Momentary Muscular Failure better than Repetition Maximum: Protocol Differences (part 2)

Last week, I wrote about a new piece of exercise research (The effects of low volume resistance training with and without advanced techniques in trained participants), and what makes this research valuable. I covered aspects such as the basic protocol that the three groups performed and the similarities between the specific exercise routines performed by each group. You can read that post here.

In this post, I want to discus how the protocols studied, differed between the groups – in effect what is it that the research actually looks at and provides data about.

Remember that the three groups were:

  • ssRM: individuals in this group performed a single set to (self-determined) Repetition Maximum
  • ssMMF: individuals in this group performed a single set to Momentary Muscular Failure
  • ssRP: individuals in this group performed a single Rest Pause set to self-determined repetition maximum



The exercise protocols were designed in such a way that the relative work volume would be the same for the MMF and RM groups. By doing so, the research is able to examine the role of training to MMF in strength increases and body composition.


Rest between exercises

Before we get to the differences in exercise protocol between the three groups, I want to discuss one more area of similarity they all shared: that of rest between exercises.

The participants in all three groups in the study rested “only as long as required to move from one exercise to the next”. This mirrors traditional HIT protocol, which often involves the “rush-factor”, where the exerciser moves on to the next exercise in the sequence as quickly as possible.

Whilst this “rush-factor” may not be a requirement for optimal cardiovascular health improvements via exercise, it does entrain the metabolism specifically to a “rush-factor” style of exercise.

Obviously, it is important for the accuracy of the research that all three groups rest for a similar period of time between exercises for fair comparison of results. The use of the rush-factor style should have helped to keep the rest periods between exercises similar between individuals of all three groups.

Instead of a rush-factor style, the researchers could have used a timed 30-second (or 60-second, or if deemed necessary, longer) rest period between exercises to improve standardization of rest periods between individuals, groups and exercises further. It is likely however the researchers wanted to use the “rush-factor” either for convenience, and/or to adhere to a traditional (to HIT) and commonly used approach to inter-exercise rest periods.

Now on to those differences between protocols…


Warm up sets used

The only group to perform a separate warm up set in addition to their single working set of each given exercise was the ssRP (single set Rest Pause) group. The ssRP group performed one warm up set of 5 repetitions using 50% of their “working” weight, prior to their main set of each exercise.

I assume this was done because the version of RP used had the subjects initially use a load that was 90% of their pre-intervention maximal isometric strength for single repetitions. Perhaps the researchers wanted the subjects to experience increased blood flow and weeping lubrication of the joints and/or additional mental/physiological preparation prior to handling a relatively heavy load for singly performed repetitions.

5 repetitions of 50% of the working load in this scenario is not enough exposure to this level of load to significantly fatigue the musculature prior to the working set. And yet if greater volume of exercise is considered to have importance, then we would expect the ssRP group to have a slight advantage over the other two groups due to increased volume provided by their warm up sets and as we shall see later, the number of reps they were instructed to perform before load increase was earned.


Initial load selection

The loads that each individual used, for each exercise at the start of the research, were based on readings of pre-intervention tests of their maximal isometric strength produced on each machine that they would go on to perform exercise on during the research.

As already mentioned above, the individuals in the ssRP group would initially use a load that was 90% of their tested maximal isometric strength for each given exercise.

The individuals in the ssMMF group would use an initial load that was 80% of their own tested maximal isometric strength for each given exercise.

And the individuals of the ssRM group used just 60% of their own tested maximal isometric strength for each given exercise.

One reason that the researchers gave for the differing percentages between groups was their desired intention to match “relative work volume” between the ssRM and ssMMF groups. Of course the ssRP group had a higher relative work volume due to in part due to the increased load used, and an increased repetition target too.


Load progression

In the ssRM group, load was only progressed on an exercise when the individual had completed more than 12 repetitions prior to reaching their self determined RM. At which juncture the load was increased by 5% on that exercise at the next scheduled workout. At the cadence used the participants in this group would be exposed to 120 seconds of exercise with a given load before the load would be increased.

