Intravascular low intensity laser therapy (ILILT) was popular in Russia in 1980s and in China in 1990s, respectively. There is photobiomodulation on blood cells and blood in vitro if the radiation intensity is so low that the photodynamic effects of endogenous photosensitizer can not damage membrane or cell compartments and the cells are not in health or normal states. The present in vivo research is of problem as the tip intensity of the fiber-optic used in ILILT might induce the apoptosis or necrosis of the blood cells near to the tip. Obviously, the in vivo research should be further done.

If the radiation intensity is so low that the photodynamic effects of endogenous photosensitizers can not damage membrane or cell compartments, there would be photobiomodulation on delayed onset muscle soreness (DOMS) at the radiation dose chosen according to the biological information model of photobiomodulation since the intracellular proteolysis of damaged proteins by ubiquitin-proteasome pathway should be the key process for DOMS recovery.

Yin-yang concepts of traditional Chinese medicine (TCM) for TCM objects such as whole body, five zangs or six fus are widely used to discuss cellular processes. In this paper, the concept of the degree of difficulty (DD) of a process was put forward to redefine yin and yang and extend TCM yin-yang model to DD yin-yang model. It was shown that healthy cells are in DD yin ping yang mi so that there is no photobiomodulation, and there is photobiomodulation on non-healthy cells until the cells become healthy so that photobiomodulation can be called cellular rehabilitation.