Bodybuilding is not the same sport as weightlifting. Rather, bodybuilders use weightlifting, special diets, cardiovascular exercise, supplements and special exercise techniques to maximize the size and definition of their muscles. Pre-exhaust training is a supplemental exercise technique used to quickly define and enlarge the primary muscle of whatever body part to which the technique is applied. The pre-exhaust principle requires that the primary muscle of a given group is isolated and exhausted through the performance of a muscle-specific exercise. Then, when a normal compound muscle exercise is performed, the larger primary muscle exhausts at approximately the same time as the smaller ancillary muscles, having presumably been "pre-exhausted" by the first isolating exercise.
In regular weightlifting and bodybuilding routines, a combination of isolation and compound exercises are performed according to the athlete's chosen workout program. Most exercises are classified as compound ones due primarily to the human body's anatomical structure and its design for maximum strength in any given motion. When a regular incline bench press is performed, for instance, the maximum number of repetitions is not based on the stronger and larger pectoral muscles. Rather, the smaller accessory muscles such as the triceps and the deltoids fatigue first and thereby determine the max reps for this exercise. A pre-exhaust program attempts to base an exercise's max reps on the larger muscle's stamina instead of the smaller ones' abilities.
Exercises that isolate one muscle out of a group that usually works together are fairly difficult to find, design or perform. Bodybuilding books, magazines and Internet websites all have information on how to perform a pre-exhaust on a given muscle group, such as the chest or the back, for example. Exercisers are encouraged to move almost immediately — within seconds — from the pre-exhaust exercise to the compound exercise in order to decrease the amount of muscle rest allowed. Bodybuilders are also cautioned not to assume they will be capable of lifting the same amount of weight as they do when not utilizing a pre-exhaust exercise. The difference in the amount of weight lifted without a pre-exhaust as compared to that lifted with a pre-exhaust helps emphasize the body's natural use of every available muscle group to work collectively.
While there is enormous variability in practice, most bodybuilders usually utilize a workout routine that lasts four to twelve weeks in length. Different muscle groups are worked on alternate days to allow for muscle repair and regrowth. The routine may be essentially the same program of exercises with expected increases in strength and the amount of weight lifted or it may be a progressive series of different routines to work a given muscle in as many ways as possible. Most experts recommend that a pre-exhaust program be used only intermittently and for a much shorter period between a bodybuilder's longer workout routines. Advantages cited for this recommendation include greater gain in muscle size and definition secondary to the shock effect on the muscle.