[dav43]

Anecdata- I did this as a 13 year old in the 90s. My old man came upon it after I was repeatedly ending up in hospital in Australia with asthma as a kid. I think there was a presentation in a local scout hall!

I didn’t understand the history at the time - but it stopped me going to hospital, I ended up being able to do a controlled hold (no discomfort) of around 1:30 min and a max hold of just shy of 5 mins.

So for me it had a big impact.

I stopped in my 20s and now I am no where near able to get those numbers.