Joint angle is most simply measured using a goniometer, a device that is secured to both sides of a joint with a flexible portion that moves with it. A range of different size and shape devices are available to work with the many different types of joints in the body.
Joint angle measurements can be a useful tool for understanding movement in scenarios from simple gym exercises up to complex actions in a wide variety of sports.
Joint angle is also often measured in conjunction with other signals, such as EMG, or in response to electrical stimuli to get even more information about movement or reflexes.