You have to stop Checking Your Heart Rate so Much

When you work hard, your heart beats quicker, so that's a fantastic method to assess if you're working hard enough...right? Well, not quite. Only in some types of exercise is your heart rate an useful indicator of effort. It can even lead you astray if the figures are incorrectly calibrated.

For calorie burn, don't rely on heart rate monitors.

When your fitness tracker says you burned a specific number of calories during an exercise, it's based on your heart rate (plus a few personal details, like how big you are).

It's generally true that the greater your heart rate is during a cardio workout, such as running, the more calories you burn. However, your watch can't identify whether your heart rate is elevated for reasons other than exertion (for example, because you're frightened or hot).

For particular activities, this metric is notoriously wrong. Running and cycling are simple because you're repeating the same motion, and the way your legs move the pedals is probably not that different from the cyclist the app creators used to calibrate their formulae. But how is the watch expected to know what you're doing and how difficult it is whether you're performing a barre workout, Crossfit, or a day on the ski slopes? It doesn't, to be honest.

The fact that our calorie burn during exercise doesn't tell us much about our total calorie burn, which is what we truly care about, just adds to the confusion. When we burn a lot of calories during exercise, our bodies are good at preserving energy in everyday life. So you could burn 500 calories on a run, but then be so exhausted the rest of the day that you burn 400 fewer calories.

In the end, if you care about how many calories you burn, you shouldn't be concerned with what a heart rate monitor says. A better strategy is to simply modify your calorie intake dependent on whether the scale is rising or falling.

While strength training, don't be concerned about your heart rate.

If you do a lot of cardio, you might think of your heart rate as a good indicator of how hard you're working out. The harder you work, the greater your heart rate is during the workout. However, this is not the case with strength training.

Consider this: if you lift a light weight repeatedly, your heart rate will rise and remain elevated. For example, here's a graph of my heart rate after a ten-minute set of kettlebell clean and jerks:

That's a tough workout that will help you gain strength, but it's nothing compared to one of my regular weightlifting workouts, in which I spent almost an hour doing barbell clean and jerks, clean pulls (kind of an explosive deadlift), jerk recoveries, and core exercises on the floor. The majority of these lifts were short bursts of effort that left me gasping for air. On the graph, there are the spikes. But then I'd sit for a few minutes to recover, and that's when you'll notice my heart rate drop.

We can observe from the heart rate graphs that the ten-minute set was a consistent, relatively high-effort cardio workout. I couldn't have gone any faster or heavier because my cardiovascular system wouldn't have been able to get enough blood and oxygen to my muscles to keep up with the increased effort. From the perspective of my lungs, this looks a lot like going on a tempo run.

The barbell workout, on the other hand, was not particularly stressful on my heart and lungs, and it didn't do anything to improve my cardiovascular endurance. If you only looked at the heart rate graphs for these workouts, the barbell workout would appear to be meaningless.

However, we do not strength train for the cardiac advantage. Strength exercise forces our muscles to grow in size and strength. Heart rate isn't a good indicator of how heavy or tough a lift is. I can't tell which set was 42 kilos and which was 49 kilos just by looking at the graph; I'll have to check my training journal to find out. And, even though the weights would have been much smaller, if I were to compare this workout to one I performed a few years ago, when I was less strong, it would probably seem comparable.

If you just measure your strength exercises by your heart rate, you'll be tempted to boost your average heart rate by doing more reps of lower weight, thus turning them into cardio workouts. (Remember that ten-minute kettlebell workout I mentioned earlier? It's a good mix of aerobic and strength training, giving my heart and lungs a good workout while just giving my muscles a moderate one.) If you want to get strong, you must lift large weights, which necessitates resting between sets and allowing your pulse rate to drop.

How to train with heart rate, if you still want to

If you’re just starting to take up cycling or running or another steady-state cardio activity, you can train by effort level instead of relying on heart rate. And if you want to pay attention to your heart rate, I’d encourage you to simply notice what heart rate you see at each subjective effort level:

What number do you see when you’re walking or warming up, and not really putting any effort in yet?

What number do you see when you’re exercising at a pace where you could still easily hold a conversation?

What number do you see when you’re working at an effort level that is hard to keep up, but that you could do for maybe half an hour, or even more if you really had to?

What number do you see when you’re going all-out? (Probably no number at all, because you’re too exhausted and distracted to look at your watch, but you can check afterwards.)

Zones 1, 2, 4, and 5 correspond to those numbers, with Zone 3 falling somewhere between easy and grueling-but-I-can-hold-on.

The reason I'm asking you to notice rather than calculate is that your calculations will almost certainly be incorrect when you're new to exercise. The conventional way to describe heart rate zones is as a % of maximum heart rate, but unless you've actually put in a full-throttle, puke-inducing race-day effort, you have no idea what your maximum is.

There are several formulas for calculating your maximum heart rate; the simplest is to remove your age from 220, so a 30-year-maximum old's heart rate is 190. The difficulty with that strategy is that it's a one-size-fits-all solution that nearly no one can use.

Here's an illustration: I'm 41 years old, and my maximum heart rate is around 205. A heart rate of 152 would fit into Zone 4 according to the calculation, but I know that's a pleasant easy Zone 2 pace for me. I spent about half of my ten-minute kettlebell session at a heart rate higher than the algorithm believes is physically achievable for me. Then there are those who have maximum heart rates that are lower than the formula predicts, causing the opposite problem. They'll be out of breath, gasping, and their legs will be burning, and their watch will read Zone 3 on their wrist. That's also incorrect. Training in zones that aren't calibrated correctly can leave you fatigued or under-trained.

Your heart rate will alter as a result of your body position, as I've discovered that I can't raise my heart rate as high while cycling as I can when jogging. (Swimming, which requires your body to be horizontal, has much lower numbers.)

So, at initially, don't be concerned about your exact heart rate. Higher indicates that your cardiovascular system is working more, while lower indicates that you are exerting less effort. Adjust your "max" in your app's settings to whichever number makes the zones make sense based on how your exertion feels at a certain heart rate. Also, keep in mind that heart rate is just a tool to help you fine-tune your workout. Whether you're wearing a smartwatch or not, your body understands how hard it's working.