a kilojoule or kJ is a unit of energy, as is a calorie. A kJ is .239 kilocalories. It happens that the body is 23%-25% efficient in turning food energy into work done. Thus kilocalories burned is about equal to kilojoules. When I look at my Strava results, I figure that kJ is my calories burned or at least way, way closer than any other method of measuring them. Strava's estimate of kJ can be thrown off by headwinds or tailwinds, but if your personal and bike data entered is correct, it will be very close. It derives this number from the equations of motion, not from a heart rate monitor or other inaccurate device.

Maybe I'm not understanding but are you saying that the Kj represents calories burned? Based on every other source I've ever seen, this is really low. FWIW, when my Garmin Edge data is uploaded to Strava the elevation data is way off from other rider's devices and sites like www.ridingwithgps, etc. My Garmin will show 2300 ft. of climbing when everyone else has 2800 ft. or thereabouts.

Do the calories burned calculation using the formula 100 cal for every 5 km cycled. Or in miles that's ... um ... 100 cal/3 miles or 33 cal/mile.

Compare that with what your other calculators tell you.

If it is lower than what your other calculators tell you ... go with it. If your other calculators are lower, go with the lowest number you've got.

A 2.5 lb weight gain may or may not represent an actual gain in body fat. Weight fluctuates a lot from day to day, generally based on hydration (water retention) and, to put it delicately, the contents of your digestive system at the time you get on the scale. How often are you weighing yourself? I usually recommend weighing yourself every day, first thing in the morning, naked, and log it. Ignore the number and watch for trends instead. I attached an example from my own log to the bottom of this post as an example. The scale is 1 lb, so you can see how much variation there is.

Unfortunately, at your age it's harder to build muscle and you have less lean mass (muscle, bone, other non-fat) than younger folks. It's going to be harder to lose weight because your BMR is lower than most of the advice you'll read accommodates for. Slow and steady.

Yes, exactly. There is some variation in elevation gain among Garmin units. They are barometric and imperfect. I agree with other advice here: go with the lowest figure. IOW call it 1708 calories for that ride. For workouts not recorded on Strava, you might use the formula 1708/2800 or .61 and multiply your HRM or wristband numbers by that correction. That should get you a lot closer to your true burn and will help you resolve the apparent contradiction between your calculated CICO and your weight gain. Yes, it sucks to have to eat less but you'll get used to it quickly.

[MENTION=4588]Machka[/MENTION] 's rule of thumb for 50 miles gives 1650 burned. Strava shows a little more, but then you did some good climbing.

Yes.

As other posters have noted, the 1708 kj from Strava is a good estimate. The others are likely 69-75% high.

Some authorities use MET Metabolic Equivalent of Task which are supposed to scale with your weight. That's wrong for riders above their ideal weight because on flatter terrain most of your energy is going into overcoming aerodynamic drag which doesn't increase with weight. It's wrong because aerodynamic drag is less than proportional to weight.

The basic METs are also way off for some reason.

Gadgets based on heart rate can also be off by a factor of two.

Give some thought to what you are eating, more than calories. Pull out the carbs and sugars, replace with fats and proteins. I think you"ll see the trend reverse.

People obsess over weight a bit too much it seems.

It is just one metric of many that can be used to judge fitness.

Obsessing over 1 or 2 pounds is a bit silly.

Doesn't matter that much in the grand scheme of life.

That's exactly what I had done. Which is why the resulting gain was a surprise. When I cut back drastically on carbs I ended up feeling weak.

Just a quick question. I thought calorie burn was related to weight to some degree. At 190 lbs am I not going to burn more cals than my 125 lb gf for a given ride?

Yesterday 11 of us went off on a ride of 42 mi. There was 2600 ft. of climbing but 1600 ft. was in the first 18 mi. That amounted to 90 ft./mi. which is much more than I usually do. I worked my butt off. Most of the climbs were the long, slow kind that I suck at. So, when I'd get over a hill I had to continue to work to get back up to the group. Even the ride back was a bunch of rolling hills. Those weren't so bad 'cause I am actually good at powering over that kind of rise. Of course, by then, I was feeling kind of worn out. Point is that Strava says I burned 1495 Kj on that ride and over 1700 on the ride last week that I had referenced in this thread. Even though last week's ride was 6 mi. longer my body is telling me that can't be true.

Marginally. But if your goal is to lose weight, put your goal weight into the calculations.



42 miles? Using the 100 cal/5 km calculation, that's 1352 cal. That's what I would go with.

Strava appears to use speed. So if your average speed on this ride was, say, 18 km/h because of the climbing, Strava figures you haven't worked as hard as if you did a ride at, say, 22 km/h on a flatter ride.

But if you're trying to lose weight, just go with a lowish number of calories burned. Going low makes up for an extra calories you might have consumed.

I must be missing something. You're saying I should use 100 cal/5 km regardless of speed or elevation data?

Yes. Because the formula incorporates speed.

If you ride 20 kilometres in an hour, and you go out for a 1-hour ride, you've burned 400 cal in an hour.

If you ride 25 kilometres in an hour, and you go out for a 1-hour ride, you've burned 500 cal in an hour.


