OK, so I was doing my long ride yesterday, and it never ceases to amaze me the crazy things I start to think about to occupy my mind. Anyway, I started thinking about fat loss during long aerobic workouts. My long ride yesterday was 6.5 hours, and according to my S710 I burned around 6,000 Calories (I know the Polar Cal numbers are somewhat questionable, but it sounds plausible). So I started doing some conversions in my head:
1 pound = 454 grams
1 gram of fat = 9 Calories
1 pound of fat = 4,086 Calories
Given that I stayed aerobic the whole ride (low/mid zone 2, zone 3 on the big climbs) the rule of thumb I’ve heard is that about 30-40% of total calorie expenditure was from stored fat. That would equate to 1,800 - 2,400 calories of fat burned. Does it sound plausible that I burned ~1/2 pound of fat in one ride? Please say it’s so!
6000 kcal, would be an average power output of 256 W over 6.5 hours, which would mean either you’re an elite level cyclist/triathlete with a mass of ~ 70 kg, you’re considerably heavier, or you’re S710 is way off.
Each 454 g (1 lb) of fat is actually only 3500 kcal because of stored water.
It doesn’t matter what the fuel substrate is, you just need to cause a negative energy balance to lose fat mass.
6000 kcal, would be an average power output of 256 W over 6.5 hours, which would mean either you’re an elite level cyclist/triathlete with a mass of ~ 70 kg, you’re considerably heavier, or you’re S710 is way off.
Each 454 g (1 lb) of fat is actually only 3500 kcal because of stored water.
It doesn’t matter what the fuel substrate is, you just need to cause a negative energy balance to lose fat mass.
Ric
I’m not sure how valid Polar’s calorie counting software is, but at an average of 150 bpm and at my bodyweight of 174 lbs, it says I burn almost exactly 1000 kcal/hr.
6000 kcal, would be an average power output of 256 W over 6.5 hours, which would mean either you’re an elite level cyclist/triathlete with a mass of ~ 70 kg, you’re considerably heavier, or you’re S710 is way off.
The Polar is measuring Calories burned by the body, not the power to the drivetrain or the ground (like a PowerTap, SRM, or even Polar power unit would.) If you assume that the rider is 50% efficient, he would be producing 128 W.
6000 kcal, would be an average power output of 256 W over 6.5 hours, which would mean either you’re an elite level cyclist/triathlete with a mass of ~ 70 kg, you’re considerably heavier, or you’re S710 is way off.
The Polar is measuring Calories burned by the body, not the power to the drivetrain or the ground (like a PowerTap, SRM, or even Polar power unit would.) If you assume that the rider is 50% efficient, he would be producing 128 W.
Ray
1000 kcal per hour = 16.7 kcal per min = 1165 watts
If the rider is averaging 150 watts to the pedals, he’s less than 13% efficient. Am I missing something? Is 13% a reasonable efficiency number?
Typically, efficiency is ~ the low 20s % for trained cyclists. There’s some evidence to suggest that very elite riders (i.e., TdF) might approach or exceed 25% efficiency, but there is some question marks over this.
An excellent ball park figure for energy expenditure (the closest you can get without going to a lab) is the work done as measured by a power meter (e.g., Power Tap, SRM).
As 1 kcal = 4.18 kj and approximately cyclists are 25% efficient, everything roughly cancels and thus, for e.g., 1000 kj session (measured by a power meter) is approximately a 1000 kcal energy expenditure for the rider.
Therefore, if the Polar, by whatever means is reporting 6000 kcal, then over that time frame it’s estimating that you’re putting out 256 W. Depending on body mass, and height that’s a stageringly large figure (e.g., data from a cycling World Cup race showed an average power of 247 W for 6 or 7 hrs). Therefore, unless the rider is very large, then it’s highly likely that 6000 kcal figure is way off.
I’m not sure how valid Polar’s calorie counting software is, but at an average of 150 bpm and at my bodyweight of 174 lbs, it says I burn almost exactly 1000 kcal/hr.
That would be an average power output of 278 W. Very approximately, on flat roads, standard road bike (no aero equipment) that probably be about 38 km/hr (24 mph) average speed.
Since cycling is my downfall and I am looking to improve it! Where can I turn to and learn more about what the heck you guys are talking about? My freakin head is spinning. Thanks.
The numbers I have seen have always been based on speed and weight. For example a 175 lbs avg speed of 18 mph will be like 800 cal per hour.
