http://youtu.be/ASNNE44n_Zk
The dumbbell lateral or side raise shapes the delts – the ‘epaulettes’ of the shoulder. The delts or deltoid muscle has 3 principle parts: front, side and rear. The side or lateral portion gets a workout in this exercise and when pushing overhead. As Kirk Watt says, this exercise suits lighter dumbbells. To avoid injury, it is very important that the dumbbells are lifted with control; no swinging them up or saying, ‘Oof’ to hoist them to shoulder height. Another good indicator of having chosen a good weight lies in a sense that we can lengthen our arms through soft elbows as we lift the weight. A sense of having to draw them into us means the weight is too heavy. A good rep range for shoulders is 8 – 12. This suits the fibre type of the delts and will get the best results.
This exercise must be treated with respect to avoid injury. As the weights are lifted, the muscles on the top of the shoulders near the neck should remain relaxed. These muscles are the upper traps and their job is to lift the shoulders up. If the shoulders themselves raise when doing lateral raises, the top of our arm bone gets too close to our clavicle, narrowing the gap too much and pressing on the nerves that run through there. If this happens, we will have to stop lifting weights and endure upper body spindliness. Not to mention the pain from the trapped nerves.