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Moot
11-09-2010, 09:09 PM
I know that the calories on the keiser M3s are not very accurate.

One of my participants came to me last week & asked me an interesting question.

She is working with a personal trainer who told her to have a calorie goal when she is in the cycling class and to try to reach that limit.

For a while, she was not able to but one day, she came to me after class and said that she just reached her limit and she is so happy BUT she does not understand how that she can burn much more calories in my class compared to the other cycling teachers.

She said that overall, my class is much easier than some of the other instructors but with them, she cant burn as many as the calories she burns in my class.

I asked and she did specify that she always uses the same exact bike in each class and compares exact time duration.

So any idea what might be happening?

I am happy though that she was able to beat her calorie goal in my class :)

Moot

liveon2wheels
11-10-2010, 04:29 AM
One must always consider whether the bikes have been calibrated within say the last 6 months or so (that's about how often we do it at our club). Assuming that is not the issue, my guess is that you either cue your class to use more resistance or you just Inspire the heck out of her (I'd go with that one if I were you :))

Regarding the "much easier" aspect - it is quite likely that one can use a higher cadence with a resistance level "just below the burn" which will produce a significant amount of power. We train for efficiency and endurance that way, and it will create good wattage (and thus good calorie totals).

I also remind them (especially if their numbers are lower than they like) that the calories are not reflecting what you BURN - they are not relative to the riders metabolism. They are a reflection of the ENERGY produced. Watts can be converted to calories as both are reflections of energy. That being said, if one "beats" a previous number in Watts (especially if using the same bike), they have indeed worked harder, produced more power, and as a result burned more calories. The only thing is that the number burned is not going to be known through the bike.

Todd S
11-10-2010, 10:34 AM
Does the M3 calculate Calories based on kJ of work or do they use the much less accurate and repeatable HR method?

RaffCycles
11-10-2010, 11:08 AM
My first thought, after the fact that you're just the best coach she could have, was that her other classes may expect an all-out effort all the time rather than interspursing work with recovery (interval training).

Vivienne
11-10-2010, 11:37 AM
My first thought, after the fact that you're just the best coach she could have, was that her other classes may expect an all-out effort all the time rather than interspursing work with recovery (interval training).

Ditto.

One of the things I've noticed within the gym culture is that there's a sort of "proximity bias" in that the weight training crowd (which I guess would have to include the personal trainers) lump everything that's in the context of endurance training that doesn't include the weight room as "cardio" and is somehow done to burn calories without regard to training effect.

I'd wager that the PT involoved here would have something to say if anyone were to suggest that this client go for maximum calorie burn in his/her training session......they'd be huffing and pffing about the need to focus on a training effect and rep ranges and % 1 rep max and whatnot.

In reality it's not much different for endurance training. As a generalisation, if a class member is going to be able to burn maximum calories for each individual workout, they're going to have to be fit and strong enough to burn those calories. That's usually only acheivable by focusing on a training effect towards a long term goal in each class....the calorie burn then becomes a "second order phenomenon" (yeah, it happens......but it's not the main point to the w/o)

Vivienne

CycleGuy
11-10-2010, 11:57 AM
Does the M3 calculate Calories based on kJ of work or do they use the much less accurate and repeatable HR method?

I may stand to be corrected, but it is my understanding that the M3 calories are based on the amount of work done on the bike, based on the power calculation it does (cadence and resistance). My experience also bears this out.

liveon2wheels
11-11-2010, 06:36 AM
Yes, to reiterate and confirm, the Calories reported on the M3 are NOT the calories "burned" by the rider - they are the energy produced by the rider... and yes, they are Kj converted to calories.

Todd S
11-11-2010, 11:11 AM
Yes, to reiterate and confirm, the Calories reported on the M3 are NOT the calories "burned" by the rider - they are the energy produced by the rider... and yes, they are Kj converted to calories.

????????

Seems weird. Normally kJs are used as a proxy for Calories or kcal as when you do the conversion and take into acount typical efficiencies of about 24% yadda yadda.... KJ's of work is pretty much equal to Calories burned (close enough for government work).

Are you saying the Calories indicator on the M3 has to be divided by 4 to estimate Calories burned or does the indicator simply show kJs and label it Calories?

liveon2wheels
11-13-2010, 05:46 AM
????????

