Infrared Radiation and its unique ability to heat parts of the body
Infrared radiation is a convenient system to heat parts of our body. It has the advantage over direct contact in that radiation can heat directly the area where the blood capillaries and neuron terminals are. When heat comes from a direct contact source it has to heat the external layer of the skin, and heat is transferred to the deeper layer by conduction. Since heat conduction needs a temperature gradient to proceed, and there is a maximum temperature that can be safely used (around 42°C), this means lower temperature where warming is needed.
Infrared (IR for short) is the part of the electromagnetic radiation spectrum comprised between 0,78 μm and 1 mm wavelength. It is usually divided into three sections:
IR-A, from 0,78 to 1,4 μm.
IR-B, from 1,4 to 3 μm.
IR-C, from 3 μm to 1 mm.
IR radiation is more useful than the visible radiation for heating our body because we absorb most of it, compared to a strong reflection of visible light. Penetration depth of infrared radiation in our skin is dependent of wavelength. IR-A is the most penetrating, and reaches some millimeters, IR-B penetrates into the dermis (about 1 mm), and IR-C is mostly absorbed in the external layer of the epidermis(estratum corneum). For this reason the lamps used for therapeutic purposes produce mainly IR-A radiation.
Mechanism of action, and indications
Heat creates higher tissue temperatures, which produces vasodilation that increases the supply of oxygen, and nutrients and the elimination of carbon dioxide and metabolic waste.
Heat therapy is useful for muscle spasms, myalgia, fibromyalgia, contracture, bursitis.
Because heat is a vasodilator, it should be avoided in tissues with inadequate vascular supply, in case of acute injury, in bleeding disorders (because heat would increase bleeding), in tissues with a severe lack of sensitivity, in scars.
Heat therapy is most commonly used for rehabilitation purposes. The therapeutic effects of heat include increasing the extensibility of collagen tissues; decreasing joint stiffness; reducing pain; relieving muscle spasms; reducing inflammation, edema, and aids in the post acute phase of healing; and increasing blood flow. The increased blood flow to the affected area provides proteins, nutrients, and oxygen for better healing.
Heat therapy, also called thermotherapy, is the application of heat to the body for pain relief and health. It can take the form of a hot cloth, hot water, ultrasound, heating pad, hydrocollator packs, whirlpool baths, cordless FIR heat therapy wrap, and many others. It can be beneficial to those with arthritis and stiff muscles and injuries to the deep tissue of the skin. Heat may be an effective self-care treatment for conditions like rheumatoid arthritis.