Football injuries are a regular occurrence no matter what level an athlete participates.

Injuries in football are associated with many complex factors , such as the position that an athlete plays, the athlete’s age, their muscle tightness, and joint flexibility. Football injuries are also affected by things such as the weather, field conditions, equipment such as shoes, and the interaction of the shoe itself to the surface played upon [1–6].

The cleat patterns of football shoes and their relationship to the type of surface they are used upon have been blamed for all types of lower extremity injuries, from toe sprains and metatarsal fractures, to mid-foot and ankle injuries, to shin splints and knee injuries as well. Often the shoe-surface interface is to blame, but indeed the construction and overall stiffness and function of the shoes themselves, as well as the overall cleat pattern, can affect lower limb injuries of many types [3–14].

What relationship, if any, do cleat patterns have to rotational traction and potential injury in football? Translational traction is needed for players to run fast and to start and stop quickly. Rotational traction is necessary for turning or pivoting and quickly changing direction. An increase in rotational traction can lead to an increased rate of injury and any increase in translational traction , forward and backward movements, tends to have less overall risk of injury [9, 13].

One of the first large studies on football cleat design and Anterior Cruciate Ligament (ACL) rupture risks, done over a 3-year period, was published in 1996. This was done with high school athletes using four different types of football shoes. They found that shoes with longer cleats at the edge of the shoe were associated with higher risk of ACL rupture [8].

The authors demonstrated that increased rotational traction can lead to “foot fixation,” which they found to be a common factor in ACL injuries and also with other ankle and knee injuries. High frictional forces between the cleat and the playing surface result in this foot fixation and may be partially responsible for knee ligament injuries. The athletes that are injured the most, 80% of the time, are defensive backs, linebackers, wide receivers, and running backs. All of these players do a lot of plant and cut maneuvers when playing their positions making them more susceptible to these injuries.

Axial loads can be up to six times body weight when an athlete plants and cuts.

“Cleat-catching”—occurs mainly in grass, when a cleat becomes “caught” or “dug into” the natural grass and may lead to increased frictional and rotational forces in that area where the shoe is caught. “Crow-hopping”—seen usually on artificial turf, occurs when a turf shoe hits a peak load limit and then suddenly releases in a hopping motion [12, 14]. These types of shoe-surface effects can cause an increase in shear, braking, or rotational forces along with friction resistance. All of these forces, combined with the cutting motions of football, can result in valgus and axial moments that can be transmitted proximally and lead to injury at the foot, ankle, and knee [12–14].

A study looked at the association of lower limb injuries versus soccer shoe design. The authors determined that sports-medical teams need to make sure that players are wearing appropriate shoes according to a player’s individual physiology and specific position played [15]. The authors seemed to imply that if this is done that it should decrease certain risk factors for injury. Traction in footwear is good up to a point. Beyond that beneficial point, though, the risk of injury to the athlete increases incrementally [9, 13].

The effect of weather and the playing surface in relation to football shoes can also affect the risk of injury [16]. A study examined studded cleats and pressure loading patterns during cutting maneuvers on both natural grass and artificial turf with in-fill. On turf, higher central forefoot and lesser toe pressures were noted vs. grass surfaces. In contrast, with grass there were higher medial forefoot and lateral mid-foot pressures. The authors noted that this has something to do with the “Cleat-Catch” mechanism mentioned above [12, 14]. This has been shown statistically to occur with deeper cleats or studs catching on grass and leading to a higher incidence of ACL injuries in the Australian Football League [15].

A study on soccer cleats looked at the plantar pressures of amateur soccer players wearing both bladed and studded soccer cleats on artificial turf. The players performed a straight run and a run cutting at a 60° angle. They found that bladed cleats showed higher pressures under the lateral aspect of the foot and studded cleats showed higher pressures on the medial aspect of the foot. The center of pressure in the shoes with the studded cleats mimicked more normal shoe pressures much more than the shoes with bladed cleats. These results indicate that bladed cleats could predispose athletes to lateral metatarsal fracture risk [6, 17].

Another study comparing five types of rugby shoes on natural grass surface measured stiffness and peak torque of the shoes [17]. These shoes were then compared to studies of soccer shoes that were previously published in the literature. The authors found that the rugby shoes tended to be stiffer than the soccer shoes [17]. They determined that in the shoes studied there was a higher peak rotational stiffness in the shoes with “the longest studs and a small tip diameter.” The authors apparently felt this specific cleat configuration allowed for deeper penetration of the stud into the ground and likely would lead to more rotational traction and increased torque. The authors also commented that a shoe with more stiffness would likely bother players who moved and cut faster than other players who did not participate in much movement [17].

