A guest post by BE reader and community member Patrick Wyman

After taking an initial look at questions of longevity in my last piece, it seems appropriate to dig deeper into the rich data to answer additional questions for which space and time didn't allow. Although I'd suggest that you read the first installment (shameless plug), let's recap some key points of what we learned:

1) On average, fighters tend to begin their decline around 9.5 years after the date of their first fight. In a sample of 48 fighters, nine was the most frequently occurring time, followed by ten and eight. In cases where fighters declined before the nine-year mark, they were extreme outliers in terms of taking damage (Frank Mir) or number of fights (Miguel Torres); alternatively, they might have had a long career in other combat sports (Mirko Filipovic) or unusually severe injuries (Norifumi Yamamoto, Brock Lesnar).

2) The oft-cited "Nine-Year Rule", the previous standard for longevity research in MMA, greatly understates the potential for a fighter's prime to continue beyond that point. A significant reason for this was the piece's focus on winning percentage as the sole marker of decline, and to correct that flaw, we employed a diverse set of criteria for evaluating decline. These criteria included damage sustained, stylistic stagnation, and the use of betting odds as a way of approximating public perception of one's talent at a given point, in addition to winning percentage.

3) Fighters with a base in grappling or wrestling tend to have greater potential for longevity than those with a striking base, Anderson Silva excepted. While this might sound obvious, it bears repeating: human beings have a finite capacity for absorbing brain trauma, and the less you experience before the beginning of your MMA career, the better off you are in the long term. As a corollary, damage sustained (as measured indirectly by strikes absorbed/minute) tends to be a good predictor of longevity.

Having answered a number of relatively basic queries about longevity and decline, let's examine our expanded sample of 48 fighters with a few more questions in mind. First, is age important in absolute terms, or is length of career the decisive variable in longevity? Second, can we rule out any other variables in terms of longevity? Third, are there any indications that patterns in longevity are changing with a new generation of fighters, or are they relatively constant? Fourth, can we use this data to make predictions about current fighters who haven't yet reached the point of decline?

Let's start with age. As counterintuitive as it may seem at first glance, age - in absolute terms - doesn't seem to be a particularly important factor in a fighter's decline. In other words, fighters don't have a single age after which they're no longer in their prime. The average for the sample is 31.7, with a standard deviation of 3.5; if we remove Randy Couture, the most extreme outlier in the group, the average drops to 31.4 with a standard deviation of 2.89, which indicates a much more stable sample.

While age alone isn't predictive of a fighter's decline, there are two important conclusions that we can draw from these data. The first is that there is a range of ages after which a fighter's performance is almost certain to decline. Very few fighters put in their best work after age 34, and this does make intuitive sense: when we compare MMA to other sports, especially baseball (for which the best analytical work of this kind has been done), the range for the beginning of performance decline tends to fall between 32 and 34. I highly doubt that this is a coincidence; instead, it's likely that most highly athletic men, from whom these samples are drawn, tend to experience a drop in athleticism and its underlying components - hormone levels, recovery from injury, reflexes, etc. - around these ages.

When we examine fighters who declined before age 30, they tend to be guys who meet one or more of the following criteria: first, they came from a striking background, meaning that they absorbed quite a bit of damage before beginning their MMA career (Martin Kampmann); second, they started young, meaning that they'd reached the average time of decline before 30 (Manny Gamburyan); third, they took a lot of damage relative to their peers (Forrest Griffin); and last, they suffered a severe series of injuries (Shogun Rua). While there are exceptions, these factors tend to be clear.

The second important point is that the fighters who do start to decline after age 34 tend to do so in dramatic ways. Fightnomics did a fantastic piece on precisely this question, and found that fighters experience a drastic spike in the likelihood of getting knocked out after age 34. At the time he ran the data (May of last year), fighters between 36 and 38 were more than twice as likely to be slept as fighters in their early 20s. In other words, a guy who declines at 31 might experience a string of decision losses, while one who declines at 37 might be viciously KO'd numerous times. Compare the difference between Tito Ortiz - four decisions and one KO in his first winless streak between 31 and 35 - and Chuck Liddell, who had four knockout losses and one decision loss between 37 and 40.

Age, then, isn't as important a factor as the length of a fighter's career. What other components of a career, however, seem to matter and which don't? The most intriguing thing suggested by the data, I'd argue, is that the number of fights a guy has over the course of his career isn't particularly relevant to either an early decline or extreme longevity. As with age, this is counterintuitive: one would assume that a guy with more fights on his record would have a shorter career, but this doesn't seem to be the case.

