There are a few major sports records that most people would classify as "unbreakable."

A couple that come to mind include Cal Ripken Jr.'s consecutive games-played streak (2,632), Wayne Gretzky's 215 points in a season, Pete Rose's 4,256 all-time hits, Pistol Pete's average of 44.2 points-per-game in a college career, Brett Favre's consecutive games-played streak (297), and Cy Young's 511 career wins.All six of those records seem ridiculous when you put them into perspective. While I go more in depth at

sportssanctuary.blogspot.com, I feel as if another performance-based record has joined the ranks as one of the unbreakables.Due to a number of factors, I believe that Emmitt Smith's career rushing mark of 18,355 yards will stand the test of time and last for many years to come. That, or until football turns into Sarcastaball (see blog).First of all, I'm not too naive to realize that Barry Sanders would probably hold this record had he not abruptly retired after ten seasons and 15,269 yards. He later admitted that the record wasn't important to him and the multiple losing seasons had taken their toll on him. Kind of makes you respect the guy a little bit more, huh? I don't know how many athletes today would cut short their own shot at immortality.My main reasoning for Smith's record lasting is that the NFL has become a passing league. Whether it's the rule changes, or the new 'spread-it-out' schemes becoming prevalent, the league is pass-happy.Before 2008, only one quarterback (Dan Marino in 1984) had ever passed for more than 5,000 yards in a season. Since then it has been done five times. In that same span, quarterbacks surpassed 4,500 yards 15 times. Furthermore, 12 of the top-20 pass-attempt seasons have taken place in the last five years. Fifteen of the top-20 passes-completed seasons too.Now look at what that has done to the rushing totals. Since 2008, only three times has a running back topped 1,700 yards. Adrian Peterson did it twice while Chris Johnson did so once. Both went over 2,000 yards, but each of those seasons seem to be the outliers of the past half-decade.Perhaps even more startling are the rushing attempt numbers. The most attempts any back has gotten in the last five years was Michael Turner. His 376 carries in 2008 rank 20th all-time. One would have to look all the way down to 55th to find someone who has had the most carries since 2010 (Arian Foster with 351). As one can see, running backs aren't getting the carries that they used to. How can they get the yards when they don't get the touches?Coupled with all the passing, most teams have started using two running backs in the hopes of lessening the wear-and-tear on one guy. How many teams legitimately use one back now-a-days? Other than about five teams, everyone else either splits or runs on a 75-25 count.There is something else that has become a big problem in the NFL and may lead to less rushing attempts and yards. That would be concussions and the new protocols to deal with them.Today, if a player is suspected of having any type of head injury, they are immediately pulled and given a series of tests. If the trainers think that the player has sustained an injury then they are done for the day. The player must then pass mental and physical tests throughout the upcoming week(s) in order to be allowed to play. It could take one week. It could take five. Missed games means no yards.Now for the numbers.The Rams' Steven Jackson has the most yards of any active player with 10,135 yards. That puts him 8,220 yards behind Smith. To put that in perspective, only 38 backs in 93 years have rushed for that many yards.Peterson is second amongst active backs with 8,849 yards. Gore is third at 8,839. No other active back save Willis McGahee (8,097) has more than 7,400 yards. Quick math tells you that each of these guys would have to more than double their current career outputs in order to reach Smith. Sounds like a long shot, eh? Well, there is more.Gore turns 30 in May and has rushed for more than 1,214 yards just once in his career. Combine that with the 49ers' new system with Colin Kaepernick and I think Gore is out of the picture.Peterson will turn 28 in March. Now before I get into Peterson's dilemma, I'd like to bring up LaDainian Tomlinson. At age 28, LT had 10,650 yards and looked as if he had a realistic shot at topping Smith. Four years later he retired with 13,684 yards - roughly 5,000 yards shy of the record.Peterson averages about 1,475 yards-per-season. For arguments sake, let's say he runs like that for the next two years and gets to 11,799 yards by the time he turns 30.The number 30 is thought to be the death sentence for running backs. Most experts say a back's skills greatly diminish after they hit the big 3-0. Whether that's the case or not, let's look at those numbers.The NFL record for most rushing yards after turning 30: Emmitt Smith with 5,789. With that in mind, one sees that Peterson would have to break the post-30 record by 767 yards in order to get to Smith. He would have to rush for 6,556 yards after turning 30 on top of gaining nearly 3,000 yards over the next two seasons. If I were a betting man, which I am, I would not take those odds. And I'm not.It seems as if running backs have everything going against them in today's NFL. They aren't just fighting the hands of time anymore. They have to deal with pass-first offenses, stricter injury protocols and splitting carries with teammates. Because of all of those things, I expect future backs to be trying to 'Catch 22' for a long time to come.