Many of us religiously count what we eat and burn off, but calorie counts on cardio machines can be inaccurate by as much as 10-15%. So you could be burning 510 calories as opposed to the 600 calories that the display tells you. And those few 90-100 calories can add up enough to hinder your weight loss.
True, not all machines are created equal: you can rely more on the accuracy of machines that ask for your weight than those that don’t. But even so, caloric burn can be very different depending on a person’s body fat percentage and form efficiency, neither of which can be computed from weight alone.
That’s not to say you should ignore what the display tells you—if you use it as a bench mark from work out to work out. Here’s how.
What you want to focus on is what exercise physiologists call “rated perceived exertion.” Basically, it’s a scale you use to gage how hard you are working. Check out the table above.
The intensity that cases each of these exertions will be different for each person. You might find that running at 8:30 minutes per mile is “comfortably hard,” but your significant other might feel the same level of exertion running at 9:00 minute miles. A general guideline is to perform most of your workouts at level 3-4, or moderate to comfortably hard.
As your fitness improves, the same exercise will require less effort as your body adapts to the routine — so you should increase the intensity until it feels comfortably hard again.