Researchers have reported increased variability in frontal-plane movement at the ankle during jumping in individuals with chronic ankle instability (CAI), which may increase their risk of recurrent ankle sprain. It is not known if this behavior is present during running gait or how fatigue affects the amount of frontal-plane-movement variability in individuals with CAI. To investigate the amount of roll-angle variability at the foot during a fatiguing exercise protocol in participants with CAI. Controlled laboratory study. Motion-analysis research laboratory. A total of 18 volunteers with CAI (10 men, 8 women; age = 29.8 ± 9.2 years, height = 175.8 ± 11.2 cm, mass = 75.4 ± 10.7 kg) and 17 volunteers serving as controls (8 men, 9 women; age = 28.2 ± 6.3 years, height = 172.3 ± 10.6 cm, mass = 68.8 ± 12.9 kg). Kinematic data for foot position were collected while participants performed a functional fatigue protocol based on shuttle runs. Variability (ie, standard deviation) of the roll angle of the foot about the x-axis, corresponding to inversion-eversion, was measured at 2 discrete times: 50 milliseconds before foot strike and 65% of stance. No differences in roll-angle range or variability were observed between limbs in either group. At 65% of stance, we found a main effect for time, whereby both groups demonstrated decreased roll-angle ranges at the end of the fatigue protocol ( P = .01). A between-groups effect in the roll-angle variability at 65% of stance was noted ( P = .04), with the CAI group exhibiting higher levels of variability. No between-groups differences were observed at 50 milliseconds before foot strike. Chronic ankle instability is a complex, multifactorial condition that can affect patients in diverse ways. Identifying excessive foot-position variability in particular situations could potentially inform targeted rehabilitation programs.
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