Static Leg Extension
Working your muscles in a static position, will help increase the strength and overall size of the muscle, however due to the increase in internal muscular tension, this method should be avoided by persons who suffer from high blood pressure.
Keeping your back firmly into machine, place your feet under the footpad, about shoulder width apart, just above your ankle level.
Position yourself so that your knee joint is at the edge of the seat, not restricting your movement, some machines will enable you to adjust the back support position - always ask the gym staff to show you how to adjust the machine safely and securely.
Hold onto the side handles to keep your back pushed into the back support, and smoothly lift the weight up, allowing the front foot pad to roll naturally a few inches up your shin bone.
You may decide to work in either a single or both leg format, holding yourself statically in place for as long as comfortably possible, or alternatively holding for 5 - 10 seconds, returning back under control and repeating.
Always make sure that your leg muscles have been fully prepared by warming up the muscles with a combination of lighter lifting exercises and a good stretch. The weight you should aim to use, should only be around 50% of your normal lifting weight.