It is a sports nutrition store.

I actually get a lot of my vitamins and protein powder (whey protein) and supplements from my local grocery store.

L-arginine, in large doses, triggers production of growth hormone. It is also very good for your circulatory system. And excess is used to make nitric oxide. This doesn't sound very good in that nitric oxide tends to be a poisonous brown gas, but it also happens to be good for your circulatory system. It has side effects such as increased libido and in weight lifting terms it is anabolic: it helps you to add muscle mass.