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SINGLE-SUBJECT ANALYSIS OF PHASE-SPECIFIC FORCE AND TIME VARIABLES DURING VERTICAL HOPPING IN CHRONIC ANKLE INSTABILITY

Abstract

Jeffrey Simpson1, Nicole Rendos2, Hoon Kim3, John Harry4. 1University of West Florida, Pensacola, FL. 2Emory University, Atlanta, GA. 3University of North Carolina-Chapel Hill, Chapel Hill, NC. 4Texas Tech University, Lubbock, TX.

BACKGROUND: Altered lower limb movement dynamics are associated with chronic ankle instability (CAI), but are often presumed by the homogeneity of CAI cohorts with aggregate group comparisons. Single-subject analyses could reveal unique patient-specific movement adaptations within a heterogeneous cohort of CAI in which aggregate group analyses might identify null findings. This study compared phase-specific force and time variables during single limb vertical hopping in participants with and without CAI using a single-subject analysis approach. METHODS: Individuals with CAI (n=25; 13M, 12F; age: 24±3y; height: 168.3±12.9cm; mass: 72.2±15.2kg) and matched controls (n=25; 13M, 12F; age: 25±4y; height: 172.5±6.1cm; mass: 70.8±9.7kg) completed 3 trials of 5 consecutive single limb vertical hops on a force platform. Participants with CAI completed the hopping task on the affected limb and matched controls used their preferred limb. Vertical ground reaction force data was used to identify eccentric and propulsion phases for the middle 3 hops of each trial (e.g. 9 total hops analyzed). Peak force, time to peak force, and phase time were computed for eccentric and propulsion phases. The Model Statistic procedure (α=0.05) and Cohen’s D effect sizes (d) was used to test for significant differences between each participant with CAI to an aggregate group mean of the control group. RESULTS: A total of 10 CAI participants exhibited less peak propulsive force (CAIrange: 15.16-21.07 N/kg; mean difference: 4.38±1.99 N/kg; d=0.80-3.39), 8 CAI participants displayed longer time to peak propulsive force (CAIrange: 0.06-0.43 s; mean difference: 0.11±0.05 s; d=1.58-8.03) and longer propulsion phase time (CAIrange: 0.22-0.56 s; mean difference: 0.15±0.12 s; d=0.82-4.21) compared to controls. Additionally, 10 CAI participants displayed less time to peak eccentric force (CAIrange: 0.07-0.11 s; mean difference: 0.04±0.02 s; d=1.00-2.91) than controls. CONCLUSION: Individuals with CAI displayed differences during the propulsion phase of repetitive hopping on the affected limb. This single-subject analysis approach could help further understand patient-specific impairments associated with CAI during dynamic tasks.

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