If you want to build your legs, hamstring exercises are essential. Located on the rear of the upper leg, the bicep femoris (to give it its proper name) consists of two lobes, and is primarily used to help to curl the lower leg up towards the upper leg.
Of the various hamstring exercises available, the best choices are Squats, Lunges, and Leg Curls. We will look at each of these hamstring exercises in turn.
Squats are rightly considered to be the ultimate exercise for building strength and power in your legs - however, they are equally effective if your goal is simply to shape and tone your legs. Squats primarily work the quads, glutes, hamstrings, and hips, with secondary involvement of the upper and lower back, and the abdominals.
By changing the weight you use and the number of reps and sets, you can alter the way these will affect your body. For strength and power, work in the 6 - 12 reps arrange, while for toning, reduce the weight and perform high reps (15 - 20).
The second exercise that should be a part of your leg routine is lunges. As with squats, these are a great all round movement that can adapted for either strength or toning (as above).
Finally, it's worth looking at the different options for Leg Curls. Most people are familiar with them as a machine exercise, but you can also do some excellent variations using a Swiss ball. If you're not sure how to do these, ask a trainer to demonstrate them for you.