The individuals in the ssMMF group increased their load by 5% in a give exercise following the achievement of 9 complete repetitions prior to reaching MMF. The individuals in this group would effectively be exposed to 90 seconds of exercise with a given load before they would get a load increase.

This approach to repetition volume load progression for the ssRM and ssMMF groups provides the other half of the balance to the matching of relative work volume between the groups (60%x12 reps and 80%x9 reps). This is valuable to the usefulness of the study as it now allows a meaningful insight into the importance (or otherwise) of achieving MMF when relative work volume is the same between a group that goes to MMF and a group that stops shy of MMF.

The ssRP group also increased load by 5% but not until they had achieved 18 repetitions prior to self determined RM, equaling 180 seconds of (albeit non-continuous) tension with a given load before load increase. This is quite a chunk more volume over the other two groups: double the repetition goal of the ssMMF group and half as many reps again as the ssRM group.
This means we can also look at the impact of increased volume, or at least added volume in combination with increased load.

If higher load and higher volume of exercise performed is of greater importance than reaching MMF (within a reasonable number of repetitions), then the ssRP group should produce the greatest results out of all three groups (unless of course some greater amount of continuous tension- longer than 10 seconds, is additionally required).


The version of rest pause exercise used

The ssRP group performed a single repetition at a time, followed by a ~5-20 second deloaded rest period, followed by another repetition etc. all the way through to self determined RM.

My favored version of rest pause exercise consists of a regular continuous tension set to MMF, followed by 1-3 rest pause repetitions (with ~5-20 seconds rest after the continuous tension set and between each subsequent RP repetition). For personal interest, especially seeing how the ssRP group performed in this study (better than the ssRM group but not quite as well as the ssMMF group), I would love to see the results of my favored style of RP protocol and how it would stack up against ssMMF in a study of this nature in the future.


Summing up the protocol differences

ssRM ssMMF ssRP
Description The participants stopped the set at the end of a final full repetition, where they felt that attempting the next repetition would result in MMF. The participants stopped the set when they couldn’t produce sufficient force to complete the current repetition. The participants performed a single repetition at a time, followed by a 5-20 second rest period, followed by another repetition and another rest and so on, until they reached self determined Repetition Maximum.
Rest between reps No rest No rest 5-20 second rest period between repetitions
Warm up No warm up No warm up One warm up set of 5 repetitions using 50% of their “working” weight, prior to their main set of each exercise
Initial load selection 60% of their tested maximal isometric strength 80% of their tested maximal isometric strength 90% of their tested maximal isometric strength
Load progression 5% increase in load after achieving 12 repetitions 5% increase in load after achieving 9 repetitions 5% increase in load after achieving 18 repetitions
Time Under Load, before increasing load 120 seconds 90 seconds 180 seconds


What do the researchers mean by Momentary Muscular Failure?

In the paper, the researchers note that they consider MMF to have occurred when “a person cannot produce sufficient force to complete their current repetition.”

They also mention in the paper that both posture and repetition duration should not change whilst attempting a final concentric contraction referring readers to a previous study: Fisher J, Steele J, Bruce-Low S, Smith D. Evidence-Based Resistance Training Recommendations. Medicina Sportiva 2011 where it was stated: “(We) can perhaps define ‘momentary muscular failure’ as the inability to perform any more concentric contractions, without significant change to posture or repetition duration, against a given resistance”.

This is a pretty good summation of MMF as most people who understand HIT apply it. Certainly it is important that posture is not altered in an attempt to complete a repetition as this would both weaken the stimulus to the target musculature and increase risk of injury.

Whether repetition duration should come into the definition of MMF is perhaps more debatable. What if an individual toward the very end of a set can grind out the concentric portion of a repetition, but only over 8 seconds (as opposed to the prescribed 4 seconds of this study)? Should the set be stopped at the moment the concentric attempt goes over 4 seconds in length, or should the exerciser be allowed the 8 second concentric.

