For 808 nm, 1 mW/cm was achieved at 3.4 cm, but for 980 nm, 1 mW/cm was achieved at only 2.2 cm depth of tissue.

Donald E. Hudson, BSEE, et al. Penetration of Laser Light at 808 and 980 nm in Bovine Tissue Samples. Photomedicine and Laser Surgery Volume 31, Number 4, 2013

The time to achieve a modified Frankel score of 4 was significantly lower (P=0·0016) in the low-level laser therapy group (median 3·5 days) than the control group (median 14 days). 

W. E. Draper, et al. Low-level laser therapy reduces time to ambulation in dogs after  hemilaminectomy: a preliminary study. Journal of Small Animal Practice (2012) 53, 465–469

In chronic low back pain, low level laser therapy combined with exercise is more beneficial than exercise alone in the long term.

Gholamreza Esmaeeli, et al. In chronic low back pain [human model], low level laser therapy combinedwith exercise is more beneficial than exercise alone in the long term: a randomised trial. Australian Journal of Physiotherapy Vol 53, 2007, 155-160.

High intensity laser therapy (HILT) combined with exercise appears to be more effective in patients with chronic low back pain than either HLLT alone or placebo laser with exercise.

Alayat MS Long-term effect of high-intensity laser therapy in the treatment of patients [human model] with chronic low back pain: a randomized blinded placebo-controlled trial. Lasers Med Sci. 2013 Nov 2.

Analysis demonstrated that (exercise + laser group) TGL demonstrated significantly reduced resting lactate level and decreased muscle glycogen depletion than the animals that were exercised only, and significantly increased the cross-section area of Tibialis anterior muscle fibers compared with those in the other groups.

Patrocinio T, et al. Effect of low-level laser therapy (808 nm) in skeletal muscle after resistance exercise training in rats. Photomed Laser Surg. 2013 Oct;31(10):492-8.

Both groups noted a decrease in weekly mean pain scores during sham treatment. After the 4-week intervention, the LILT group had an additional reduction in weekly mean pain scores of -1.0 +/- 0.4 compared with -0.0 +/- 0.4 for the sham group (P = 0.07). LILT had no effect on the Toronto Clinical Neuropathy Score, nerve conduction studies, sympathetic skin response, or quantitative sensory testing.

Zinman LH, et al. Low-intensity laser therapy for painful symptoms of diabetic sensorimotor polyneuropathy: a controlled trial. Diabetes Care. 2004 Apr;27(4):921-4.