Influence of pedalling rate on the energy cost of cycling in humans <journal article>

Triathlon Forum
2

Hey Kraig, a little off topic here, but related to the last thread regarding aero positioning. I know you’ve measured frontal area, but that was from 0 degrees head-on. Have you taken any images at maybe 5 and 10 degrees? I’m curious what getting lower in the front does to you from the side, if anything. I’m sure the effect on Cd is there as well, but that is of course trickier.

Also, any new news on the redshoe? How are they supposed to work anyway? The couple of numbers you have posted seem promising in any case. I also found it amusing that my numbers are very close to yours. I did a 3 min effort at 301 watts the other day, but I think that was some form of luck, as I’m pretty damn slow. Very fun to view the powertap data as HR rises and watts fall in a sprint like that too, but I digress…

4

You know Kraig, I think most of those 60’ish most efficient cadence studies were conducted in untrained cyclists. what cadence does your grandmother use when she rides around the block? Anyhow, interesting study. At least, it points out that there is an optimum cadence and that faster is not always better. Any theory of pedaling must explain why this is true.

Not to get too picky but it was not clear in the abstract of ability level of the cyclists. Further, I would have liked to have seen if the optimum cadence changed with wattage. 150 watts doesn’t reproduce racing conditions very well, at least in the fit. When the wattage is very low, sometimes people will spin at high cadences just so they feel like they are riding.

7

I don’t think the lab tests with a limited number of untrained people will give us realy important knowledge. But there are a lot of valuable knowledge around:

  • Statistics for all 1 H world records: All record rides (except Boardman’s) was in the 100-105 RPM range. (Boardman approx 95).

  • Sience reasearch: Low cadence (60 RPM) gives a minimum of energy expence. But with higher workloads, the low cadence results in lactic acid building up, too much pressure on muscels etc - higher cadence increases the blood stream resulting in better endurance. The cadence used by the pro’s: 95 +/- 10 seems to be the optimal.

8

In fact, it seems like the scientific (however you spell it) evidence is conflicted at this point. Here are two studies using trained triathletes which are conducted in this century :wink: The first is a summary of an article but for those of us lucky to have e-journal access, the actual journal article is cited at the bottom.

http://www.findarticles.com/cf_dls/m0NHF/1_21/98594709/p1/article.jhtml Conclusion**: Pedal faster = run faster** (for 3200 meters at least)

http://www.insep.fr/Dss/Labbio/fichiers/msse.pdf Conclusion 1: Running after cycling is harder than just running (well duh?). Conclusion 2: Running stride rate increases after cycling at all cadences. Conclusion 3: Cycling at greater than ~73 rpm leads to a steady rise in Vo2 after 30 min. The authors suggest that this leads to an increased energy cost during cycling and the subsequent run. Pedal faster = increased energy consumption => possibly slower run

My conclusion: The jury is still out.

mobiusnc

9

Sometimes trying to determine the “energy costs” of riding, or some other activity, is barking up the wrong tree.

I simply DON’T CARE what the energy cost of a task measures.

What I want to know is: what is the most efficient way to perform the task at an appropriately sustainable level of power? This “appropriately sustainable level of power” is a function of the distance/time/incline/altitude/etc. and whether or not it is riding with a run to follow, or whatever iteration you may have to perform.

This can change during the race! If an average of 150 watts can be put out by a rider for 100 miles, I’m not convinced he is best served by hoping on the bike and keeping the meter set on 150 the entire way. It may be that he needs to start at 125 and warm up to 155, and as he tires, end up at 145…or whatever. In the meantime, how does this affect the run afterward? And, can he be more efficient at 75 rpms until he warms up, then drift up to 85-90, but drop down to 80-85 as he tires? There are SO MANY variations, that I don’t think a whole lot can be inferred from any one study that looks at one simple variable.

The thing I do know, is that recruitment of appropriate musculature is a beneficial thing to do for better performance. This is true because it isn’t energy expenditure that is a limiting factor in performing the races we usually talk about (I’m purposefully not trying to include ultra-distance events that last days and weeks). Even unusually thin healthy athletic people have plenty of energy stored in fat and protein to sustain them for much more than they’ll need for an ironman or two or three or ten. The problem is efficiently utilizing appropriate energy expenditure rates AND waste removal rates in the local muscle groups. Yes, I left out the neural component, because nerves don’t really get tired in our races…however, maybe I should make the term neuro-muscular, because some of the synapsal chemicals may be depleteable, I’m not really sure.