The average for the sample was 34 fights, an average of 2.7 per year. It's worth noting that there's a clear pattern in the distribution of these fights: it's not uncommon for guys to fight five times per year or more before reaching a major organization, and for the pace to then slow to no more than two or three a year. Although it's difficult to extract a meaningful pattern from the data, it's likely that fighting top competition less often rather than more can extend a fighter's career. Even without TRT, Dan Henderson's career has been abnormally long despite fighting the best in the world for many years, and the same holds true for Vitor Belfort, Hayato Sakurai, and Anderson Silva, all of whom had a relatively low number of fights in those years. Of course, the counterpoint would be BJ Penn, whose peak was average in length despite a relatively low volume of bouts.

Although the sample is very small, there seems to be a slight indication that having an extremely high number of fights - greater than one standard deviation above the average - might slightly shorten a fighter's peak. The only guy to have an abnormally high number of bouts and surpass the 10-year mark before starting his decline was Chael Sonnen, and TRT was involved at the end of his prime; Matt Hughes, Melvin Guillard, Joe Stevenson, Miguel Torres, and Sean Sherk all fall at the low end of the spectrum in terms of longevity.

Let's move on to the third question, whether there are any indications that the new generation of fighters might have different expectations for longevity than their trailblazing predecessors. I'll argue that they should expect to have slightly longer peaks: part of my reasoning is based on the available data, and part on some educated guesses based on the current shape of MMA.

When we examine the current crop of fighters in the 8+ year ranges of their careers, there are reasons to be hopeful. At heavyweight, Werdum, Overeem, and Barnett all seem to be going strong, without any real indication of decline. Light heavyweight is even more promising: Machida, Rashad Evans, Glover Teixeira, and Gegard Mousasi all seem to be comfortably in their prime years. At middleweight, Jacare Souza, Bisping, Francis Carmont, and Tim Kennedy all seem to be doing fine. Welterweight looks even better, with GSP, Carlos Condit, Robbie Lawler, and Mike Pyle holding strong. The lighter weight classes are very young, and there simply aren't enough fighters at this point in their careers to identify and evaluate a meaningful pattern. It's possible that half of the fighters I mentioned here will come out and look terrible in their next fights, but that seems less likely than the possibility that there's a genuine change in the works.

When we think about the mechanisms behind this ongoing change, two factors immediately stand out. The first is the infinitely greater amount of money available to fighters now than in the early years of the sport. More money allows for better coaching, improved facilities, the hiring of dietitians, physical therapists, and strength and conditioning experts, and most importantly, the ability to pull out of a fight with an injury instead of charging ahead in order to pay the bills. A great many fighters have done permanent damage to themselves because it wasn't financially viable for them to not take a fight. The second part is insurance. Even if the coverage isn't ideal, it still provides more consistent and higher-quality medical care than has historically been available to the vast majority of fighters, and I'd bet that we'll see the aggregate effects of this policy begin to blossom over the next several years.

Finally we reach my favorite part of working on a dataset like this, predictions for the future. What current fighters seem like good bets to have long and productive future careers? Which ones are set up for a rapid decline?

LONG AND PRODUCTIVE

1) Lyoto Machida: Although he's already at the 10-year mark in his career, Machida has shown no signs of dropping off. Of all the fighters in this sample, he's the one who most closely resembles the benchmark for long-lived strikers, Anderson Silva. He gets hit very little, doesn't cut much weight (if any) to make 205, and has only been KO'd once. Although he's at or near the end of his likely athletic prime, his understanding of range, movement, and footwork minimizes the potential drop-off. He could spend another two or three years near the top of the division, which would constitute a remarkable feat of longevity.

2) Anthony Pettis: Another Anderson clone. At the six-year mark in his career, he's almost impossible to hit both on the feet and on his back, and has showcased improving wrestling skills; while the Stephens fight was far from an entertaining barn-burner, the ability to impose a game plan like that when necessary (see Anderson vs. Lee Murray) is an important factor in longevity. Pettis is an exceptional talent, and there's every reason to think he could have a very long career.

