Glucosamine has done wonders for me. Before taking it I was unable to do any martial art
but I'm now into my second year of Aikido.
As for scientific reseach I am aware of two large scale European studies which looked at the effect of Gucosamine on patients with osteoarthritis of the knees, who where followed up after 1 year and three years. At both intervals, both x ray evidence and patient reporting indicated significant improvement of the glucosamine group over patients given a placebo.
I have also seen research which indicates that glucosamine may contribute to insulin resistanse in a small number of the population,and so may need to be taken with caution by diabetic Aikidoka.
The sulfate formulation of glucosamine is regarded to be more effective than the hydrochloride. Hope this is useful.