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Cardio Machines Are Just Guessing How Many Calories You Burned

Is my elliptical a liar?

Grant  Stoddard

Grant Stoddard

ninikas / Getty

Have you heard of the Big Mac Index? It’s a way economists measure purchasing power parity (PPP) between nations, using the local price of two all-beef patties, special sauce, lettuce, cheese, pickles and onions on a sesame seed bun as a benchmark. I too use McDonald's’ signature dish as a way of understanding the world, albeit in a much more vain way.

The iconic sandwich—launched in 1967—is a unit of energy I’m intimately familiar with. Whether it’s delicious or not is a matter of opinion but the fact that each one packs 563 calories is unassailable, constant, a matter of fact.

Consequently, I step onto an elliptical machine, enter my weight, cue up Appetite for Destruction and frantically scissor my limbs back and forth like some malfunctioning Rock ‘em Sock ‘em robot until last note of Rocket Queen decays. At that point I can be satisfied that I’ve expended enough energy to consume one Big Mac’s worth of calories more than my body requires to tick over, heal and digest food, without adding heft to my burgeoning dad bod. If I exercise and then resist the urge to replace the energy I’ve used, I theorize, I’ll create a calorie deficit and my body will begin to cannibalize its gelatinous energy stores. Indeed, that’s what I’ve been doing.

The thing is, several months into using this McRubric, I remain a skinny dude with a frustratingly pillowy midriff. Before I take ownership of that fact or rethink my Big Mac paradigm entirely, I need to point the finger of blame elsewhere. So I’m pointing it at the elliptical machine. I think the fucker’s lying to me.

Julie Daly is the biomechanics engineering manager at Life Fitness, a company that accounts for almost a third of the commercial fitness equipment market and the manufacturers of the machine I huff it out on most mornings at the Chinatown YMCA. She isn’t about to take the rap for my unsightly spare tire lying down. Daly tells me that Life Fitness uses what she calls “gold standard equations” from the American College of Sports Medicine for Life Fitness products. On products to which those formulas can’t be applied, she says, the company conducts in-house VO2 testing (a way of measuring people’s oxygen consumption during incremental exercise and an indicator of cardiorespiratory fitness).

“We test a range of people spanning gender, age, weight and fitness level at multiple submaximal exertion levels,” Daly says to me, over email. “We record the volume of oxygen that the subject utilizes during the workout at each known resistance setting. Based on the collected data, we conduct a statistical analysis to develop a calorie prediction equation.”

If she and I were standing face at that point, I would have been tempted to lift up my t-shirt, grab some adipose tissue betwixt my forefinger and thumb and ask: “Then what’s up with this shit, Julie?”

I mean, I’m already doing what she says is the most important thing a user of fitness equipment can do to get accurate calorie data: entering my weight. That number is easy to remember as it’s immutable and always 15 lbs higher than I want it to be.

“Weight is a strong factor in our calorie burn equation and just by doing that [users of cardio equipment will] get the most accurate read possible of their calorie burn,” she says, adding that other factors like heart rate and age don’t have a strong influence on calorie burn and are therefore not accounted for in the caloric equation.”

Daly says that due to the array of machines and the variability between individuals, she was unable to share a standard margin of error with me but, understandably, made a strong case for the research behind the calorie feedback Life Fitness equipment spits out. Undeterred, I looked for someone else to backup my feeling that cardio machines are way off base.

Dori Arad is a clinical dietitian nutritionist, certified diabetes educator, exercise physiologist and the director of the Metabolic, Body Composition, and Sports Performance Clinic at Mount Sinai St. Luke’s in Manhattan. I first became aware of Arad and the clinic when researching the Bod Pod about nine months ago.The Bod Pod is an egg-like contraption that uses air displacement plethysmography to reckon how much blubber those who clamber inside are sporting.

My experience in the Bod Pod revealed that I was 17.8 percent lard. That put me in the “moderately lean” category for a 40-year-old male. Not too bad, but it’s in the sub-12 percent “lean” category that the magic happens: When my rectus abdominis becomes visible to the naked eye and not merely suggested under ideal lighting conditions, two days of eating very little and flexing until I nearly poop my pants.

It was in the wake of my body composition assessment that I started thinking about the Big Mac as a benchmark unit of energy. I tried to create a daily calorie deficit of 563-ish calories per day for a weekly energy shortfall of just under 4000 calories per week. But despite all the number crunching, I look remarkably similar to how I did before I logged those hours at the Y.

When I told him about my frustrations and the hunch it birthed, Arad was happy to back me up with some science. “It’s tough to put a number on the margin of error with cardio machines because there is a large variability between different individuals,” he says, echoing Daly. “However, there is some research to show that it could be 30 percent or possibly even higher than that.”


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A potential 30 percent margin of error on my daily cardiovascular exercise is somewhere between a hash brown and a small fries on the McDonald’s scale. That’s a possible extra 1344 calories per week that I haven’t been accounting for. Is it any wonder that the waist of my pants is shown in relief on my middle two hours after I take them off each evening?

Arad went on to explain that two people of the same age, BMI, gender, background, could perform the same amount and intensity of work and and expend a significantly different amount of energy. Part of that difference, he says, can be attributed to differences in resting metabolic rate (RMR)—the amount of calories one’s body burns while idling.

“When making an accurate assessment on how much energy you burn while exercising, we need to know how much energy you burn when you don't do anything,” he says. “When you hop on a stationary bike and you exercise for an hour, the machine tells you that you’ve burned 600 calories. But the cardio machines don’t take into consideration the amount of energy you’d be burning during that time simply sitting on a chair next to the bike. If you burn a lot of calories at rest—100 per hour, just as an example—then you have to subtract that from the 600. But if you only burn 50 calories, the exercise would account for more.”

Another factor that a gym’s cardio machine can’t currently factor in is the exercise intensity sweet spot at which the body is burning the maximum amount of fat for fuel. “Anyone can make an appointment at the clinic and take the Fatmax test,” he says. “We can figure out the exact point at which the most fat is being mobilized and then they can go to the gym and exercise at that exact intensity.”

“So it’s possible that I could be exercising at an intensity that’s not optimal for losing body fat?” I asked, smirking at the irony of my failing at something because I’ve been trying too hard.

“It’s quite possible,” he says, adding that having a better idea of their metabolism is going to make a big difference in the way that people exercise and achieving whatever their goals are.

Unless AI has been stealthily progressing in a Mean Girls direction, cardio machines are probably not lying to us. What they are doing is giving users the best information they can using aggregated results from tests like the ones Arad conducts at his clinic. That educated guess is going to be right on the money for some people but significantly off target for others because, well, we are all very different.

Even if you are the same weight, height, age and gender as another individual the amount of oxygen you consume, how much fat you burn when performing the same work could be disparate. Now I know the utility of a bespoke metabolic assessment, I’ve booked some more tests with Arad. Between the results I get and a reassessment of the items on the dollar menu, I’ll be armed with everything I need to make 2018 my sveltest year in a while.

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