If you loosen up 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 loosen up tight muscles Close your eyes. Relax. Let your body loosen up
make one's body limber or suppler by stretching, as if to prepare for strenuous physical activity
If a person or situation loosens up, they become more relaxed and less tense. Young people often loosen up on the dance floor I think people have loosened up their standards
become less tense, rest, or take one's ease; "He relaxed in the hot tub"; "Let's all relax after a hard day's work"
become less tense, less formal, or less restrained, and assume a friendlier manner; "our new colleague relaxed when he saw that we were a friendly group"