SPD locks, technically called trunks, are metal components that are mounted on the sole of special cycling shoes, so-called treters. Their purpose is to create a firm but detachable connection between the shoe and a compatible foot pedal. SPD stands for "Shimano Pedaling Dynamics", a system developed by Shimano that has become one of the most widely used standards, especially in mountain biking. With this combination, the cyclist can not only push down into the pedals with force, but also actively pull their foot upwards during the turn. This increases the efficiency of power transfer and makes pedalling smoother. At the same time, the foot stays firmly on the pedal and cannot slip off, providing better control of the bike in technical terrain. The foot is released from the pedal by a simple and natural movement, namely by turning the heel sideways.
