If you are shaking my guess is that your core is weak.
Try holding the top position of the pushup for 30 seconds 10 times per day for 1 week.
After that try your pushups again and see if you notice a change.
the website 100 push ups got me from 25 to 50 in about 3 weeks if you can believe it.
I slacked off for a while and got back to being able to only do about 30 and now am back up to 40, could probably push it to 50 but don't like to strain on push ups
To get better at doing push-ups, do push-ups.
To keep your pull balanced with your push, do supine rows.
To keep your shoulder healthy, do external rotation work.
Do all these things properly and you will succeed. If you skip them, you are going to have a bad time.
Originally Posted by Emevas
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