Achilles Tendinopathy Toolkit: Appendix B

Achilles Tendinopathy: Low Level Laser Therapy Dosage Calculation

Current recommendations specify that LLLT dosage be provided in Joules (J, total energy), rather than the previous
recommended Joules/cm2 (J/cm2, energy density). Use Joules rather than Joules/cm2 to specify how much energy is
delivered in a treatment.

In Laser devices that do not calculate Joules automatically, dose can be determined in seconds of exposure required to give
the desired Joules by using the following calculation:

  • Joules = watts.seconds
  • hence, Seconds = Joules/watts

For example:

  • For a 50 mW Laser (= 0.050 Watts), with a required dose = 2 J per point…
  • Seconds exposure = 2 / 0.05 = 40 secs

This change is very important clinically as the use of the previously recommended Joules/cm2 resulted in confusion when
comparing dosages between protocols. The resultant dose in Joules/cm2 could be the consequence of a number of
different treatment options.

For example, 4 J/cm2 can be delivered by:

Option #1

  • a 20 mW Laser with a beam cross section of 0.5 cm2 in 100 seconds
  • i.e., 4 = (0.02/0.5 x 100)

Option #2

  • a 10 mW laser with a beam cross‐section of 0.25 cm2 in 100 seconds
  • i.e., 4 = (0.01/0.25 x 100)


In Option #1, the total energy delivered would be 2 J

In Option #2 the total energy would be 1 J


This example illustrates that using Joules/cm2 resulted in one patient receiving twice the total amount of energy that is
received by the other patient!

Therefore, all physical therapists using LLLT should be delivering dosages based on Joules rather than Joules/cm2.

Using Joules rather than Joules/cm2 will enable better standardization of dosage and permit comparison across different
treatment regimes.

The World Association of Laser Therapy (WALT) provides dosage guidelines using Joules for various conditions. These
dosage guidelines are based upon the best evidence from the literature in conjunction with expert opinion.

Physical Therapists are encouraged to set LLLT dose according to the WALT guidelines found via this link. (Note that the WALT guidelines are given for surface exposure.)

Download Achilles Tendinopathy Toolkit: Appendix B

File:Download Appendix B - Low Level Laser Therapy Dosage Calculation.pdf