Heat Therapy - Application

Application

Direct contact

Moist heat therapy has been believed to be more effective at warming tissues than dry heat, because water transfers heat more quickly than air. Clinical studies do not support the popular belief that moist heat is more effective then dry heat. Moist heat results in the perception that the tissue is heated more deeply. In fact, recent studies indicate that vasodilation, the expansion of the blood capillaries (vessels) to allow more blood flow, is improved with dry heat therapy. Expansion of the blood capillaries is the primary objective of heat therapy. A recent study clearly concluded the positive results of dry heat therapy versus moist heat therapy. Heat therapy increases the effect on muscles, joints, and soft tissue. Heat is typically applied by placing a warming device on the relevant body part.

Newer breeds of heat therapy devices combine a carbon fiber heater with a cordless rechargeable lithium battery and are built into the specific body wrap (i.e., shoulder wrap or back wrap) for targeted heat therapy. Such devices can be used as alternatives to chemical or plugged-in heating pads, but have not been shown to improve the clinical benefit. All devices primarily provide heat to promote vasodilation.

Infrared radiation

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 segments:

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 infrared lamps used for therapeutic purposes produce mainly IR-A radiation.