Function-specific homeostasis (FSH) has been defined as a negative-feedback response of a biosystem to maintain its interior function-specific conditions so that the function is perfectly performed. There is no photobiomodulation of intranasal low intensity laser therapy (ILILT) on a function in its FSH, but ILILT could modulate a function far from its FSH. This rehabilitation has been found to be mediated by the ratio of intracellular nicotinamide adenine dinucleotide (NAD+) and its reduced form NADH, NAD+/NADH, and then sirtuin 1 (SIRT1). There might be FSH-specific NAD+/NADH (FSN) and SIRT1 activity (FSA). ILILT might enhance NAD+/NADH and SIRT1 activity until they arrive at FSN and FSA, respectively. The NAD+/NADH and SIRT1 activity of related cells of many athletic diseases such as upper respiratory tract infection, asthma, osteoarthritis, exercise-induced muscle damage, wound, traumatic brain injury, and osteoporosis are lower than FSN and FSA, respectively. Therefore, there may be therapeutic effects of ILILT on those athletic diseases. Furthermore, many phenomena and the ILILT mechanism have been integrated to support the prophylaxis effects of ILILT on the swine-origin influenza A (H1N1).