Before you talk about cardiac output’s effect on the mix, yes, there is training that needs to occur (mostly in stroke volume) there, too. And hemoglobin levels can have an effect on performance at certain levels. So can sodium pump effectiveness, hormonal levels, blood volume, etc. Then, you have to consider appropriate fluid intake during the task, which may include electrolytes. Don’t forget caloric uptake/digestion/processing, etc.

There are so many energy burning things going on, that to state 150 watts at X rpms is more or less efficient (and therefore more or less desireable) is mostly a waste of time…especially since energy expenditure is NOT a measure of efficiency at the wheel of a bicycle, NOR does a term like energy expenditure necessarily even have a meaningful relationship to performance.

What is important is: an individual’s ability to efficiently perform a sustainable rate of work appropriate to perform the task(s) at hand (and this rate may be constantly changing). Trying to isolate rpms in this equation is difficult, at best, and may be worthless without other factors considered.

10

Good point, I had wondered about this a bit. The title of the article suggests (to me at least) a measurement of running performance after cycling was made. But in the final paragraph the authors just appear to conclude “if you use a higher cycling cadence the v02 slow component could negatively affect your run performance” - forgive my paraphrasing here. Did you read it this way too?

I was trying to make the point that there is some conflicting evidence in the peer reviewed literature, although I don’t know how trusted a journal “Medicine in Sports & Exercise” is. There is a lot of anecdotal evidence floating around, and some people have very definite opinions what is right. But is there any definitive proof?

BTW, I tend to settle in around 90 rpm and feel my run off the bike is best this way :slight_smile:

mobiusnc

11

I simply DON’T CARE what the energy cost of a task measures…

The thing I do know, is that recruitment of appropriate musculature is a beneficial thing to do for better performance. This is true because it isn’t energy expenditure that is a limiting factor in performing the races we usually talk about (I’m purposefully not trying to include ultra-distance events that last days and weeks). Even unusually thin healthy athletic people have plenty of energy stored in fat and protein to sustain them for much more than they’ll need for an ironman or two or three or ten. The problem is efficiently utilizing appropriate energy expenditure rates AND waste removal rates in the local muscle groups.

Haven’t you ever bonked?

All that energy stored in fat and protein will only let you walk or coast home if your muscle glycogen is depleted. If your event lasts more than a couple hours, glycogen conservation is a major concern.

You minimize glycogen utilization by:

  1. Maximizing your running velocity or riding power at VO2 max to allow sub max intensities to be as fast and as ‘aerobic’ as possible. That will allow the metabolism of lipids to be as high as possible (by keeping your race pace as ‘aerobic’ as possible). By ‘aerobic’, I’m not talking simply keeping HR as low as possible or keeping O2 consumption as low as possible. You should be keeping you respiratory quotient as low as possible at any given running speed or cycling power output. Low O2 consumption or HR is of little value if you’re exhaling a comparatively large volume of CO2 with every breath (indicating higher glycogen utilization). Higher cadences may increase O2 consumption, but the rider’s respiratory quotient should be lower (indicating greater lipid utilization / less glycogen utilization).

  2. You minimize the forces your muscles are forced to exert. Smaller, aerobic, slow twitch muscle fibers are recruited first. Faster twitch motor units aren’t recruited if the forces required can be handled by the smaller slow twitch fibers. The recruitment of your IIa’s & IIb’s is minimized with low force demands. Minimize recruitment of faster twitch muscle fibers - minimize glycogen utilization.

12

You minimize glycogen utilization by:

  1. Maximizing your running velocity or riding power at VO2 max to allow sub max intensities to be as fast and as ‘aerobic’ as possible. That will allow the metabolism of lipids to be as high as possible (by keeping your race pace as ‘aerobic’ as possible). By ‘aerobic’, I’m not talking simply keeping HR as low as possible or keeping O2 consumption as low as possible. You should be keeping you respiratory quotient as low as possible at any given running speed or cycling power output. Low O2 consumption or HR is of little value if you’re exhaling a comparatively large volume of CO2 with every breath (indicating higher glycogen utilization). Higher cadences may increase O2 consumption, but the rider’s respiratory quotient should be lower (indicating greater lipid utilization / less glycogen utilization).

