Introduction[]
Coursing Through is an Infinite mode achievement in Run 3. This achievement is found in Infinite Mode level 290.
Suggested Characters: 
Gameplay[]
In a transition from a large level into a smaller one, most characters will treat the upward incline of the buffer area between the two tunnels as a slope, similar to a ramp, and gain a tiny bit of airtime at the start of the second level. (This phenomenon is easily observed between levels G-2 and G-3.) When this airtime happens in IM-290, it immediately fails the "don't leave the ground" check. It is possible to dodge this phenomenon with a precisely landed jump, but to more consistently avoid this kind of "air pocket," it is recommended only to attempt the achievement when the level directly prior to IM-290 is smaller in size, or when you spawn into IM-290 as the first level in Infinite Mode.
That being said, the best choice for achievement completian would be the Pastafarian because her light bridge fills in the holes in the tunnel, meaning that if you avoid the slow conveyors, you can earn this easily.
If you don't have the Pastafarian, try the Runner or the Lizard. They work well here because of their great maneuverability.
If you find a box you can stop at in this level you can get better control, because that does not count as slowing down for the purposes of this achievement. You can do this easily by the "Find more boxes in Infinite Mode" upgrade a few times. Only touching the backward conveyors will disqualify you from the achievement.
One more thing that will help is to not go over the forward conveyors too much. You need extra maneuverability and speed will reduce that. It's okay and recommended to use them - in fact they directly outline the best route for obtaining the achievement - but don't overuse them.