Kcal Calculation for M3 Bike
Kcals produced as a function of Watts generated (from standard
conversion tables)
1 Newton-meter (Nm) = 1Joule (J) = 1 Watt-sec (Ws)
1 kilogram (kg) = 9.80665 N
1 kilogram-meter (kgm) = 9.80665 Nm = 9.80665 Ws
1 kgm/second = 9.80665 W
1 kgm/minute = 1 kpm = 9.80665/60 W = 0.16344 W
1 W = 6.11845 kpm
1 Kcal = 4186 J
1 W = 1 J/sec
1 Kcal/second = 4186 W
1 Kcal/minute = 4186/60 = 69.77 W
1 W = 0.01433349 Kcal/min

Therefore the number of Kcal/min = Watts/69.77
i.e. @ 100W, Kcal = 100/69.77 = 1.43 Kcal/min

The Kcals it takes for a rider to generate the above power in Watts
1 W = 6.11845 kpm
1 kpm = 1.76 ml O2/min
1 W = 10.77 ml O2/min
1 liter O2/min = 5 Kcal; therefore, 1 Kcal = 200 ml O2/min

The Energy Expenditure (EE) to turn the crank of a bike at 50-60 rpm
against no resistance is approx. 3.5 ml O2/min/kg of body wt.

For each Watt of energy produced, a 70 kg riderís EE (above rest) is:
EE = 10.77 ml O2/min/Watt + 70 kg X 3.5 ml O2/min/kg
= 10.77 ml O2/min/Watt + 245 ml O2/min
= 0.0539 Kcal/Watt/min + 1.23 Kcal/min
i.e. @ 100W, EE = 0.0539 X 100 + 1.23 = 6.62 Kcal/min

Moot
11-13-2010, 12:39 PM
thanks Gino & guys,

I never went to the other class where i was told instructor is very hard. But I was told that he uses a lot more resistance than me throughout the class.

I will check with maintenance about last time they calibrated the bikes. We have only been open since April. We are just going into our 7th month. I will make sure that they calibrate the bikes soon.

I will explain to the member about the watt & calorie relationship & I am thinking of bringing my garmin forerunner to class to let her try it so she can see what calories she would be at.

I think she would like that :)

Moot

Todd S
11-13-2010, 01:00 PM
The Kcals it takes for a rider to generate the above power in Watts
1 W = 6.11845 kpm
1 kpm = 1.76 ml O2/min
1 W = 10.77 ml O2/min
1 liter O2/min = 5 Kcal; therefore, 1 Kcal = 200 ml O2/min

The Energy Expenditure (EE) to turn the crank of a bike at 50-60 rpm
against no resistance is approx. 3.5 ml O2/min/kg of body wt.


That's enough to make my head hurt, and I'm an engineer. Why do they make it so hard?

The text quoted above is where they make an estimate (watts vs O2 energy cost) that's only accurate to (I'm guessing) 10 to 20 percent or so as you're not correcting for RQ, etc. So any more than 2 or 3 significant digits in your calc is overkill.

Rather than rely on indirect calorimetry swags, why don't they just take advantage of the fact that 1 kj = 0.24 kcal? Since we're all about 24% efficient in turning metabolic energy into mechanical energy at the pedals ( http://www.ncbi.nlm.nih.gov/pubmed/8933490 ), the work you put into the pedals in kJ is close to the calories you burn in kcal or Calories. I'll bet it's no less accurate than the method they're using.

At least they're not using HR for their estimate.

(and FWIW, 1 watt = 6.118 kilopond meter/minute - it's tough to keep track of units when you make the calc so complicated)

Todd S
11-13-2010, 01:14 PM
i.e. @ 100W, EE = 0.0539 X 100 + 1.23 = 6.62 Kcal/min


My rule of thumb method gives 6 kcal/min for 100 watts - way easier as you can read kJ with any power meter - and no less accurate as I'm guessing neither of our numbers is closer than 10 to 20 percent of the true Calorie burn.

thosknox
01-05-2011, 08:19 AM
It is my understanding that the Keiser bikes with meters base the calorie calculation on a 150 lb man, so it doesn't matter who is on the bike. Also, the meters on the Keiser bikes that I ride, flip back and forth between calorie count and wattage output. I think, then, that the trainer's suggestion to the participant to work on beating previous calorie readings is a good one.

Also, distance traveled is NOT really distance traveled as we would think. According to the Keiser website (and this is where I got the above information), distance is calculated by rpms and 200 rpms is equivalent to 1 (mile?). So, at the end of the ride, if your distance reads 12, then you've turned the pedals 2400 times.

I've recently started teaching in a facility that has the Keiser bikes, so to prepare myself, I did a little bike specific research.