This article is relating to a football player who broke his neck with a head down block. The G forces relate more to the force required to break a neck.

The statement "A concussion occurs at roughly 90 to 100 g-force, "which is like smashing your head against a wall at 20 mph," Broglio said... may be a result of research that shows a immediate manifestation of symptoms.

Broglio mentions the sub-concussive impacts sustained during a football season. Nor does he mention the cumulative damage caused by those subconcussive impacts.

Glasshead, you likely have suffered many impacts prior to your concussion. Plus, there are many factors besides G force that cause a concussion.

What they do not mention is whether the 90 to 100 G's force is measured at the helmet or the skull. There can be quite a difference between the two, easily a factor or 2 meaning 100 G's at the helmet surface can be 50 G's at the skull with just 1/8th inch of deflection.

You also should not discount the speed of your head movement. 20 mph is 29 feet per second. Between the speed of the body movement and the whipping action of the head and neck, the speed at impact can be much higher than one would suspect.

But, I think the primary issue is your brain has developed a sensitivity from sub-concussive impacts that makes minor impacts enough to cause a concussion.