1.
If a person or situation loosens up, they become more relaxed and less tense.
Young people often ~ on the dance floor...
I think people have loosened up their standards.
PHRASAL VERB: V P, V P n
2.
If you ~ your body, or if it loosens up, you do simple exercises to get your muscles ready for a difficult physical activity, such as running or playing football.
Squeeze the foot with both hands, again to ~ tight muscles...
Close your eyes. Relax. Let your body ~.
PHRASAL VERB: V P n (not pron), V P, also V n P