I terms of losing weight, you have to run a calorie deficit over a period of time. About 3500-3600 calories per pound of fat. So if you wanted to lose a 1/2 lb of fat in one day, you would have to burn 1700+ calories more than you ingested.
This is quite a feat, but possible. Beware however, because weight loss at such an extreme pace is very dangerous. Better to shoot for 1-2 lbs per week. That equates to a 500 - 1000 calorie deficit per day, which is more reasonable and safer. Even 2 lbs per week would be considered fairly extreme!
It’s incorrect to base energy expenditure on speed and mass. what would happen if you coasted downhill at 50 km/hr? Energy expended is ~ equal to the work done and is therefore power x time, i.e., 278 W x 1-hr = 0.278 x 3600 = 1000 kj.
I don’t understand your reasoning with the energy deficit. If you want to burn a 1lb of fat, you’d by definition have to expend 3500 kcal more than you ingested, not 1700+ kcal.
First I said AVG speed. Try finding a ride that is 100% down hill. Kinda like finding a mass less frictionless pulley physics people are always talking about. Over the entire course of a ride your average speed will include both UP and DOWN hills as well as some “flat” sections.
Also, I said to lose 1/2 a lb of fat you would have to burn 1700+ calories more than you ingest. 3500 divided by 2 = 1750. I rounded off, I hope that this doesn’t offend your sense of scientific precision.
You all have missed the spirit of the question and gotten into a debate about physics. I was trying to help the person who asked the question in terms he could understand.
i stand by my first statement that weight and speed can’t be used to anywhere near correctly estimate energy expenditure. it can’t. period. If these were anywhere near useful for estimating ee, we wouldn’t need power meters.
my apologies on the second point, i missinterpreted what you’d written, i hadn’t realised you’d said 0.5 lbs (1/2) i thought you wrote 1lb.
Run energy expenditure for me is approximately 140kCal/mile, independent of the pace of the run (run faster => higher burn rate, less time spent running the mile). Lighter runners burn fewer calories, but not much. Most runners, I’d guess, burn between 120kCal/mile and 160kCal/mile.
Bike expenditure for me is between about 600 kCal/hour easy pace, 700-800 for a tempo (hard) pace, and about 1100kCal/hour at TT pace (~25mph).
Part of the original question was whether he had burned 1/2 pound of fat in a 6.5 hr long ride. Regardless of how you do the calculation and to what level of accuracy, I think we can all agree that he probably expended a significant number of calories that day.
My question is, how many of those calories expended really come from fat being burned? How much is from glycogen and other energy sources stored in the body that are not in the form of fat? As I understand it, in addition to fat your body can store some number of calories as glycogen within your muscle tissue, some more calories in your liver, and if needed can get some more energy by breaking down proteins under some conditions.
So for a long distance ride, where he’s working mostly aerobically but might go a little anaerobic going up hills (well, maybe the original poster doesn’t but I certainly do!) is there any way to get a rough ballpark of the % of calories coming from fat vs. other sources of energy?
So how do you suggest that us poor slobs who can’t afford a power meter gauge our energy expenditure on the bike? How about the run?
Craig
Craig,
there really isn’t a satisfactory way of measuring energy expenditure without a power meter. from what i’ve seen of the HRM that estimate EE, they’re wildly off, and aren’t even useful in comparing one session to another.
if you want to get a better idea of EE (without going to the expense of either a Power Tap or SRM), then your best bet is to go to www.analyticcycling.com and use power given speed form. You’ll have to make some basic assumptions on the form and change a lot of the data, but if you know all the main metrics (e.g., CdA, environmental and topographical conditions, speed) then the calculators are able to predict power to within 1 or 2 W. Once you know your power output, multiplying it out by the duration of your ride will give energy expenditure.
If you’re unsure of what data to input, or what to use as default settings etc, shoot me an email or put a message up here.
Running is much easier to deal with energy expenditure from mass and velocity, simply because power isn’t affected in the same way by environmental and topographical conditions that occur during cycling.
Thanks Lee. This is exactly what I was getting at. At 6’0" 163 lbs, I’m not really as preoccupied with losing weight as I was 3 years ago when I weighed 210 lbs. As you reiterated, my question was really just curiosity about what’s going on physiologically during long sustained aerobic efforts.
PS- the triple crankset is how I stay aerobic on long climbs
