Don't know about the HARP system but is the breath holding time for simply staying submerged and holding ones breath? In real world, for example when diving, increased physical activity means increased consumption of oxygen. These activities include swimming, trying to swim faster (the faster you go the more resistance the water offers) or lifting/moving obstacles/barriers etc. Increased physical activity can seriously cut the time available for underwater operations in scuba diving with self contained oxygen reserves and should apply also to unassisted diving.
Bingo!!
I was thinking the same thing.
The problem is not the rules as they are. Holding a breath for 3 minutes is not a problem for professionals (in game terms = fantasy tough guys).
You could just add another house rule to take into account the oxigem consumption while stressed, for example:
* Relaxed = rules as they are.
* Rushed, swiming 2x pace = 1/2 time
* Dashing, fighting, strugling = 1/4 time
I used to swim underwater a LOT, and I do remmember that I could swinm back and forward underwater 4 times in my pool (9 meters= 72 meters with the help of the walls) when I kept a nice and easy pace and kept my body, and MIND relaxed. And I assure you I am a poor swimer.
BUT when I wrestle my brothers inside the pool (eventually underwater), I used to loose my breath in like 20 seconds.
PS: once a girl choked me out cold underwater in less than 3 seconds... oh man! THAT was embarassing.