On 2014 Jun 27, Andrea Manca commented:

Beyond the unfortunate misprints for which we apologize and thank the commenter (90 mW instead of 90 W; 30 mW instead of 35 mW), our apparatus was set at the maximum power output for each diode (30 W x 3 diodes = 90 W), within the well-acknowledged therapeutic wavelength emission (904 nm) and for a treatment time of 10 minutes (600 seconds). The laser probe was in firm contact with the skin which allowed an optimal penetration (Prentice et al. 2005). In our sample only one trigger point (TP) had to be treated, since patients with a single TP in the upper trapezius muscle (in position TrP2) were preferentially recruited. This was done to avoid conflicting attributions of effects and sub-group analyses which would have reduced the statistical power. The commenter raised a concern about the power density. The power density measured by the commenter is 8.8 mW/cm2 (35 mW/4 cm2) which is higher than the 5 mW/cm2 recommended by the most recent guidelines for low level laser therapy treatment dosages (World Association for Laser Therapy-WALT, 2010). However, in our case the actual emitting area (2.35 cm2) was smaller than the contact surface of the probe (4 cm2) making the ratio between them even more favorable. In fact, the average output of 35 mW was spread over 2.35 cm2, resulting in a power density of 14.8 mW/cm2, which, is, again, higher than that recommended by WALT. The commenter defines such value of power density “as relatively low”. Basing on which criteria 8.8 or 22 mW/cm2 are rated as “relatively low power densities”, since in the cited WALT recommendations there is no indication on low or high power densities and only minimum requirements are stated? And how can the commenter state: “WALT recommendation for a TP is not 18 J, but 2-4 J per point” if no dosage specifications for trigger points are actually available in the cited most recent WALT recommendations? In summary, regarding the treatment doses for class 3B, 904 nm-GaAs low level laser therapy, the minimum requirements recommended by WALT are: peak pulse output > 1 Watt (here: 90 W); mean output > 5 mW (here: 35 mW), power density > 5mW/cm2 (here: 14.8 mW); irradiation time of 4 minutes per point or cm2 (here: 10 minutes); total dose 4 joules per point (here: 18 joules). All the recommended parameters were fully respected and treatment dosages delivered here were well above the minimum requirements. Moreover, assuming an emitting area of 2.35 cm2 and an average size of a TP in the upper trapezius of 0.16 cm2 (Sidkar et al. 2009), we are confident that the target was effectively irradiated by the laser beam with a definitely adequate power density. Then the conclusions of this trial are based on straightforward results which were obtained through appropriate procedures.

References:

Prentice W, Quillen W, Underwood F. 2005, “Therapeutic Modalities in Rehabilitation”, New York: McGraw-Hill 2005.

Sikdar, S., Shah, J.P., Gebreab, T., Yen, R.-., Gilliams, E., Danoff, J. & Gerber, L.H. 2009, "Novel Applications of Ultrasound Technology to Visualize and Characterize Myofascial Trigger Points and Surrounding Soft Tissue", Archives of Physical Medicine and Rehabilitation, vol. 90, no. 11, pp. 1829-1838.

WALT - World Association for Laser Therapy – Recommended dosages for low level laser therapy (2010). http://waltza.co.za/documentation-links/recommendations/dosage-recommendations/

On 2014 Feb 01, Jan Tunér commented:

In the paper, the parameters are described: According to the acknowledged guidelines (WALT, 2004), delivery parameters were: wavelength 904 nm; pulse duration 200 ns; pulse frequency 1953 Hz; peak power 90 mW; average output 30 mW; power density 22.5mWcm2; treatment time 600 seconds; energy dose 18 J per session; spot size 4 cm2 and treatment frequency five times/week. Laser probe (head size: 4 cm2) was applied steady in skin contact with no pressure over the MTP. The 904 nm laser cannot possibly have a peak power of 90 mW. Let us accept this as a misprint for 90 watt. If so, the average output is 35 mW (not 30), which is reasonable for a TP. However, the “spot” is 4 cm2, so the 30 mW is spread over a large area, producing a power density which is very low. And in fact even lower than the one stated in the paper. Assuming that the peak power is 90 watt instead of 90 mW, the average output power can be calculated to 35 mW. Spot size is said to be 4 cm2. Then the power density will become 7.5 mW/cm2 (if 39 mW is used) or 8,8 mW/cm2 (if 35 mW is used). How are the stated 22.5 mW/cm2 calculated? Anyway, both 22 and 8 mW/cm2 are relatively low power densities. Further, WALT recommendation for a TP is not 18 J, but 2-4 J per point and certainly not one single TP. The conclusion of this study is based upon flawed parameters.

