First of all, it should be said that such behavior among scaly creatures with limbs is a way of communication. 
Yes, you and I are used to communicating with sounds, but not all lizards have the ability to reproduce them.
So many of them use rhythmic movements to transmit information to their fellows and representatives of other species.
My muscles will speak for me.
At the same time, these "push-ups" can mean completely different concepts. 1) This can happen when a lizard feels threatened or needs to assert dominance in its territory. In this case, the signal is intended for fellow lizards. 2) Sometimes lizards do push-ups to show potential partners their best features, such as beautiful color patterns. This is also a signal for representatives of their own species, but of the opposite sex. 3) And sometimes this is a warning to predators. Animals perform push-up exercises when they are in a threatening pose facing the enemy. This shows the predator that the lizard is aware of the presence of an enemy and is ready to fight back. 4) There is also a version that such movements help regulate body temperature. As cold-blooded creatures, lizards need to conserve heat, and such movements help achieve their goal.
Oh, yes, how nice it is in the bathhouse after a workout!
Of course, push-ups are just one manifestation of "body language". There are still a lot of different gestures and body movements that have a semantic load, but people are still far from fully understanding them.
Sports for everyone.
