Dumbbells are one of the most widely used weight-training equipment pieces. One dumbbell consists of two equal weights that are attached to a handle, and the weights can be fixed or removable. The main reason why people use dumbbells is to build and tone muscles, and they can be used to develop muscles in most parts of the body. Dumbbells come in many different weights and sizes, and they can be made of metal, concrete or other materials.

The concept of the dumbbell was first introduced nearly 2,000 years ago. The ancient Greeks invented a piece of equipment called the haltere, which was a crescent-shaped stone with a handle. This forerunner of the dumbbell was used as a lifting weight as well as a weight in long jump events. Another kind of "dumbbell" that was invented during the ancient times was the "nal." This equipment was used by the Indians for more than a thousand years, and it resembled a club. It was longer than a dumbbell but shorter than a barbell, and it was used by bodybuilders, wrestlers and sportsmen to build muscle size and strength.

The word "dumbbell" was created during the Tudor era in England. At that time, athletes were using hand-held church bells to train their arms and upper bodies. Since the bells were making a lot of noise during training, they decided to remove the clappers. As such, the bells became "dumb," and they called the equipment the "dumbbell."

Presently, there are three main types of dumbbells: adjustable dumbbells, fixed weight dumbbells and selectorized dumbbells. Adjustable dumbbells are made of metal, and their handles feature a crosshatch pattern to give users a better grip. The weight disks can be easily slid onto the ends of the handle and secured with collars or clips. Fixed-weight dumbbells have weights that cannot be removed, and they are either made of cast iron or plastic shells filled with concrete. Selectorized dumbbells also have adjustable weights, and they offer a more convenient way for users to change weights. Weights can be easily changed by moving selector pins or turning a dial.

Over the years, many new techniques of using dumbbells have been developed, and presently, they can be used to train almost every part of the body. Some of the more common dumbbell exercises include decline seated bicep curls, hammer curls, preacher curls, French presses, overhead triceps extensions, triceps kickbacks, flat and incline chest presses, flat and incline chest flies, lateral raises, seated shoulder presses, front raise, reverse flies, upright rows, shrugs, lunges, half squats, seated calf raises and single-leg calf presses.

There are a number of dumbbell exercise rules that you can follow to minimize the risk of injuries and gain better results. Before you begin your dumbbell training, do some warming up to prepare your muscles for the workout. Make sure that you choose the right dumbbells, because you may over-strain your muscles if the weights are too heavy. If you feel pain when doing an exercise, reduce the weights or repetitions. If the pain continues, you have to stop exercising and take a rest. When you start a new exercise, it is best that you try the lighter weights first.