Frictional resistance between the cleat and the surface of play is nonlinear in regard to actual or physiological conditions [11]. According to this study, most shoes are tested in a lab and not under true physiological conditions. The authors felt this makes a huge difference in the testing results. They suggested taking the shoe manufacturers suggestions as to how the shoe will function “with a grain of salt.” To be safe, using a lower friction cleat type would be suggested for athletes returning from injuries until they are fully recovered. The specific arrangement of cleats on the sole of the shoe does not seem to make much difference in rotational traction. Suffice to say, any shoe that is said to give an increase in traction for cutting is likely a high-risk shoe for injury at the ankle and knee [14]. In general, shoes making these claims would likely have deeper and larger clusters of studs or spikes at the plantar shoe edges, versus a shoe with low translational traction, more likely to have larger clusters of studs that are much more shallow and rounded, i.e., turf shoes or cleats [14]. One study showed that turf cleats have the lowest torque, or rotational traction, of all tested football shoes [9].

On a contradictory note, another study comparing several different types of soccer shoes worn by professional soccer players had the players run straight ahead and do a sidestep cutting technique at both 30° and 60°. The researchers tracked knee internal tibia axial and valgus moments, anterior joint forces, and flexion angles. Ultimately their conclusion was that there were no differences in forces measured between types of soccer shoes worn. They did feel that it is more the cutting maneuvers themselves that lend risk to knee injuries, with less influence overall from the shoes themselves [6].

Finally, the NFL, FIFA, and the governing body of Rugby all do testing on shoes to determine rotational traction [12]. Unfortunately these numbers are not released to teams or medical staffs. For the well-being of these leagues and their players, this practice needs to change. Important research results such as these should be shared so that players, teams, and medical staffs can inform their players on what may be best for them depending on the weather and type of turf. Research like this can substantially help reduce injuries.

How does the upper construction of a football shoe affect its function in relation to injuries? In respect to rotational stiffness (previously discussed), shoes that had the highest degree of stiffness were shoes with a combination of both a very stiff sole and upper. According to two studies on shoes using cadaveric feet and legs [18, 19], football shoes with more flexible uppers are less likely to be involved in injuries to ankle ligaments vs. a shoe with a more rigid upper. The authors in both studies evaluated cadaveric ankle/foot complexes and put high and low-top football shoes on the study specimens. They then externally rotated the ankle/foot complex to test the upper flexibility and likelihood of injury. They noted that [18, 19] medial ankle injuries occurred in five of six stiff shoes vs. three of six in the flexible shoes. Ankle syndesmotic injuries were seen in five of six stiff shoes tests vs. four of six tests in flexible shoes. There were also combination injuries of both the syndesmosis and medial ankle ligaments; however only one of six of the tests in flexible shoes had a combination of both, while five of six stiff shoe tests showed a combination injury pattern. Bone injuries occurred more often in those specimens tested with stiff shoes and less in flexible shoes. Ultimately the authors feel that there may be fewer ankle injuries in shoes with a more flexible upper compared to a shoe with a stiff upper [18, 19].

In another study looking at stiffness issue in shoes [9], one of the shoes tested had a very pliable upper and also had a much lower rotational stiffness at the sole or cleat area of the shoe. Surprisingly the authors found that this still allowed for rotational traction even after the shoe had reached its breakaway point, the point where the shoe released from the field surface [9]. The authors felt that this type of shoe may allow for a lower incidence of overall injury in athletes who perform cutting maneuvers, while still allowing for good translational and rotational traction and decreasing both ankle and knee injury risks.

Finally a study looked at comfort of football shoes according to athletes [19]. The authors found that athletes rated the high-top cleats lowest because they were considered to be uncomfortable and heavy. The mid- and high-top cleats were deemed most stable by the athletes in the study. The overall conclusion of the authors was that ankle motions can be limited by high-top cleats without negating performance. Unfortunately, the athletes did not rate the heavier, more stable cleats as favorably as the lighter mid-top and low-top cleats indicating that the athletes themselves may choose a shoe that is more likely to contribute to an injury [19].

The final shoe component to discuss is the segmental and overall stiffness of the sole of football cleats, also known as LBS, or longitudinal bending stiffness. The stiffness of the sole of football shoes is vitally important when considering injury risk. Often stiffer shoes are sought out by certain playing positions to protect against injuries such as turf toe. Quicker cutting athletes have been suggested to prefer less stiff shoes [20]. Regardless of preference, the LBS of the shoe, if too stiff, can affect injury risk above the level of the foot.

A study comparing landing mechanics of running shoes, bladed soccer cleats, and soccer turf shoes found that increased sole stiffness, LBS, in bladed soccer cleats may affect the need for increased plantarflexion and dorsiflexion of the ankle joint during landing. This, according to the authors [21], could increase the risk of injury to the Achilles tendon and should be watched carefully by the medical staff, and studied much more intensely during running and other soccer maneuvers . Another suggestion from the authors was that each athlete be screened in a much more detailed fashion for their landing mechanics according to their specific sporting conditions of play and in relation to the specific shoes to be worn for competition.