One more comment and I’ll check out before this turns into another PowerCranks debate…

Any study that simply uses oxygen consumption as it’s sole dependent variable to compare the economy or efficiency of one cadence vs another is missing the boat. Some folks use indirect calorimetry to determine anaerobic thresholds or whatever and I’m not sure that’s totally valid, but I think indirect calorimetry is directly applicable when comparing the economy of different cadences. With a given rider at a given power output, lower O2 consumption at one cadence vs another is not enough to base any riding economy conclusions on IMHO. When muscles burn glycogen for fuel AND when blood lactate is being buffered, CO2 output rises disproportionately to oxygen consumption (thus raising the respiratory quotient). Lower intake of O2 probably only indicates a more ‘economical’ effort when comparing one cadence to another if that lowered intake of O2 is NOT accompanied by a disproportionately higher output of CO2. If the respiratory quotient increases, lowered O2 consumption is meaningless when comparing one cadence to another at the same power output (at sub VO2max intensities when O2 consumption is not limiting the effort). If you see a riding economy study that used O2 consumption as its ONLY dependent variable I’d view it with a bit of scepticism.

13

You make my point exactly. Yes, I’ve bonked before. Guess what? It wasn’t because I used up all the energy stores in my body. Plain old energy consumption isn’t a problem in Ironman -length endurance events. Your body has plenty of energy stored to do much more than an Ironman. I bonked because I exceeded the rate at which my local muscle fiber’s energy producers could provide the energy (glycogen is of major importance, just as you stated) in the manner required to continue working, and/or to clear the waste products sufficiently to continue working at anything much more than minimal effort. That’s why simply measuring energy consumption has little value, it is the local muscle fiber burn rate that is important.

Of course, there are circumstances that cause depletion of glycogen faster than other circumstances. That’s bad for endurance athletes and performance. RQ is good to keep as low as possible for the effort required. However, simply looking at TOTAL energy consumed is misleading. I will consume more energy at a given wattage by using my legs compared to using my arms, as long as you are talking about a wattage my arms could achieve for the length of the test. So, if you did a study that looked at energy consumption, arms would consume less energy…if for no other reason, but that they are more coordinated (an efficiency aspect) and have much less muscle mass to burn energy…however, I don’t think anyone will say it would be better to use the arms to pedal because they use less energy. That’s what I’m saying about a study that just looks at cadence and energy consumed. It’s not really sophisticated enough to take into consideration the factors that really matter.

I think if you’ll re-read what I wrote, you’ll see we aren’t disagreeing at all. I just went a little further…

If someone says that accessory muscles aren’t important, I’d point them to the arms/legs example…legs are better at cycling partly because of the increase in muscle available to spread the local muscle fiber’s rate of energy consumption (and therefore glycogen thirst) required to produce the wattage at the wheel.

Just like using the larger leg muscles, compared to using arm muscles, adding more muscle from accessory muscles to perform the stroke (hip flexors, etc.) DECREASES the rate of energy consumption at the individual muscle fiber in the main pushing muscles at a given wattage.

As you said, decreasing each muscle fiber’s thirst for glycogen is a good thing. However, when using accessory muscles, even if TOTAL energy consumption of the athlete increases because of inefficiencies of the accessory muscles, it it much more important that LOCAL muscle fiber glycogen burning rates in the big muscles are LOWER.

THAT is why I say that simple energy expenditure comparisons aren’t important to me. I’d much rather know if an energy expenditure rate is exceeding local muscle fiber glycogen burning rate. This isn’t the same as saying that I KNOW higher rpm’s are better or worse. I also think that rpms may be somewhat individually determined. It’s just much more complicated than saying 65 rpms isn’t as good as X rpm’s because one used more energy than another to produce a certain wattage.

I know I can ramble on too long. Here it is in a nutshell: Local muscle fiber glycogen burning rate is much more important that total energy consumed.

