape may find the Karvonen method beneficial for calculating heart rate zones. Particularly fit athletes and those training for endurance events sometimes have resting heart rates substantially lower than average. The Karvonen method subtracts a person’s resting heart rate from his or her maximum heart rate to find the heart rate reserve. Once a person knows his or her heart rate reserve, he or she can multiply that number by the percentage he or she hopes to achieve during a workout, then add that result to his or her resting heart rate to find his or her target heart rate for a workout. For example, if a marathoner had a resting heart rate of 55 beats per minute and a maximum heart rate of 195, his or her heart rate reserve would be 140 beats per minute. If this runner wanted to complete a tempo run, aiming to hit 80 percent of his or her maximum heart rate, his or her target heart rate would be 167 beats per minute.

“The key point is that heart rate really provides you with real-time feedback and accurate feedback to how your body is responding every second to your exercise,” Gorelick says. “It’s a dynamic response to your body. You don’t get that with anything else.”