Elite athletes use it -- and you can, too.
It was the hardest stretch of the race, 1,000 feet of what seemed like nearly vertical incline between me and the finish line. As I approached the summit, my heart felt like it was about to burst through my chest. I didn't need my Fitbit to tell me I was working hard on this hill, but I looked down at my wrist and there it was: 185 beats per minute. I had reached my peak heart rate.
Heart-rate tracking is a standard feature on many fitness trackers such as the Apple Watch , Galaxy Watch and most Fitbits, but they rarely explain what to do with that information.
Before training for a half marathon, I wasn't really sure what to do with that heart-rate data, but once I figured it out, I was able to use it to improve my performance and achieve my goal of completing it in just under two hours.
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Heart rate can tell a lot about your overall health and it's one of the best ways to measure overall fitness, according to Dr. Anthony Luke, director of primary care sports medicine at the University of California San Francisco.
The lower your heart rate, the greater your cardiovascular fitness. "If your base heart rate is slow it means your body is more efficient and you don't have to rev things up to get things moving," says Dr. Luke.
According to the Mayo Clinic, a normal healthy adult should have a resting heart rate from 60 to 100 beats per minute, although some elite athletes may have a resting heart rate closer to 40 bpm.
When you're working out, your heart beats faster to deliver the nutrient- and oxygen-rich blood your muscles need to keep you moving. In turn, you can use your heart rate as a gauge of how intense your workouts are -- the higher your heart rate, the harder your body is working. But there's more to it than that.
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You don't really need a fitness tracker or a chest strap to measure your heart rate. Just feeling my pulse on my wrist, or the side of my neck would have confirmed the thumps I was already feeling inside my chest while scaling that hill.
That said, smartwatches and fitness trackers have made this information so easily available that all you need to do is glance at your wrist. That's especially helpful when you're working out, because stopping in the middle of a run to take your pulse manually is a lot less convenient.
Without buying anything extra, you can also measure your heart rate with your smartphone.
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If you're just starting your fitness journey, it's probably too early to dig into your heart-rate data. Any form of physical activity that gets you off the couch and gets your heart pumping above your baseline is progress. But eventually, understanding your heart rate can help you stay focused on your long-term fitness goals, like losing weight or increasing your speed.
Most importantly, heart rate can help you answer the question, "Are my workouts effective?" To find that answer, you'll need to first figure out your maximum heart rate.
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Maximum heart rate is the upper limit of what your cardiovascular system can handle during physical activity, according to the Mayo Clinic. This number isn't always straightforward, because there are other factors to consider -- including gender -- but for a very basic calculation, subtract your age from 220. For example, if you're 30 years old, your MHR would be 220 - 30 = 190 bpm.
Once you know your MHR, you can then calculate your heart rate training "zones," which help guide your workouts.
Some fitness trackers and apps do this for you. Fitbit, for example, breaks it up into three zones: fat burn, cardio and peak. However there can be more than three zones, and the names and numbers will change slightly depending on your program.
Here's a very general look of what these zones mean and what you can achieve at each one.
50-70% of your MHR: This is what the American Heart Association considers to be moderate exercise, and can also be referred to as "fat burn" zone. Working out in this zone will, as the name suggests, burn fat and also build endurance.
70-85% of your MHR: Vigorous exercise, also known as aerobic or cardio zone. Working out in this zone can help improve cardiovascular fitness and build strength.
85-95% of your MHR: This is high-intensity or anaerobic exercise, which can increase speed.
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Not everyone needs to pay attention to heart-rate zones while exercising. If your main goal is to lose weight, burning more calories is key. All of the above training zones burn calories, but the more intense your workout, the more calories you burn. But before you push yourself to your heart-rate limits during your next workout, know that while a higher intensity workout will burn calories faster, it may also make you burn out faster and increase your risk of injury, which could put you behind in your training.
In fact, some evidence suggests that heart-rate zones aren't always what they promise and that the main goal for weight loss should be burning calories. This is why a longer, moderate workout can be just as effective at achieving weight loss or in some cases even more effective in the long term, because it's more sustainable over time.
If like me, however, you're preparing for a race, the intensity of your workout matters. I knew I needed to increase my speed to reach my time goal, so I aimed to stay in vigorous exercise for most of my runs and made sure I was pushing myself to high-intensity exercise for a few minutes in each session.
Regardless of what training zone you target, there are a lot of factors that can affect heart rate and it's best to check with your doctor before drastically changing your fitness routine, especially if you're over 50 or have had a history of heart-related conditions.
If you're an elite athlete, you'll want to get even more details about your heart rate than what a traditional optical heart-rate sensor (found on most fitness trackers) can provide. That's why serious athletes prefer chest straps, which track the electrical activity of the heart.
But perhaps the most important measure of success will be your resting heart rate, and you don't need a chest strap to measure it. You'll know your exercise journey is paying off if you notice your resting heart rate has decreased over time. This won't happen overnight, but it can have lasting effects on your health. Lowering your resting heart rate will help strengthen your heart and decrease your risk of heart disease.