eli5: Why is time more important than distance/effort when calculating calories burned during exercise?

Question

When using my fitness tracker to calculate calories burned, I’ve noticed that the main factor is length of time exercising. If it used to take me 60 minutes to swim 1 mile (1800 yards) freestyle, but now I can go the same distance in closer to 50 minutes, doesn’t that mean I’m working harder, but for a shorter period of time?
Walking one mile in 15 min wouldn’t use up more calories than running the mile in 10 minutes, would it?

In: 1

Answer 1

It should take the same amount of energy to complete the same amount of ‘work’, regardless of time taken I’m pretty sure. Perhaps your counter is including your basal metabolic rate too? Is the difference really big?