14

Mr. Curious,

Thanks for pointing out that minimizing the stress of any one muscle will minimize the glycogen use of that muscle. By the PC’s spreading out the pedaling forces around the entire circle this may be one of the “efficiency” benefits of the cranks. However, you don’t want this to get into a PC discussion.

What I want to say is that for the endurance athlete I think it is just asimportant to train the alternative energy systems for optimum performance. Muscles don’t have enough glycogen to last an entire IM. It is not possible to replenish glycogen at a rate to allow its use as the primary energy source for an entire race. Therefore, alternative energy pathways must be used.

The main one of these are the fat metabolism pathways. I think the endurance athlete should train these as much as anything. It makes little sense to me that the athlete should try to replenish carbohydrates on long trainig rides like they would in a race. I think carbohydrate witholding is a better strategy, at least often enough to develop the fatty metabolism enzymes that will respond to these recurrent stresses. If they are develped then they can be utilized during a race. If they are not develped they cannot be.

It would be interesting to look at the fat vs carbohydrate metabolism usage of the Debooms, Reids, and Browns of the world coming down Alii drive compared to those 30 minutes or 4 hours later.

Frank

15

In Reply To

I think carbohydrate witholding is a better strategy, at least often enough to develop the fatty metabolism enzymes that will respond to these recurrent stresses. If they are develped then they can be utilized during a race. If they are not develped they cannot be.

Although intuitively I agree with you, and have (to an extent) practiced such training, I have also read sports-science-type people categorically refute such an idea, saying that fat metabolism cannot be stimulated in this way and all that one is doing is training unoptimally (because of the diminished glycogen reserves). I have further read “fat burns in a carbohydrate fire” - ie to increase fat metabolism, you should take in carbs.

duncan

16

One of the amazing aspects of living organisms is they adapt to repeated stress such that the next time that stress is encountered it will be easier to tolerate or less stressful. It is why we train and why those who train harder are better than those who don’t.

I don’t believe that such mechanisms cannot be stimulated. Now, it may not be to such an extent that it will help in athletic performance but I want to see the data.

17

One way or another, this always ends up as a PC debate.

Here’s where your logic is flawed…

At sub max intensities, the metabolic cost of using the smaller, comparatively mechanically disadvantaged hip flexors far outweighs the comparatively miniscule savings in the larger, mechanically advantaged, more fatigue resistant muscles of your legs and glutes.

It’s the physiological equivalent of lifting up on your bumper as hard as you can while you raise your car with a hydraulic jack. You end up exhausted by the effort and the jack barely noticed the difference. Might as well let the jack do the job until it reaches the limits of its capabilities.

18

One way or another, this always ends up as a PC debate.

Here’s where your logic is flawed…

At sub max intensities, the metabolic cost of using the smaller, comparatively mechanically disadvantaged hip flexors far outweighs the comparatively miniscule savings in the larger, mechanically advantaged, more fatigue resistant muscles of your legs and glutes.

It’s the physiological equivalent of lifting up on your bumper as hard as you can while you raise your car with a hydraulic jack. You end up exhausted by the effort and the jack barely noticed the difference. Might as well let the jack do the job until it reaches the limits of its capabilities.

I would agree. One way to prove this if it were possible would be to spring load the PC cranks so
that in addition to leading the cranks in the normal
idling areas, you had to use some generated power
to keep those cranks in the usual straight line of
normal cranks. It would be interesting to discover
how long the best PC’ers could continue to generate
this very small amount of additional pedal power with
their weaker pulling back and up muscles. If PC’s
do as they are supposed to, eliminate the dead spot
area and apply power on the pulling up section, it
should be no problem?

19

Curious wrote: "Here’s where your logic is flawed…

At sub max intensities, the metabolic cost of using the smaller, comparatively mechanically disadvantaged hip flexors far outweighs the comparatively miniscule savings in the larger, mechanically advantaged, more fatigue resistant muscles of your legs and glutes.

It’s the physiological equivalent of lifting up on your bumper as hard as you can while you raise your car with a hydraulic jack. You end up exhausted by the effort and the jack barely noticed the difference. Might as well let the jack do the job until it reaches the limits of its capabilities. "

Later perfection agreed.

