In fitness, variable resistance refers to a type of weightlifting in which the amount of resistance that the weight applies will vary throughout the exercise's motion. As a result, the muscles must achieve a more consistent level of exertion to complete the lift and thus receive a more intense overall workout. In order to provide different amounts of resistance at different times, these exercises require complex machines designed specifically for this type of athletic training.
Despite what the name implies, variable resistance exercises actually provide a more constant resistance to the muscles that a particular exercise engages. For instance, when an athlete performs arm curls using traditional free weights, the amount of weight in his hands does not vary. However, as the angle of the arms changes, the amount of strain on the biceps does change. The biceps must work hardest at the beginning of the lift, but once the athlete has curled the arms to the final position, the biceps are doing almost no work at all.
Performing arm curls using a variable resistance machine will provide a constant resistance on the biceps even as the angle of the arms changes. The total amount of weight changes in order to compensate for the change in the position of the arms. As a result, the biceps get a more complete workout because they are under a constant resistance level.
The increased demand this training puts on the targeted muscles makes this form of athletic training more effective than traditional free weight exercises for building muscle strength. The muscles have to work harder to perform a single repetition, so athletes do not have to perform as many repetitions of a lift in order to get the same benefit that they would get from more repetitions using free weights. Also, because the muscle must work throughout the entire range of motion, variable resistance training provides a more complete workout for various stabilizer muscles, which can improve overall athletic performance.
One drawback to this type of training is that it requires highly specialized equipment. The amount of weight must change throughout the exercise, so variable resistance machines must use an elaborate network of pulleys to make the proper adjustments. Also, because these machines compensate for the different angles of the body during an exercise, they must be specialized to a certain lift. An athlete can use a single set of dumbbells to perform a variety of exercises, but a variable resistance machine will enable the athlete to perform only one type of lift. To get a complete workout of the entire body would require the athlete to use several machines.