I'd tend to agree with MetalPedaler on this one, but only on the basis of the experienced athlete being more efficient than the inexperienced rider. The difference in energy expenditure with experience is more pronounced in some activities than it is in others. For instance, not being much of a swimmer, I'm sure that I use much more energy to move through the water than my wife, the ex-life guard. I doubt the difference is as pronounced for cyclists, but I think there is some difference.

You're missing the part that says "waste products of fermentation still contain plenty of energy."

Anaerobically, you take a molecule of glucose and produce 2 molecules of ATP and 2 molecules of lactate. Then you send this lactate into the liver where it takes 6 molecules of ATP to convert it back into a molecule of glucose. (That only happens after you get off the bike, when there's excess oxygen available to make ATP aerobically.) In essence, lactate pathway has 1/3 the efficiency of the aerobic pathway. Not 100%, but not 1/15'th either.

Also, you need to subtract initial energy stores in the muscles. When you start the activity, there's some ATP already present in the muscles and there's some creatine phosphate that can release ATP.

Cool! This stuff is fascinating!

It is fun to think about the path from glucose to power at the cranks. Somehow the glucose has to turn into muscle contraction, and the ATP is a key link in that chain. But from muscle contraction to power at the cranks - maybe training can reduce inefficiencies there, too.

Surely there is a lot more technique involved with swimming than with biking. But still... a nice smooth spinning of the pedals is not quite trivial, either.

One funny thing to think about when considering the conversion of food energy to mechanical energy. Holding up some weight, just standing still holding weights in one's hands - pick your favorite position, arms down or straight out in front, whatever. No mechanical work is being done at all. But surely there are muscles contracting and glucose molecules getting metabolized.

This sort of thing can happen, surely happens, when pedaling a bike. For example, how much downward pressure is kept on the pedal as it reaches bottom dead center? That is muscular work that performs no mechanical work.

Yeah, I carry my 5 pound Kryptonite lock up the hills, then dissipate all that mechanical energy through my brakes and rims on the way back down the hill! Crazy!

Yes, I'll buy that, but we're now talking about a different thing. The experienced and skilled cyclist will possibly have a more efficient pedal stroke. That may mean it takes her slightly less power, and therefore a few less calories, to achieve the same result. But in that case the power/calorie savings are the result of technique, not of increased fitness. When the fit athlete puts out 200w they are burning the same number of calories as the unfit athlete who puts out 200 watts, give or take individual variations in metabolism. I admit I'd be very interested in a physiologist's opinion about whether an individual's metabolic efficiency varies with aerobic fitness. If it does, you and metalpedaller may have a point. But it may go in the other direction. That is, the active, muscular individual may burn more calories at rest and therefore negate any reduction in consumption through increased efficiency during exercise.*

Maybe less than you imagine. The most relaxed position you can adopt while on your feet in the "guardsman's posture" - feet slightly apart,, back straight, chest out, head balanced and looking straight ahead, arms by your sides. You're then taking maximum advantage of your skeletal structure, with the muscles having to do very little to support your weight. And in any event, the vast majority of our food energy is consumed not by movement, but to maintain our body temperature. Being warm-blooded has many advantages, but the price we pay is that we have to eat far more than would be needed just to repair ourselves and move around. Reptiles get by on tiny amounts of food relative to their bodyweight, because they rely on the sun to warm them up. They're not too quick in cold weather, of course....

But if you are fortunate enough to have two legs, then a correct pedaling technique will limit the damage to close to zero, because as you reach the bottom of the pedal stroke with one leg, the other leg will be pushing through the top of the stroke to take over. When one "pulls up" on the upstroke one is actually exerting rather minor force, but the sensation of pulling up means that one is aggressively unweighting that pedal, and making sure that the leg pushing the pedal down does not have to overcome any resistance imposed by the weight of your other leg on the other pedal. So if you are doing it right, the small amount of mechnical energy expended on the upstroke isn't a waste, it is maximising the extent to which power exerted by the other leg goes into actually propelling the bike forward.

^but isn't the effort greater @ 15mph for the unfit rider?
and doesn't that greater effort translate into greater calorie usage?

There is a direct relationship between power output and calories burned. That is an objective relationship unaffected by perceived effort. A watt doesn't care how strong or weak the person doing the lifting is, or how hard they think they are trying.

The only argument here is whether the fit athlete has acquired a more efficient metabolism so they are more efficient at turning energy into power. The usual estimate is that we are around 25% efficient. It's possible, I guess, that training changes this marginally but we await an expert.

Just a postscript to this. One reason why HRM-derived estimates of calories burned are often inaccurate is that the HRM doesn't know how fit you are. If you train and your VO2 max increases, your HR will fall for a given level of effort. So if you are doing the same amount of work, in an objective sense - your power output and energy consumption remain constant - maintaining that output will require a smaller percentage of your maximal effort, your HR (and perceived effort) will fall and your HRM will estimate that you are consuming fewer calories, even though that is not the case. This problem would only be overcome if the HRM could be calibrated to reflect changes in VO2 max, so that the relationship between HR and power output was adjusted to reflect increasing fitness.

