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Running backs and BMI

Posted by Chase Stuart on February 21, 2008

Most of you have probably heard of the Body Mass Index, a ratio that's pretty simple to calculate and can be a useful tool to gauge someone's health, but with a key caveat. Muscular people have very high BMIs, and high BMIs are usually associated with poor health (because most people that weigh a lot are fat, not muscular). In football, the opposite is true: the better athletes usually have higher BMIs, because that means they've got more muscle on their frame. For the most part, skill position players in the NFL don't have much fat on them, so we can assume the added weight is solid muscle. Using weight is a poor way to measure the type of muscle we're interested in when looking at running backs, since a 5-10, 225 lb RB is more solidly built than a 6-2, 240 lb running back. The former is Ricky Williams or Emmitt Smith; the latter is LenDale White or James Stewart.

The BMI formula is simply:

703 * weight/ (height^2)

Here's a list of the BMIs of the 50 RBs with the most rushing yards, among those that entered the league in 1970 or later. Height is in inches, weight is in pounds.

			ryds	ht	wt	bmi
Jerome Bettis		13662	71	252	35.1
Jamal Lewis		 9105	71	240	33.5
Ricky Williams		 7112	70	226	32.4
Earl Campbell		 9407	71	232	32.4
Emmitt Smith		18355	70	221	31.7
LaDainian Tomlinson	10650	70	221	31.7
Priest Holmes		 8172	69	213	31.5
Shaun Alexander		 9429	71	225	31.4
Stephen Davis		 8052	72	230	31.2
Fred Taylor		10715	73	234	30.9
Barry Sanders		15269	68	203	30.9
Earnest Byner		 8261	70	215	30.8
Rodney Hampton		 6897	71	221	30.8
Gerald Riggs		 8188	73	230	30.3
Marshall Faulk		12279	70	211	30.3
Freeman McNeil		 8074	71	216	30.1
Roger Craig		 8189	72	222	30.1
Mike Pruitt		 7378	72	222	30.1
Garrison Hearst		 7966	71	215	30.0
Antowain Smith		 6881	74	232	29.8
Corey Dillon		11241	73	225	29.7
Herschel Walker		 8225	73	225	29.7
Franco Harris		12120	74	230	29.5
John Riggins		11352	74	230	29.5
Ahman Green		 8751	72	217	29.4
Eddie George		10441	75	235	29.4
Curtis Martin		14101	71	210	29.3
Chris Warren		 7696	74	228	29.3
George Rogers		 7176	74	228	29.3
Terry Allen		 8614	70	204	29.3
Edgerrin James		11617	72	214	29.0
Terrell Davis		 7607	71	206	28.7
Walter Payton		16726	70	200	28.7
Thurman Thomas		12074	70	200	28.7
Tiki Barber		10449	70	200	28.7
Mark van Eeghen		 6651	74	223	28.6
Ricky Watters		10643	73	217	28.6
Clinton Portis		 7715	71	205	28.6
Curt Warner		 6844	71	205	28.6
Chuck Muncie		 6702	75	227	28.4
Ottis Anderson		10273	74	220	28.2
Wilbert Montgomery	 6789	70	196	28.1
Eric Dickerson		13259	75	220	27.5
Charlie Garner		 7097	70	190	27.3
Robert Smith		 6818	74	212	27.2
Lawrence McCutcheon	 6578	73	205	27.0
Marcus Allen		12243	74	210	27.0
Tony Dorsett		12739	71	192	26.8
Warrick Dunn		10179	69	180	26.6
James Brooks		 7962	70	180	25.8

Average	                 9694	72	216	29.5

A weighted average using rushing yards produces an average BMI of 29.6; the top 10 rushers of all time have a BMI of 29.7. It looks pretty clear that a BMI of close to 30 is ideal for a running back. Barry Sanders is sometimes remembered as a small back, but that's really a misnomer. He was short, but he had a BMI of 30.9. Curtis Martin and Walter Payton had BMIs below the average, but most of the top RBs had BMIs over 30. Emmit Smith and LaDainian Tomlinson are the exact same height and weight (BMI of 31.7), and Earl Campbell, Shaun Alexander and Marshall Faulk -- three MVPs -- have BMIs in the thirties. Marcus Allen, Thurman Thomas, Eric Dickerson and Tiki Barber had a ton of success with BMIs in the 27.0-28.7 range, but all relied on other skills besides sheer power. And outside of Barber, all entered the league in the '80s, when everyone was a lot smaller. Here's a look at the BMIs of some of the more notable running backs in the league today, that haven't yet hit the 5,000 yard rushing mark:

Maurice Jones-Drew	1709	68	205	31.2
Willis McGahee		4572	72	228	30.9
Brian Westbrook		4785	68	200	30.4
Larry Johnson		4764	73	228	30.1
Willie Parker		4198	70	209	30.0
Joseph Addai		2153	71	210	29.3
Adrian Peterson		1341	73	217	28.6
Reggie Bush		1146	72	200	27.1

The trend certainly isn't towards backs with lower BMIs. Jim Brown was a man among boys, and he had a BMI of "only" 29.8; there's no doubt that modern RBs have more muscle on the same frame, making them stronger and faster and harder to tackle (which is necessary, to keep up with the bigger defenders of today). Once again, Jones-Drew is often called a small back, but he's just short: his BMI is very high. Even a RB like Westbrook is pretty solidly built: maybe that's why comparisons to Reggie Bush are off the mark.

