Muscles have sensation, as do tendons and joint capsules.
Each contains sensory receptors whose activation informs the motor system about the rate of change of muscle length, tension levels in tendons, and stresses in ligaments. This information tells the motor system whether its components are moving appropriately. Memory and experience also teach the motor system to anticipate the amount of force it must produce to perform certain activities. For instance, we adjust our posture before we move, not just during movements. Activity in an agonist produces a volley of neuronal activity that inhibits its antagonist.