Does Zion Williamson’s frame make him injury prone?

Zion Williamson’s injury has brought about questions about his long-term health and weight. Does his size actually make him injury prone?

Most iterations of the NBA Draft have a front-runner. For one reason or another, one player usually asserts themselves as far and away the best prospect of the class, or at least the number one pick. Last year, with Luka Doncic and Deandre Ayton competing for headlines, was an outlier. Instead, we usually see something like what we have with Zion Williamson this year — a player who is a clear cut above the rest of his peers.

However, that doesn’t stop the human mind from injecting doubt and skepticism into the argument. Whenever there is a clear top pick choice, inevitably there will be a crowd that second-guesses the consensus. Ben Simmons didn’t win enough and quit on LSU, and that led to people putting Brandon Ingram on par with him. Anthony Davis was thought to be too thin for the NBA. People focused on how Karl-Anthony Towns didn’t play 30 minutes a game, ignoring how dominant he was in the minutes he did play. Luka Doncic was doubted for his seeming lack of athleticism and the fact that he didn’t play in college, despite a mountain of evidence that he was succeeding on a higher plane of basketball. And this year, Zion Williamson is too heavy to be this athletic, and must be injury prone.

This has been a narrative throughout the year, but it really picked up after the first Duke – North Carolina game, when early in the first half Williamson tried to make a dribble move and slipped, causing a mild knee sprain that has kept him out since. Williamson’s unnatural frame — 6-foot-6, with a reported weight of 285 pounds — and freakish athleticism is something we haven’t seen before, and that has caused people to wonder — is Zion more prone to significant injury than your average player because of his weight?

The rationale behind this is a simple physics problem. Force equals mass times acceleration, and the idea is that if you have more mass than most people, and you can accelerate more quickly than most people, you’re probably causing more force — not just outwardly, but on your own body as well. Memorable injuries to explosive players in the past — Zach LaVine’s ACL tear and obviously Shaun Livingston’s devastating injury come to mind — color our perception as well. That’s made Williamson’s injury — a freak accident caused by Williamson slipping and his shoe literally exploding — proof of the theory that he’s destined to be undone by some major injury in his future.

However, when you look at data from injury surveillance done by the league and the sports medicine community, is that actually the case? Are bigger, more explosive players actually more prone to injury than their counterparts, or are we biased by what we see and remember? To answer that, I dug around for some injury tracking data that may help us figure this out.

The biggest help is the National Basketball Association Epidemiology study, published in 2010 using data from the 1988-89 through 2004-05 season. Unfortunately, there’s no new data since then for my search, but this gives us 17 years of injury data in a time when strength and conditioning weren’t on par with where it is today. The study found no significant correlation between injury rate and height or weight, and while this is simplistic — it’s across all heights and weights, and there’s no analysis between the interaction of the two — it does show that the mass part of the force problem probably isn’t that significant.

We can also use NFL data to help us, given that Zion is the size of a large defensive end or small offensive lineman. An NFL study was performed for the 2012-2014 seasons and looked at injury rate by position. You would expect, using common sense logic, that offensive and defensive linemen would be pretty high up the list, but they were the two position groups that were injured the least often per 1000 “athletes at risk,” an estimate of the number of snaps a player sees.

But what about more high force injuries? It’s not assumed that Zion is going to be suffering more ankle sprains because of his weight. The concern is for more long-term injuries, like ACL sprains. What we see does hint at some risk. Military patients showed an increased risk of ACL injury due to Body Mass Index (BMI), and similar results have been found in pediatric patients. But in these studies, the BMI alone was not the only culprit, and it’s a similar case in other major acute leg injuries.

That multi-factor risk is why the cause for concern for Williamson is overblown. A higher BMI might be related to increased risk of ACL tears, but it’s far from the most problematic. Most knee injury risk studies focus far less on weight and far more on things like conditioning, and biomechanics, and consistently return far more concrete risk from these things than weight alone. In particular, jump landing and pivoting mechanics — the way the leg bends to be able to absorb force when a player comes down from a jump, and the coordination of the way a player pivots – are the most predictive factors for ACL injuries, outside of gender (women suffer more ACL injuries). Essentially, whether or not Zion’s knees buckle in when he lands or changes directions is dramatically more important than whether he’s 285 or 270. And while Zion’s knees do collapse in slightly when he lands, it’s not dramatic (I’d argue Ja Morant, who is much more out of control with his landings when he attacks the basket, is more of a risk), and his coordination does give confidence that this aspect isn’t going to be an issue.

Conditioning and injury history are also important factors. If a player has a previous history of knee injury, they’re more likely to have another one; if a player isn’t in good shape, they’re less likely to maintain those good mechanics and more likely to suffer injury. If there’s a concern for injury with Zion, it’s here. He obviously doesn’t have a previous history of injury, but his conditioning has been a question, somewhat reductively because of the weight and partly because of his minute load, which has been spaced with frequent short rests to keep him humming. But conditioning is also the most treatable of these issues, and something that’s probably going to improve. If he gets into better shape to hold up in an 82-game season, he’s going to be fine — not to mention that it’ll probably mean shedding 10 pounds, which helps solve the supposed force problem, too.

Zion Williamson is a freakish athlete in an unconventional body. That makes him tougher to project in terms of injury risk than other players if you don’t know what to look for. But if you do, you’ll see why Zion isn’t the injury risk that most people think he is. Zion isn’t a major risk to tear an ACL or blow an Achilles because of his weight — if anything, he’s more likely to develop degenerative problems early on, but that means when he’s in his mid-30s, long after he’s established a good return on investment for the team that drafts him. Zion is one of the most powerful and explosive players in this generation of players, and he’s built like a brick wall. But that doesn’t mean he’s any more likely to get injured than any of the other freakish athletes that we’ve seen in the last few years.