So the fit athlete moving 200lbs at 15mph will be burning the same number of calories as the unfit 200lb 15mph athlete. The difference is that the former may be operating at only 50% of their much larger potential, while the latter may be maxed out.

Swimming is a technique intensive sport. Your wasted on energy in swimming is purely due to inefficient technique. Cycling not so much. The only obvious one in cycling is body position.

This makes sense. The only thing to add to the equation, is that the unfit person will usually weigh more/have higher percentage of fat to their muscle mass, which will cause them to burn more calories.

Hi,

I understand it maxes out at about 30% for even the fittest, the rest is turned
into heat, which is why you get hot exercising. I assume that is aerobic and
anaerobic which doesn't come into cycling much, much worse.

Also generally as you get fitter you will burn more calories per hour, even if
you lose a lot of weight, you just generally go faster with less apparent effort.

Weighing 180 lbs and breezing up a hill still takes more power output than
weighing 220 lbs and struggling up it at a snails pace. Although of course
the heavier person will likely expend more energy getting up the hill.
(If you fly up the hill with significant aero drag you can still use up more
energy getting up it than a heavier slower person up the same hill.)

The physics of biking are such that initially hills and headwinds are horrible.
But as your power output on the flat improves they will become much easier.

As your average power output improves (and the calories per hour burned)
your flat speed will increase but due to aerodynamics by about the cube root
of your power improvement.

One things for sure : say you have a 25 mile course you start off on that
takes you two hours. When you can do it easily in significantly less time
you will be burning more calories than when you started, even if you
lose a lot of weight, than just means you'll go even faster.

Its not the same as running. Say you always ran 10 miles. As you
get fitter, faster and lighter total calories won't change much.

As you get fitter on a bike the calories you burn for the same
distance will increase significantly for small increases in speed.

rgds, sreten.

This is interesting. Suppose somebody is cycling who is very fit but in a different sport, so they have lots of upper body strength. The heart has to pump blood through all those muscles that aren't doing any good. Two people could weigh the same and have the same VO2 max, the same cardio-vascular fitness, yet the experienced biker will surely outperform the arm wrestling champ or whomever. Does outperform translate into burning few calories?

Certainly any sort of muscular activity that isn't tied to spinning the pedals, that's a kind of inefficiency, calories burned that don't make the bike go faster. How significant is circulation through fat or through inapplicable muscle? Darned if I know!

Hi,

Most body builders can't run for a bus without getting knackered.
Arm wrestling is very anaerobic, like weightlifting.

The experienced cyclist will outperform a say same size and weight swimmer
who doesn't use their legs much by being able to burn a shedload more calories
in a given period, i.e. much higher power output, not by using less calories.

The swimmers legs will go, well before any other difficulties.

rgds, sreten.

You are surely correct about this. But another interesting question still remains: suppose the cyclist and swimmer go out for a moderately paced bike ride together. Maybe the cyclist finds it very easy and the swimmer is a bit more challenged but still nothing too crazy. Will they have burned the same number of calories?

The same amount of energy was delivered to the pedals. But if the swimmer's heart had to pump blood through extra arm muscles, that is energy expended that doesn't go to the pedals.

There is still the question, too, of efficient pedal spinning. Maybe the swimmer had trained in biking some years back so still has a good cycling form. Or maybe this cyclist hasn't cycled much at all and so is perhaps pushing down too much on the back, upward moving pedal, thereby doing muscular work that actually reduces the power to the crank.

Anyway this stuff is all might speculative! I just happen to love such explorations of energy pathways!

These days one of the books I am reading is The Pleasure Trap by Lisle and Goldhammer. The basic idea is quite similar to that of Good Calories, Bad Calories by Taubes. It is impractical to try to manage weight by calorie counting. Our bodies have finely tuning feedback systems to regulate food intake. What throws those mechanisms off is the crazy food we eat, combinations that are very unlike those our bodies have evolved to work with. What works, so these authors say, is to get back to more natural foods and food combinations. I fear I cannot really confirm this theory. My fat percentage is something like 27% and I expect chocolate bars have something to do with that. And fig bars. Yum!

One place I would expect this sort of calorie computation might be useful is for planning nutrition on long rides. You don't want to run out of snacks out in the middle of nowhere on a double century... but you don't want to lug too many extra snacks along either! If your trained and experienced double century rider friend carries along X calories of snacks, and you are just getting into cycling and pushing your limits, should you just bring along the same X calories of snacks or maybe anticipate some inefficiency so maybe 1.2 * X might be advisable?

Hi,

They will use up essentially the same amount of calories.
Efficiency remains very near the same for calories burnt.

Note that to go 23mph needs ~ 50% more power output
than 20mph, (flat, no wind). So if you did a 10 mile time
trial at the two speeds, one would take 30 mins the other
26 mins, the latter using ~ 30% more calories in the process.

For the experienced and a fit newbie both doing a double
century you would both need less calories than the amount
the experienced rider would typically use on the ride.

