Several confounding factors make it difficult to determine statistical associations between footwear and injuries in basketball, but attitudes toward shoes among National Basketball Association (NBA) players suggest both positive and negative trends with regard to potential injury risk.
By Will Carroll
There is no question that the game of basketball and the business of basketball have been revolutionized by the shoe industry. Over the last 30 years, basketball footwear has experienced a commercialization and technological advancement that hasn’t been seen in any other sport at any level. Although football cleats aren’t going to be worn to the club, a sweet pair of kicks from a collection endorsed by a basketball star are as much fashion staple as athletic equipment.
But the improvements in performance and function associated with basketball shoes have not led to any apparent decreases in injury rates among players, even at the professional level. Several confounding factors make it difficult to determine statistical associations between footwear and injuries in basketball, but attitudes toward shoes among National Basketball Association (NBA) players suggest both positive and negative trends with regard to potential injury risk. Many players’ shoe preferences tend to be dictated by fashion, which can create fitting challenges that could potentially increase injury risks. On the other hand, many players also place a premium on comfort—in relation to both the design of a shoe and the way it is worn—which could help reduce those risks.
Some players would rather deal with injuries than change shoes. Detroit Pistons forward Stanley Johnson made headlines in October 2016 for resisting suggestions from team medical staff and Coach Stan Van Gundy that he switch shoes to help address persistent pain in his left foot, particularly when pushing off.1 Although Johnson’s shoe contract allowed him to wear any model made by Nike, he continued to wear the Kobe 11 style, named for former Los Angeles Lakers star Kobe Bryant and the third most popular shoe among NBA players at the time. Johnson insisted the Kobe 11 model was “comfortable,” despite the issues. (However, in early 2017 he was seen wearing a different style, the new Kobe A.D.)
“There are often significant differences in shoes and models, both between brands and within brands themselves. Marketing drives the shoe industry, unfortunately. Because of this, there are often great-looking popular shoes supported by great athletes that function like crap!” said Bruce Williams, DPM, director of gait analysis studies for the Weil Foot & Ankle Institute in the greater Chicago area. “I will say that I have seen improvements in function over the last ten years in most shoes in most sports. That said, it does not appear that the injury rate has decreased. While I think shoes can definitely make things worse, there is an even bigger issue with team sports medical professionals not knowing how to evaluate and screen the foot properly to minimize the most common risks for a season-ending injury like fifth metatarsal fracture.”
Surprisingly, there are only five footwear manufacturers that have more than five NBA wearers. Those are Nike, adidas, Nike’s Jordan Brand, Underarmour, and relative newcomer Peak, a Chinese brand more known for its Li-Ning brand. There are 13 other companies, including well-known brands like Reebok, Spalding, and New Balance that have five or fewer players (and in most cases, only one) that wears this brand.
Shoes and injuries in basketball: A sabermetric challenge
The lack of data on both injuries in the National Basketball Association (NBA) and on who wears what shoes creates multiple issues in analyzing the relationship. I spoke with a leading sabermetric consulting firm that deals in injury information to get the most up-to-date data. (Because they contract with several teams around the league, they asked not to be identified.)
I limited this data to the 2015-2016 season for consistency and completeness. The entire data set is fixed and most players do not change shoe models during the season, though as noted, it is impossible to completely control for this because of a lack of monitoring. During this period, the NBA had 319 injuries to the foot and ankle for which shoes could have been a contributing factor.
To further control, I focused on the eight metatarsal fractures that occurred and the 187 instances of ankle sprain. The ankle sprain number is consistent with the incidence rate reported by an Australian study,5 even though that study was based on recreational players (3.85 per 1000 for the study, 4.1 per 1000 in this season for the NBA.)
I attempted to match each of the NBA injuries with a shoe. However, changes in color combinations make it difficult if not impossible to completely control for this. There are 125 instances in which there is a high degree of confidence that a specific shoe was worn at the time of a specific injury. These were identified using pictures and video, as well as the SLAMOnline shoe database.
Broadly speaking, there doesn’t appear to be one particular shoe or brand that stands out as a problem. Injuries seem to be in line with the overall percentage of shoe wearers. (That is, injuries seem to occur at the same rate regardless of shoe brand.) And, because of the wide range of shoe brands, models, and types, it’s difficult to draw any more specific conclusions.
While officials from Nike and adidas declined to speak on the record or to make available the terms or lists of their athletes, it’s relatively easy to determine which players are wearing which shoes. What’s more difficult to assess is how players wear the shoes. NBA players can go through several pair of shoes in a game—sometimes based on comfort and feel, but more often than not, on habit and superstition. Some players elect to change shoes at almost any opportunity, ignoring most principles of break-in and alleging the stiffness and out-of-the-box “freshness” of the shoe puts it at the most pure state.
