Where is potential energy stored in a human body?

Question

Where is potential energy stored in a human body? See, humans need energy to live. Using this energy we can do work, so this is potential energy. When we raise a body to a height $h$, then the potential energy of $ mgh$ is stored in it. So, why do we need food to survive when we can just go to a height $h$ using stairs, a lift, or any other method? When we reach this height $h$, we will have potential energy stored in the our bodies and we can use that energy to do work. If this is not possible, then it means that when we reach a height $h$, the body doesn't have any potential energy stored in it.

Steeven · Answer 1 · 2025-05-08T15:07:30.887

In addition to Mark's answer, also note that the potential energy you are describing as $mgh$ is in fact not stored within the body.

This energy is known as gravitational potential energy and exists because the Earth pulls in you and you in the Earth with gravitational forces. This kind of energy is associated with the system as a whole and not just with any of the objects involved.* Were the Earth to suddenly disappear, then this energy would immediately vanish, so it is intuitively not stored within your body alone, and there is no reason to associate the energy with your body specifically rather than with the Earth.

_{* Granted, people often do say that an object or body "has" potential energy, but strictly speaking this is incorrect wording. Potential energy belongs to the system as a whole, not only to any of the constitutent objects of the system.}

When an object falls to the ground then the work done indeed does come from the stored potential energy, but keep in mind that it is not the object (not forces within the object, so to say) that does this work - it is rather gravity (the gravitational force) that does the work. So we shouldn't at all think of gravitational potential energy as energy that our muscles have available for doing work.

For that reason you might consider potential energies to be fairly abstract and less tangible than contained/carried energy forms such as kinetic energy.

score 29 · Answer 2 · answered May 05 '25 at 09:48

In order to keep a person alive, it is not enough that some process provides a certain amount of energy. That energy must be in the correct form so that the biological processes can access that energy. It's the same reason why stuffing a hamburger into a car's gas tank won't help the car move. The car's engine is not capable of digesting a hamburger, only of burning gasoline. A human body is not capable of feeding itself by descending from a height. It cannot access gravitational potential energy. It can only access chemical potential energy from food, and only certain foods. Gasoline may have a lot of chemical potential energy, but a human body does not have the right chemical processes to access it.

score 9 · Answer 3 · answered May 05 '25 at 14:57

Besides Mechanical energy (mechanical energy = kinetic energy + potential energy) there are also other kinds of energy. These may be also kinetic and potential energies, but on microscopic level (remember, Newtonian mechanics treats objects as point-like, neglecting their internal structure) - internal energy, heat, etc.

In this sens,e treating a human body in terms of Newtonian mechanics is somewhat simplistic. It is better viewed in thermodynamic terms as a heat engine, obtaining energy from one reservoir (by splitting food molecules), storing it in terms of ATP, and performing useful work by splitting ATP (and rejecting the unused energy into the environment in form of heat, sweat, energy of teh final reaction products like $CO_2$, etc.)

Related: Why does holding something up cost energy while no work is being done?

score 4 · Answer 4 · answered May 06 '25 at 09:39

The human body primarily stores potential energy in the form of chemical energy within molecules such as adenosine triphosphate (ATP), glycogen, and fatty acids. These energy reserves are utilized during metabolic processes to perform work, including muscle contraction, nerve impulse transmission, and cellular repair. Wikipedia

While elevating the body to a certain height increases its gravitational potential energy (calculated as mgh), this form of energy is not biologically accessible for metabolic activities. Gravitational potential energy is a property of the system comprising both the body and the Earth and cannot be harnessed by the body to sustain life processes.

Therefore, the body's energy needs are met through the biochemical breakdown of nutrients, not by changes in its position relative to Earth's gravity.

hyde · Answer 5 · 2025-05-08T11:13:41.537

Basically all energy is stored in some kind of a field between some objects or particles.

Gravitational potential energy is stored in the gravitational field. It changes, mainly transforms to and from kinetic energy, as objects in the gravitational field change position and speed (also can change to electric potential energy, when charged particles move). The General Relativity Theory is the tool for understanding this domain, but for nearly all practical applications, classical physics and Newton's laws of motion and gravitation are plenty good.

Body heat ultimately belongs to the above category too, but for almost all practical purposes, shortcuts are again taken and it is considered just it's own kind of energy: heat.

"Food" energy is chemical energy, and is stored in the electric field which holds atoms in a molecule together. When chemical reactions happen, for example when ATP in your cells is used to cause muscle proteins to contract, it is these electric fields that change. Maxwell's equations cover the electric fields if you dig into the theory, but in practice chemical energy calculations are done based on what atoms etc are involved, and what has been empirically measured as the energy of different chemical bonds.

So, to answer your actual question:

We don't need food to survive as such. We need ATP (Adenosine Triphosphate) to survive. And there are not many ways body can make ATP. The ways body does have need food (digested and broken down to necessary basic molecules), both as the source material, and as the source of energy, and as means to transfer the energy to each individual cell.

It is not as if a body or a cell decides "I make ATP from food". What a cell "decides" is to "guide" certain molecules (sugar as fuel, very specific proteins as machinery) to be in close proximity, so that just right chemical reactions happen and ATP is produced.

