Whenever you do any type of exercise, the movement of your body during the exercise is known as the range of motion. The more difficult the range of motion is, the more effective the exercise will be, because your body has to work twice as hard to perform the movement.
Bicep curls - Free Weights or Weight Training Machines
Take for the instance the classic dumbbell bicep curl. If you aren't familiar with the exercise, it is performed by standing up straight with your palms facing forward, and a pair of dumbbells held down by your sides. You'll contract your biceps to bring the dumbbells up to your shoulder height, then repeat the exercise as many times as you wish.
Using that same movement for exercise on a bicep curl machine, you should sit down, brace your upper arms on a pad, grasp 2 handles that are in front of you, then perform the same movement as above to move the handles in an upward motion.
Now, looking at the muscle contractions in this exercise, you are contracting essentially your biceps if you are using the curl machine, and that is pretty much all you are doing. When you use the machine you are sitting down, which will limit just how much your shoulders give. The machine has several muscles used in this exercise limited to the biceps, as well as the muscles in your forearms and fingers.
Limited Range of Motion with Machines
[caption id="attachment_29752" align="alignright" width="250"] Weight training Machines[/caption]
Most of the time, when using machine weights, you will always be limited as to what type of exercise you can perform. You must always follow a strict procedure, which is pretty much the same with free weights. Unlike free weights, machine weights offer a certain degree of resistance.
One of the best thing about free weights is the fact that you move a little chuck around to select the weight you want to use. Instead of dragging it over to your exercise area, you simply select it on the machine. When you are tired during a workout, this can be a blessing.