Because a human with move 30 feet can only move 60 feet / 6 secs, which is right in the middle of an average jogging pace....

And because many human athletes can reliably do a four-minute mile, which is equivalent to Move 66 ft. with a Dash of 66 ft.... or, put another way, a move of 33 ft plus a Dash... plus a Dash... plus a Dash.

Here's an alternate movement rule that nobody asked for....

Sprinting

Sprint Action. A creature moves a multiple of their Speed, depending on their Athletics proficiency.

• For a creature without Athletics proficiency, the sprint multiple = 1. You're better off with the Dash action.
• For a creature Proficient with Athletics, the sprint multiple = 2.
• For a creature with Expertise in Athletics, the sprint multiple = 3.
• A creature cannot take the Sprint action over Difficult Terrain. The dungeon master may declare other restrictions. i.e. for Flying and Swimming, high winds or currents would be adverse to sprinting; climbing faster could require plentiful and obvious handholds, etc. For comparison, the four-minute mile is usually run on a track... a flat and even surface meant for running.
• A creature cannot sprint using a move type it does not have natively.
• A creature cannot sprint while prone or crawling.
• A character cannot take the Sprint action during a round in which they make a turn with a radius of less than 30 feet. Slow down, take the corner, and then accelerate again.

Sprint Exertion

Sprinting is limited by your exertion level, which is limited by your Constitution and Athletics ability.

Your Exertion level goes up by 1 for each round you take the Sprint action and goes down by 1 for every 2 consecutive rounds you do not Sprint.

Your Exertion Threshold equals your Constitution modifier + your Athletics ability (minimum 1).

Take 1 level of Exhaustion each time your Exertion level is above 0 and has reached a multiple of your Exertion Threshold.

That's it!

I created this one day before Dadi at Mystic Arts posted a Youtube video about his very similar ideas, so I stole some of those and reworked it a little. His video is about Chase rules, my idea was always just allowing for very fast people to run very fast. If this idea interests you at all, I suggest watching his video. He spent a lot more time thinking about it than I did.

It too complicated? Not useful at all? Looking for advice to tighten it up .

Note that taking two levels of exhaustion causes movement to be halved, so you lose all the benefit of sprinting if you let it go that far.

This is really best for chase scene mechanics and the rare burst of speed where individual differences in speed matter. It's probably not super-useful within most combats.

There's probably room for abuse, which is why all the very specific restrictions.

The minimum turning radius of 30 ft is not based on anything scientific... its meant to represent that you can't turn on a dime when moving that fast. I myself have never moved that fast, so I have no experience with what the real number should be.

This rule is tied to Athletics proficiency because a 4-minute mile is not something everyone can do. You have to be a pretty high-level athlete.

Feedback encouraged and welcomed!