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Professor of Physical Therapy at Nova Southeastern University Discusses Beneficial Effect of Low Level Light Lasers

Samuel Cheng, an Assistant Professor of the Physical Therapy Program at Nova Southeastern University, spoke recently at a clinical symposium for The Athletic Trainers’ Association of Florida, on the parameters, impact and use of low level light lasers to treat pain and injury. Low level laser light treatments are a new, painless, sterile, non-invasive treatment used to treat a variety of pain conditions, injuries, wounds, fracture, and neurological conditions.

Cheng, who used low level light lasers in Taiwan, said the Law of Grotthus-Draper confirms that the body must absorb the energy from the laser before it can have an “effect.” He said the light’s depth of penetration depended on the laser’s wavelength which is measured in nanometers and the power of light which is delivered to the skin.

Using a power-point presentation, Cheng explained that low level light or “cold” lasers can trigger many cellular changes including the production of enzymes and protein substances vital for innumerable bio-chemical actions. He added, “The laser light also stimulates the cell’s mitochondria, the biochemical engine that produces enzymes essential for cell function.

Cheng described the pain reduction benefits of low level light lasers as “using light to reduce the excitability of nervous tissue, reactivate enzymes, and increase ATP (Adenosine Triphosphate) release and energize inactivated enzymes.” He described the laser as “sending energy to jumpstart a system.”

He noted that the laser’s parameters include wavelength – measured in nanometers, power--measured in milliwatts, energy density – measured in joules, and frequency. Cheng said some machines deliver a steady stream light while others deliver pulsed light. He added that studies indicate skin absorbs light best in a range of 600-1000 nanometers.

Cheng, who brought two lasers with him to the lecture, said the two most common low power lasers were Helium Neon – a visible gas in the 400-700 nm light range and Gallium Arsenide, which usually had a wavelength between 600-1200 nm.

The U.S. Food and Drug Administration cleared the first low level light laser (ML830) in 2002 for pain relief for Carpel Tunnel Syndrome, a pinched nerve problem in the wrist that affects about 8 million Americans annually.

Cheng explained that lasers were classified into four groups: Class 1 includes lasers used for CD players, Class II describes a laser which could be used as a laser pointer, Class IIIa and Class IIIb are therapeutic lasers and Class IV encompasses surgical lasers.

Cheng cautioned members of his audience to know which class of lasers they used. “If you use a Class IV laser, you can burn the skin,” he said.

In offering clinical evidence for using lasers, Cheng said one should place the head of the laser directly on the skin at the pain point or “right where it hurts.”

He also said the clinician should hold the laser over each pain point for approximately 10-30 seconds. Regarding contraindications, Cheng said clinicians should avoid using the laser over the eye and over the fetus of a pregnant woman.

He concluded his talk by demonstrating two lasers, the ML830 and the Erchonia 635. Both are Class IIIA lasers, yet ML830 offers direct light and Erchonia offers pulsed light.

Cheng’s final remarks to the athletic trainers stressed the positive: low level light lasers are very helpful to combat pain and inflammation.

M. Samuel Cheng, PT, MS, Sc.D, Assistant Professor of the Physical Therapy Program at Nova Southeastern University, can be reached at or (954) 262-1273.