I have been practicing this technique (which I though I knew but turns out it was actually Valsalva). I think I've got it right now but is there a way to make sure that I actually have the epliglottis closed? I tried doing it with empty lungs and it still seems to work but I still feel my diaphragm working really hard. My second quesiton is: do you notice that frenzel is a lot less oxygen efficient than Valsalva? It seems like I cannot hold my breath as long when I attempt frenzel because it takes more effort (body contraptions). I just want to know if everyone is experiencing the same or if I am just doing something wrong.