Intensity is a term used in various fields, including physics, exercise, and sound. In physics, intensity refers to the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy. It is used most frequently with waves such as acoustic waves (sound) or electromagnetic waves such as light or radio waves, in which case the average power transfer over one period of the wave is used. The SI unit for intensity is watts per square meter (W/m2) ). In exercise, intensity refers to how hard the body is working during physical activity. It is typically described as low, moderate, or vigorous, and can be measured using target heart rates, the talk test, or the exertion rating scale. In sound, intensity is defined as the amount of energy transmitted through a unit area per unit time in the direction in which the sound wave is traveling. The intensity of a sound wave depends on both particle velocity and pressure, and is comprised of both pressure and particle velocity components. The unit for sound intensity is watts per square meter (W/m2) .