The player's X and Z motion will remain at 0.0d unless the player jumps while sprinting, then it updates to the actual motion for about 1-3 seconds, then goes back to 0.0d.

I really have no other way of explaining this then to say just try it out. Use this command in a repeating command block.

execute as @a store result score @s [score] run data get entity @s Motion[0] 100000

Set the [score] to your sidebar, and try just running around. The score will stay on 0 until you start sprint-jumping.