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I feel more tired walking 1 km than cycling 1 km at the same speed. However when cycling I am moving the extra weight of the cycle along!

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closed as off-topic by Jon Custer, David Z Oct 5 '16 at 15:13

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    $\begingroup$ But you get to roll with no action required by you - that is hard to do walking. And you are sitting on a seat, not having to walk and keep yourself upright. $\endgroup$ – Jon Custer Sep 30 '16 at 14:08
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    $\begingroup$ Another answer mentioned it, but I want to highlight it: yes, you have to get the mass of the bike up to speed, but only once, or a few times, in 1km. After that it doesn't matter, you only have to combat air resistance and friction. $\endgroup$ – hobbs Sep 30 '16 at 15:36
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    $\begingroup$ Related: physics.stackexchange.com/q/280200/2451 $\endgroup$ – Qmechanic Sep 30 '16 at 16:09
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    $\begingroup$ I can't answer due to rep/protected question, so here's what I got from this Casio walking calculator and Casio cycling calculator. A 25 year old male @ 180cm/80kg burns 19kCal cycling @ 8.9km/h for 6.74 min (~1km), and burns 81kCal walking (jogging) @ 8.0km/h for 7.5 min (~1km). Thus said male burns over 4x as many calories jogging as he does biking! $\endgroup$ – Doktor J Sep 30 '16 at 17:08
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    $\begingroup$ This question should be closed immediately, and I voted to close it. Asking "how efficient is a bike" is like asking "how long is a piece of string". You literally might as well ask: "Are Engines powerful?!" It's that vague. This is a physics site, for goodness sake. Any question about pushbikes instantly and wholly concerns the road surface; pushbikes-roads are a system. Silly stuff. $\endgroup$ – Fattie Oct 3 '16 at 11:19
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This is one of those cases where the physics definition of "work done" does not match your experience.

If you move an object that is subject to gravity along a horizontal surface, physics tells us the only work done is the work done to accelerate the object, and overcome the force of friction.

Biologically, "walking" is a complex action that involves many muscles contracting and stretching. But muscles are not a reversible system (unlike a spring) - work done contracting is not returned when they stretch again (incidentally this is why some animals like kangaroos have highly elastic tendons... this greatly improves the efficiency of their jumping). So if you do a deep squat, returning to the same position, you will have expended (chemical) energy, even though you "did no net work" in the physics sense. Walking involves continuous (small) changes in the height of your center of mass, and so a lot of "shallow squats". Even if you could walk smoothly without bouncing your center of mass up and down, your legs will bend and stretch as you absorb the shocks of the road (your leg has to be straight when it is placed in front of you, and bend when it is directly underneath you - or you have to move your center of gravity).

When you look at cycling, you don't have to carry your entire weight on your legs - the only work you need to do is work required to overcome the small rolling friction (at walking speed) and air drag (if you go a little faster). Also, your center of mass stays at a constant height, so there is no energy lost in "bouncing" so much.

If you look at calories burned, this is confirmed. Riding a fast mile on a bicycle you will burn about 50 kcal, and much less if you go more slowly; running a mile will burn about 130 kcal (depending on how heavy you are - this is for 170 pound runner).

UPDATE

In Umberger et al, "A model of human muscle energy expenditure", Computer Methods in Biomechanics and Biomedical Engineering, 2003 Vol. 6 (2), pp. 99–111 the authors give a detailed model of energy expenditure of different muscles, showing clearly that load, not just extension, play a big role. And obviously when you carry your entire weight, you are carrying more of the load. They include the following diagram showing what muscles are loaded during what part of the walking cycle:

enter image description here

It occurred to me that the earliest "bicycle" that I am aware of was the velocipede, a contraption that allowed one to "walk" while part of the body weight was carried by the "bike". This immediately reduced the effort required for locomotion and provides further evidence for the above.