3) Luke Rockhold: Gets hit very little? Check. Didn't start exceptionally young? Check. Ability to impose a top-control game plan when necessary? Check. Solid chin? Check - I don't think you can hold a Belfort spinning kick against him. Another fighter at the six-year mark, Rockhold has all the hallmarks of a guy who could last for a very long time at the top. His injury history is a concern, but Rockhold is one three-fight year away from a long-term slot in the top five of the division.

4) Phil Davis: Davis gets hit less than almost any fighter in the UFC. In fact, he most closely resembles Chael Sonnen, minus the glaring hole where his submission defense is supposed to be. Former collegiate wrestlers have an outstanding track record in terms of longevity, and while Davis is still young - only five years into his career - all the signs are positive.

5) Cain Velasquez: Currently sitting at seven years into his career, there's every reason to believe that Cain can maintain his peak until the 11-12 year mark. He barely gets hit (1.56 strikes absorbed/minute, more than a full standard deviation below the norm), can take dangerous strikers out of their game, and doesn't rely on exceptional explosiveness to get the job done. While his chin might be a concern in the future - he's been KO'd, and more worryingly, knocked down on multiple occasions - Cain's a solid bet.

6) Jake Ellenberger: Top control, a solid chin, and outstanding defense are all good signs. The only worrisome thing is his exceptionally high volume of fights (4.12 per year), which traditionally hasn't boded well, but his 80 percent finishing rate means that those fights haven't been particularly wearing on his body. If nothing else, he's a fascinating case study for that particular variable.

DON'T COUNT ON IT

1) Donald Cerrone: If I had to place a bet on one fighter declining before the nine-year mark, it'd be Cerrone. He came from a striking background, which has traditionally portended an early decline. He gets hit a very great deal (3.77 strikes absorbed/minute); although that number is skewed by the Diaz fight, in which he was hit a record 238 times, that fight is an extreme example of the norm rather than an exception. Finally, he's already 30, and the lighter weight classes have few fighters who maintain their peak past age 31 or 32.

2) Stefan Struve: He started fighting at age 17, which would be a poor sign in any weight class, but is especially worrisome at heavyweight. He gets hit an exceptional amount (3.96/minute), and his already poor chin isn't going to improve with age. Moreover, he's already close to the nine-year mark.

3) Alan Belcher: Striking base? Check. Gets hit a lot? Check. Lots of fights? Check. Severe injury history? Check. At the nine-year point in his career, there are already signs that Belcher is falling off his peak.

4) Chan Sung Jung: I hate to say this, because I'm a huge fan of the Zombie, but guys who engage in the kinds of wars he has early in his career generally don't age well. He gets hit a great deal - 3.77 strikes absorbed/minute, almost twice the average of the group with great longevity - and it isn't a function of his defense so much as his incredible pace. A fight with Aldo isn't likely to improve that number.

5) Rory MacDonald: There are a couple of reasons to be less than confident about Rory's future prospects. First, he's suffered a long string of injuries that have severely limited his time in the cage; moreover, if you're getting injured a great deal at 22 or 23, there's little reason to think that you're going to get better as you age. Second, guys who started fighting before 18 don't have a great track record for longevity; while Rory is a good deal more talented than Joe Stevenson, Manny Gamburyan, Karo Parisyan, or even Thiago Alves, there's a strong trend that clearly points in a negative direction. Finally, Rory gets hit quite a bit (2.26 strikes/minute) for not having fought the best competition. There's little reason to think that number goes down as he starts to fight the Ellenbergers, Hendricks, and GSPs of the division.

6) Johny Hendricks: This is a bit of a stretch, as Hendricks is still a young guy in the sport. Unlike Dan Henderson, who's probably the closest analogue to Hendricks' skill sets and style, he gets hit a lot (3.07/minute average) even by relatively low-volume strikers. Fighters who can stuff his takedowns and circle to their left - and there are a fair few of them at welterweight - are only going to drive that number upwards, and no matter how good his chin is right now, eventually someone will catch him. In short, unless he drastically improves his defense and expands his striking game beyond the left hand it's hard to see his peak lasting past the nine-year mark.

Longevity isn't the happiest topic. It forces us to confront the fact that time doesn't stand still, our favorite fighters won't last forever, and the end probably won't be pretty. This isn't baseball or basketball, where aging players simply get their minutes cut; aging fighters tend to end up laid out on the canvas, often in brutal fashion. Nevertheless, it's an important thing to explore and understand. How do fighters age? What drives this process? What contributes to longevity? While these two articles are far from the last word on the topic, I hope we've started to feel our way toward some answers.