Skepticism is always healthy. Finding double blind studies, the gold standard in my opinion, will take more time than I am willing to invest. There are many studies on the positive effects of nitrate on athletes and coronary patients to sift through.
https://pubmed.ncbi.nlm.nih.gov/21407132/. Read the citations below the article as well.
https://www.mdpi.com/2072-6643/13/9/3183/htm
https://pubmed.ncbi.nlm.nih.gov/29412076/
If you are skeptical then so be it. That’s fine. I have no dog in this fight. All I know is that I have found positive results which probably means I am not a highly trained athlete or am enjoying the placebo effect.