David Craig, LAT, ATC, the longtime athletic trainer for the Indiana Pacers and currently a consultant for St. Vincent Sports Performance in Indianapolis, agreed with this conclusion. In his experience, shoe choice tended to be handled almost entirely by the players, and the team medical staff would just have to keep up.
“Some players would have boxes of shoes—the same, different—inside their lockers or stored somewhere. [The player] was responsible for how they broke them in unless we had customized it somehow for him with pads, orthotics, or cushions. At that point, we got more involved because we had to adjust to the player. If he changed shoes every game, we had to change along with him,” Craig explained.
What is surprising is that, with these shoes, there is little in the way of personalization or customization, particularly in terms of fit. There’s a widely held belief that endorsement deals lead to shoes that are custom designed for an athlete’s feet. Instead, the customization is more general. Representatives from both adidas and Nike told me a shoe is not made for or based on an athlete’s foot, but is guided by the athlete’s preferences.
“Some players like more support. Some like more cushion,” said Leo Chang, lead designer for Beaverton, OR-based Nike. “It’s more like a guide than a full custom. There’s no custom last or mold for an individual athlete once we get beyond a prototype stage.”
That said, some aspects of Kevin Durant’s signature Nike shoes were revisited after the Golden State Warriors’ small forward sustained a Jones fracture in October 2014, when he was playing for Oklahoma City.
“In most players, you’ll see the heel flare up first on a pressure map, then the forefoot, and then the toe. Durant actually has a lot of pressure in the midfoot, where he had the metatarsal Jones fracture,” Chang said. “We shifted the silhouette of the outsole so that it accounts for that. A lot of running shoes will sculpt away on the outer side of the midfoot, but if you sculpt away from there, you’re not giving him enough cushioning or support. We shifted that to the lateral side to help give him more cushioning.”
The players themselves seem to focus on looks as much as performance. When Durant wanted Flywire (a stretchy, socklike fabric embedded with structural filaments for support) added to his shoe, it was because of the look and its inclusion on Kobe Bryant’s shoe, not the performance aspects.
“When [Flywire] first jumped on the scene,” Durant told NiceKicks.com while discussing his new shoe,2 “I was telling my guys, ‘Man, I would love to have that on my shoe.’ It looked so nice, first of all, but I didn’t know how it played. To see Kobe in it, I was a little jealous.”
In most cases, athletes work with designers on the shoe concept within predetermined functional parameters, and the resulting design is then adapted for mass manufacturing. The customization process is more like adding options to a car than designing the car itself.
For lower extremity practitioners who work with basketball players at less-elite levels, it may be reassuring to know that even NBA stars with huge endorsement deals sometimes have difficulty reconciling fashion-forward preferences with fit and performance.
“If you love the Air system [pressurized air cells in the midsole], and you love where the KD6 Elite [his previous model] was, but you didn’t like the way it was a little slappier, didn’t bend, and was a little clunkier, those are the things that KD himself experienced,” Chang said. “On [Durant’s] previous model, he loved that Zoom sensation [more air cushioning in the heel, less in the forefoot], but he just said it felt like he was swimming in mud a little bit, because it was way too stiff and clunky. That’s something I learned a ton from, and I said, ‘Ok, I love that you hated it. I can make that better for you.’ We tried to do that.”
Aside from anecdotal reports, such as a 2013 article suggesting a run of NBA injuries in adidas endorsers,3 there is little to suggest any one shoe model or manufacturer is associated with a higher or lower injury risk. The anecdotal information tends to be based around pattern recognition more than true causal relationships.
An injury database analysis conducted in conjunction with this article also found no evidence that injury incidence in the NBA is associated with shoe brand or design (see sidebar). This parity is predictable. Although each shoe manufacturer has its own technology or methodology, the technological underpinnings of the shoes are relatively similar. Shoe stiffness, construction, friction, and cushioning tend to vary in subtle ways that seem to be based more on comfort and preference than performance.
The medical literature is similarly inconclusive about footwear and injury risk in basketball. In a 2008 study of college basketball players published in the Journal of Athletic Training,4 researchers found no difference in ankle sprain rates between shoes with a cushioned column system in the heel and shoes with a traditional heel counter.
A 2013 Australian study of recreational basketball players found ankle injuries were 4.3 times more likely to occur in players wearing shoes with air cells in the heel than those wearing shoes without air cells.5 The authors suggested, however, that recreational players wear their expensive shoes for too long, using them after the cushion, stability, and grip is compromised. In addition, the Australians noted very few of the players in their study—even those with a history of ankle injury—used tape or ankle braces, which could have affected injury rates.
