Pin load selection machines are exercise machines that use a pin to select the desired weight for the exercise. These machines typically have a stack of weight plates with a pin that can be inserted into the selected weight plate to add resistance to the exercise. Seated leg curl machines are designed to target the muscles in the back of the thigh (hamstrings). The user sits on the machine with their legs extended in front of them and places their ankles or calves under a padded lever. By flexing the knees and curling the legs towards the buttocks, the hamstrings are engaged and contracted. Seated leg extension machines, on the other hand, target the muscles in the front of the thigh (quadriceps). The user sits on the machine with their legs extended in front of them and places their shins or ankles under a padded lever. By extending the knees and straightening the legs against resistance, the quadriceps are engaged and contracted. Both seated leg curl and leg extension machines are commonly found in gyms and fitness centers, and they provide a safe and controlled way to strengthen and tone the leg muscles. The pin load selection feature allows users to easily adjust the weight resistance to their desired level, making these machines suitable for users of different fitness levels and abilities.