The Effect of Football Boots on the Structure and Function of the Midfoot and the Relationship to Lower-Extremity Overuse Injuries

Lower extremity injuries appear to be a problem in the sport of football. An injury questionnaire study revealed that nearly 92% of college and university football players sustained a lower-extremity injury during a single football season and that 25% of these injuries were caused by repetitive-stress or overuse mechanisms. Since footwear has been implicated as one of the causes of lower-extremity overuse injuries, it was identified as an area that needed further investigation. It was theorized that stud placement on the sole of a football boot, with limited midfoot support, adversely affected the function of the foot which could lead to repetitive stress injuries.
The effect of a modified loading condition, with the forefoot and heel elevated to the height of a moulded stud football boot, under static loading conditions showed no differences. It was determined that in order to obtain a truer picture of foot function, dynamic data needed to be collected. Navicular drop was selected as a criterion for measurement because the height of the arch is believed to be functionally significant for the mechanics of the foot. A dynamic method of measuring navicular drop during walking was developed utilizing a ProReflex® motion analysis system. Data were collected for the barefoot condition and while wearing turf trainers, football boots, and sports trainers.
Statistical differences were found between static and dynamic barefoot navicular drop measurements. When using a large sample size, a corrolational relationship was found between the static and dynamic conditions leading to the conclusion that the foot may function similarly between static and dynamic loading conditions. However, further analysis of the timing of the movements showed that the maximum navicular drop occurred late in the stance phase and therefore static measurements might not reflect true foot function during dynamic activity.
The timing curves obtained from the ProReflex® showed that shoes do seem to impair foot function, particularly during the recovery period. All of the shod conditions demonstrated a shorter recovery period, indicating that the foot may be unable to recover fully, and subsequently, may not become a fully rigid structure for propulsion. Maximum navicular drop values were also lower for the shod conditions, with the least amount of deformation occurring with the football boot. This might be caused by the rigid sole of the shoe not allowing the foot to unlock fully so that it can absorb impact forces and adapt to varying terrain.
The effect of footwear on subtalar joint motion was also addressed using the ProReflex® system. No relationship was found between the amount of subtalar pronation or initial pronation velocity and navicular drop measurements in any of the conditions. However, motion curves showed that both structures were pronating to some extent, except the midfoot continued pronating while the rearfoot was beginning to supinate.
The analysis of the motion curves of the navicular drop and subtalar joint indicate that the timing of foot motion is more important than the amount of linear or angular displacement. The relationship between displacement measurements may be negligible when determining the effect of the amount of pronation on the risk of injury. The timing variations seen within the subtalar joint and midfoot could lead to dysfunction of other structures, specifically the soft tissues, which would have to compensate for the altered movement patterns. A weakness or abnormality could lead to a breakdown, which in turn, could lead to injury.