Adventures in Heart Rate Monitors... or that One Time I Went to Orange Theory Fitness

Adventures in Heart Rate Monitors... or that One Time I Went to Orange Theory Fitness
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Nikki slid the heart rate monitor onto my arm and fastened it around my bicep, then handed me a laminated piece of paper with a large, colorful bar graph. "During your workout," she said, "the monitor is going to tell you which 'zone' you're in." She pointed to the handout. "You're going to do most of your workout here in the blue or green zones. But during part of the workout we're going to ask that you really push yourself into the orange and maybe even the red zones." I thought I’d hear more explanation of zones, to be honest. I’d come into Orange Theory Fitness to test the technology but also the whole premise of their zone-based training. Nikki paused, "So what are your goals exactly?"

It was the first week of January, and I'm not sure how many of these speeches Nikki had already given to prospective gym members. I was trying to play it cool and not reveal that in fact, the only reason I was taking this class was because I was working on an article. Well, that and I've heard so many fellow runners say that OTF is where they do their strength training. So yeah, I was curious. It was a Thursday, so I also wanted to get a run in, and I’m trying to not find the treadmill a grind.

I am not, however, interested in losing weight, and I think that's the next part of the spiel that Nikki was prepared to give me. Because that's part of the big "sell" of that orange zone -- the “orange theory, if you will. From the company's website: "This is where the magic happens and where you achieve “EPOC” (Excess Post-Exercise Oxygen Consumption) – what we call the 'Orange Effect / Afterburn.' The goal is to accumulate 12 minutes or more in this zone within a 60-minute period to achieve the maximum caloric burn for up to 24 hours AFTER your workout is completed."

If I joined the gym today, Nikki said, not only could I take advantage of a great New Year's deal, but I could enter the contest to be the person to lose the most weight in the next six months. Or gain the most muscle, she quickly added, pointing to the scale by the front door. "We will measure your weight and your body fat when you sign up." (No matter how well the workout went, no matter how much I enjoyed myself, no matter how amazing the technology, this was the moment that I decided I would not be joining this gym.)

Rebecca the trainer came over to show me around the gym, which was lit with this weird orange glow that's signature to the company. "I've never used a rower," I admitted. "Oh I'll show you. It's easy," she said. Indeed, the bigger challenge, I found, was remembering to log in and out of the machines. Doing so ensured the exercise machine -- the rower, the bike, the treadmill -- was linked to my heart rate monitor, which would then broadcast my performance onto large screens in the corner — your name and your zone for everyone to see. "You get 'splats' every time you're in the orange or red zone," Rebecca said excitedly. "It's great for a little friendly competition."

Or it's absolutely mortifying. Or even counter-productive. (1)

"You're probably going to be in the red zone a lot, but don't worry," the trainer said in a reassuring tone. "I know you said you're a runner, but the heart rate monitor doesn't know that, so it's going to say what zone you're in based on your age. So don't pay too much attention to the color. Just have fun today." So much for precise technology. So much for the whole orange "theory."

By the time Rebecca had finished my orientation, the other class members had arrived — midday on a Thursday, and the class was packed with about 20 people, men and women with a range of age and ethnicity and body size. Indeed, Orange Theory Fitness has become one of the most popular group fitness franchises in the US since it was founded in 2010, with over 1300 studios in the US and around one million members. Part of the appeal is the promise of a fun 60-minute workout that combines cardio and strength training.(2) But really, the big appeal is the promise of that "orange effect" — a post-workout calorie burn (that is, weight loss). And, of course, part of the appeal is the promise of personalized data via fitness technology. I mean, that's why I'm there.

And my workout was fun, I guess, in the way that moving through "centers" in kindergarten was fun. You were never doing one thing long enough to really get into it or enough to really get bored — 5 minutes on the rower, then 5 minutes lifting weights, then back on the rower, then back with the weights, then rower, then weights, then on to the treadmill, then back to the weights, and back to the treadmill, with Rebecca, like a harried preschool teacher, barking out orders and paying attention to everybody while paying attention to no one. In fairness, she did come over once to tell me to grab a heavier dumbbell, and as I think women tend to undershoot what they can (and should) lift, I appreciated that.(3) But even so, I'm not sure it was a good workout (4), as it wasn't quite heavy enough for resistance training nor it wasn't quite easy enough for cardiovascular adaptation nor was it quite hard enough for interval training. But most damning, I think: the technology simply didn't work.

