Dr. Teitelbaum, who wrote From Fatigued to Fantastic, has done studies with D-Ribose and explains it pretty well. D-ribose causes an increase in cellular energy production in the muscle and can help heal muscle tissue and reduce pain. It also regulates how much energy we have. Dr. Teitelbaum does recommend taking 5 grams three times a day for three weeks and then down to twice a day.
I am so glad you asked about this - when I pulled my book out I had a big bookmark on the page about this because I wanted to try it!