# Calculating workout energy burned per rep

I received this machine as a gift. Now, the name is a bit ridiculous and implies I only need to use it 5 minutes per day in order to slim. From a physics perspective that doesn't make any sense. In order to slim, your calorie intake needs to be less than your calorie burn. So I decided to bust out the math and physics and try to calculate how many calories a rep burns on this thing and figure out how many reps I need to do per day.

My take on this is it lifts your middle section. I am assuming my lower body weights about half of my total body mass

m = mbody * 0.5 = 65kg * 0.5 = 32.5


The device lifts that mass about 30 centimeters, so potential energy to lift is:

E = m*g*h = 32.5 * 9.8 * 0.3 = 95.55 Joules = 0.022 kcal or 0.022 food calories


A can of coke has 100 food cal, so that results tells me I have to do 4545 reps on the machine to burn a can of coke. Something is off, or reality is simply that harsh. Where are my calculations going wrong?

Thanks for the help!

• Note: I am neglecting friction and the horizontal component of the movement (which, without friction would zero out anyway I think?) I don't think they could explain why my calculations result in such low energy consumption. – Ed Rowlett-Barbu Nov 22 '16 at 7:47
• I haven't looked at it in detail but two things spring to mind: first of all you are assuming what you are doing is completely efficient which is far from true. However it is known to be the case that, unless you do really extreme amounts of exercise you don't burn enough energy to lose weight: if you want to get thinner you really do need to eat less unless you're running marathons or something, because there's a lot of energy in food. So your result is plausible. – tfb Nov 22 '16 at 8:34
• Hey, thanks for the comment! Can you link to any research? It is frustrating how many people say you need to exercise, but the math doesn't add up to me. – Ed Rowlett-Barbu Nov 22 '16 at 9:06
• To give an idea just how much exercise needs to be done to burn off some calories: "Typically, a person must take 26,471 steps to burn 1,000 calories. On average, a total of 2,250 steps is equivalent to 1 mile. A 160-pound person walking at a pace of 3 miles per hour burns 85 calories per mile and 255 per hour." reference.com/health/… . Machines like yours can definitely work to tone muscle but are impractical to burn calories on. Yes, reality is that harsh! – Gert Nov 22 '16 at 10:47
• There is research that suggest short bursts of intense exercise can raise your metabolic rate, such that you begin to burn calories more quickly whilst not exercising. However, I agree with the other comments - unless you are doing aerobic exercise for literally hours, the direct calorie consumption from the exercise is fairly insignificant - about 400-500 calories per hour if you run at a fair pace. – Rob Jeffries Nov 22 '16 at 14:08