My technology didn't work, at least. I wasn't able to link my heart rate monitor to the machines, and I wasn't able log in. When I received my email afterwards, breaking down how I'd performed — 22 splat points — it didn't register any of the time I'd spent on the treadmill. But even if the heart rate monitor had worked perfectly and I'd been able to log in and out of the various machines, the heart rate zone data still would have been inaccurate, as Rebecca had cautioned.

The default settings for heart rate zones — on the OTF device as well as on almost all personal fitness trackers and watches — is based on the Fox formula: 220 minus your age gives you your maximum heart-rate, and the zones are then a percentage of that.(5) That would put my max heart-rate at 168; according to the heart rate monitor, I hit 180 at some point in the workout.

You can tell a lot about what a fitness technology thinks matters based on how much it highlights "calories burned" -- a figure that is, without a doubt, utterly incorrect

After the workout, Rebecca and Nikki went over my performance, trying very hard to convince me to join the gym. I asked about my problem with my monitor — does this happen often? Can I just bring my own? Indeed, yes yes you can — or you can buy the white-labeled version that Orange Theory Fitness sells for $120. Or you can rent one each visit (for $10). But you can't use your own watch or a different manufacturer's heart rate monitor — these can't connect to the big screens. (I mean, they probably can, but that would mean more tech set-up and fewer device sales.)

My chart said I'd spent about a third of the workout in the orange and red zones, but Rebecca assured me that, if I came regularly — "like, five times," Nikki chimed in — "the algorithm" would be able to gauge my level of fitness and adjust the zones accordingly. And while I have no doubt that "the algorithm" would make some adjustments once it had more data about me, it simply isn't true that it would be able to accurately determine my maximum heart rate or my zones after a few visits to the gym. The company press release says it takes 20 visits, and it's not that Nikki was really trying to close the deal by making shit up — I mean, she was — but the whole notion that our bodies are so easily quantifiable is simply not true.

Yet this is a foundational element of fitness technology. It's a fundamental part of "zone training," which has become wildly popular with the rise of heart rate monitoring on specially designed devices — chest and arm straps — as well as on fitness watches. But our physiology is just not as cut-and-dried as "the algorithm" or the gadget wants us to believe.

I'll have more to say about this — about "zone training" and heart rate monitors in coming weeks: the history of these devices as well as some of the science behind the training. So consider this part 1 of a series on the tech. And as I visited another local franchise on Friday — my very first Pilates reformer class — I'll have more to say about all sorts of fitness technologies this year as well as the business models and marketing that are helping these gyms pop up all over the place.


(1) Many sports scientists and trainers recommend "polarized training," in which the vast majority of an athlete's training sessions are devoted to "easy" stuff — running slowly, for example, in Zone 2 — with a smaller proportion of sessions for hard, high intensity stuff — sprint intervals and such. A common split, popularized by Dr. Stephen Seiler in the early 2000s, is 80/20: 80% easy sessions and 20% hard. Sessions, to be clear, not a percentage of minutes within a workout.

(2) The "strength" portion of the class uses mostly body weight, light dumbbells, and a high number of reps. I have a bias towards the barbell, I admit, but truly lifting light or heavy does not matter as long as you're lifting to a couple of reps away from "failure" (that is, where you can't move the weight at all anymore). And I'm not sure that happens at an OTF class — even the "light" weight is not heavy enough. Also strength training shouldn't be cardio; these are different modalities for strengthening different parts of the body — muscles and bones versus heart and lungs.

(3) You can lift heavier. You can. Check out Casey Johnston's Couch to Barbell.

(4) Do you love Orange Theory Fitness? That's cool! This post isn't about you. It's about the company and the technology. There are a gazillion different workout programs and gyms and fitness gadgets. On one hand, it's important to pick something(s) and do them consistently. The Department of Health and Human Services says we should get at least 150 minutes of moderate aerobic exercise a week – it doesn't specify what that exercise need be. (Indeed, it may be even more important that you put in the time doing strength training.) But on the other hand, our time is limited, and as such it's not ideal to spend that time (and spend your money) on something that might put you at risk of injury. I was a little shocked that, after Rebecca and Nikki had finished trying to sell me on joining Orange Theory, there was a long line of folks waiting to talk to them – folks who'd hurt themselves or who were in pain after the workout.

(5) A 2020 study published in the International Journal of Exercise Science found that, among the various formulas used to estimate maximum heart rate, the Fox formula was the least likely to over- or underestimate max heart rate. However the researchers said that all the formulas were, in fact, inaccurate and that if you want correct data, you need to do a graded exercise stress test on a treadmill. I'll have more to say soon on the history of the formula and — soon after — the development of heart rate monitors and how this all got "hard coded" into the tech.