For the past forty years footwear traction has been thought to be one of the causes of noncontact lower extremity injury in sport. Previous studies have shown that rotational traction was associated with ACL injury, however, no studies have determined the relationship between footwear traction, both translational and rotational, and all lower extremity non-contact injuries. Therefore, the purposes of this thesis were to 1) determine if a relationship exists between an athlete’s specific footwear traction (both translational and rotational) and lower extremity non-contact injury and 2) determine how independently altering translational and rotational traction affects ankle and knee joint loading.

Over the course of three years, 555 athletes had their footwear traction tested on the actual playing surface;​ either an artificial or natural grass field. The athletes were followed over each season and any injury that they sustained during a game was recorded by certified athletic therapists on site at the field.

No differences in injury rate were seen between the artificial and natural grass surfaces. A relationship was found between rotational traction and lower extremity non-contact injury, with increases in rotational traction leading to an increase in injury rate. A relationship was also seen between translational traction and injury with the mid-range of translational traction leading to a higher injury rate.

To determine how translational and rotational traction affect injury mechanism, three shoes were constructed that had independent alterations in translational and rotational traction. The footwear conditions consisted of a control shoe, a low rotational traction shoe and a high translational traction shoe. Joint loading was calculated with inverse dynamics on 10 athletes performing a v-cut and an s-cut movement in the three footwear conditions.

The results indicate that both rotational traction as well as translational traction can affect the ankle and knee joint loading during football related movements. Coupled with the results of the injury study, although less clear for translational traction, it is believed that these increases in joint loading (joint moments and angular impulses) in the transverse and frontal plane are one of the possible mechanisms in terms of lower extremity noncontact injury