I am sorry, your argument is pure conjecture. I was unaware that there was any data to suggest that the hip flexors are “comparatively mechanically disadvantaged” to the anti-gravity muscles. If this were true one would expect the PC user to get slower with PC training. I haven’t seen a single report of that result and there are enough users at this site alone that someone would have spoken up by now. Further, it is not in keeping with the efficiency improvements recently reported by Luttrell and Potteiger.

Despite what it looks like, if you will carefully examine all the data with an open mind you will find that the world really isn’t flat.

20

No PC debate intended. Don’t even consider PC’s in this conversation. Back to pure physiology: Simple measurement of total body energy consumption (by commonly used methods, which basically look at total body energy consumption measured by gas sampling), is NOT necessarily an indicator of “better” or “worse” for an endurance athlete, at least up to the level of Ironman competitions. Ultradistance athletics may be slightly different, but, maybe not. What is “better” or “worse” for an endurance athlete is local muscle fiber energy availability (and, probably to a lessor extent; waste product removal from the local muscle fiber site), which is closely related to RATE of energy use at the local muscle fiber site.

Although I agree 100% that the pushing muscles, and their energy delivery systems should be developed to their maximum, this leaves out other sources of power. Such as coordination, comfort, venous blood return, aerodynamics, and even…horror of horrors…accessory muscle development. If you think the quads are the most efficient pushing down muscles, why develop the hamstrings at all? After all, the hamstrings must use energy if they fire…so what if they stabilize the leg as well as bring it rearward during a pedal stroke? Using your logic of development only of the “most efficient muscles for the pedal stroke”, then you are saying there is no benefit to actively assisting your foot rearward using muscles…just let the foot follow the pedal because the quads are the most efficient at the pedal stroke. Or, is it the glutes that are most efficient? Well, then don’t use the quads.

Or, are they all basically equal in efficiency? If this is true, then only then should they all be used? Are hip flexors really less efficient? Or, just untrained?

Once the muscles you choose to state as “most efficient” are doing all that you can train them to do, what next? If total energy consumption rate is THE most important thing in the pedal stroke, you’re done. That’s all your body can do, and it can’t do any more. I disagree. I think if you relieve X amount of the force that your extensors are producinging in order to pick up your rising foot, the wattage at the back wheel will increase almost exactly X…because the bicycle chain mechanism is very efficient.

Are you saying that the extra energy required by the muscles that lift the foot is somehow stealing available energy from the pushing down muscles? It ain’t so. Your cardiac output and respiratory system are perfectly capable of providing the extra blood flow to these accessory muscles, because neither cardiac output nor lung function are THE limiters to exercise. It’s local muscle fiber energy availability that is THE limiter to exercise.

In my model, I’m saying you can either have more power in the pedal stroke by using accessory muscles EVEN IF total energy consumption increases (I don’t know if hip flexors use more energy per watt produced, or not, but it doesn’t matter for reasons stated above), OR you can have less rate of energy consumption in the individual muscle fiber of the main muscles at a given wattage by using accessory muscles to take some of the load. Both conditions are good things.

I never said PC’s are required to develop accessory muscles. But, I don’t know of any way that is better than PC’s to develop these muscles. I also know I am faster running and riding after training on PC’s. And I’m an old man, I’m not getting better simply because I’m aging.

21

Later perfection agreed.

I am sorry, your argument is pure conjecture. I was unaware that there was any data to suggest that the hip flexors are “comparatively mechanically disadvantaged” to the anti-gravity muscles. If this were true one would expect the PC user to get slower with PC training. I haven’t seen a single report of that result and there are enough users at this site alone that someone would have spoken up by now. Further, it is not in keeping with the efficiency improvements recently reported by Luttrell and Potteiger.

Despite what it looks like, if you will carefully examine all the data with an open mind you will find that the world really isn’t flat.

You will improve with PC’s because they force you to
totally unweight the idling pedals but there the
advantage ends when you are pedaling at a cadence
of 90+. The only way the dead spot area can receive
effective power application at that cadence is when
that area is part of your main power application
pedal stroke. That ends my PC contribution.