In Are there mechanical disadvantages to being unable to breathe for a handful of rounds? I asked if there were any disadvantages to fighting while unable to breathe, due to a creature's special attack, before you get to the point of suffocating according to the game rules on PHB p. 183. The answers there mostly focus on explaining the existing rules for suffocating, which don't help, and suggesting that maybe you are automatically suffocating rather than holding your breath, as soon as you are a victim of such an attack, but Jeremy Crawford has issued a ruling that you can hold your breath, so that is not relevant.
What I was after was figuring out whether there are any rules that say that you can't fight at full efficiency, move at full speed, etc. when holding your breath. It "seems obvious" that you won't be able to hold your breath for the same amount of time if you're exerting yourself as if you're sitting quietly.
Since that question has garnered no answers talking about rules relevant to how holding one's breath impacts one's ability to fight, and I can't find anything in any of the core books either, I was wondering if anyone has house rules they'd like to share that address this. As usual, for a house rule to be a good answer on RPG.stackexchange, it needs to be play tested.