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What is Momentary Muscular Failure, Why We Seek It Out… and How To Get There

Achieving Momentary Muscular Failure (MMF) has long been a key tenet of High Intensity Training (HIT): the goal, the pinnacle, the crowning achievement for each exercise performed in a routine.


What is MMF and why does it occur?

Let’s simplify things by looking at MMF specifically within the context of dynamic exercise consisting of concentric (lifting) and eccentric (lowering) muscle actions. In this context, momentary muscular failure refers to the moment in an exercise set, when the force output of the targeted musculature has been reduced to a level equal to the force of the chosen load, due to fatigue of the targeted musculature, particularly fatigue of type IIa and type IIx fibers, (as type I fibers will actually recycle during the set). At this point in the exercise no further concentric movement is possible.



Once you have been training in a HIT manner for a while, it just makes sense at an unconscious level that MMF is how our exercises will culminate; it becomes ingrained in us over time. We become experts at recruiting and fatiguing muscle tissue through to the point of MMF. Or at least we are on a journey to becoming experts at doing this.

MMF is not however an instinctive or natural place to want to go to, in fact the feedback from our physiology is SHOUTING at us in no uncertain terms to PLEASE STOP prior to MMF, particularly during the last 20-30 seconds of a set.

It is a fact that any exercise that approaches being meaningful, is going to be temporarily uncomfortable, that is inevitable, even 60 seconds of an exercise that we could perform for 120 seconds is going to be beginning to feel unpleasant.


So, why do we do it?

The goals of formal exercise are primarily to:

  • Increase strength
  • Stimulate muscular hypertrophy
  • Improve cardiovascular fitness

As it happens, exercise that appropriately addresses these goals will also stimulate other related and downstream benefits including bone strength, flexibility, a beneficial hormonal profile etc. Note that the goals of formal exercise do not include, nor is it appropriate for them to include training for skill acquisition required for a sport or other activity-specific movement patterns.


What does the research say?

How we can go about maximizing our main goals of strength, hypertrophy and cardiovascular fitness, via exercise?


On Maximizing Strength

“Persons should train until momentary muscular failure to actively recruit all of the available motor units and muscle fibres, as opposed to a pre-determined number of repetitions.”

Fisher J, Steele J, Bruce-Low S, Smith D, “Evidence-Based Resistance Training Recommendations”, Medicina Sportiva, Med Sport 15 (3): 147-162, 2011


On Maximizing Hypertrophy

“Thus, recruiting as many motor units as possible through training to momentary muscular failure appears optimal for muscular hypertrophy.”

Fisher J, Steele J, Smith D, “Evidence-Based Resistance Training Recommendations For Muscular Hypertrophy”, Medicina Sportiva Med Sport 17 (4): 217-235, 2013


On Cardiovascular Fitness

“A plethora of research demonstrates the positive physiological adaptations that may mediate the observed improvement in CV fitness as a result of RT. It is also clear that these adaptations are, for the most part, a result of RT at high intensity (i.e., performed to failure).”

Steele J, Fisher J, McGuff D, Bruce-Low S, Smith D, “Resistance Training to Momentary Muscular Failure Improves Cardiovascular Fitness in Humans: A Review of Acute Physiological Responses and Chronic Physiological Adaptations”, JEPonline 2012;15(3):53- 80


The Common Denominator

All three of our main goals or desired outcomes for formal exercise appear to be optimized by performing exercise to MMF. That’s a pretty good deal, in fact that is a great incentive to tolerate or ideally welcome the temporary discomfort of performing exercise to MMF.

This speaks to another critical point about MMF; it is not simply a physical event that just occurs, it must be volitionally driven. Although our muscles are performing the physical work, they are driven to do so by our conscious minds.

Therefore, we need intellectual understanding of the reasons for wilfully doing something that is uncomfortable. If we have an intellectual understanding of the benefits of exercising to MMF and we value those benefits highly enough then we have the motivation to volitionally pursue MMF despite the sensations of physical discomfort.

It is easy to talk or write about MMF (and it’s attainment) as an abstract concept, it is quite another to seek it out when the load is bearing down on you, so to speak.

Individuals, who are Personal Trainers, are likely to be highly motivated in their own exercise expression, not all of their clients will hold the same degree of enthusiasm for their own workouts, or indeed harbour the same desire to reach MMF (at least initially).

The trainer’s goal, however, is to get the client to achieve MMF, or to encourage them to get as close to MMF as that particular client is currently capable, safely.


How to Get the Client To Go There

  • This starts out with communicating effectively what MMF is and the previously mentioned reasons for MMF being a desirable goal in exercise, the client must grasp the concept of MMF intellectually.
  • Next, the client must be made aware that the uncomfortable physical sensations associated with MMF are inevitable but only temporary.
  • They must also clearly understand the difference between the sensation of meaningful muscular exertion and the sensation of potentially damaging pain. For example you could say the following to a client:

“The sensation of muscular exertion is perfectly safe, it is a gradually building burning-like sensation in the muscles you are working, that increases constantly throughout the set and may feel quite uncomfortable by the time you reach the end of the set.
However, as soon as you stop the exercise the burning sensation will dissipate very quickly and you will be left with a residual sensation of fatigue in the worked muscles. We need you to get used to this sensation, as the stimulus for muscular improvement occurs when this sensation is strongest: at the end of a set.

On the other hand pain is either: sudden, sharp and jarring, like a flash of lightening in how quickly it arises- this is acute pain.

Or, it is fairly continually present in the case of chronic pain, causing a lower level of discomfort than acute pain, more of a nuisance that may however become acute if it is aggravated. Both chronic and acute pain, are most commonly felt in the joints, or in close proximity to the joints (rather than the muscles themselves).”

  • The client must then get used to and become skilled at performing exercise that approaches MMF and the physiological and psychological challenge of doing so. This will require repetition, time, feedback and encouragement.


Watch Simon instruct a set to momentary muscular failure


Whether you only train yourself or you train others too MMF is your responsibility.

  • It is an acquired and learned skill to be able to achieve MMF safely and effectively.
  • This skill is continually refined and developed through all stages of a trainee’s advancement.
  • It is your responsibility, to keep yourself (or your clients) focused on refining this skill to enable you (or them) to maximize ability to reach MMF appropriately.
  • Doing the above helps an individual to get the most out of the exercise stimulus and its potential results.


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