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The pull-up mainly uses your biceps and your lats, which are exclusively upper body muscles. So would raising your legs during a pull-up reduces the energy used in those muscles? Let's say the energy used in your abs and cores are irrelevant here, even though in reality your lats do somewhat stabilize your core.

  • Arguments for reducing: When you raised your legs, your center of gravity moves a shorter distance, thus you use less energy to hoist your body up.

  • Arguments for not reducing: Because your upper body muscles move the same distance regardless of whether or not your legs are raised, and because they hoist the same weight, they use the same amount of energy.

So which one is correct?

Photo reference for what I'm talking about: enter image description here

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  • $\begingroup$ "Let's say the energy used in your abs and cores are irrelevant here, even though in reality your lats do somewhat stabilize your core." If that's the assumption you wish to make, it's fine. But the picture you show doesn't fit the assumption. Keeping the legs horizontal definitely uses the abdominal muscles. Your picture should show the legs straight down. $\endgroup$
    – Bob D
    Mar 30, 2020 at 23:59

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The mechanical energy needed in both cases to lift the body will stay the same. You say "Arguments for reducing: When you raised your legs, your center of gravity moves a shorter distance, thus you use less energy to hoist your body up". This is not true. Once you have lifted your legs, your center of gravity will be higher to start with, but the movements of the arms will move the center of gravity by the same distance when compared to the straight legs situation. Your center of gravity moves the same distance in both cases.

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  • $\begingroup$ In the picture shown above, there is a large torque on the elbow due to body weight, which tries to straighten the elbow. The bicep muscles are contracting to counter this torque. Raised legs are actually balancing some torque due to weight due to their position wrt to elbow axis of rotation. The force required to stay above the ground is still the same as you pointed. However, pulling up with elbow bent feels easier when legs are raised, this can be easily experienced practically. $\endgroup$
    – dark knight
    Oct 3, 2021 at 17:56

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