Why does bench pressing your own bodyweight feel so much harder than doing a push-up?
I have my own theories about the weight being distributed over multiple points (like in a push-up) but would just like to get a definite answer.
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36$\begingroup$ Draw a free body diagram showing all of the forces. Your feet are supplying some of the upward force, giving leverage. $\endgroup$ – Sean E. Lake Dec 5 '16 at 1:38
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5$\begingroup$ Look at where the center of mass of your body is. Look at the pivot around which your body rotates when doing a push up. Look at the lever provided by the offset of your arms. You can now calculate the proportion of your body weight you are lifting when doing a push-up. $\endgroup$ – njzk2 Dec 5 '16 at 3:34
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4$\begingroup$ Just a side note: you can also use your feet during a bench press to assist you, albeit not to the extent during a pushup. The leg drive is part of the technique for the bench press, used predominantly by powerlifters, as if your goal is to develop your chest, the less you assist it, the better. $\endgroup$ – JamalS Dec 5 '16 at 11:10
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3$\begingroup$ Imagine spreading the weights evenly on the lift bar, placing the end of the bar on the floor between your feet (while lying on your back), and lifting it from the other end like a pivot. Much easier, no? $\endgroup$ – J... Dec 5 '16 at 13:50
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4$\begingroup$ Also there is such a thing as a 'handstand push up' where you are pushing up all your body weight. $\endgroup$ – Pete Kirkham Dec 5 '16 at 13:52
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While doing push-ups, you don't push your whole body weight. You have your toes on the ground, so your body weight is distributed between your feet and your arms.
While benching, you have no support from feet. You hold the whole weight with your arms, so benching your body weight is always tougher.
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33$\begingroup$ If you want to see how much weight you're lifting during a push-up, put your hands on scales. If you have only one, use blocks of wood or some books to even it out for the other hand and feet. You'll also notice the weight slightly increases and you lower your body because the centre of mass shifts forwards. $\endgroup$ – Reti43 Dec 5 '16 at 14:52
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7$\begingroup$ This answer misses the critical role that torque plays in this comparison. $\endgroup$ – Dancrumb Dec 5 '16 at 18:32
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14$\begingroup$ @Dancrumb it doesn't miss it, it states the reason clearly without having to go into it. Also, with ideal form, the torque during a push-up should be zero, so using these terms would only confuse the issue. $\endgroup$ – Sam Dec 5 '16 at 22:23
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2$\begingroup$ To get a similar force to push-ups, when bench-pressing you could let one side of the weight lie on the ground, while only pushing the other side up. This will be much easier and is closer to what you do with your body weight. - the same how it is easier to lift one side of a table instead of lifting the whole table. $\endgroup$ – Falco Dec 6 '16 at 12:58
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2$\begingroup$ And to get a feel for bench-pressing your body weight in push-up form, try a handstand pushup. $\endgroup$ – Daniel Dec 6 '16 at 20:36
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It's harder because you are benching more weight. Benching your bodyweight requires your upper body to complete 100% of the lift.
When your feet are on the ground and you are pushing yourself up you are only lifting approximately 1/3 of your body weight. You should be able to do much more push-ups than repetitions of your weight on the bench press.
Consider this, is it easier to get off the couch or squat your body weight? The answer has the same basic principle, the more an object weighs the harder it is to lift.
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7$\begingroup$ “When your feet are on the ground and you are pushing yourself up you are only lifting approximately 1/3 of your body weight.” As somebody who’s carried people: The head side is much heavier, I’d say it’s ⅔ of the weight. Even with arms hanging down a standing person’s center of gravity is roughly at the belly button. $\endgroup$ – Michael Dec 5 '16 at 7:52
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$\begingroup$ Let's say you weight 180 lbs, for example. Then your push-up would be 120lbs if it was 2/3 of your weight. If you are in good shape I'm sure you can do 20 or 30 push-ups without experiencing too much strain. Consider laying on the bench and benching 120 lbs, which would be 37 and 1/2 lbs on each side (assuming the bar weighs the standard 45 pounds). For most people, after 12 or 15 reps you are going to experience some muscle strain. Maybe I'm a little low on my approximation with 1/3 and 2/3 seems a little high. A closer approximation may be something like 45% of your body weight. $\endgroup$ – Frederick John Dec 6 '16 at 21:55
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$\begingroup$ Michael is correct in his ⅔ approximation for exactly the reasons he stated. An 80 kg person would read about 25-30 kg on the scales if he put each hand on one. There is some variance depending on the hand width (how flared the shoulders are affects the centre of mass) and the point in the movement you are. As you lower your body, the centre of mass moves towards your head, which makes the bottom of the movement a little heavier. $\endgroup$ – Reti43 Dec 7 '16 at 11:42
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Consider leverage. Assume as in @Michael's comment that the centre of mass is somewhere near the middle. Further assume that the toes are fixed to the floor. If the torso and legs are rigid the centre of mass does not lift as far as the shoulders (at which the pressing force is exerted), so you've got leverage in your favour. This probably reduces the lift to about 2/3 or 3/4 of what it would be if you didn't put any weight on your feet.
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When you're doing press-ups, your arms have a mechanical advantage over the mass of your body. The force that they exert does not pass through your COM and, instead, exerts a torque on your mass with your feet being the fulcrum of the lever.
When you benchpress, your arms are exerting a force that passes straight through the mass of the weights. As such, there is no torque and no mechanical advantage.
Put another way, with each exercise, your arms move the same distance x. With a benchpress, the weights move this full distance, but with pushups, your COM does not move the full distance; thus, the work done during pushups is lower.
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When doing pushups, you're not lifting all of your body weight the full distance. Your heels don't move any appreciable amount and a point halfway between shoulders and toes only moves about half the height.
Consider an iron bar, 1m in length. Lifting the whole thing 1m requires twice as much energy as lifting it half a meter. Lifting one end to a height of 1m and leaving the other end on the floor means lifting the mass half a meter on the average.
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When doing push-ups, you are making your body into a lever! Your feet are the fulcrum. So you get the mechanical advantage that makes levers useful. It's just like how lifting the handles of a wheelbarrow (pivoting on the wheel) is a lot easier than simply picking up the contents of the wheelbarrow.
For similar reasons, doing dips with your legs freely dangling is a lot harder than doing a bench dip where your legs are extended with heels on the ground.
