Don't give up on heart rate training just yet. It can help you make the most of your workouts, and it doesn't have to be complicated. “Your heart rate gives you instantaneous feedback on what's going on inside your body during exercise,”says six-time Ironman World Champion and professional triathlon coach, . “As your heart rate rises, it indicates that your body is under higher and higher demands physiologically.”
This level of exertion, in turn, correlates to what type of fuel your body is using. During low- to moderate-intensity exercise, your body burns mostly fat. “That's because fat takes a lot of oxygen to help break it down to release its stored energy. It's like a diesel fuel, slow-burning but sustained,” says Allen. But when your workout gets more intense, your body starts using less oxygen and switches to burning carbohydrates, a “high-octane jet fuel” that requires less oxygen to break down.
Burning those carbs is good in short, occasional bursts—it revs metabolism and helps push your muscles and cardiovascular system so they come back faster and stronger. But too much anaerobic training can leave you worn out, prone to injury and illness, and unable to recover quickly.
Your goal with heart-rate training, then, is to find that sweet spot right at or below the threshold between aerobic and anaerobic effort, where you should spend the majority—about 80 percent—of your training: this is your maximum aerobic heart rate.
Perhaps the easiest way to get this number is through this formula that Allen suggests using:
1. Subtract your age from 180.
2. Take this number and correct it by the following:
- If you do not work out, subtract another five beats.
- If you work out three to five times a week, keep the number where it is.
- If you've been working out six or more times a week for the past year, add five beats.
3. Now add a quarter beat for every year you are under 40, or subtract a quarter beat for every year you are over. (If you're 30, for example, you'd add two to three beats. If you're 44, subtract one.)
This is your maximum aerobic heart rate—about of your maximum overall effort. By keeping your beats per minute at this rate during most of your workouts, you can gauge progress over time.
“If, for example, last month you ran nine-minute miles or cycled at 200 watts while maintaing your max aerobic heart rate, but this month you are running eight-minute miles or cycling at 240 watts, that shows you have made pure, raw fitness gains that are irrefutable,” says Allen. “Without the consistent heart rate, you would not know if you garnered those gains because you are more fit or simply because you pushed harder.”
If you've never paid attention to your heart rate before, you may find that, initially, staying in your fat-burning zone seems almost too easy to yield fitness benefit. “To run at my max aerobic heart rate without going over,” Allen says of his early triathlon days, “I had to slow my run pace down over three and a half minutes a mile and walk up every hill. I felt like I was crawling.”
Eventually, though, he got faster—without pushing himself above his threshold. “My physiology did come around, and when I then added in some strategically placed speedwork, I was able to run a 5:30 mile and still be at or below my max of 155 bpm.” And because his heart rate stayed lower than it had in the past, he could hold that pace for much longer.
Bottom line: “Regardless of whether you're targeting a 5K or a marathon, you will benefit from doing the bulk of your workouts in your aerobic training zone,” says Allen—specifically, the top 10 beats of that zone. Dipping into your anaerobic zone is okay for one or two hard workouts a week, but otherwise it's best to be patient, take your time, and let the improvements come to you. And the only way to accurately know what zone you're in—for now—is to measure your heart rate.