[762236]

For a CO2 tolerance test, you continuously exhale (a tiny trickle) to ensure no accidental inhale. See if that makes it harder for you.

[greggyb]

When I was singing, I could hiss for 90 seconds without specific practice. For definitional purposes, a hiss was an unbroken, continuous, audible, 'sss' sound. This was an exercise our chorus director sometimes did with us.

I get bored more than anything else. Just did 70 seconds with one deep breath of prep. I have not sung in years.