Girl in bikini building muscles on the beach, late 1950s

A girl in a bikini is laughing as she tries out what used to be called a 'chest expander' on a concrete beach at the bottom of a set of cliffs. The picture shows her hands are moving as the picture was taken, so I guess she is quite vigorously moving her arms in and out whilst her friends and companions look on.

The style of the swim ware being worn suggests this was probably taken in the mid to late 1950s.