08-09-06, 07:59 AM
I work out equally hard on the fancy LifeCycle in the gym as I do while road cycling. The LifeCycle machine says I'm burning more than 900 calories an hour. That's close to Cycling Magazine's formula which says I'm burning about 1077. But when I enter my stuff into FitLinxx, it coughs up a paltry 604.
Stats: 204 lbs, 18 mph sustained, altitude 940 ft.
08-09-06, 10:29 AM
FitLinxx did the same thing to me. 30 mins in a spinning class netted almost 3x the points than 2 hours on the stationary bike.
The way around that is to enter it as an "other" exercise, but you still won't earn as many points as any of the machines attached to FitLinxx.
08-09-06, 12:47 PM
Fitlinxx is simply more conservative in the formula they use on the principle it's better to err on the short side than the long. Each one of us is a "one off" product, due to heritability of various factors and as a general population, there is a bell shaped statistical curve for X effort = Y kcal burned based on the basal metabolism in the center of the curve +/- a given statistical skew. Fitlinxx just uses the lower end of the curve.
Man.....did that sound geeky? http://smileys.smileycentral.com/cat/36/36_1_37.gif
Use whichever number will make you feel good enough about your accomplishments to keep coming back.
08-24-06, 01:40 PM
Thanks for the replies.
I wrote a letter to FitLinxx using their online feedback, and received a nastygram from work. They wanted to know why I'd "threatened" FitLinxx, that I couldn't do that as the company had contracted with them and I was an employee of the company, blah, blah.
My e-mail to FitLinxx included links to two sites used by professional bicyclists to estimate (quite accurately) the actual work done (in watts) given numerous factors, including average riding direction (degrees), wind direction, grade, distance, time, whether it was open course or loop, riding surface (yes, there's a difference between riding on gravel and concrete), weight of bike, weight of rider, frontal area of rider, type of position, type of tires, and a few more.
I'm an aerospace engineer. The calculations I did are very close to the results given in the links I provided to FitLinxx, but they're grossly different (by a factor of more than 2) front FitLinxx, with the difference getting even wider the faster you go.
FitLinxx's response said they used estimates and formulas recommended by (I think) the American Academy of Sports Medicine (may have gotten that partially wrong). Regardless, if that's the case, then either FitLinxx programmers are out to lunch, or this Academy is out to lunch. Probably the result of a study done back in the 1940s, when smoking was supposed to be "good" for you.
Heinlein once said, "Always listen to the experts. They'll tell you what can't be done, and why. Then, go do it." I'm glad the programmers at this site didn't listen to the self-proclaimed "experts."
Racing bicycle, hands on tops
Rider's Height 71
Rider's Weight 204
Bicycle Weight 21.3
Air Temperature 51
Height above SeaLevel 1150
Slope of Road -.023%
Wind Speed 0
Pedaling Cadence 85/min
Tires: medium-wide, high-pressure slicks
Speed: 25.8 mph
Distance: 6.5 miles.
Results: 554 watts, 480 kcal burned.
Let's see what FitLinxx says:
Timed out. Let's try again.
Time out. Last try:
I'm in: 285.77 kcal.
Hmmm.. And that's at the (10) Very Very Strong (highest) selectable activity level.
This actually makes sense, because one of the other things FitLinxx said was that going twice as fast only took about 2.27 times as much power (watts). Divide 480 kcal by 2.27 and you get 211 kcal, which is fairly close to FitLinxx' 285 kcal, the increase probably accountable by my Very Very Strong selection. In fact, I just have to bump it down to Very Strong (7) to get 208 kcal, nearly dead on with their computations.
So, FitLinxx's calculations, regardless of the voluminous Degrees Behind Their Sources, are dead wrong. They're wrong with a capital W, and claiming that they're "the most accurate model around" is pathetically stupid, equivalent to shoving one's head in a small, sandy hole and making sounds like the cuckoo bird from Cocoa Puffs.
In reality, since wind friction increases with the square of the velocity while rolling friction is proportional to the velocity, and wind friction is the largest component, depending on the difference between two velocities, a, and b, where b = 2*a, the wind friction component can range from 2 to 9 times greater than the rolling friction component. In other words, for my bike tripe, it the wind friction component was 3.7 times greater than the rolling friction component. After digging into my physics texts and doing some estimates, I figured I was doing between around 450 and 600 watts, so I was in the ballpark with kreuzotter's calculations, and his calculations match, within 50 watts, the four other online sites that use correct physics instead of "estimates" like FitLinxx does.
Sorry, FitLinxx - facts don't lie. Physics doesn't lie. And when the top five sites specific to cycling say one thing within 10% of each other, and that matches the calculations derived through the principles of aerospace engineering and you say another that's off by more than 40%, it's not them who's doing the lying.
Now - let's take the trip home. FitLinxx makes no allowance for hills, type of pavement, winds, or road grade. So it's answer is the same: 285.77 kcal.
Let's see what the best site in the world says: 225 Watts and 271 kcal.
Hmmm... And this was corroborated by the same top five sites.
Since I put forth the same level of effort cycling to work and returning home, but spend that same effort over a much longer time biking up the hill home, it appears all the calculators suffer from one flaw or another.