I am modifying my answer because in January I started working out and had some muscle soreness. So the lady at the gym recommended that I use an amino acid supplement the morning I work out and post work out. I did it and I noticed my hair grew about an inch in two months. Since I was not measuring I cannot say exactly but I did notice my hair is longer.
Some of the ladies in the other forum said it could bethe exercise and/or a combination of things. After doing a little checking on the amino acid I found out that L-Cysteine, L-methionine, L-cystine, L-arginine and L-lysine have an effect on hair growth.
I am not sure if this is a fluke or will level off in a month or two but if you need a boost this may be one way to do it. Oh I should also say my hair grows very slowly as well I think about 1/4 of an inch and even slower in the winter.
Again not sure if it will work but if you want more details like what products I was using and all that pm me and I will give you all the details.