Nitric oxide supplements

Here is an article about how beetroot juice increases apnea performance:
http://www.sciencedirect.com/science/article/pii/S1569904812001036

I believe someone may have already mentioned it in another thread. Beetroot works because it is high in nitrate which is converted to NO. The science behind L-arginine is very limited regarding its ability to increase NO. It has shown to enhance NO synthesis at altitude when it can become deficient so I could see it working for repeated apnea performance. At sea-level it will likely not enhance the performance of a single apnea. There is a supplement called N03 with arginine nitrate, but it is very costly. The amino acid N-acetylcytseine has been shown to greatly increase hematocrit. I use it as a substitute for altitude training on my athletes. Here is a study about it:
http://www.ncbi.nlm.nih.gov/pubmed/19093729