Complex sentence: Contemporary Dance has also had a strong influence on what we regard as physical theatre, partly because most physical theatre requires actors to have a level of physical control and flexibility rarely found in those who do not have some sort of movement background.
Split into simpler sentences: Contemporary Dance has also had a strong influence on what we regard as physical theatre, partly because most physical theatre requires actors to have a level of physical control and flexibility. Those qualities are rarely found in those who do not have some sort of movement background.