The primary muscles involved are the quads, glutes, and hamstrings. Secondary are your core abdominal muscles and lower back. Like most leg exercise the incorporation of the abdominal muscles is utilised in this exercise – hence the importance of training legs for good abdominal muscle development. 

To perform this exercise sit in place on the leg press machine with your feet about shoulder width apart and firmly planted on the platform with your toes pointing forward. Push up with both legs, driving through your quadriceps muscles. Make sure you feet stay firmly planted on the platform as you lower the weight slowly. Go down as far as possible – so choose a weight that allows you to use a full range of motion, and not one that is too heavy where you are only performing half repetitions.  By utilising a full range of motion you will be stimulating maximum muscle fibres.

It is also very important to not lock out at your knees at the top of the movement. This is a common mistake at most gyms and can put unnecessary stress on your knees and also releases tension from your legs during the exercise.