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.
Gamma rays, X-rays, and the higher ultraviolet part of the electromagnetic spectrum are ionizing, whereas the lower ultraviolet part of the electromagnetic spectrum, visible light (including nearly all types of laser light), infrared, microwaves, and radio waves are considered non-ionizing radiation.osmic rays and the decay of radioactive isotopes are the primary sources of natural ionizing radiation on Earth referred to as background radiation. In space, natural thermal radiation emissions from matter at extremely high temperatures (e.g. plasma discharge or the corona of the Sun) may be ionizing.