Image from that article:

enter image description here

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  • $\begingroup$ There must be a way to describe this process thermodynamically, although that's perhaps beyond the scope of the question (since it's tagged newtonian-mechanics). $\endgroup$ – jpmc26 Sep 30 '16 at 23:25
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    $\begingroup$ Why are you going at length describing "shallow squats" and "shocks of the road", when the main problem with energy expenditure in humans is not with height changes or similar outer work, but with the fact that skeletal muscles actually WORK BY PULSING at 10-100 Hz, with each of the pulses irreversibly consuming chemical energy. The muscles consume energy without (visible outer) movement too, as anyone staying in an inconvenient position or doing static exercise would testify, so it's not like if you'd try to move without changing your height it would be easier, probably the contrary. $\endgroup$ – nightingale Oct 1 '16 at 11:37
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    $\begingroup$ @nightingale indeed holding a muscle under tension requires expenditure of energy - which is one reason why any motion returning to its origin requires energy expenditure. My point was that walking requires muscles to be under tension - more so than standing or cycling. So I thought it was worth explaining the many ways muscles were under greater tension during walking. $\endgroup$ – Floris Oct 1 '16 at 12:22
  • $\begingroup$ @Floris Thankyou for the quick answer. $\endgroup$ – Martin Oct 3 '16 at 5:54
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Since you can travel the distance faster on a bicycle for the same amount or less of physical tiredness within the time, it's clear that the bicycle uses less energy.

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    $\begingroup$ Wouldn't the angle of the plain be a big factor? I mean ride down a hill or up one. Big difference. $\endgroup$ – william deets Sep 30 '16 at 14:21
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    $\begingroup$ Downhill would require no energy at all on a bicycle. $\endgroup$ – Suzu Hirose Sep 30 '16 at 14:37
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    $\begingroup$ "the same amount or less of physical tiredness within the time". Totally wrong. Try riding a "mountain" bike through a one mile field, and then simply walk over a one-mile field. You may be thinking of riding on extremely well engineer "super-bike" - AND on a platonic, billiard-table surface, perhaps made from steel for the entire length. $\endgroup$ – Fattie Oct 2 '16 at 15:28
  • $\begingroup$ @JoeBlow please try reading the thing you're responding to before commenting. $\endgroup$ – Suzu Hirose Oct 2 '16 at 22:47
  • $\begingroup$ @Suzu Thankyou. what you said (travelling farther with same amount of energy on bike...) does makes sense, but science has this uncanny way of upsetting our logical assumptions sometimes :) $\endgroup$ – Martin Oct 3 '16 at 14:16
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I run, have been jogging and running most of my 70 years of age.Have ran many marathons and will run again in Los Angeles marathon on March 2017.

As I keep track of my own efficiency and pace over the years I am a good candidate to have personal information on this.

Running is not conserving energy like a spring or a machine made up of joints and levers that would look like a humanoid robot.

Efficiency plays a great role; age and endurance do as well. Experienced runners take advantage of the stride and bounce over the landing foot as much as possible, but even that is not going to return much of work you used to land the foot. Every movement is consuming energy and creating heat and undesired toxins in your body. Muscles which seem not contributing to your locomotion are working hard to keep your head up and your torso erect!

My time on marathon was 3:45 hrs:mins now I am happy with 5:50.
Because my muscles and joints are not as efficient as before. While I burn more energy for the same track.

When you ride a bicycle you are taking advantage of efficiency of the machine. The more efficient the machine the less energy you burn.

As a good contrast if you ride a bicycle downhill you don't use energy but if you run downhill you still burn energy and can also hurt your joints!

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  • $\begingroup$ I run quite a bit, we must run on radically different tracks, Kam. Try a 10km run through an ordinary forest, on typical trails, maybe up and down a small valley. Totally trivial for you or even me. Now try that on a bike. the world's most elite bikers couldn't even complete the course. $\endgroup$ – Fattie Oct 2 '16 at 15:30
  • $\begingroup$ I run for fun on golf courses sometimes, as a rolling hills course. last week on Ojai course alarmed security guys gave chase, some on electrical carts, but I outran them! $\endgroup$ – kamran Oct 2 '16 at 15:50
  • $\begingroup$ a pushbike would have just fallen over in those conditions. bikes (like TGVs) exist only as a system with the prepared surface. this QA is totally non-founded $\endgroup$ – Fattie Oct 2 '16 at 23:43
  • $\begingroup$ @kamran Thankyou. as we get older cycling seems to be less demanding on our joints than walking or jogging :) $\endgroup$ – Martin Oct 3 '16 at 6:00

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