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On high slopes and rugged terrains, riding a bicycle while standing on the pedals is easier. Even though I cannot physically define what is "easy"; since it is a feeling that my body generates based on the ratio of work output to the energy expenditure and degree of tiredness of my muscles, I am pretty sure a humanoid robot moving exactly like us would also spend much less energy standing and cycling. Why is it so?

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    $\begingroup$ Might this question be better suited for Bicycles? $\endgroup$
    – ACuriousMind
    Jul 6, 2023 at 7:52
  • $\begingroup$ @ACuriousMind I don't think it would help, since the question is about the physical aspects of cycling. Moreover, the question applies to any machines which require pedaling, so it's not just about bicycles. $\endgroup$
    – AlphaLife
    Jul 6, 2023 at 8:56
  • $\begingroup$ I'm not knowledgable enough to answer, but I found a study about it (pubmed.ncbi.nlm.nih.gov/31996561) via an article (bicycling.com/news/a33350362/…). The study said you use less of your knees but more of your hips and ankles when standing up, which could generate more power in some cases. $\endgroup$
    – KC Wong
    Jul 7, 2023 at 5:22
  • $\begingroup$ On my lowrider it is definitely not easier to stand up and pedal. Standing up requires me to focus on the balance. $\endgroup$
    – d-b
    Jul 7, 2023 at 13:49

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Standing up on a bike is a method to maximize the force/torque on the pedals. And it is usually only done when there is no adequate gear for the required torque on the rear wheel.

Which is quite common. A bike can easily exceed 30km/h on the plain, and steep ascends may just as easily force the same rider to 5km/h or lower (depending on their weight). That's a minimum gear spread of 6x, which is already beyond any internal gear hub, and not exactly common for chain shift bikes. As such, virtually all bikes do not have sufficiently low gears for the steepest ascends, and riders compensate by increasing the torque on the pedals.

Also note, that a steep ascent moves the rider's center of gravity backwards with respect to the pedals. This reduces the possible pedaling torque in seated position while making the front wheel prone to rise into the air. Both are not good.

However, there is a cost for the additional torque: Upright pedaling is strenous. The forces on the muscles are much greater, and most of the body's effort goes into providing the static forces. Forces which cost the body energy, but do not produce any work at the wheel. That's why cyclists will always drop back down onto the saddle once standing pedaling is not required anymore.

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  • $\begingroup$ A gear spread of 6× is beyond any internal gear hub, but the Pinion bottom bracket hub reaches 636% and is, when cycling, functionally similar to an internal gear hub. $\endgroup$
    – gerrit
    Jul 7, 2023 at 6:38
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    $\begingroup$ @rooby Indeed, that statement was a bit too sweeping. Another good reason for briefly standing up is to ride over bumps in the road. Standing up allows your muscles to act as a suspension, allowing the light-weight bike to follow the ground profile while keeping yourself on a straight line. I've defused that statement now. $\endgroup$ Jul 7, 2023 at 9:02
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When standing on the pedals you are using your weight to contribute to the force on the pedals, whereas when you are sitting your weight is supported by the saddle and frame. Of course, your leg muscles now have to support your weight when standing, but because they are used to doing this when you are standing up anyway, this feels like less effort than pushing against the pedals from a sitting position.

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    $\begingroup$ It's worth noting that all the force pushing down on the pedals ultimately comes from the rider's own weight, regardless of whether they are sitting or standing - a seated rider doesn't pull themselves down onto the seat using the handlebars, they stay there solely due to their weight. It's really just the biomechanics of how it feels to support your full body weight on a fully extended leg versus supporting only part of your body weight on a partially extended leg. $\endgroup$ Jul 6, 2023 at 17:39
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    $\begingroup$ @NuclearHoagie when clipped into the pedals, that's not quite true: some of the force comes from pulling with the upwards-travelling leg, which both adds torque directly to that crank as well as increase the force that can be put down on the other pedal. Though this is generally a much smaller contribution than the downwards push from rider weight. $\endgroup$ Jul 6, 2023 at 18:01
  • $\begingroup$ @NuclearHoagie A seated rider doesn't pull themselves down using the handlebars, but a rider standing on the pedals certainly does, particularly when sprinting. $\endgroup$
    – NLambert
    Jul 6, 2023 at 22:38
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It is not easier, you are just using different muscle groups to do the task.

When you're cycling "while standing", you're practically doing something similar to single-leg squats. By doing this you can generate more force (torque) which helps to overcome the height difference.

