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The Cardio Load calculation is a metric the Fitbit app uses to suggest how much Pixel Watch and Fitbit users should exercise, but it can be hard to understand. It’s also recently been updated for the new version of the app, and it works a bit differently there. Here’s how you should use this number, and what it means to hit your target.

What is cardio load?

Cardio load is a way of understanding how much exercise you’ve been doing, whether the app logged it as a workout or not. Exercising for a longer time, and exercising at a higher intensity, both increase your cardio load. 

For example, on a day that you go for a five-mile run at an easy pace, you’ll have a higher cardio load in the Fitbit app than a day you ran three miles at an easy pace. If you run three miles at a more intense pace—say you race a 5K—your cardio load will be somewhere in between.

Here are a few examples from some workouts of my own: 

• A track workout that had me alternating between moderate and peak heart rate zones for an hour (total five miles) had a cardio load of 117.

• 20 minutes of detangling my kid’s hair got logged as a workout, but since my heart rate was in the light zone the whole time, I didn’t get any cardio load.

• A 53-minute gym workout, which included a mix of heavy lifts and lighter continuous work, clocked in at a cardio load of 63. 

The “load” here is in the sense of “workload.” If this summer you were exercising an hour a day, and right now you’re only getting in 30 minutes every other day, your cardio load for the week (and for each day) will be lower than it was in the summer. Makes sense, right? If you were to spend all next week exercising an hour a day, that would be way higher than your current cardio load—and the Fitbit app would let you know that you’ve suddenly increased your cardio load, and might want to chill a bit.

What is your target cardio load? 

The Fitbit app automatically calculates a target cardio load based on what you’re used to doing. You can choose whether you want to improve your fitness (in which case it will nudge you to crank your load up a little higher each week) or maintain your current fitness. You’ll find this setting when you look at your cardio load in the app—just tap on “fitness target” near the bottom.

How the new FItbit app handles cardio load

In the original implementation, your cardio load target could change from day to day. Fitbit recently released a preview of the new version of its app, and that version now tracks cardio load weekly, which makes much more sense. So instead of being told that you should hit a certain load today, you’ll be told that you’re, say, 41% of the way toward your target load for the week.

The upcoming version of the Fitbit app (currently in “public preview”)
Credit: Beth Skwarecki/Fitbit

Which devices support cardio load?

Currently, the devices that have cardio load are:

• Pixel Watches 1, 2, 3, and 4

• Fitbit Charge 5 and 6

• Fitbit Versa 2, 3, and 4

• Fitbit Sense 1 and 2

• FItbit Luxe

• Fitbit Inspire 2 and 3

Fitbit Charge 6

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The Pixel watches can show you your cardio load on-screen, but for the others, you’ll need to view it in the phone app.

Other apps and platforms have their own versions of cardio load. For example, some Garmin devices measure a Training Load (along with acute/chronic load, and load focus), but it’s calculated and displayed a bit differently from Fitbit’s. This article is just discussing the Fitbit/Pixel version.

The difference between cardio load and active zone minutes

Both metrics describe how much exercise you’re getting, and give you extra credit for hard exercise compared to moderate exercise. But they have different purposes, and are calculated a bit differently. 

The purpose of active zone minutes is to figure out whether you’re meeting some basic exercise targets for health. Active zone minutes match the U.S. Physical Activity Guidelines, which recommend that we all get 150 minutes of moderate exercise per week, or 75 minutes of vigorous exercise. In other words, it’s a count of minutes, with vigorous exercise (like running) counting double. This is why your 30-minute workout might count for 45 zone minutes, if 15 of those minutes were moderate and 15 were vigorous (15 x 2 = 30). 

(There’s a caveat on that: Fitbit uses your heart rate to estimate whether a given minute of exercise was vigorous or moderate for you. The original guidelines used METs, not heart rate, so it’s not a perfect match. But it’s close enough to be useful.)

Cardio load, meanwhile, is a metric more often used by athletes to make sure their exercise effort is within the optimal range to improve or maintain their fitness. Fitbit uses a modified version of the TRIMP algorithm, which basically multiplies your heart rate times the number of minutes you were at that heart rate. Higher heart rates are weighted a little more than lower ones, as Google explains in this document. If your heart rate is below a certain level, it doesn’t get counted, which is why my hair-brushing sessions didn’t count for any cardio load.

With cardio load, you aren’t just looking to beat a minimum to give yourself a passing grade—you’re trying to stay within a specific window, which is defined by the amount of exercise you’re used to doing. If you do a little more exercise every week, you can stay within your target range while pushing up the boundaries of that target range. That’s how you get fitter.

On the other hand, if you’re doing a lot more or a lot less exercise this week than your body is used to, you could end up losing some fitness (if you’re doing less) or making yourself more fatigued than usual (if you’re doing more). Depending on where you are in your training, these outcomes aren’t necessarily a bad thing. But with a cardio target to compare your load to, at least you know where you stand.