The body maintains near the same efficiency for a wide
range of power output. An experienced rider can output
more power, more smoothly, under varied conditions
than a similarly fit cycling newbie - who generally
will vary output more in different conditions and
not be able to sustain as high an average output.

Very little energy is lost pumping extra blood to muscles
not used, as you need to do this anyway to sweat effectively.

Though as your legs develop inevitably more blood
relatively will flow through them more easily.

Runners would have an advantage over swimmers.

rgds, sreten.

Very interesting stuff! I tend to bnelieve what you say, Sreten (Otherwise, if I were right about burning fewer calories as you get more fit/your body becomes accustomed to an exercise, many pro racers would be fat! ).

The extra muscle will only make a difference in calories burned if it adds weight. If they are the same weight, it will take the same number of calories to move them at the same speed even if one is more muscular than the other

As it happens, you are mistaken about this, because how much you should eat while riding is dictated not by how many calories you burn, but by how many you can absorb. Most of us can absorb only about 60g of carbohydrates per hour, which equates to around 240 calories. So you can't replace calories as fast as you are burning them even at relatively moderate intensities. If you eat more than that while riding you'll still be digesting it long after you've stopped.

This just adds to the mystery! How do people do these crazy ultra events like PBP or RAAM etc. They've got a stock of glycogen etc. to start with, then they can replenish some along the way. If they keep riding, the energy has to come from somewhere!

That's perfectly simple, actually. If you are riding at an easy pace (easy for you, that is - well below your lactate threshold) you draw virtually all your energy directly from fat stores. And even the skinniest athlete has enough body fat to fuel him/her for days rather than hours. So for the endurance athlete, the benefit of being very fit is that your threshold is higher, and the intensity you can sustain without depleting your glycogen (carbohydrate) stores is much higher. So, if you are ingesting 250 kcal per hour of carbs, and cruising, you will be replacing all the glycogen you are burning even though your total calorie expenditure is much greater. You'll just be losing fat.

Makes sense. To be able to increase the rate of burning fat, so you can keep going at a reasonable clip from fat and limited snacking, that seems like a real key to endurance.

Hi,

I used to go swimming. My technique got reasonable as I'd swim about 30 lengths (25m each) usually.
Meanwhile they was a guy who used to plough up and down much slower than me with just about
the worst swimming technique I have ever seen, (other than not being able to swim), as he was
continually surrounded by plumes of spray to go along with each stroke he was making.
Terrible technique, but he was undoubtedly very fit to keep doing it for as long as he did.

Probably much fitter than I was, but much slower, doesn't happen on a bike.

I'd tend to say it doesn't happen running either, (I used to run too), but out on the
bike since Christmas, I've seen some good runners and some spectacularly slow
runners who seem to have no idea how to run properly at all, which is beyond me,
and for the exercise that they getting they are giving their joints a real pounding,
not in maximum stress, but repetitions, I've seen say 1/3 proper stride length.

If you can't run properly, at 50+ don't run at all. I suspect some of the cases I've
seen are people trying to limit existing problems but probably making them worse.
Good stride length and flexible tendons are the key to running.
Otherwise go for a longer but good stiff walk taking in some hills and scenery.

Still I was surprised at relatively young runners running with very poor form.

rgds, sreten.

Hi,

You wouldn't believe the amount of food a good triathelete eats each day
in training, about 10K calories, 4 times more than most need or should eat.

Pro racers can put out ~ 4 times the average power and output higher peak
power for ~ 4 times as long as a reasonably fit person used to riding a bike.

That capability needs fueling by calories.

rgds, sreten.

Yeah there was a cool video about Bradley Wiggins where at one point I think a trainer said he could put out 440 watts for half an hour. I don't have a power meter on my bike but there is one on my Concept 2 rower. I can put out 100 watts for half an hour no problem. Maybe even 120 watts. That's about it. 400 watts... maybe for 30 seconds?

Mr. Wiggins has a very different category of physiology from mine - no surprise, of course, but the numbers sure do expose the gap rather starkly!

You might think that intuitively but as sreten explains above as you get fitter you are capable of putting out more power which burns more calories. Efficiency doesn't change with increasing fitness.

Hi,

Generally no. The unfit person has low power output and will go slower than the
fit person. Generally they will end up burning less calories over a given course,
as lower speed is fundamentally much more efficient for covering distances
than high speed due to the cubic drag versus speed coefficients.

Porky, unfit riders, simply won't burn anything like the calories the fastest
will around a given course, the latter will be fighting aerodynamics more
than anything else, and that is a near cubic function for power to speed.

Though the fastest riders do it in a shorter time, always the statistics
indicate the fastest has used the most energy, in a shorter time than
everyone else. Power output rules in racing, the cubic function vicious.

rgds, sreten.

All good for as you get fitter and lose weight on a bike.

Forgive me if this has been addressed, I kinda lost track of this tread.

Do you think you'd burn more calories spinning or mashing? I was thinking about this the other day as I was riding into a head wind. I was putting more force into pedaling a higher gear, but turning the cranks a lot more in a lower gear? A power meter would probably tell me this in a couple of minutes.