Decrease in Calories Burned: Weight? Efficiency? Age?

istockphoto.com

I started spinning about seven years ago because the brochure promised that some people could burn as much as 400 calories in one session. As someone who is always watching calories and the scale that sounded really appealing. So I signed up. Looking back at my training records, the first year or so, I did burn an average of 400 calories per session. The calorie count is reasonably accurate because I use a heart rate monitor that takes my fitness level, weight, height and age into consideration.

But something’s happened. Fast forward six years. Now my average calorie burn per class for 10 classes is 312. The class lasts an average of 8 minutes more and is harder. (I call my instructor Leo the Maniac – with 4 speed drills and other harder maneuvers throughout the session). And my statistics show it’s harder, because my average training load (a measure of exertion based on heart rate and duration of exercise) is 97.4), whereas six years ago it was 91.5. So what’s going on here?

Is it weight? You burn more calories if you weight more. Well, I don’t have records of exactly how much I weighed six years ago, but I have records for several years around then and know I could have only been about 10 pounds heavier. I don’t feel like doing the math, but somehow I don’t feel even if I was 10 pounds heavier, it could have made that much difference, and looking at the records, it’s likely I was only five pounds heavier.

Is it an increase in efficiency? Some experts claim that your body gets used to an exercise and becomes more efficient, and therefore burns fewer calories. I’ve reviewed several articles and it’s doubtful that I have gained enough efficiency over the past six years to account for the difference. One article states Lance Armstrong, training over six hours a day, only increased efficiency by 1% a year.

Is it age? I’m six years older and VO₂ max (an indicator of oxygen intake which indicates physical fitness) decreases with age. I’m not sure of the connection between VO₂ max and efficiency, but logic tells me if you are less efficient, you’d have to work harder (burn more calories?). Any experts out there care to help us understand this?

Whatever the reason for the decreasing calorie burn, it stinks! That’s 88 calories fewer a session, and assuming I exercise only four times a week (I actually exercise six times a week), over a year that’s 18,304 calories fewer per year, or 5.23* pounds a year! No wonder I have to eat less and exercise more to maintain my weight at 15 pounds more than I weighed in my 30s.

On the brighter side, at least that keeps me jumping, and spinning, and jogging which will hopefully keep me enjoying the finer things in life for many years to come.

PS – this week I go on Medicare – that sort of makes me feel old. But if you took a soft focus picture of me (to hide the wrinkles) in my exercise clothes, you might mistake me for one of those 30 somethings! And I can keep up with them in spinning. Just don’t ask me for my 5K time. So all the hard work does have its benefits.

So keep your exercise program up, even if you do burn fewer calories!

* Calcuation for pounds per year based on 88 fewer calories per exercise session: (88 calories * 4 days/week * 52 weeks/year = calories in a year / 3500 calories per pound) = 5.23