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nikipedia's avatar

Why can my muscles lift, pull, and push more than my body weight?

Asked by nikipedia (27669points) October 13th, 2010

Okay, most of my muscles can’t. But my legs can push more than my body weight, and there are those ants who can lift like, 800 times their own weight, right? While I realize force and energy are very different, the part of my brain that understands conservation of energy is confused by this.

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7 Answers

Rarebear's avatar

It’s a question of leverage. You can’t push your body weight if you don’t have anything to push against.

Ltryptophan's avatar

That’s because the muscles have stored energy that is released through the contraction. That energy that gets released has superior force than the weight of the actual muscle.

Vortico's avatar

The weight (or mass) of a machine does not relate to a type of mechanical energy. The body is simply converting chemical and elastic energy into kinetic, thermal, and gravitational potential energy. A small mass of explosives does not break the laws of physics when it releases its millions of Joules of energy. It is simply converting one form (chemical) to another (kinetic, thermal, sound, etc.) at a rate known as its power.

gasman's avatar

The fact that you remain standing or lying in one place—not crashing through the floor—means that your weight is opposed by forces generated by the floor or mattress. The gravitational potential energy of your body thus remains constant and energy is conserved in that sense.

When your muscles do work, such as lifting weight, chemical reactions in muscle cells generate large pushing or pulling forces—the energy source is chemicals derived from food. The strength of these forces is not related to body weight per se, though natural selection tends to give animals (including homo sapiens) the muscle power they need but no more.

You stand up, instead of collapsing into a heap at your feet, because the various muscles in your body hold you upright. I’m no expert on body mechanics, but I know that some muscle attachments work as 3rd class levers—trading speed for force. This means that the muscle must generate larger forces than the resistance to be opposed, in order to move through a large arc, analogous to pushing a door near its hinges.

Perhaps our ancestors needed the ability to jump, which certainly requires forces exceeding body weight. Also, mothers who carry offspring use leg and back muscles that bear their combined weight even when standing still.

bob_'s avatar

I’m no biology or physics expert, but from what I remember from high school, it’s a matter of constructing a free body diagram, and everything is explained.

Y’all should also check this out.

genkan's avatar

It has to do with levers. For example, for your biceps to lift a 7kg dumbbell, the muscle has to exert 70kg worth of force. The body is set up this way to allow the dumbbell to be moved a greater distance at a higher velocity than the amount that the muscle itself moves. (If you want a detailed explanation of the physics and calculations just ask)

In essence, your body’s muscles can generate huge amounts of force just for the sake of propelling things quickly.

kess's avatar

The nature of Life is that it always gives more than it gets,
Thus no wonder these things occur, cause we are of Life.

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