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Muscle failure is a body-building term used to describe the inability to complete one additional movement or repetition. There are three types of muscle fibers used to lift weight — type I, type IIA, and type IIB. The lowest classification, type I, is used to describe muscle fibers with a lower threshold for repeated movement. These fibers are typically exhausted first during heavy weight-lifting, leaving the higher threshold muscle fibers to take up the load. In this process, all fibers progressively weaken until muscle failure occurs.
Type IIA and IIB muscles generally grow much faster than low-threshold fibers. In traditional body-building, the higher threshold muscle fibers carry much less load as lifting repetitions are performed, no matter how weak muscles become during sets. If lower threshold muscles can carry the majority of weight throughout the set, the higher muscle fibers sustain little or no tearing. Tearing is necessary in body-building, however, for adding muscle mass.
The idea behind training muscles to the point of muscle failure is to work these higher threshold fibers. The process is similar to working over-time for muscles. For instance, if double the hourly pay rate was paid to an employee after eight hours of work, he would be more likely to work extra hours. Muscle failure is thought to work in much the same way. Muscles are worked until higher threshold fibers, type IIA and IIB, take over the weight load. These fibers offer faster gain, like over-time pay.
There are health concerns related to muscle failure workouts. As muscles fatigue, proper form may not be followed which can lead to injury and pain. Improperly warming up muscles and training to failure on a daily basis can also lead to muscle injuries. These injuries may be prevented with proper routine planning.
In order to work a muscle to failure, one weight lifter and two spotters, or assistants, are typically needed. A predetermined amount of weight is placed on a lifting bar. As the lifter presses to failure, the weight is removed but the set continues. This process is repeated until muscles are no longer able to lift even small amounts of weight, including the weight of attached body parts.
An example of a muscle failure workout could include beginning a bench press set with 225 lbs (about 102 kg) on the bar. When the weight cannot be lifted for one more repetition, 10 lbs (about 4.5 kg) can be removed from each side. The lifter can resume repetitions until muscle failure occurs again, and the process is repeated until no weight is left on the bar.