STR has a stable upkeep if the threshold END is also the same level. Basically, average strength characters can do things at an 'average' level (we're talking about humans here) for an extended amount of time based on their END. In this case, it would also be average. By pushing themselves to do more than that, it'd be a staining task and will incur a slight fatigue penalty or consequence, be it actual harm or complications, for the character. For those who are imbalanced in this area, the more END you have than your STR, the more you can push yourself essentially. With the inverse effect if higher tiers STR of strength are used without corresponding END. One-and-done, as it were.

Think of it as a stamina bar in Souls/Bloodborne. Except in story form, of course.

You will find you will be running out of breath quite easily at this point, notably those with the 'sin' weapons, so having teamwork to cover each other in your moments of vulnerability and fatigue is key.

Don't worry about keeping tally or whatever, as this is an intangible method. I'll be constantly monitoring your character's status as they do things throughout the story. During a fight or action scene(s), take your own posts as suggestions or anticipated outcomes and mine as what actually happens. Keeps things suspenseful when you don't know if things are gonna work out or not, I think. Just keep an eye out for certain cues and specific details in my responding posts, especially if you are tagged in one, as they will have determined the effectiveness of your intended actions. When I say something happens, that's what I've determined is most reasonable and that's about final. I must state now that hold no biases in my assessments, nor will I kill any characters outright without proper warning*.

*Unless your name starts with 'Z', and ends with 'ombehs'.