Final answer:
To measure knee flexion, the client or patient is usually positioned prone, which means lying face-down, to allow for an accurate measurement of the knee's range of motion.
Step-by-step explanation:
When measuring knee flexion, the position in which the client or patient should be is dependent on the specific assessment or the preference of the clinician. Typically, knee flexion is measured with the individual in a prone position. This is because when prone, the individual lies face-down, allowing the clinician to measure the angle of the knee joint accurately as the leg is bent at the knee. A prone position aligns with the description: 'The person is prone with upper limbs, including palms, touching sides and lower limbs touching at sides.' This positioning facilitates an optimal measurement of the knee's range of motion.