Context: An arthrogenic muscle response (AMR) of the soleus and peroneal muscles has been previously demonstrated in individuals with chronic ankle instability (CAI), but the presence of AMR in muscles acting on joints proximal to unstable ankles has not been previously explored.
Objective: To determine if AMR is present in the quadriceps and hamstrings muscles of those with and without unilateral CAI.
Design: Case control.
Setting: University research laboratory.
Patients or other participants: Twenty subjects with unilateral CAI (12 males, 8 females: age = 19.9 +/- 3.7 years; height = 170.3 +/- 15.6 cm; mass = 78.0 +/- 23.1 kg) and 21 controls (16 males, 5 females: age = 23.2 +/- 5.4 years; height = 173.9 +/- 12.7 cm; mass = 87.2 +/- 24.6 kg) with no previous ankle injuries.
Main outcome measure(s): The central activation ratio (CAR), a measure of motoneuron pool excitability during maximal voluntary isometric contraction, for the hamstrings and quadriceps muscles was measured in both limbs using the superimposed burst technique.
Results: The CAI group demonstrated quadriceps CARs that were significantly larger in their involved limbs (.87 +/- .09), as compared with their uninvolved limbs (.84 +/- .08), whereas no significant side-to-side difference was seen in the control group (sham involved = .80 +/- .11, sham uninvolved = .81 +/- .11). When values from both the involved and uninvolved limbs were averaged, the hamstrings CAR was significantly lower for the CAI group (.94 +/- .03) than for the control group (.96 +/- .03).
Conclusions: Arthrogenic inhibition of the hamstrings muscles bilaterally and facilitation of the quadriceps muscle ipsilateral to the involved limb were noted in subjects with unilateral CAI. Motoneuron pool excitability appears to be altered in muscles that act on joints proximal to the ankle in those with unilateral CAI.
Keywords: ankle sprain; functional ankle instability; muscle inhibition.