Apparatus (20) is provided for improving athletic performance of a user, including a flexible insole (40), adapted for insertion into a shoe, the insole shaped so as to define one or more chambers (22, 24). The apparatus also includes a stimulator (50) and a control unit (30). The control unit is adapted to detect respective pressures in the chambers, and to drive the stimulator to apply a stimulation to the user responsive to the detected pressures and a desired parameter of athletic performance.