Context: Abdominal training may decrease the risk of lower extremity injuries through improved balance and postural control. Objective: To determine the effect of an eight-week abdominal-training program on center of pressure, lower extremity joint angles, and abdominal muscle activation during a single-leg drop landing. The effects of abdominal training on abdominal muscle thickness was assessed. Design: A cohort research design. Setting: Research laboratory. Other Participants: Sixty healthy physically active college-aged students participated. They were divided into three groups: Control, Chronic ankle instability (CAI), and Healthy. Nineteen Control (age = 22.0 ± 2.72 yrs, mass = 74.1 ± 13.8 kg, height = 172.6 ± 11.3 cm, BMI = 24.8 ± 3.1 %), 21 CAI (age = 22.1 ± 2.3 yrs, mass = 77.6 ± 14.0 kg, height = 175.4 ± 12.3 cm, BMI = 25.1 ± 2.6 %), and 20 healthy (age = 22.9 ± 3.4 yrs, mass = 70.9 ± 15.6 kg, height = 172.2 ± 8.9 cm, BMI = 23.7 ± 3.3 %). Subjects in the CAI group had a history of CAI and functional ankle instability (FAI). The Ankle Instability Index and the Functional Ankle Ability Measure were used to self-report CAI and FAI respectively. Interventions: The CAI and Healthy groups participated in an eight-week abdominal-training program while the Control group maintained their normal activities of daily living and level of physical activity. Main Outcome Measures: Abdominal muscle thickness was measured biweekly throughout the study. Center of pressure excursion, muscle activation, vertical ground reaction force, and lower extremity joint angles were measured during a single-leg drop landing, pre- and postabdominal training. Results: Muscle thickness at rest increased in the rectus abdominis and external oblique muscles follow training. Eight weeks of abdominal training decreased vertical ground reaction forces and muscle activation down the lower kinetic chain. Center of pressure excursion and velocity were increased following training. Conclusions: Eight-weeks of abdominal training increased abdominal muscle thickness. Training improved neuromuscular efficiency throughout the kinetic chain and may have improved dynamic postural control. Our data also suggest CAI subjects may utilize both feedforward and feedback mechanisms to maintain postural control.