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There is resistance when you stretch a rubber band. That makes sense to me because the energy you exert is turned into potential energy of the rubber band, but if you hold the rubber band in the same stretched position, it requires constant energy from your body to keep it stretched, but the rubber band doesn't gain any extra potential energy. Where does that energy go?

marked as duplicate by sammy gerbil, Jon Custer, ZeroTheHero, Qmechanic Apr 19 '17 at 4:28

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Holding the rubber band at a constant stretched position/length causes you to contract your muscles, but the energy you expend (from food) just heats your muscles instead of doing mechanical work on the rubber band.

  • How about if you've tightly wound a spring, say one which is contained in a thin cylinder. Then, while holding the cylinder and preventing the spring from unwinding you file away the cylinder/spring until nothing is left, without allowing the spring to unwind whilst doing so. What happened to the energy contained in the spring, and how does the situation differ from one where the spring wasn't wound first? – user3810 Sep 9 '15 at 11:43

Holding a rubber band stretched is the same as holding a weight above the ground. You aren't adding any energy to the weight, just maintaining its position. However, your muscles' actin and myosin require energy input just to maintain a force. This energy ends up heating the muscles, and is lost.

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