Loosen up and Sit back

Loosen up verb - To free from obstruction or difficulty.

Sit back and loosen up are semantically related in relax topic. In some cases you can use "Sit back" instead a verb "Loosen up", when it comes to topics like be or feel at ease.

Sit back verb - Settle into a comfortable sitting position.

Loosen up and sit back are semantically related in relax topic. You can use "Loosen up" instead a verb "Sit back", if it concerns topics such as be or feel at ease.