Limber up is an expression that denotes to prepare oneself for physical activity, mainly by doing exercises to warm up the muscles. Some of the antonyms for limber up include stiffen, freeze, immobilize, rigidify, and tense up. These words signify a state of lack of movement, flexibility, or looseness and are contrary in meaning to the notion of limber up. When one is stiff or frozen, they are unable to move or have restricted mobility, which is the opposite of being limber. Thus, it is essential to engage in regular physical activity and limber up before any strenuous exercise to prevent stiffness and improve flexibility.