Redefining effort: why METs are the future of activity tracking

What’s the first thing you think of when you hear “METs”? Most people have no idea — and that’s a problem because METs are one of the most powerful fitness metrics out there. If you’ve been chasing calorie burn or staring at your step count, wondering what it all means, METs are about to be your new best friend.

METs — Metabolic Equivalent of Task — are one of those things you’ve probably heard about in health advice.

METs measure how hard your body is working compared to rest and make fitness measurable. They don’t just tell you what you did but how much effort it took.

Let’s dig into where they actually came from. Spoiler: they’re not some modern fitness trend — it’s old-school science.

Back in the mid-20th century, researchers were diving into how to measure energy expenditure. They needed a simple way to compare physical activity levels between people without sticking everyone in a lab. Enter METs. The idea was to standardize how we talk about energy use by basing it on the metabolic rate while sitting quietly (aka your baseline). This is around 1 kcal/kg/hour — literally how much energy your body burns just to keep you alive while chilling on the couch.

The concept really took off thanks to the work of researchers like Sid Robinson and J. Thomas McArdle, who studied energy expenditure in the 1940s and 1950s. They laid the groundwork, and then people like Ainsworth et al. in the 1990s made it practical by creating a Compendium of Physical Activities. This compendium assigned MET values to a ton of everyday tasks — from walking to vacuuming — making it easy to estimate how much energy you burn during different activities.

For example:

But the thing is, standard METs follow a “one-size-fits-all” approach, which doesn’t really reflect how different we all are.

Imagine two people going for a walk. Person A is super fit with a resting heart rate of 50 bpm. When they’re walking, their heart rate only bumps up to 90 bpm — pretty low for a walk. Since they’re in such great shape, their METs score comes out to 5.8, which is just about a third of their max effort. For them, it doesn’t even feel like a workout. Person B isn’t as fit and has a resting heart rate of 75 bpm. On the same walk, their heart rate hits 100 bpm, which is totally fine for them. But their METs score is 3, or half their max effort. So, for them, the walk feels like a solid aerobic workout.

The difference in METs between these two people is almost double — just from walking. That’s why we’ve completely reimagined METs: to factor in individual differences and make your effort level truly reflect your endurance.

When we set out to create the best activity analysis in the world, we hit a major roadblock: traditional metrics like VO₂ max and calories burned aren’t just rough estimates — they’re wildly inconsistent.

Calorie burn predictions depend on body composition, gender, and even the activity type you select on your tracker. Change the settings, and your results can swing dramatically — even on the same device.

VO₂ max is even trickier. Without a gas analyzer mask and lab-grade tools, it’s all just guesswork. Different devices use different formulas, often based on gender. In one real-life test, changing the gender setting on the same watch boosted VO₂ max from the mid-40s to the 60s — just because the device assumes men have higher numbers.

Bottom line: VO₂ max comparisons only make sense if you use the same device with the same settings. Even then, they’re still an educated guess — not the kind of accuracy we’re after.

In our research, our scientists found that METs are a much better option. But even they’re not perfect. Take Apple — they’re great at tracking metrics, but their METs and VO₂ max calculations are based on predictions, not measurements. Most other apps do the same, simply pulling that data — still predicting, not actually measuring.

We ditched the averages and decided to actually measure your METs — making them meaningful and personalized. By using your real-time heart rate, resting heart rate, and Max METs, we created an activity feature that truly gets you.

First, we gather data to define your personal range — from chilling to going all out — based on your resting heart rate, Max METs, and how your heart behaves throughout the day.

Imagine two people with the same resting heart rate of 60 bpm and a current workout heart rate of 160 bpm. Both would hit 11 METs based on heart effort alone. But here’s where personalization kicks in:

Thus, an 11 METs effort might push one person close to their limit, while for someone fitter, it’s just moderate intensity. This personalized approach means your activity stats reflect your true effort, not some generic standard.

We use METs to measure your activity intensity with precision. But not all METs are created equal — what really matters for your heart and fitness are Beneficial METs.

To put it simply:

For example, a 3-hour slow walk might rack up 450 Total METs, but if your heart rate never crosses the exercise threshold, your Beneficial METs stay at 0 — meaning no real cardiovascular gains.

Your beneficial activity threshold adjusts daily based on your heart rate, fitness level, and real-time performance — ensuring your training is tailored to you.

With this approach, you’ll see the real difference between staying active and making progress.

We already have the smartest HR zones out there — but there’s always room to level up. Your body responds differently at different effort levels — and those responses aren’t the same for everyone. Our new zones don’t just adjust to your heart rate; they also adapt to your maximum METs potential, giving you an even more precise real-time reflection of your current fitness level. Plus, you now have 5 zones instead of 4, making sure every move counts.

Here’s how it works:

This two-step calculation allows us to personalize your zones:

As your fitness improves, your Heart Rate Zones adjust to reflect your growing capacity. If your max METs increase, the zones shift to keep challenging you. Conversely, if your condition changes, the zones will adapt to help you work out safely.

It’s also important to note that training shouldn’t drain you to the point where your overall daily activity drops. Good recovery includes proper nutrition, hydration, rest, and maintaining your usual activity levels. Avoid scaling back daily movements like walking or taking stairs because of fatigue from workouts — that’s a sign of overtraining.

This approach adjusts for your fitness and effort levels, body composition, and overall health, making your activity insights data truly personalized. Plus, while most other apps still fail to understand that people shouldn’t be working out 365 days a year, we focus on proper rest and real effort that’s good for your body and doesn’t lead to obsessions, overtraining, and guilt.

Let’s have a little fun here and make METs easier to picture. Imagine your body is a car, and its favorite fuel is pizza. METs are like your car’s speedometer, measuring how fast you burn through slices depending on your activity. When you’re active, your body burns fuel faster, just like driving fast eats up gas. When you’re resting, the fuel lasts longer because your engine’s barely running.

To illustrate the point, we created this infographic:

Most trackers calculate calories burned based on heart rate and weight. But: with the same heart rate, a woman — who typically weighs less — would get a lower calorie count on these devices. That’s what we’re used to seeing. But if you look at METs instead, the story flips. Despite weighing less, The Badass Woman actually burns more calories because she’s working at a higher intensity. If both ran for an hour at a target heart rate, say 135, the Badass Woman would cover way more distance since she’s lighter and better adapted to the load, meaning she’d burn far more calories. But Apple Watches (and most trackers) would still say the Dude burned more, which makes no sense.

If everyone’s body worked exactly the same way and 1 MET always equaled 3.5 ml of oxygen per kg per minute (ml/kg/min), then calculating calories or VO2max would be super precise. But in reality, that number varies. For some people, 1 MET is 2.5ml/kg/min, while for others, it’s 3.7ml/kg/min. It all depends on factors like lung capacity, hemoglobin levels, red blood cell count, etc. That’s why converting METs into calories without using a gas analyzer is always just an estimate. But METs on their own are incredibly accurate. No matter who you are, 5 METs will always mean the same level of effort. The calories burned at those 5 METs might vary, but the METs themselves don’t lie.

And this precision matters: even small gains in max MET can make a big difference for your health. Just one extra max MET cuts your cardiovascular risk by 15%. That’s huge.

METs give you a no-BS, science-backed way to see exactly how hard your body’s grinding — based on actually measured (not predicted!) data. The app tailors METs to your level, so you get all the gains (six-pack, buns of steel, unbreakable stamina — or whatever floats your fitness boat), track every ounce of progress, and push past your limits — all while keeping your heart happy and healthy. With our new and improved activity analysis, you’re not just working out harder; you’re working out smarter. Always.