Taking a short break from technology and building things to talk about fitness and weight loss. I’ll present a 3 part series of posts to talk about what I’ve learned over the past few years.
RMR Oxygen and CO2
There’s been a lot of books I’ve read over the years about losing weight and getting fitter. Low Carbs. No Meat. 10,000 Steps. Count Calories. But it wasn’t until I went to have my Resting Metabolic Rate (RMR) measured that I truly woke up to the real science of metabolism and weight loss.
A metabolic cart does something real simple, it measures Oxygen (O2) In and Carbon Dioxide (CO2) Out. It does this for about 20 minutes and then it inputs the results into the Weir Equation and calculates your calories per minute. See Below:
Weir Equation is EE (kcal/min) = (3.941 x VO2) + 1.106 X VCO2)
To substitute my measured numbers (3.941 x .354L/min + 1.106 x .292 L/min) ~= 1.718 * 1440 = 2474 calories / day
Fascinating. Metabolism is really just about how much O2 you breathe in and how much CO2 you breathe out. But while I found this super helpful, what about all the folks that say steps per day or you must do cardio? Well this is a little more complicated but it still all comes back to Oxygen.
METs or Metabolically Equivalent Task
A MET or Metabolically Equivalent Task. This is defined as 3.5 milliliters of oxygen per kg of body weight per minute. Now this will vary per person and some people will burn more oxygen per minute some will burn less based on fitness level. Here are some sample MET values below.
| Activity | METs |
| Walking 3mph, 10 minute mile | 3.5 |
| Running 6mph, 10minute mile | 9.8 |
| Bicycling 10-12mph | 6.8 |
| Swimming freestyle | 7.0 |
| Weight Lifting | 3.0 |
So the equation for this is below:
Calories Burned = MET value x body weight in kg x duration in hours
Keeping Math Simple, walking 20min/mile pace yields, 3.5 Mets x 100 kg x 0.333 = 116.55 calories per 2000 steps.
Subtract your RMR from this number, so at rest a 100kg person burned 34.32 calories, for net gain of 82.335 calories per 2000 steps.
So the cardio crowd or the 10,000 steps crowd wasn’t wrong. A 100kg person will burn 82 more calories per 2000 steps walking than sitting on their butt. But if your fitness tracker or your treadmill typically has these numbers in the 150s or 200s per 20min it’s way off.