Calories Burned - How my treadmill does it
Tuesday, June 14, 2011
People often ask about the variation between treadmill (or other machine) reported calorie burn, and spark reported calorie burn. Some of the typical responses include "Your treadmill knows how hard you worked" or "The treadmill treats everyone as a 150lb man".
So I did some experimentation on the STEX treadmill in my gym, to see exactly what variables it uses when reporting the calorie burn figure.
Each of these workouts is five minutes long and each pair isolates just one variable, to see if the machine uses that.
Two identical workouts were programmed in. Throughout both I maintained the same average HR of 133 bpm. Therefore the only difference is the weight that I entered on the machine before starting.
At 60kg (132lbs) it told me I'd burned 26 calories
At 90kg (198lbs) it told me I'd burned 41 calories
This treadmill uses the weight you've entered in showing how many calories you burned. It does not program calorie burn for everyone as if you're a 150lb man.
Abolishing the Heart Rate Monitor so the machine had no feedback on heart rate, and using a manual 'quick start' setting to go without entering a user's weight, the following two workouts were performed:
Low: 5kph (3.1mph) with 0% incline
High: 7ph (4.3mph) with 6% incline
The variable factor here is "how hard it was". This is the "your treadmill knows how hard you worked out" factor.
Low: 17 calories
High: 41 calories
Yep, this treadmill knows how hard I worked out. It uses the intensity settings in determining calorie burn.
For two identical workouts (same as first set) programmed into the machine, and no setting for weight at all, it was given my actual HR (average 133) while performing the workout, and my HR while standing next to the machine doing nothing. While standing, because I had just worked out, my HR started at about 130, was 115 by 2 mins, and down to 105 by 4 mins.
The variable here is HR. If the treadmill is using my physical effort as measured by my HR in determining calorie burn we'll see a lower burn on the standing workout.
Working: 27 cals
Standing: 27 cals
On this one, it's a fail. It does not use the person's HR to determine calorie burn. It presumably only reports it to keep you in the "fat burning zone" or whatever you have chosen when you use those settings. It does not figure into the calories burned equation.
BUT WAIT, THERE'S MORE
Notice that the final workout, where I actually worked, that is, is identical to the original one where weight was entered. The same workout pattern was performed, the same HR maintained. It's interesting to note that the machine gave me the same calorie burn (with no information on my actual weight) as for a 60kg person. It's particularly interesting because I weigh 90kg.
In other words, if I don't tell this machine what I weigh, it's assuming it's around 60kg. If I wanted to use the calories burned figure from this machine, I would certainly be best served by ensuring I input my actual weight, not just hit Quick Start and go.