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A dumbbell is a piece of equipment used in weight training. It is now referred to as a free weight. It is a weight that is held in one hand. Dumbbells therefore normally come in pairs. The forerunner of the dumbbell was the ones used in India for more than a millennium, shaped like a club. The design of the "Nal" as the equipment was referred to can be seen as a halfway point between a barbell and a dumbbell. It was generally used in pairs, in workouts by the wrestlers and others wishing to increase strength. Dumbbells, as a word originated in Tudor England—the devices used for ringing church bells were widely known for their impact on increasing muscle size, creating a trend in the 16th Century which saw rich young men installing similar devices in their homes, consisting of a pulley with a weighted rope which the user pulled as though they were ringing a church bell. These were known as "bells", but as there were no actual bells on the end of the pulling ropes and were silent, they came to be known colloquially as "dumb-bells". Over the centuries, the pulley and weighted rope fell out of fashion, leaving just the weight. By the early 19th Century, the familiar shape of the dumbbell, with two equal weights attached to a handle, had appeared. There are currently two main types of dumbbell:
- Adjustable dumbbells consist of 14 inch (35 centimetre) long steel bars that are one inch (2.5 centimetres) in diameter. They look like miniature barbells. The centre portion is engraved with a crosshatch pattern (knurling) to help users get a good grip. One to 40 kg of cast iron weight disks (plates) are slid onto the outer portions of the dumbbell to obtain the desired total weight. These weights are secured with clips or collars. A "spinlock" dumbbell's outer portions are threaded, and the collars are large nuts that screw on and secure the plates through friction.
- Fixed-weight dumbbells are weights created in a dumbbell shape. Expensive varieties consist of cast iron coated with rubber. Cheaper versions consist of a rigid plastic shell that is filled with concrete.
Due to their flexibility, dumbbells can be used in all types of resistance weight training, but the most popular dumbbell exercises remain the Bench press and the Bicep curl.
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