Muscular failure

Muscular failure is a poorly understood term in the fitness industry because it is frequently assumed to be an involuntary process when it is actually always a voluntary process. Here is a exact explanation of how we reach muscular failure during any given strength training set.

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#1. Muscular failure is more correctly understood as "task failure"

It is likely that many fitness industry experts struggle to define muscular failure appropriately because the terminology is itself very misleading. Indeed, discussions often arise when an influencer wakes up and realizes that "muscular failure" does not really mean that the muscle has totally failed because of course more reps can still be performed if the weight on the bar is reduced or if the range of motion is limited. Indeed, this type of confusion is exactly why fatigue researchers use the term "task failure" to refer to what is happening. When a lifter finds themselves unable to continue performing a set of reps, this point is described as task failure.

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#2. Muscular failure is caused by a lack of central motor command

Although 99% of fitness industry experts will tell you that muscular failure is reached when the muscle cannot produce enough force to lift the weight on the bar and thereby complete the desired repetition, it is easy to show that this is untrue. The fact that muscles have voluntary activation deficits is evidence that muscles are usually perfectly capable of producing the required force to lift the weight another time, but the central motor command is simply not high enough to increase the level of motor unit recruitment and activate more muscle fibers. In large muscles, these voluntary activation deficits can be extremely substantial.

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#3. The lack of central motor command is caused by perceived effort

Physiology research has shown that the central motor command we are able to create is limited by the maximum tolerable perception of effort that we are prepared to tolerate. The central motor command creates a copy of itself (called the corollary discharge) and sends this copy signal to the sensory part of the brain, where it produces a perception of effort. When this perception of effort reaches a maximum tolerable level, we stop increasing the central motor command in order to stop increasing the corollary discharge. In other words, a lack of central motor command is always caused by us voluntarily deciding that we cannot tolerate the pain and discomfort associated with the exercise we are performing. So muscular failure is always a voluntary act and never an involuntary act.

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Conclusions

The term "muscular failure" is misleading, which is why fatigue researchers more commonly use the more self-evident expression "task failure" instead. Task failure obviously just means that we are unable to continue performing an exercise bout beyond a certain point, which is what "muscular failure" is really trying to describe. Although it is often assumed that muscular failure during strength training is reached when the working muscle itself can no longer exert enough force to lift the weight on the bar and complete the desired repetition, this is untrue. Indeed, the existence of voluntary activation deficits is evidence enough that muscles are almost always capable of producing the required force to lift the weight another time, but that the central motor command for some reason is not increased so as to increase the level of motor unit recruitment and activate compensatory muscle fibers. Thus, muscular failure during strength training sets always occurs because of a lack of central motor command and not because of a lack of muscle force-producing capacity at the peripheral level. Moreover, this lack of central motor command occurs because we reach our maximum tolerable perception of effort. Whenever we generate a central motor command, we also produce a similar-sized corollary discharge that creates a perception of effort. When this perception of effort reaches our maximum tolerable limit, we have to stop increasing the corollary discharge. To do this, we must stop increasing the central motor command. Thus, muscular failure actually always occurs because we voluntarily stop increasing central motor command because we have decided that the level of discomfort we are experiencing due to our perception of effort has reached a maximum level.​