Part I available here.

Michael Oriard, a former Chiefs offensive lineman, wrote a piece for Deadspin illustrating the tremendous physical toll playing football has on its participants.

But what has really jolted me is the less sensational, more mundane research by Kevin Guskiewicz of the University of North Carolina's sports concussion research program. For those who haven't yet read about it, Guskiewicz and his team fitted sensors in the helmets of UNC players through which they could measure the impact (or g-force) of every blow to the head. The magnitude ranges from small to more than 100 g's, the equivalent of a head hitting a windshield in a 25 mph collision (without a seatbelt). Even in practices without full pads players received blows with g-forces in the 50s, 60s, 70s, and 80s. A typical lineman suffered 31 blows during one day of training camp (I'm guessing that that meant two practices). A similar study at the University of Oklahoma determined that linemen experience blows of 20-30 g's on every routine play. And they add up: one neurologist reports that Mike Webster, the first of the former players to be diagnosed with CTE, "endured probably 25,000 violent collisions during his career."

Sadly this is nothing new. One physicists reported that football players collide with the equivalent force of small killer whales. The sheer repetition of violent collisions as a result of football is just too much force for a human body to withstand. The same could be said of boxing, which requires the participants to absorb dozens, if not hundreds of blows to the head in a single fight.

But don't MMA fighters endure similar punishment? Yes and no.

Yes, MMA fighters are at risk to absorb blows to the head but the volume of such violent collisions is exponentially lower than the meat grinder boxers and football players are forced to endure. Not to mention the difference between gloves in boxing and MMA fundamentally changes the forces involved in the strikes (explained more here).

It isn't just head injuries. Garret Wolfe of the Chicago Bears suffered a lacerated kidney on Sunday adding his name to the growing list of players, e.g., Chris Sims and Ryan Clark, who have endured serious internal trauma as a result of playing football

MMA detractors will counter that MMA fighters may experience crippling knockouts like the below video of Vitor Belfort knocking out Matt Lindland.

But what about this video of Cal's Javhid Best suffering a concussion while scoring a touchdown. The knockout is nearly identical to the Lindland knockout. 

These two videos do not represent the status quo of either sport rather the extreme ranges of what can happen.