The allowance of a slower concentric at the end of the set will help the exerciser get closer to an MMF where no further movement is possible at all. Which raises the question do we consider MMF to be achieved when movement slows below a predetermined cadence on the concentric or do we consider positive or concentric MMF to occur when no further concentric movement is possible at all against a given load? And does this distinction make any difference whatsoever to the outcome? Perhaps it may do considering the exponential improvement in results of the ssMMF group in comparison to the ssRM group in this study.

In my own exercise application, I go for that extra inch or extra few centimeters regardless of how slowly movement occurs- the set is complete when I am sure I cannot move the load another millimeter. This may ultimately be splitting hairs of course, especially with the results of the MMF group being so good in this study. I do wonder is there any room for further improvement by pushing the set that little bit further to complete concentric standstill- maybe there is, maybe there is not- it would be interesting to find out. Are all motor units and fibers engaged and fatigued enough for best results at the point a subject cannot keep up with a predetermined cadence, or at the point where further concentric action is impossible?

One reason that the researchers may have decided to use inability to maintain the given cadence as an indicator of MMF is that at least the fully completed reps are standardized and comparable rather than having the final full repetition of any given set be of any potential length from let’s say a 4 second concentric to a 14 second concentric as this may potential skew the data- altering TUL exposure for the number of repetitions performed.


What do the researchers mean by Repetition Maximum?

The ssRM and ssRP groups did not train to MMF but instead to a self determined Repetition Maximum.

Repetition Maximum is in some ways a confusing end point for an exercise set, as the researchers acknowledge in the article. A true repetition maximum culminates at the completion of a final fully controlled, full range eccentric. At this point if the subject were to attempt to continue with a further repetition they would reach MMF at some point during the very next concentric (they would not attempt this final repetition).

True repetition maximum exercise would require pre-knowledge of the exact load that would allow a given individual to achieve a desired number of full repetitions. In reality, this is not practical- if you test a load with an individual to find this out then the test will temporarily weaken the musculature- when should the subject then exercise again after the test. The test itself could also act as an exercise stimulus: potentially changing the RM by testing the RM (and blurring the results of a study if testing was performed during the exercise intervention being studied).

We are therefore left with exercising to “self-determined” repetition maximum as the only currently viable option for researching RM training. Self-determined RM means the exerciser stops the set after completion of a final full repetition, believing that they will hit MMF at some point during the very next repetition if it were to be attempted (it is not attempted).

The challenge is for the exerciser knowing when to stop the set live in the moment. The researchers indeed point out that it is a problem with any research that uses RM as an endpoint, as it is difficult to know if the exerciser stopped the set too soon, hit RM exactly or indeed went too far and accidentally trained into the MMF repetition. They point out that typically “Even experienced trainees… under-predict the number of possible repetitions to MMF.”

This certainly rings true for me, there are many occasions that I can think of where I thought I was going to hit MMF on the next repetition but I was able to complete another full repetition, when I really upped the mental intention and focused on digging deep into the set.

Nevertheless self determined RM is currently the only viable way of utilizing RM in research. Therefore the ssRM group and the ssRP group were both instructed to exercise to the point where they predicted they would hit MMF on the next repetition (without attempting that predicted MMF repetition).

When talking about the difference of working to RM vs MMF in a study, it is important to remember that we are dealing with humans and not machines. Factors such as overall psychological motivation to exercise in general, motivation on the particular day, and motivation during the individual exercise within the workout all come in to play to affect the outcome.

What is perhaps practically important is the participants clearly have the intent of the culmination point of their sets explained to them, that their understanding of this is verified and they are reminded of it prior to exercise. When the intention is clear in as many of the participant’s minds as possible, hopefully their effort levels and motivation throughout the study would be a good match to potential exercisers from the wider population. These thoughts of course apply to any research in the exercise field where participant motivation and understanding can impact the results of the study.


Having fully understood now the specific protocols and application of exercise used in this research paper, including rest periods between exercises, the use of a warm up set, initial load selection, load progression, the version of Rest Pause exercise used and the researchers’ interpretation of MMF and RM, in the next and last part, we shall look at the results of the study and the conclusions the researchers make, in more details.


This article was posted on November 2, 2014 by in The science of HIT

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