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I should, first of all, state that I have very limited knowledge of physics but as a fitness enthusiast the following question has puzzled me for a while. When I do squats on the gym holding a kettlebell (say 30kg) close to my chest I guess the weight is exactly on my center of mass. However, when I lift the same weight using a barbell I feel like it is much easier to lift probably because the weight, in the case of the barbell, is distributed evenly across the iron bar [assume an iron bar weighting 30 kg with no added weight].

So I was wondering if there is an equation that can be used to calculate how much weight I need to increase the barbell squats in order to feel like the kettlebell squats if that makes any sense ? e.g. if I can do 30kg squats with the weight on my center of mass, how heavy needs the weight to be when it is distributed evenly (barbell) in order to do the same Work (I guess that's what you call it in Physics ?).

Sorry, if this question is stupid and consider my complete lack of knowledge of physics :)

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  • $\begingroup$ how do you hold the barbell? $\endgroup$ – borilla May 2 '15 at 11:17
  • $\begingroup$ Just the regular hold, the bar sort of lies across your shoulders. $\endgroup$ – user1845360 May 2 '15 at 12:33
  • $\begingroup$ weights on your shoulders will travel a greater distance (difference of height) than weights on your chest during a squat. So you have to work harder with weights on your shoulders. This is angular momentum law. If you feel it is easier it might be because you use different muscles $\endgroup$ – borilla May 2 '15 at 12:40
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From "what is a kettlebell" website:

So just what is a kettlebell? A kettlebell is a cast iron ball with a handle attached to the top of it (picture a cannonball with a handle on the top). This design makes kettlebells different from training with dumbbells because the weight of a kettlebell is not distributed evenly, thus creating the need to counter balance and stabilize during your workout (Aha ... core strength!)

So I think the issue is that a kettlebell exercise is fundamentally different from a barbell exercise - since it has a very small moment of inertia, it doesn't stabilize you in the same way and this means you have to recruit additional muscle groups during the exercise.

From a physics perspective, the "work done" during the lift will be the same if the weight is the same. But that's the same physics that will tell you that you are doing "no work" if you just stand there holding a 200 pound weight overhead for, say, an hour. And anyone will know that that would be quite tiring.

So - don't look to physics for all the answers; in this case, just listen to your body. It is not the same exercise, so you can't replicate a 30 pound kettlebell exercise with an X pound barbell: it is just not the same exercise.

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