However, whereas walking is a low-impact activity because one foot is always in contact with the ground, in jogging and in running, impact is introduced. This is a high-impact exercise that places strain on the body, notably the joints of the knee.
Most background radiation comes from natural sources, while most artificial radiation comes from medical examinations, such as x-ray photographs. Radiation can damage cells and make them cancerous.
Definitions: Whole sky microwave radiation is easy to discern (it is all non-earth based microwave radiation). Foreground microwave radiation is defined as the microwave radiation coming from anything made of normal matter (solids, liquids, gas and plasma) which includes all the galaxies, stars, gas and dust.