The leg extension is probably the best way to work the thigh. The thigh is scientifically known as the quadriceps. It consists of four muscles: rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. Each muscle functions to extend the knee. Instructions for the leg extension are as follows:

Select the desired weight you wish to use. This is usually done via pin selector weight stack. It may be necessary to make adjustments to the shin pads and seat position as well. Sit on the seat and place your legs behind the shin pads. Slowly extend your knee to full flexion. Return to the starting position.