Are pushups bad for your wrists?
Bad form is bad for your wrists. When you place your palms flat on the floor to do a pushup, you are placing your hands in a position called dorsiflexion. This is an EXTREME RANGE OF MOTION. One should always strive to only move in their mid range of motion. When you move in the extreme, you can stretch your tendons. That is okay but tendons don't have a direct blood supply and extreme stretches can cause micro-tears to them which won't readily heal. Instead, the body places scar tissue there as a quick fix and scar tissue doesn't stretch. The next time you push up, you will re-tear the scar tissue. Do this enough and you will develop long flexor tendonitis which will lead to median nerve entrapment (cArPaL tUnNel sYnDrOmE).
If you must do pushups, at least pay careful attention to your form. The goal is to stretch and tear muscle, not tendons or ligaments. Muscles heal, the others, not so much.
Have you ever played Jenga? That is a game where you build a tower like structure of small blocks, then remove the lower ones and place them on the top. The goal is not to make the tower imbalanced to the point that it topples over. If you are able to place the blocks precisely and perfectly aligned, the tower remains standing. The moment one of them is off balance (including the once that move when you pull its neighbor out), its tiny weight is enough to topple the whole tower. When performing pushups (or everything), your body needs this same perfect alignment.
Have you ever heard of someone throwing their back out while picking up a piece of paper? It is not the weight of the paper but their alignment which causes the pain. Like the Jenga tower, there was a subtle unbalance of alignment and something gave.
Pushups likewise require an ergonomic alignment and an even distribution of weight. A lot of people like to change the location of the hands such as close together or far apart. They do this to target ancillary muscles or to target different areas of a muscle. But having the hands too close in or too far apart will add strain and stress to ulnar or radial parts of the wrist and the ligaments between other joints. The bones, tendons and ligaments are okay as long as everything is aligned and straight down upon one another as designed. The second there is an imbalance, you may not topple like a Jenga tower but, something will give. Often the tiny little ligaments between all the bones within the wrist. If you're lucky you will develop long flexor tendonitis which can be easily healed if you know how (proper movement - not drugs or splints or rest or injections or PT).
Take the ACL within the knee. It is a very strong ligament and essentially holds our tibia and femur together. If you were to walk knock kneed or bow legged, no longer will the femur and tibia be perfectly aligned one on top of the other, and this imbalance can cause strain to supporting tissues. Worse, if your weight is just a bit too far off center, or if the compensating muscles give way or you slip, the mighty ACL can tear like a piece of tissue paper. Tendons are fibrous. They are bundles of "cords" and you know what would happen if you fray a rope (which is a bundle of cords) . . .
Sprained ankles are nothing more than torn muscles and ligaments (sometimes fractures of bone) between the bones of the ankle, just like the wrist. They are caused when there is imbalance and something tears because of the torque.
Pushups require perfect alignment and you need to be conscious of your butt, back, elbows, hand position, and even the direction your fingers are pointing. You must do a pushup like your body is a Jenga tower, perfectly aligned. Belie the laws of physics and those laws will crush you. Proper form is required not only to target the correct muscles but to prevent injury. Too bad pianists and typists didn't know this, we could stave off the epidemic of carpal tunnel syndrome. Don't worry, doctors like all the money we throw at them to tell us, "Come back in six weeks." Pharmacists love selling your drugs. PT's love designing your splints and braces. Here is a dirty secret (looks left, looks right) . . . . just move properly and you will heal.
Electricity travels from point A to point B. If you somehow come between A and B, the electricity will strike you instead of passing by. The weight and energy of your body wants to go straight down into the floor. As long as your bones and tendons are aligned, you will be okay. Allow an imbalance and instead of going into the floor, all the energy of your weight will go into your joint or into the point of the imbalance such as your wrist.
There are cheat ways to do pushups with minimal strain. You may do them on something with a handle such as a dumbbell, on your elbows between two chairs, some people do them on their knuckles which I don't advise, others do them on their fingers which can be intriguing ergonomically (like a cathedral dome) but I don't advise that either.
The real question is why? You don't need more muscle than you already have. If you need more, do the task and the body will give them to you. But to weight lift just to look good? Remember, your body has to last you about 80 years. A seemingly insignificant injury or strain today, that minor laxity today can insidiously compound over the years and haunt you in your golden years. Do you want to look good today but have aches and pains when your are 60 or do you want to be able to run and play pain free with your grand kids when you are 70?