Context: Selected muscles in the kinetic chain may help explain the body’s ability to avert injury during unexpected perturbation. Objective: To determine the activation of the ipsilateral rectus femoris (RF), gluteus maximus (MA), gluteus medius (ME), and contralateral external obliques (EO) during normal and perturbed gait. Design: Single-factor, repeated measures. Setting: University research laboratory. Participants: 32 physically active, college-age subjects. Intervention: Subjects walked a total of 20 trials the length of a 6.1-m custom runway capable of releasing either side into 30° of unexpected inversion. During 5 trials, the platform released into inversion. Main Outcome Measures: Average, peak, and time to peak EMG were analyzed across the 4 muscles, and comparisons were made between the walking trials and perturbed trials. Results: Significantly higher average and peak muscle activity were noted for the perturbed condition for RF, MA, and EO. Time to peak muscle activity was faster during the perturbed condition for the EO. Conclusion: Rapid contractions of selected postural muscles in the kinetic chain help explain the body’s reaction to unexpected perturbation.
Keywords: ankle, dynamic stabilization, electromyography, inversion