A regular, or fixed, dumbbell is a set weight. You most commonly see these dumbbells in commercial gyms and fitness centers. You cannot change the weight of a regular dumbbell, but you can change the weight of an adjustable dumbbell, available as a "selectorized" or plate-loaded unit. Either type of dumbbell has benefits and drawbacks to using it.
Regular dumbbells are available in a hex or pro style. The weight heads on a hex dumbbell have six sides; the weight heads on a pro dumbbell are circular. Hex dumbbells start at 1 pound and go up to 100 pounds per dumbbell. Pro dumbbells also start at 1 pound, but they go up to 150 pounds or more per dumbbell. Regular dumbbells have either a painted enamel finish or a rubber coating on the weight heads. The rubber coating protects your floors from scratches and marring.
Adjustable dumbbells are also available in two styles. A plate-loaded adjustable dumbbell is a small, 12- to 15-inch bar with end sleeves that hold standard weight plates. The durability of the bar and the length of the weight sleeves limit the amount of weight you can load on the dumbbell.
A selectorized dumbbell is a set of weights in one dumbbell block. The handle sits inside a series of weighted plates. Turn a knob or slide a weight pin in the block to select the desired weight. Only the selected weight pulls out of the block with the handle. Selectorized dumbbells vary in weight, depending on the brand and model. Some offer up to 45 pounds per dumbbell; others offer up to 100 pounds per dumbbell.
Regular Dumbbell Benefits
Because of the nature of the dumbbell, adjustable dumbbells are more likely to come loose --- possibly causing injury --- than a regular dumbbell. Use weight collars to hold the plates on a standard adjustable dumbbell. If the collar loosens and falls off, the plates will fall off the bar, too. If you don't lock a selectorized dumbbell, the handle may detach from the selected weights. Any of these scenarios could result in injury.
You can change out weights with regular dumbbells more quickly than you can with adjustable dumbbells --- just grab a different set of dumbbells.
Adjustable Dumbbell Benefits
Adjustable dumbbells take up significantly less space than regular dumbbells. If you use dumbbells for a variety of exercises, you need a variety of dumbbell weights. Six or eight sets of regular dumbbells take up considerable space, but you can get 12 to 16 sets of dumbbell weights in one selectorized dumbbell block. This benefit is the main reason you might choose to use adjustable dumbbells in your home gym.