Differences of ground reaction forces and kinematics of lower extremity according to landing height between flat and normal feet.

The study compared lower extremity kinematics and kinetics between male subjects with flat and normal feet when landing on both feet from platforms at different heights. Ten subjects with a flat feet arch and 10 subjects with a normal foot arch were recruited. They performed a double limb drop landing from 20, 40, and 60 cm onto a force-plate. A three-dimensional motion analysis system, force plates, and electromyography were used to analyze lower extremity kinetic and kinematic data. The GRF and angle of sagittal plane significantly increased with landing height in the flat foot group. In particular, hip joint angles at a height of 60 cm were significantly greater. The electromyography values were significantly higher for the tibialis anterior and vastus lateralis muscles, but were significantly lower in the abductor hallucis, gastrocnemius, and biceps femoris muscles in the flat foot group. GRF, joint angles, and muscle activity patterns in the lower extremities increases more with height in flat footed individuals than in people with a normal foot arch. Flat feet may aggravate the risk of shock on landing from a height; this might be ameliorated by a compensatory strategy at the hip joints to facilitate load distribution.