What does"Muscles have memory" mean?

Like riding a bicycle. Your muscle response becomes automatic -- that is you do not have to think about it very much...

The physiological adaptation of the body to repetition of a specific physical activity, resulting in increased neuromuscular control when performing that activity again.

https://en.wiktionary.org/wiki/muscle_memory

https://legionathletics.com/muscle-memory/

Muscle memory has been used to describe the observation that various muscle-related tasks seem to be easier to perform after previous practice, even if the task has not been performed for a while. It is as if the muscles “remember”. The term could relate to tasks as disparate as playing the clarinet[1] and weight-lifting, i.e., the observation that strength trained athletes experience a rapid return of muscle mass and strength even after long periods of inactivity

more......

https://en.wikipedia.org/wiki/Muscle_memory_(stren...

http://www.menshealth.co.uk/building-muscle/what-i...

It means if you do some particular physical activity many times, you tend to become able to do it automatically, without having to think about it, after a while.