The effects of ankle protectors on lower-limb kinematics of association football players: A comparison to braced and unbraced ankles

Abstract

Association football (football) players have a high risk of injuring the lower extremities with ankles being one of the predominantly injured sites. To reduce the risk of ankle-contusion injuries ankle protectors made from ethylene-vinyl acetate foam can be used. To reduce the risk of ankle-inversion injuries ankle braces, which contain rigid plastic polymer strips located along the medial and lateral sides of the support, can be worn. However, athletes can only wear one of these devices at a time. Ankle protectors have previously been found to be effective at reducing the risk of contusion injuries by reducing forces being transferred to the ankle. Ankle braces have previously been found to reduce the risk of ankle-inversion injuries by reducing ankle-inversion angle, and ankle-inversion velocity. However, ankle protectors effect on lower-limb kinematics has previously had no attention. As the location of ankle protectors are the same as ankle braces there is a possibility that they reduce the risk of ankle-inversion injuries as well as protect against contusion injuries. Therefore, this thesis aimed to assess the effects of ankle protectors on lower-limb kinematics during sporting movements that commonly occur in football and compare them to braced and unbraced ankles. The four movements selected to be investigated were; running, a countermovement vertical jump (CMVJ), 45˚ cutting manoeuvre, and on the stance limb during kicking a football. Kinetic and kinematic data were collected from male and female participants in three test conditions for each movement; wearing ankle protectors (PROTECTOR), wearing ankle braces (BRACE) and with uncovered ankles (WITHOUT). All kinematic data obtained within this thesis were recorded using an eight-camera Qualysis motion capture system and a single Kistler force plate was used to collect kinetic data. As the main aim of this thesis was to assess the effects of ankle protectors on lower-limb kinematics, and not to investigate gender differences, throughout this thesis the data for each movement is grouped by gender and analysed separately using repeated measures ANOVAs.
The running study found that for males’ ankle protectors provided very little restriction to the ankle and did not restrict the ankle like ankle braces. Although no restrictions were seen in the coronal plane there were reductions in sagittal plane motion; ankle protectors significantly (P ≤ 0.01) reduced angle at toe-off (WITHOUT = -23.65˚, PROTECTOR = -21.69˚, & BRACE = -21.32˚), absolute range of motion (ROM) (WITHOUT = 42.66˚, PROTECTOR = 40.15˚, & BRACE = 38.34˚), and peak plantarflexion velocity (WITHOUT = -665.97˚/s, PROTECTOR = -619.33˚/s, & BRACE = -595.27˚/s) when compared to uncovered ankles. For the females significant (P ≤ 0.01) restrictions were found in the coronal plane when wearing ankle protectors for relative ROM (WITHOUT = 15.50˚, PROTECTOR = 14.37˚, & BRACE = 11.13˚) and peak inversion velocity (WITHOUT = 159.90˚/s, PROTECTOR = 140.67˚/s, & BRACE = 122.58˚/s) when compared to uncovered ankles. Additionally, there were significant (P ≤ 0.01) reductions found in sagittal plane motion for the angle at toe-off (WITHOUT = -27.35˚, PROTECTOR = -25.07˚, & BRACE = -23.86˚), absolute ROM (WITHOUT = 44.83˚, PROTECTOR = 41.99˚, & BRACE = 39.33˚), peak dorsiflexion velocity (WITHOUT = 348.29˚/s, PROTECTOR = 339.88˚/s, & BRACE = 313.78˚/s), and peak plantarflexion velocity (WITHOUT = -651.55˚/s, PROTECTOR = -593.63˚/s, & BRACE = -563.13˚/s) when compared to uncovered ankles. The running study concluded that for both males and females’ ankle protectors are only effective at reducing the risk of contusion injuries and cannot protect against ankle-inversion injuries. However, the sagittal plane reductions could possibly increase energy demand needed for locomotion and affect performance of other football related movements. The CMVJ study found for males’ ankle protectors did not restrict any plane of motion for the ankle, knee, or hip during take-off or landing and did not decrease jump height. For females’ ankle protectors were found to significantly (P ≤ 0.01) reduce jump height (WITHOUT = 0.35m, PROTECTOR = 0.34m, & BRACE = 0.33m) and this reduction was likely due to the significant (P ≤ 0.01) restrictions found in the sagittal plane for the angle at take-off (WITHOUT = -36.38˚, PROTECTOR = -33.44˚, & BRACE = -31.50˚), absolute ROM (WITHOUT = 63.36˚, PROTECTOR = 59.85˚, & BRACE = 54.99˚), and peak plantarflexion velocity (WITHOUT = -839.34˚/s, PROTECTOR = -794.05˚/s, & BRACE = -733.10˚/s) when compared to uncovered ankles. During landing ankle protectors did not restrict any plane of motion for the ankle, knee, or hip when used by the females. It was concluded that for both males and females during a CMVJ ankle protectors are only effective at reducing the risk of contusion injuries and cannot protect against ankle-inversion injuries during this manoeuvre. The 45˚ cutting manoeuvre study found ankle protectors do not restrict any plane of motion for the ankle, knee, or hip for either the dominant or non-dominant limb for males or females. This study again concluded that ankle protectors are only effective at reducing the risk of contusion injuries and cannot protect against ankle-inversion injuries. The final study investigating the effects on the stance limb during kicking a football again found ankle protectors did not restrict any plane of motion for the ankle, knee, or hip when used by males or females. This study also concluded that ankle protectors are only effective at reducing the risk of contusion injuries and cannot protect against ankle-inversion injuries during this manoeuvre.
Overall the key finding of this thesis is that ankle protectors can only protect against contusion injuries and cannot protect against inversion injuries. Additionally, the current “one size fits all” design should be re-evaluated as it can cause significant alterations to sagittal plane kinematics of the ankle for some footballing related movements. The current design of ankle protectors, could benefit from changes in material construct to either make them better at dissipating forces, by using newer materials, or by the introduction of firmer materials which are integrated into the foam to protect against both contusion and inversion injuries.