Calorie burn is not easy to measure. The most accurate measurements are taken using a machine that analyzes the air you exhale while you're working out, not a fitness tracker you wear on your wrist. Those machines are expensive and cumbersome, and basically only laboratories and hospitals have them. Because of this, exercise scientists took tome to come up with a way to measure calorie burn accurately without having to use this bulky machine.
It was known for decades that there was a mathematical relationship between heart rate and calorie burn. However, heart rate alone is not an accurate predictor of how many calories you're burning. It doesn't match up with what the machines that analyze your exhaled air calculate. So, to increase accuracy, they figured out that some other things needed to be taken into account.
Weight is one example. Moving a 175-pound person for one mile on a treadmill requires more energy than moving a 150-pound person, right? Expending more energy means burning more calories. This is why your fitness trackers ask for your weight when you, and why you should update your weight regularly.
Another factor that increases the accuracy of a heart-rate-based prediction of calories burned is gender. Why? Well, physiologically, women burn fewer calories during physical activity than men. Women generally have a higher body fat percentage than men (that's a good thing ladies!). Since muscle cells burn more calories than fat cells do, and men's bodies tend to more muscle cells, men inherently
burn more calories during physical activity.
Today, there are two different formulas are generally accepted by exercise scientists as providing the most accurate prediction of calorie burn. Both formulas include gender as a variable. This means that a fitness tracker would generate a different calorie burn count for a man and a woman for the same routine, every single time, even if they are the same height, same weight, same age, and work out at the same intensity. The woman's burn will always, be lower — and both numbers will always be equally accurate.
If you want to play around with this, check out this Heart-Rate-Based Calorie Burn Calculator.
Try putting your data into the calculator, and then change the gender variable to Man, it will estimate a completely different calorie burn! Remember, both estimates are equally accurate, and both are based on averages and generalities, just like most exercise science (and most medicine, for that matter).
Sorry ladies most athletic studies are done on men and generalized for women. I could do many many entire blog posts about that, so I'll save that rant for another day.
So comparing a man's calorie burn to a woman's isn't really a fair comparison of how hard they worked out. If you want to compare something, it would be more reasonable to compare how long you are in a fat-burning heart rate zone. Or stop comparing yourself to others and compare yourself today to yourself yesterday. How are you trending over time?
I hope you all enjoy your workouts this week!