Why can a person cycle more in a day than they can walk or run?

  • #1
Summary:
What's the physics behind the efficiency of cycling versus walking or running?
Hello All

Numbers vary, but the concensus is that an average person can cycle much further in a given time than they can walk or run. The world record for running is about 300km in 24 hours, whereas the cycling record is about 900km. A more typical comparison might be that a fit athlete could run a marathon in a day (and be pretty tired at the end of it) but could probably easily cycle 100 miles in a day.

Why is this so? The cyclist has to move the weight of the bike over the distance as well as his/her body, so isn't the total work needed more on a bike than when running?

I'm assuming that the start and end points are at the same altitude, so that the cyclist can't just free-wheel the whole distance.

best regards ... Stef
 

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  • #2
PeroK
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Summary:: What's the physics behind the efficiency of cycling versus walking or running?
It's all to do with a thing called the wheel.
 
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  • #3
BvU
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Summary:: What's the physics behind the efficiency of cycling versus walking or running?

The cyclist has to move the weight of the bike over the distance as well as his/her body
None of these cost energy: weight is a vertical force and the motion is horzontal So ##\vec F\cdot\vec s = 0\ ##.
(this is also true for walking!)
 
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PeroK
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Can you explain this in terms of Mechanics?
It doesn't take any energy to continue moving with constant speed (on a flat surface). All the energy you use walking or cycling at a constant speed is through mechanical inefficieny. A wheel has almost no friction or resistance and conserves linear momentum.
 
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  • #6
A.T.
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The cyclist has to move the weight of the bike over the distance as well as his/her body, so isn't the total work needed more on a bike than when running?
Do you mean over the horizontal distance traveled? Check out the exact definition of work. What do you get if force and displacement are at 90°?

https://en.wikipedia.org/wiki/Work_(physics)

Walking and running involves moving the center of mass up against gravity in each cycle, which happens much less in cycling. Instead you have some rolling resistance, which can be pretty high too (like on sand) but can also be made very low on hard surfaces.
 
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  • #7
One answer may be in the structure of the human leg. It has to support the weight of the person (which on a bike is supported by the seat via the buttocks) and propel the body along when walking and running.

Once it's relieved of having to support weight, perhaps it's more efficient at producing the rotation needed to drive the pedals of the bike?
 
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Once it's relieved of having to support weight, perhaps it's more efficient at producing the rotation needed to drive the pedals of the bike?
Why do you have to drive the pedals to cycle at constant speed?
 
  • #9
russ_watters
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One answer may be in the structure of the human leg. It has to support the weight of the person (which on a bike is supported by the seat via the buttocks) and propel the body along when walking and running.

Once it's relieved of having to support weight, perhaps it's more efficient at producing the rotation needed to drive the pedals of the bike?
I feel like you didn't absorb what the others told you regarding the definition of "work".
 
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  • #10
A.T.
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One answer may be in the structure of the human leg. It has to support the weight of the person (which on a bike is supported by the seat via the buttocks) and propel the body along when walking and running.
That's part of it. Muscles use energy, even if they don't lift the center of mass, just to generate the forces for holding it against gravity. But walking and running also involves lifting the center of mass, even on level ground.

Once it's relieved of having to support weight, perhaps it's more efficient at producing the rotation needed to drive the pedals of the bike?
The legs are not naturally optimized for driving pedals, but do they adapt if you do it a lot.
 
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  • #11
Lnewqban
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Walking is a complex coordinated group of movements, contractions and extensions of muscles, as well as accelerations of bones and joints.
Being that complicated makes it more flexible in terms of terrain irregularities that it can take, as well as climbing and jumping capabilities respect to cycling.

Please, see:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3223624/pdf/rsif20110182.pdf

:cool:
 
  • #12
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None of these cost energy: weight is a vertical force and the motion is horzontal So ##\vec F\cdot\vec s = 0\ ##.
(this is also true for walking!)

Do note that in walking and running there is an up/down motion with each step.
 
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  • #13
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A more typical comparison might be that a fit athlete could run a marathon in a day (and be pretty tired at the end of it) but could probably easily cycle 100 miles in a day.

TThis is only true when cycling on hard surfaces. So after you've put a lot of energy in making the road first. Try this comparison in the woods.
 
  • #14
BvU
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Do note that in walking and running there is an up/down motion with each step.
Yes, and you swing your arms too. Yet another (...) motion cyclists try to avoid :biggrin:

##\ ##
 
  • #15
jbriggs444
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The key, in my opinion, is the "strike" in walking. That is when the heal of your lead foot touches down and your foot and leg is forced to absorb the downward momentum of your body. Human muscles do not regenerate energy. The impact energy is lost. *poof*.

By contrast, in a bicycle there is no impact energy to lose. You can coast.

Then too, as I think has been pointed out, human muscles use energy just to maintain tension. To the extent that you walk in a smooth stride with legs slightly bent, you'll be wasting energy just supporting yourself against gravity.

By contrast, in a bicycle you have a seat.
 
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  • #16
PeroK
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The key, in my opinion, is the "strike" in walking. That is when the heal of your lead foot touches down and your foot and leg is forced to absorb the downward momentum of your body. Human muscles do not regenerate energy. The impact energy is lost. *poof*.

By contrast, in a bicycle there is no impact energy to lose. You can coast.
A reasonable comparison, perhaps, is skating and cycling. Skates on ice also allow you to maintain your momentum with no impact.
 
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  • #17
On a bike you can gain speed on a downhill section knowing that you will get most of that kinetic energy back as you coast either on a subsequent flat or uphill section. I don't think you can reproduce this effect if you are running.
 
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  • #18
berkeman
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A reasonable comparison, perhaps, is skating and cycling. Skates on ice also allow you to maintain your momentum with no impact.
Good point. I wonder what the comparable "record" is for skating for 24 hours. Presumably it would around some large frozen lake...
 
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Skates on ice also allow you to maintain your momentum with no impact.
Unless you fall down -- then there's an impact :oldbiggrin:
 
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  • #20
Vanadium 50
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Presumably it would around some large frozen lake...

One that is thawing, which will ensure the skater is extra motivated. :wink:

Seriously, there is something called "Nordic skating", which is long-distance ice skating. I don't know much about it; it's a Canadian thing.
 
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  • #21
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One that is thawing, which will ensure the skater is extra motivated. :wink:

Seriously, there is something called "Nordic skating", which is long-distance ice skating. I don't know much about it; it's a Canadian thing.
I'll think you'll find, maybe not surprisingly, that it is originally a Nordic thing particularly popular in Sweden. ;) There is a similar activity om the Netherlands where they distance skate on the canals.

Other activities that could be interesting to use as a comparison is inline skating and roller skiing.

Cross country skiing is also a interesting data point.
 
  • #22
BvU
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you will get most of that kinetic energy back
Nonsense. Almost all kinetic energy is dissipated in wind resistance.
 
  • #23
berkeman
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Nonsense. Almost all kinetic energy is dissipated in wind resistance.
Good point. :smile:

1616630558623.png

https://cyclingtips.com/wp-content/uploads/2021/02/supertuck.jpg
 
  • #24
jrmichler
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Unless you fall down -- then there's an impact
A face plant on ice is far less painful than a face plant on pavement. On ice it's WHAM and slide, while on pavement it's WHAM and sudden stop with skin removal. I learned this a few years ago when I caught my toe while trying for speed on my ice skates. Right in front of the local bar. More than once.
 
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  • #25
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A face plant on ice is far less painful than a face plant on pavement.
But one seldom stabs oneself in the butt when doing a faceplant on pavement. Don't ask me how I know this...
 
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