As for elevation ... usually, what goes up must come down. So you spend some time and energy getting up the hill, but then you coast down the other side and you don't expend much energy at all for the speed you're going.

Where can I see this formula? Thanks.

Machka's formula is simplifying things quite a bit; climbing definitely affects calorie burn, and the heavier you are the more that is true. Speed also affects calorie burn, because of aerodynamics; the faster you're going, the more calories you'll burn per mile. Having said that, her formula is a pretty decent one to use for weight-loss purposes, because it's better to underestimate the calories you're burning than to over-estimate.

You seem to be pretty focused on getting an accurate calorie count, but the reality is the only way to do so is with a power meter. Anything else is going to be just an estimate, there are just too many variables to factor in.

The number from Strava will be better than most other estimates, provided you understand it's limitations. You need to enter an accurate body weight and bike weight in your profile. You also need to understand that Strava's calculation doesn't factor in wind or drafting/pacelines. So if you're riding with a tailwind or in a group and getting a significant draft, Strava will overestimate calories.

For weight-loss purposes, your best bet is to get a power meter. Second-best, use the lower number between Strava's estimate and Machka's formula for a given ride. It's not about getting the highest calorie number possible; it's about making sure you don't eat too much relative to the work you're doing.

Energy (calories) from climbing is dead simple. m*g*h. Kilograms times gravity times meters climbed equals joules. By a mathematical and physiological quirk, kilojoules is about the same as nutritional calories used.

This is additional due to climbing, plus whatever you'd have burned if it was flat. Hard as it may be to believe, simple as that.

The body going into starvation mode is known to be more or less a myth nowadays. The dip in metabolism people are concerned about is transitory. You're just hungrier and eat more, due in part to an increase in some hormones, and the base metabolic rate is slowed somewhat immediately after severe dieting.

Despite all the theories and math, converting distance, speed, climbing, etc to calories is only possible if you're looking for ballpark numbers. That's true even with a power meter.

There are too many variables, and while a power meter will address some of them such as varying wind drag, is can't address one big one, which is that human engines vary greatly in efficiency. So the calories needed to produce a given output (if it's measured correctly) will vary among people, and even in the same person with changes in temperature or other conditions.

So, rather than sweat trying to pin calories down precisely, accept them as a rough guideline based on simple formulas (or a power meter) and let the long term average things out for you.

Very true, and even kilojoules to calories is very ballpark, a few percent off in fact.

But using math again can put the ballpark into perspective. Our expected metabolic efficiency is given at 22% plus or minus 4%. So bottom line if some formula says "25 calories" it might really be 24 calories, or 26 calories. I think it's pretty useful for that level of precision, though it's true you'll never get an exact number this way.

There's a rule of logic that you can't draw specific conclusions from generalities. The efficiency conversion number itself is an approximation, and while it may get into a fairly tight band over time and numbers of people, it's actual variation is greater. So, you're still back to calculations that are only as accurate as the size of the database, or time interval allows.

It's like the old story of the statistician who drowned crossing a river with an average depth of 3'.

Of course everybody has his own approach and/or belief in numbers, but I'm an old school (before computers made complex calculations practical), and prefer to step pack and look at the big picture.

Watch weight over time for gain or loss. Don't fret if it seems to be 3 steps forward and 2 back, you only care about the trend. At the same time track your riding (also in a big picture sense, ie 100miles/week).

After a while you'll get a picture which will tell you if, on balance, the riding you do, however you tend to do it, is burning more or less than your calorie input supports. The rest is common sense and there are plenty of guides about what to eat, when to do it, and so on. Meanwhile, if you decide you need to shave 1,500 calories/per week (for example) you know if you can do it by cutting out deserts, portion control, giving up starches or whatever -- your call.

The results (over time) will prove the estimates, and you'll have to make your own decisions about sustainability.

In a way, this kind of thing is like a pointillist painting. You can focus on each of the dots or you can step back far enough to let the big picture emerge.

I take objection to that. The statistician isn't the person who demands certainty and precision and will be more aware of the risk of deeper water than the other. Practically all medical science is predicated on probabilities and confidence intervals.

Every person is not going to have metabolic efficiency between 18% and 26% but the odds are very strong that a given individual will. Especially if we're willing to account for extreme outliers, and reasonably consider healthy adults having decent medical care, reasonable diet, at least moderate levels of physical activity etc.

The assumption that it is all about metabolic efficiency is yet another generality that fails.

100 cal/5 km.

Or if you prefer ...

33 cal/mile.

How so? I'm interested in why the energy used climbing (additional to the bike ride if it were flat) is about more than mgh and metabolic efficiency.

I think that this description is precisely correct, not a generality at all, but I've been wrong now and again. So seriously, what's your reasoning here?

Note that sprince puts out just shy of 2000 watts when he rides ... like Mark Cavendish does when he is in a full-on sprint for the line.


Post 6 - https://www.bikeforums.net/18876308-post6.html

Sorry. I still don't get it. It doesn't look like a "formula" to me. It looks more like a result of a computation. Where does that take into account weight, gender, age, speed, climbing, etc? There's no difference between a 30 mi. ride at 16 mph and 3,000 ft. of climbing and a 30 mi. ride at 10 mph with 1,000 ft of climbing? Anytime you ride you burn 33 cal/mile?