There is no cellular machinery to convert even a wrong kind of chemical energy to ATP, it's gotta be just right. Converting kinetic energy to ATP is right out. And you'll just go SPLAT if you convert your gravitational potential energy to too much kinetic energy and then release it into your body by colliding with the ground...

score 1 · Answer 6 · answered May 06 '25 at 19:54

There is a tiny amount of physical potential energy stored in your body. Lift your arm up, and it holds potential energy. Let it drop down and the potential energy is released.

Most of the energy is there in chemical form. For example the muscles of a well-trained athlete contain enough chemical energy to run a marathon. There is much more energy stored in your fat reserves. Every pound of fat contains about 3,500 kilocalories, which are about 15 megajoule. There are plenty of people with a whole gigajoule of energy in fat reserves (which is an unhealthy amount). Importantly for the question, compared to this the potential energy in your body is practically nothing.

ΩrionΛPrime · Answer 7 · 2025-05-07T06:10:06.470

Please read this too to share my insight.

What is energy?

What you are describing is a doubt in the definition of energy. Remember that energy is not a big physical quantity that we can feel like we can feel speed (vision of photons of same frequencies showing normal shift), force (electron-electron repulsion between atoms of our skin and external atoms), etc. Energy is another physical quantity SIMPLY because it has a unit. But although its magnitude has a unit like other perceptible quantities, it is "perceived" a bit differently. But does it not have an effect? Of course it does. Kinetic energy causes speed, if that speedy particle hits you you feel force— the sense of touch.

About the GPE

If the Gravitational potential energy stored in you is given by mgh (forget everything else in this system) then your energy increases with height *{1}. But realise that this energy is a form potential energy, which was simply "invented" to balance energy conservation logic, it is that form of energy (the numerical value) whose effect is not seen in any dimension we can feel, e.g., force or speed. Hence it is called stored energy. Where is it stored? In any physics problem, you priorly choose the sytem and isolate is from any external effect as being external and not internal to that system— here "you+earth" system stores that GPE. If you look at the original generalised formula mentioned below, m and M are both included, so energy applies to a system rather than an indivisible subsystem. ("You" and earth each are indivisible here because we are not peeking into trillion molecules inside earth or inside you, unless we are doing the following:)

What is the role of energy is vitality?

This is a concept whose importance is defined not by curricular inclusion but by confusions in students like you and us. Let's get a bit into biophyiscs. What is life? In elementary (as in my class 10 NCERT) biology, a very good description is: Life is any entity characterised by METABOLISM (sum total of all biochemical reactioms) and preservation of living structures (called organelles, cells, tissues, organs, org sys, organism) due to maintenance and repair functions called life process. At the end all these are BIOCHEMICAL REACTIONS, which need: raw materials, contact, conditions (like sufficient energy or some chemical catalysts like chlorophyll), which has processed a very intricate system via evolution. This system could be someone like you. Let's say so. But let us freeze you, all your molecules are classically at rest. Will reaction occur? Will you be alive for long? Some experiments are heard about "cryosleep" but even in cryosleep, can you be alive at all if within a big time interval starting from after you body is completely frozen until it is unfrozen, your metabolism is ZERO or possible <0? Now let us unfreeze someone such that he didn't die, possibly our definition will tell us what happens now— all reactions or most will resume at the normal rate (during freeze the rate was not zero but positive, only very slow), but what are these mediated by? MOLECULAR MOVEMENT. Who gave you the power to move molecules along the potential difference? (Note: I use cryosleep-like idea, but not really the same) Energy. What form of energy? Which source? How will it be converted to keep you alive? This leads us to a machine much more complex than the nuclear reactors. But all I can let you know is:

Molecular movement visibly have kinetic energy, which you see in microscope as the quantity called speed. This sets the rest of life processes like a single accident causing a catastrophe.
Multiple molecular movements take us multiple sites, etc in biology chapters, and the reactions occur. What reactions? Like electron exchange, synthesis, etc which will preserve your living cell structures.
But what form of energy? Could be potential: You know there is a potential difference in ion channels, in simple diffusion, in electric field in reactions, otherwise molecules would have already been in their lowest state, tending not to react further. Kinetic: Movement = kinetic.
What what source? The previously existing movements and PD have created way for further PD and molecules. As I said this is much more complex than technological machines, but heres an example: Photons from light energy get refracted through your crystalline lens and fall onto the electron cloud of your retinal rods and cones and energize them, whereby photoexcited electrons are ejected along the optic nerve to reach you brain and get processed as colour according to energy in photon, in about 0.0625 seconds.

So what happens to your atoms when you are high up, like 100 m above ground?

Answer: Nothing. Nothing happens to your atoms individually, only you as whole (hence consider yourself indivisible, like a fundamental particle) is affected. How? Only your body is following laws of physics, hence it realises it has room for further lower energy state. All of your body atoms or rather tissues want to fall down, and certain processes are affected when a person is falling or grounded on the mountains. Like oxygen deficiency.

Endnotes

*{1} Does this mean if you slowly fly up and reach 1 light year away from earth, you will overflow with energy? Even if that is not the vital energy still GPE will overflow kinda? No. Because you will in class 11 learn another formula like $-\frac{GMm}{r}$ which significantly reduces GPE at such distances. But realise that in this context, all heights are << R (much less than radius of earth), which is the only case mgh works.

And I like to answer comments.