Stanford running back Christian McCaffrey, right, carried the ball 337 times as a sophomore and 252 as a junior before opting to skip the Cardinal’s bowl game and avoid taking more hits like this one. (Marcio Jose Sanchez/Associated Press)

By the time an old friend of mine played his last high school football game in the early 1980s, he had rushed with a football more times than all but one running back in Texas schoolboy history, Billy Sims. Sims went on to win the Heisman Trophy at Oklahoma and get drafted No. 1 in the NFL. But Sims survived just five years in the pros after his knee gave out on him midway through the 1984 NFL season. He was spent.

My friend didn’t get that far.

Jimmy Shelby’s knee tore apart in a high school all-star game. He never played for Texas A&M, where he was expected to be The Next Big Thing. But at least the Aggies honored his scholarship.

The NFL isn’t so altruistic. Show up damaged or diminished at its locker room stoop, and the league keeps the door shut.

That’s why what this season’s two best college running backs — Stanford’s Christian McCaffrey and LSU’s Leonard Fournette — just decided to do makes so much sense. After announcing earlier this season that they would pass on their senior seasons to enter next year’s NFL draft, they announced separately in the past few days that they also would not play for their teams in season-ending bowl games. Why chance a career-threatening or career-ending injury or even add wear and tear to their already beaten bodies in what are meaningless games — at least to everyone except sponsors looking to push product before the public? And to broadcasters needing to fill airtime? And — how could I forget? — college coaches and athletic directors who get bonuses for producing a bowl team off the blood, sweat and tears of athletes remunerated for their labor with tuition, room and board?

LSU running back Leonard Fournette, here hurdling Colin Jeter in a game against Texas Tech, played in only seven games this season and decided to preserve his health and pro prospects by sitting out the Citrus Bowl. (Bob Levey/Associated Press)

What McCaffrey and Fournette did was a long time in coming and should be a new page in the playbook of college football players with professional potential. Players have too much to lose and too little to gain by playing more football than is necessary. Linebacker Jaylon Smith, playing for Notre Dame in last season’s bowl game, tore knee ligaments and fell from being a potential top-five NFL draftee into the second round and, as a result, lost upward of $19 million in guaranteed salary. He may have suffered nerve damage that could be career ending, too. We will see. He is rehabilitating with the Dallas Cowboys.

But running backs, the No. 1 human bull’s-eyes on the football field, have the most to lose by playing too much football in a short period of time. And it seems, at least anecdotally, that college programs are sapping running backs and leaving them with less and less for which to cash in at the pay-for-play level.

The 2015 Heisman Trophy winner, Derrick Henry, rushed 395 times for Alabama that season before leaving early for the NFL draft. He has struggled to find his burst with the Tennessee Titans and has fought a calf injury he suffered merely warming up for a game.

Ameer Abdullah carried the football 813 times for Nebraska from 2011 to 2014. This season, his second in the NFL, he played the first two games. Since then he has been laid up with a bad foot.

Montee Ball rushed 924 times for Wisconsin before the Broncos drafted him in 2013. He managed 175 carries in two NFL seasons before injuries chased him. (Then he got busted for domestic violence and sent to jail.)

Trent Richardson carried the football 283 times in his junior year at Alabama in 2011 before turning pro. He is out of football after struggling through three seasons and having knee surgery.

The list goes on.

There are, of course, exceptions in recent years. After an injury-stalled college career at Oklahoma, DeMarco Murray led the NFL in rushing with the Cowboys two seasons ago. But for the most part, it seems guys are getting worn out more quickly than ever.

The average NFL career decreased by more than two years since 2008 after being relatively steady since the early 1990s. Running backs saw their average shelf life dip below three years. A study published in 2009 in the American Journal of Sports Medicine concluded: “College football players should be advised of how specific injuries influence the percentage of athletes who play professional football based on position and their durability in the league.” It pointed to back and leg injuries having a disproportionate impact on running backs’ careers.

It all is enough to make me wonder whether carry counts, like pitch counts for pitchers, should be employed to give college running backs a better chance to make it as pros. I recalled a few years ago when onetime major league pitching phenom Ben McDonald, baseball’s No. 1 draft pick in 1989, pointed out what he thought was the likely cause of his derailment as a can’t-miss Hall of Fame pitcher.

“From my sophomore year at LSU through the Olympics and then through my junior season, I threw 352 innings in basically a 14-month period,” McDonald, a would-be Orioles star, reflected in the New York Times in the summer of 2009. “Obviously, that didn’t help my arm, either. Thank God they aren’t doing that anymore.”

A worn-out shoulder forced McDonald to give up baseball at age 30. He won just 78 games. His career encouraged baseball to consider how it used up prospects before they could prosper in the pros.

It has long been time for football to think similarly about its most-celebrated position, the one cast in bronze as the Heisman Trophy, the running back. Coaches need to start governing their touches. There is one study that purports 370 carries in a season is a point of no return for NFL running backs. For a college running back, that would be around 277 carries, given they play two or three or four fewer games. Five backs at major college programs, like Texas’s D’Onta Foreman , have exceeded that threshold this season.

But if college coaches won’t be so considerate, in part because they have no incentive to do so, then running backs need to take the fiduciary responsibility to themselves into their own hands like McCaffrey and Fournette.

Kevin B. Blackistone, ESPN panelist and visiting professor at the Philip Merrill College of Journalism at the University of Maryland, writes sports commentary for The Washington Post.