Bench Leg lift
Beginners and persons with lower back pain should avoid this exercise.
Sit on the edge of a bench or step-box, leaning back slightly, with both hands behind you, securing your upper-body position with your arms, whilst protecting your lower back from hyper extending (arching backwards).
Exhale and contract your quadriceps (thigh muscles), whilst using your lower abs to lift both your legs off the floor in a smooth controlled manner, aiming to keep your legs straight, feet pointing upwards.
Concentrate on lifting the legs as high as comfortable possible, whilst keeping the legs and back straight.
Inhale and slowly lower under control either back to the floor intermediates or keeping the feet off the floor to maintain the contraction throughout the muscles for advanced.

Intermediates should aim for 2 sets of 8 - 10+ slow steady reps.
Advanced aim for the above, however aim to hold in the final phase for 1 - 2 seconds.
Never force yourself to finish the desired amount of reps, by sacrificing poor technique or risk of injury.
If you find the exercise uncomfortable, lower your feet to the floor for all the reps, or alternatively keep a slight bend in the legs, aiming to progress the exercise at your own level.
You can also perform this exercise whilst seated directly on the floor, however this will increase the risk of lower back injury, so care should be taken to avoid working at speed. or lowering the feet to far to the ground.
Advanced athletes, may decide to work whilst keeping their back flat on the bench, taking their feet almost to the floor, however always work within your own limits - begin with the easier option, if you can perform this without any discomfort, then progress.