isotonic

adjective

• 1 Physiology (of muscle action) taking place with normal contraction.

• 2 Physiology denoting or relating to a solution having the same osmotic pressure as some other solution, especially one in a cell or a body fluid.

• 3(of a drink) containing essential salts and minerals in the same concentration as in the body and intended to replace those lost as a result of sweating during vigorous exercise.