by Kris Pitcher
See? I'm getting excited. I'll settle down. We talked about the basic difference in energy expenditure between weight vs. non-weight-bearing exercise. So, why does everyone LOVE the elliptical? I'll tell you why. Great marketing. The calorie count - that's why. But let's break it down. Just how does that machine know how many calories YOU burn?
Caloric expenditure relative to exercise, and resting, metabolism has to do with the rate at which oxygen is delivered to active tissue (muscle) and utilized. The more muscle we have (active tissue) the more blood we need to deliver (it's the highway carrying our oxygen) for use. The tissue needs the oxygen to metabolise fat (when we're doing cardio in the right HR zone for example). The calorie is the byproduct, of the metabolic process. A calorie is a measurement of heat - it's the amount of energy needed to increase 1 gram of water one degree Celsius.
So, if our calorie expenditure is a function of how much oxygen we use - our volume of oxygen or VO2...what does the elliptical machine know about that? It's simple really, all we need to know is our VO2 (mL/kg/min) x BW. Then we convert that to L/min...divide by 1000. Then to convert the L/min to calories we just multiply VO2 L/min x 5. What? You're lost?
Yeah...it's not simple. You can have a maximal treadmill test done at your cardiologist's office to determine your volume of oxygen uptake. That won't be fun. You can have a sub maximal VO2 test if your gym offers it. It's done on a bicycle, monitoring your heart rate and blood pressure - increasing intensity based on a prescriptive protocol. From those results your trainer can determine just how many calories you are burning per minute.
OR the machine can just ESTIMATE BASED ON YOUR BODY WEIGHT. And that's what it does. All the machines typically assume you weigh 150 pounds, and I have no idea how they determine what caloric expenditure per minute to use. I imagine they test a bunch of average people and take an average of that and call it good. My point is - IT'S NOT ACCURATE!
The big picture take away here is stop living your life by the calorie count on the machine. It's not like a savings bank. It doesn't mean you have burned EXACTLY 350 calories. It gives you an idea. You might be over or under. What we do know, is that weight-bearing exercise expends more calories than non-weight-bearing.
We also know there are some devices which more accurately track your metabolic expenditure based on data you put in. You wear these things and it tracks your activity and expenditure. There are lots of charts on line which can give you an idea of your activities from hiking to gardening...to skipping rope.
The cardio machine doesn't know anything about your VO2, your body composition - how much muscle you have, or therefore how many calories YOU burn per minute. Don't get caught up in the minutia. Keep the big picture in mind. Plus you won't get weirded out if "your machine" isn't available at the gym. Get burning!