This invention relates to improvements in foot brakes for bicycles of the type that when turning the pedals in the direction opposite to forward, a mechanism is set in motion which prevents turning of one of the bicycle''s wheels. This mechanism consists of lever including an annular portion coupled to the pedal and a lug pivotly fixed at one end of a guiding and joining structure which slidingly housed a portion of a bolt, the other portion of which is fixed to a yoke which is the brake as such.