These two factors are obviously not the case in the NBA, though again, replacement of shoes is inconsistent and there is also no requirement for bracing with most teams, though most players do use tape or fitted braces regularly.
Both the Nike and adidas representatives I spoke with suggested anther variable that’s entirely reliant on the player: lacing. Perhaps, because of the emphasis on comfort, many NBA players tend to lace their shoes loosely, which can compromise both the fit and the support. The actual structural rigidity, support, and fit will change each time the shoes are laced, and may differ significantly from the designers’ intentions. There is no consistency.
“Ideally, there would be a consistent and custom tension for each player, like we see with tennis rackets,” said the Nike staffer. “That’s impossible, or at least impractical, so we tend to design for a range, giving a minimum stiffness at a minimum tension.”
Nike in particular is conscious of this issue and has recently shifted away from laces on some of its shoe styles in favor of supportive stretch fabrics.
Several NBA staffers pointed out that NBA feet are, almost by definition, larger than those of the general population. While NBA players’ shoe sizes range from a relatively normal 10.5 to an astounding 20 (Brook Lopez), most teams’ average shoe size is in a very tight range between 14 and 15. Scaling shoe designs to accommodate these larger feet is typically not an issue, experts said, and the modern use of lightweight materials has limited the extent to which a larger shoe is necessarily a heavier shoe. But design efforts to minimize shoe weight also run the risk of limiting the shoe’s ability to withstand the repetitive loading associated with basketball,6-9 especially in larger players.
The area that appears most ripe for study is friction, or “stick.” A 2014 study from China suggests that, as the shoe-surface interface in basketball has evolved to allow for quicker acceleration and harder stops, the in-shoe shear stresses generated during cutting as a result could be problematic.10 Basketball could benefit from additional research on factors affecting shoe-surface interface, which has been more plentifully studied in football (American and European).
Another interesting possibility is that shoe design may not make a difference, or that the seeming parity between shoe models and manufacturers means that shoes are a neutral in the causation of injuries. The focus on comfort over performance lends to this theory, which seems consistent with that proposed by University of Calgary biomechanist Benno Nigg, PhD, in relation to running shoes and injury risk.11
Even if, on balance, footwear choices based on fashion and personal preference do not appear to have affected injury rates in basketball players, opportunities still exist for lower extremity practitioners to improve fit and function in players of all levels by matching each athlete with the most appropriate shoe. Determining that best match, however, is a complex challenge—and hopefully one that will be the focus of future research.
- Stanley Johnson’s Coach Blames His Nikes for Foot Problem — But Will He Give Them Up? CBSDetroit website. http://detroit.cbslocal.com/2016/10/18/stanley-johnsons-coach-blames-his-nikes-for-foot-problem-but-will-he-give-them-up/. Published October 18, 2016. Accessed February, 2, 2017.
- Kevin Durant Discusses the New Nike KD9 And His Approach to the Game. http://www.nicekicks.com/kevin-durant-discusses-nike-kd9-lets-just-hoop/. Published July 6, 2016. Accessed February, 2, 2017.
- Are Adidas Shoes to Blame for NBA Injuries? http://www.opposingviews.com/i/sports/nba/are-adidas-shoes-blame-nba-injuries. Published April 9, 2013. Accessed February, 2, 2017.
- Curtis CK, Laudner KG, McLoda TA, McCaw ST. The role of shoe design in ankle sprain rates among collegiate basketball players. J Athl Train 2008;43(3):230-233.
- McKay GD, Goldie PA, Payne WR, Oakes BW. Ankle injuries in basketball: injury rate and risk factors. Br J Sports Med 2001;35(2):103-108.
- Pau M, Ciuti C. Stresses in the plantar region for long-and short-range throws in women basketball players. Eur J Sports Sci 2013;13(5):575-581.
- Struzik A, Pietraszewski B, Zawadzki J. Biomechanical analysis of the jumpshot in basketball. J Hum Kinet 2014;10(42):73-79.
- Cowley HG, Ford KR, Myer GD, et al. Differences in neuromuscular strategies between landing and cutting tasks in female basketball and soccer athletes. J Athl Train 2006;41(1):67-73.
- Kelly LA, Lichtwark G, Cresswell AG. Active regulation of longitudinal arch compression and recoil during walking and running. JR Soc Interfac 2015;12(102);20141076.
- Cong Y, Lam WK, Cheung JT, Zhang M. In-shoe plantar tri-axial stress profiles during maximum-effort cutting maneuvers. J Biomech 2014;47(16):3799-3806.
- Nigg BM, Baltich J, Hoerzer S, Enders H. Running shoes and running injuries: mythbusting and a proposal for two new paradigms: ‘preferred movement path’ and ‘comfort filter’. Br J Sports Med 2015;49(20):1290-1294.