Hydrodynamic equations of active-materials have been developed and used to predict the behaviour of biological and synthetic materials that produce mechanical energy. In this talk, I will discuss methods to couple angular momentum in these equations. This coupling of angular momentum is relevant for active materials where the mechanical energy is produced in the form of active-rotation. Examples of such systems have been extensively studied in experimental labs. In this talk, I will show how new terms are generated in the hydrodynamic models and will discuss how odd--response functions show up in these equations and what they mean from a phenomenological point of view.