Cardio load gets a major fix in the new Fitbit app, which Android users can test out starting this week in a “public preview.” (This is the same preview that gives you access to the AI fitness coach, which I tested yesterday, with baffling results.) Cardio load will now be tracked weekly, making it much easier for the app to make sensible recommendations.

What is (and was) cardio load? 

The cardio load feature is Fitbit’s attempt to guide you in how much to exercise. Obviously a beginner shouldn’t jump into hour-long hard workouts right out of the gate, nor should a person training for a marathon slack off for no reason. Cardio load is an attempt to put a number on the amount of exercise that would be neither too much nor too little for you. 

Plenty of athletes and trainers use some kind of model for exercise volume, whether it’s runners counting miles in a spreadsheet, or a coach going by their gut and saying “let’s take it easy today.” 

Fitbit uses a hilariously-named TRIMP approach (“TRaining IMPulse”), where every minute with an elevated heart rate counts toward your cardio load, with higher heart rates counting as more effort. I have more on this calculation here. 

Why cardio load was confusing

The idea sounded good: Fitbit would calculate how much cardio load you should aim for each day, based on how much exercise you’d been doing. You could tell the app whether you wanted to increase your fitness, or just maintain the fitness you have, and it would adjust its numbers accordingly. 

But for a lot of people, the numbers never made sense. The numbers would fluctuate from day to day, often mismatched with what a person’s history and health actually called for. Many users found that the recommended cardio load went up and up, and rest days brought warnings of undertraining.

A sampling of Reddit threads from r/fitbit include titles like “Cardio load baffles me,” “Cardio load, I hate you,” “Cardio load unrealistic,” “Cardio load is not just wrong, it’s dangerous,” and “Fitbit, either fix cardio load or scrap it.” 

Why the new feature may be better

Credit: Beth Skwarecki/Fitbit

Google explained that it’s implementing a fairly simple fix—calculating cardio load recommendations by the week instead of by the day. The cardio load calculations themselves won’t change at all.

After all, it’s normal to have hard days alternating with easy days or rest days, and any load management guidance should be able to handle that. Google also points out that your background activity level (like how much you walk when you go grocery shopping) also adds to your cardio load, and that also makes day-to-day recommendations hard to follow. 

The new version of the Fitbit app now shows a big donut on the top of the screen with your progress toward your weekly goal. With a couple of quick runs, I’m now 41% of the way toward my weekly target. There’s even a graph showing where my target is versus what it considers “overreaching.” This makes a lot more sense.

YouTube’s going through a lot of changes right now, and according to the company, that’s to help it better stand out on TVs. Today, YouTube announced that it’s going to allow creators to upload bigger thumbnails, plus make browsing and shopping while watching on a TV a bit more convenient. But there’s also a big change coming to content itself, and it’s not just limited to TVs.

Soon, YouTube is going to start using AI to automatically upscale any videos with resolutions lower than 1080p. While you can technically still upload videos that are 720p nowadays, with smartphone cameras getting better and better, that essentially reads to me as “old videos.” It’s a bit concerning to me, as someone who’s been watching a lot of TV shows from the ’90s and early 2000s on YouTube as of late.

Credit: YouTube

Done right, AI upscaling is a simple way to de-noise a video, and is more resistant to hallucination than generations made from whole cloth. But it’s not without its own hiccups, and some creators have actually accused YouTube of using AI upscaling already, without telling them, and with some undesirable results. The accusations have been limited to YouTube Shorts for now, but notably, even Will Smith seems to have possibly run afoul of the system’s hidden AI, as the celebrity was himself accused of generating a crowd with AI in a YouTube Short of a recent concert. However, internet sleuths have determined the footage is likely legit, but was automatically made to look like “AI slop” by YouTube. Note, for instance, how different the footage looks on Instagram.

Luckily, YouTube says that this version of AI upscaling will be fully in the hands of creators and users. According to the feature’s announcement “Creators will retain complete control over their library, as both original files and original video resolution will be kept intact, with a clear option to opt-out of these enhancements.” Viewers, meanwhile, will be able to see when AI upscaling has been used thanks to a “super resolution” label in the resolution selection settings, and opt for the original resolution instead.

Additionally, YouTube told The Verge that videos that were shot below 1080p, but manually remastered and uploaded in 1080p or above, won’t be affected by the upscaling tech. What matters is the resolution the video was uploaded in.

All of that’s a relief for folks like me, who don’t want bizarre seven-fingered extras in our sitcoms, although it’s unclear whether this control will also extend to YouTube Shorts, or if YouTube might continue experimenting with mandatory AI upscaling there behind-the-scenes (which, to be fair, has not yet been confirmed).

Regardless, it makes sense why YouTube is making this change, as it tries to capture more eyes across more devices. Low resolution videos might look fine on a six-inch smartphone display, but blown up to 50+ inches on a TV, not so much.

YouTube hasn’t said exactly when the feature will go live, but if you notice what looks like weird AI artifacting the next time you’re watching a YouTube video, try checking the resolution settings by mousing over the video and tapping or clicking the cog icon.