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    $\begingroup$ +1 but I think the setting is more complicated. I would expect that a leg could exert the same force while seated or upright, but a rider can pedal hard without being lifted from the seat, so there must be some reason for being able to exert more force when standing. Additionally, the rider's centre of gravity doesn't move while seating but it may move while standing, and that might allow the ride to exert force in a larger part of the pedal cycle. $\endgroup$
    – Pere
    Jul 6, 2023 at 17:48
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    $\begingroup$ "but your speed significantly decreases" I don't think this bit is necessarily true - a sprint finish of a cycle race has everyone out of the saddle. $\endgroup$
    – NLambert
    Jul 6, 2023 at 22:40
  • $\begingroup$ @Pere You're right, the mechanics of how torque is generated is complicated, and that is why I did not want to open that topic. My answer is more about what I experience while cycling. $\endgroup$ Jul 7, 2023 at 9:32
  • $\begingroup$ @NLambert Noted, I'll remove that part from the answer. Thanks for pointing it out! $\endgroup$ Jul 7, 2023 at 9:33
  • $\begingroup$ @NLambert. True, but in my experience I can't pedal harder while standing but not very fast. I stand to start accelerating and then I must seat to keep accelerating because I can't go faster while standing. I suspect racing cyclists have way longer gears than me to be used in sprints, in addition to being able to pedal way faster than me in any setting. $\endgroup$
    – Pere
    Jul 7, 2023 at 13:49
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You mention two aspects:

"On high slopes"

I suppose you mean on steep climbs. I wouldn't really agree that it's easier to pedal out of the saddle here. What is true is that you can put more torque into the pedals, but easier? Easier is to instead switch to a lighter gear where you don't need so much torque. The high pedal torque does also enable putting more power down, but it's not for free: riding out of the saddle is a lot more exhausting.

But, why can you put more torque down? It's a combination of multiple effects:

  1. The legs get to be fully extended. A simplified model of the leg action during pedalling is a two-bar linkage (upper and lower leg) driven by muscle torque $\tau_\text{h}$ at the hip (glutes muscles?) to push the pedal down vertically with force $F_\text{v}$. If you do the math, you'll find that the ratio $\frac{F_\text{v}}{\tau_\text{h}}$ is maximised by making the knee almost fully straight.
    Most of this effect is already exploited by putting the saddle high enough, but one generally wants at least a little bit of leeway while in the saddle, so standing up does add some more extension.
  2. You can "follow" the pedals more. While seated, the hips can't help much with the movement, forcing the legs to do it all (and consequently, to be quite crammed at the top of the pedal stroke, the opposite of the optimal-force position). Out of the saddle, you can move quite a bit sideways. With good coordination, all of this movement is incorporated to provide power.
  3. The bike can move too. This allows even the arms to contribute to the effort: by actively tilting the bike against the pedal movement at each stroke.

The flip side in terms of pedalling is that the combined down force of both legs must always be enough to hold the body up. If that's more than actually needed for the pedals, then some of the force will actually be carried by the upwards-travelling leg, and that incurs just completely wasted power. Therefore, pedalling out of the saddle should always be done with high torque (either on a steep climb or in a high gear). Even then there's no getting around the fact that some of the whole sloshing-around motion is wasting power, which is why road and cross-country bicycling happens mostly in the saddle.

"and rugged terrains"

That's a completely different matter. On rough ground, getting out of the saddle is helpful mostly for control and comfort. The higher power sometimes comes in handy too, but it's not the main reason.

  1. While seated, the lower body and therefore at least half of the body mass is quite rigidly connected with the frame. That limits how well you can control the movement of the bicycle, both for direction changes and guiding over bumps. All the control you have is through the handlebars – which is perfectly sufficient on smooth riding surfaces, but not on rocks and roots. For these, you want to be able to shift around your body weight to manoeuvre around and over the obstacles.
    The extreme of this are trials bicycles, which are designed to maximise movement freedom, to the point that it's not even possible to ride seated anymore. But also in downhill and enduro mountainbiking this is the main reason to get out of the saddle (and usually to lower it, nowadays done with remote-controlled dropper seatposts).
  2. Any bumps you hit while seated hit directly into your bottom, which does just not feel very good. This is most severe on rigid bicycles, but even full-suspension mountainbikes feel rough on sufficiently gnarly terrain. Obviously, standing up prevents this, allowing the legs to act as extra shock absorbers for the body.
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Multiple reasons. When standing you shift all of your weight to one side at a time, using the force created from (almost) all of your mass to push down the pedal. I say almost, because some is used for balance.

When sitting, you use your weight, but it also depends on the strength of the muscles around the "levers" deployed in your hip and knee. Standing depends less on the strength of those muscles and more on mass.

Also, if you're like me, when you stand to make it "easier" up hills or to accelerate, you may even pull down on the handlebars on the same side as your weight in order to engage those arm and finger muscles in applying more downforce.

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