In light of all this evidence, what would you think of a RB that was 6-2, 205, with a BMI of 26.3? Of the RBs on the first list, only James Brooks has a BMI lower than that. Those numbers were the measurements of Darren McFadden in his senior year at Arkansas. This post over on the Footballguys.com message board got me thinking about McFadden's height/weight ratio. It appears that he's up to 215 now, which raises his BMI to 27.6, but that's still pretty low for a supposed workhorse. McFadden is known as a guy that's tough, loves contact, and is a bruiser with speed. In college, that worked. But at 6'2, he's got to weigh a bit more than 215 without losing his speed to be as effective. How about some of the other RBs in this draft?

 1	 Darren McFadden, Arkansas 	74	215	27.6
 2	 Jonathan Stewart, Oregon 	71	234	32.6
 3	 Felix Jones, Arkansas 		72	207	28.1
 4	 Jamaal Charles, Texas 		73	190	25.1
 5	 Rashard Mendenhall, Illinois 	71	210	29.3
 6	 Ray Rice, Rutgers 		69	195	28.8
 7	 Kevin Smith<, Central Florida 	73	211	27.8
 8	 Justin Forsett, California 	68	196	29.8
 9	 Mike Hart, Michigan 		69	196	28.9
10	 Chris Johnson, East Carolina 	71	195	27.2
11	 Steve Slaton, West Virginia 	70	195	28.0
12	 Matt Forte, Tulane 		74	233	29.9
13	 BenJarvus Green-Ellis, Ole Miss71	225	31.4
14	 Thomas Brown, Georgia 		68	200	30.4
15	 Dantrell Savage, OK State 	71	185	25.8

Mendenhall, Stewart, Rice and Jones have been placed above McFadden on some draft rankings boards, a new development that may have as much to do with a desire to be different as anything else. But if Rice can run a sub-4.40 40-yard dash as some project, and Stewart and Mendenhall are almost that fast, you can see how those bigger backs might be more attractive. Felix Jones is listed at 6-0, 200 on the 2007 Razorbacks roster (compared to McFadden's 6-2, 205) and is now at 207 on most websites. He's shorter, but arguably sturdier than his college teammate, and just as fast.

I'm not saying McFadden is going to be a bust, or that he's too small to play in the NFL. But he is built more like Charlie Garner than Tiki Barber, much less Bo Jackson (6-1, 227), Barry Sanders, or LaDainian Tomlinson. Put simply, he's got skinny legs and looks like a wide receiver, not a running back. He's about the same weight as Laurence Maroney, but a full four inches taller. Can he put the weight on? Almost certainly, although it's unclear if he can do it and retain his other attributes. McFadden's a good prospect, no doubt, but he played his senior year at about 13 pounds lighter (and the same height or taller) than Adrian Peterson did last year, and I think that's a significant enough difference to question if he's really the same level of prospect.

I don't have the 2007 draft data in an easy file yet, but I looked at the ten drafts from 1997-2006. 164 running backs were selected, and 155 of them had a BMI higher than 27.6, McFadden's BMI based on his projected weight of 215 pounds.

Chris	 Brown	  2003	Colorado	 219	75	27.4
Ciatrick Fason	  2005	Florida		 207	73	27.3
Reggie	 Bush	  2006	USC		 200	72	27.1
Justin	 Hamilton 2006	Virginia Tech	 217	75	27.1
Kenny	 Bynum	  1997	So. Carolina St. 191	71	26.6
Charlie	 Rogers	  1999	Georgia Tech	 180	69	26.6
Warrick	 Dunn	  1997	Florida St.	 180	69	26.6
De'Mond	 Parker	  1999	Oklahoma	 185	70	26.5
Tatum	 Bell	  2004	Oklahoma St.	 190	71	26.5

Among the 30 running backs drafted in the first round, the average BMI was 30.6, and only Bush, Dunn and John Avery had BMIs under 28.5. Steven Jackson has the fifth lowest BMI of those 30 backs, and he's only an inch taller than McFadden but fourteen pounds heavier than him now, and 24 pounds heavier than McFadden was a couple of months ago.

Since 1990, only one RB has been drafted that's 6'2 or taller and weighed 215 pounds or less -- Robert Smith. Chris Brown (6'3, 219) was arguably just as lean, but Smith and Brown were talented backs that spent a large portion of their career on the injured list -- only once in thirteen combined seasons did either RB play 16 games. In the '07 draft, first round picks Peterson and Marshawn Lynch (30.0 BMI) were bigger, as were regular season surprises Selvin Young (28.9) and playoff star Ahmad Bradshaw (29.2). Jerious Norwood (27.8) has been a very productive running back so far, but almost everyone thinks he's not big enough to be an everydown running back. And McFadden is lighter than him.

I know I'm not the first person to question McFadden's size or build, but I was unaware just how lean he truly is.

This entry was posted on Thursday, February 21st, 2008 at 9:51 am and is filed under College, History, NFL Draft, Statgeekery. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.