Abstract
BACKGROUND: It is well established that chronic ankle instability (CAI) is associated with reduced strength in the muscles around the ankle joint complex.
OBJECTIVE: To examine the quadriceps femoris (QF) function in individuals with CAI.
METHODS: The mechanical properties of the QF were assessed in10 physically active individuals with unilateral CAI, and were compared with 10 healthy controls. Peak torque, rate of torque development, and stretch-shortening cycle function were determined in both legs. Injured subjects were selected based on an instability index score, and were matched with controls by gender, weight, and leg dominance.
RESULTS: In the CAI group, when the injured leg's performance was expressed as percent of the healthy, the fast velocity concentric torque and rate of torque development were smaller compared to the controls'. In the same group, reduced positive work and mechanical efficiency, and increased stretch-shortening cycle contraction time were associated with the magnitude of the ankle instability.
CONCLUSIONS: CAI patients may suffer from high velocity contractility impairment in the QF of the injured side, possibly due to reduced recruitment of fast motor units. The severity of ankle instability may influence stretch-shortening cycle function, indicating reduced ability to store and reuse elastic energy.