On 2014 Feb 01, Jan Tunér commented:

In the paper, the parameters are described: According to the acknowledged guidelines (WALT, 2004), delivery parameters were: wavelength 904 nm; pulse duration 200 ns; pulse frequency 1953 Hz; peak power 90 mW; average output 30 mW; power density 22.5mWcm2; treatment time 600 seconds; energy dose 18 J per session; spot size 4 cm2 and treatment frequency five times/week. Laser probe (head size: 4 cm2) was applied steady in skin contact with no pressure over the MTP. The 904 nm laser cannot possibly have a peak power of 90 mW. Let us accept this as a misprint for 90 watt. If so, the average output is 35 mW (not 30), which is reasonable for a TP. However, the “spot” is 4 cm2, so the 30 mW is spread over a large area, producing a power density which is very low. And in fact even lower than the one stated in the paper. Assuming that the peak power is 90 watt instead of 90 mW, the average output power can be calculated to 35 mW. Spot size is said to be 4 cm2. Then the power density will become 7.5 mW/cm2 (if 39 mW is used) or 8,8 mW/cm2 (if 35 mW is used). How are the stated 22.5 mW/cm2 calculated? Anyway, both 22 and 8 mW/cm2 are relatively low power densities. Further, WALT recommendation for a TP is not 18 J, but 2-4 J per point and certainly not one single TP. The conclusion of this study is based upon flawed parameters.

On 2014 Jun 27, Andrea Manca commented:

Beyond the unfortunate misprints for which we apologize and thank the commenter (90 mW instead of 90 W; 30 mW instead of 35 mW), our apparatus was set at the maximum power output for each diode (30 W x 3 diodes = 90 W), within the well-acknowledged therapeutic wavelength emission (904 nm) and for a treatment time of 10 minutes (600 seconds). The laser probe was in firm contact with the skin which allowed an optimal penetration (Prentice et al. 2005). In our sample only one trigger point (TP) had to be treated, since patients with a single TP in the upper trapezius muscle (in position TrP2) were preferentially recruited. This was done to avoid conflicting attributions of effects and sub-group analyses which would have reduced the statistical power. The commenter raised a concern about the power density. The power density measured by the commenter is 8.8 mW/cm2 (35 mW/4 cm2) which is higher than the 5 mW/cm2 recommended by the most recent guidelines for low level laser therapy treatment dosages (World Association for Laser Therapy-WALT, 2010). However, in our case the actual emitting area (2.35 cm2) was smaller than the contact surface of the probe (4 cm2) making the ratio between them even more favorable. In fact, the average output of 35 mW was spread over 2.35 cm2, resulting in a power density of 14.8 mW/cm2, which, is, again, higher than that recommended by WALT. The commenter defines such value of power density “as relatively low”. Basing on which criteria 8.8 or 22 mW/cm2 are rated as “relatively low power densities”, since in the cited WALT recommendations there is no indication on low or high power densities and only minimum requirements are stated? And how can the commenter state: “WALT recommendation for a TP is not 18 J, but 2-4 J per point” if no dosage specifications for trigger points are actually available in the cited most recent WALT recommendations? In summary, regarding the treatment doses for class 3B, 904 nm-GaAs low level laser therapy, the minimum requirements recommended by WALT are: peak pulse output > 1 Watt (here: 90 W); mean output > 5 mW (here: 35 mW), power density > 5mW/cm2 (here: 14.8 mW); irradiation time of 4 minutes per point or cm2 (here: 10 minutes); total dose 4 joules per point (here: 18 joules). All the recommended parameters were fully respected and treatment dosages delivered here were well above the minimum requirements. Moreover, assuming an emitting area of 2.35 cm2 and an average size of a TP in the upper trapezius of 0.16 cm2 (Sidkar et al. 2009), we are confident that the target was effectively irradiated by the laser beam with a definitely adequate power density. Then the conclusions of this trial are based on straightforward results which were obtained through appropriate procedures.

References:

Prentice W, Quillen W, Underwood F. 2005, “Therapeutic Modalities in Rehabilitation”, New York: McGraw-Hill 2005.

Sikdar, S., Shah, J.P., Gebreab, T., Yen, R.-., Gilliams, E., Danoff, J. & Gerber, L.H. 2009, "Novel Applications of Ultrasound Technology to Visualize and Characterize Myofascial Trigger Points and Surrounding Soft Tissue", Archives of Physical Medicine and Rehabilitation, vol. 90, no. 11, pp. 1829-1838.

WALT - World Association for Laser Therapy – Recommended dosages for low level laser therapy (2010). http://waltza.co.za/documentation-links/recommendations/dosage-recommendations/