Understanding Acute Fatigue….Or Not


Written By: Kevin Cann


I had a very good conversation with Quinn Henoch about acute fatigue.  I then posed this same question and had this same discussion with Mike Amato of Barbell Medicine.  I feel sharing some of these thoughts will be entertaining at the least.


The question that Quinn asked me was “Why can’t you squat your true 1RM for a double?”  My response: “Hold my beer.”  This led to a pretty long discussion afterwards.  I hope Quinn does not mind, but I am going to share his take on this:


“As with all of this, I think it is multifactorial, but yes (physical issues lead to not doubling your true 1RM).  I think physiology plays a role.  Everyone has a max at every rep range.  What stops them from getting 1,2, or 10 more reps, I don’t know-but I am not ready to discard physiology…I fully concede that the psychological element is a big time player.”


I think this is a fantastic explanation of the situation.  I actually agree with 99% of it.  Like most things, we agree on the majority, but get really hung up on the smaller pieces.  For now I am going to focus on that 1%.


I agree that it is an interplay between physical and psychological factors, that is undeniable. However, I am reluctant to call fatigue the culprit of the inability to double my 1RM and here is why.


ATP-PC lasts for about 10 seconds.  A hard single is 3-5 seconds.  I do not see ATP being an issue here.  If we were discussing a triple, perhaps.  A more confusing piece of this puzzle lies with our motor units.  This excerpt comes from “A motor unit-based model of muscle fatigue” written by Jim Polvin and Andrew Fuglevand


“Fig 5C shows the force contribution of the individual MUs over the course of the 100% force trial.  It is important to note that, at the outset of the trial, before any fatigue occurred, the forces produced by the highest threshold MUs were less than their theoretical forces.  For example, MU120 had a capacity to generate 100 times more force than MU1, yet its initial force at 100% MVE was only 57 times greater than MU1. This was due to: a) the imposed “onion skin” organization that limits the maximum firing rates of high threshold MUs to be less than that of low threshold MUs, and b) the briefer contraction times of high threshold MUs which decreased their normalized firing rates and led to lower forces.  This implies that there is a reserve capacity of force that is not normally accessed even during maximal voluntary efforts.”


Is it fatigue if our body is holding reserves, or is it just the fact that we are not trained or adapted to handle that?  Is it that we accept that our 1RM is our 1RM, and we believe that we can’t double that, so we accept we can’t?  To be fair, no one knows the answer to this, and we are most likely far away from that answer, but it is fun to think about.


The majority of this research is performed on endurance events.  This is due to the fact that inducing measurable fatigue with intensity, in a laboratory setting, is very difficult, if not impossible.  It gets even more difficult to measure afterwards as central and peripheral fatigue recovers very quickly.  Muscle damage is the only measurable piece that lasts more than a few hours.


This does not mean that fatigue is not present.  We can’t measure it.  This probably speaks more to our lack of understanding with what it is.  It also does not rule out that it is not a culprit in this situation.


Quinn then asked, “But could “acute fatigue” not just be a proxy term for the accumulation of factors that cause us to fail a set?”  This made a light bulb go off in my head.  We are disagreeing about “fatigue” in this case because we are defining it differently.


I have always associated fatigue with being tired, either physically or psychologically.  I have watched lifters miss a weight 2 weeks in a row, only to come back week 3 and hit it, and never miss it again.  We did not pull back in these cases.  In some we pushed even harder.  These lifters weren’t tired, they just weren’t adapted was my response to myself.


With a different definition, I think communication can be improved on this topic.  I proposed this definition of fatigue to Mike Amato:


“A decrease in performance that is a result of psychological factors that include mood, perceptions, expectations, and cultural beliefs, as well as physical properties that include available energy stores, heart rate, and core temperature.  These two pieces are not exclusive as it is the same individual. Biological processes such as motor unit recruitment is a combination of both physical and psychological factors and is a contributor to decreases in performance.  Fatigue is a multifactorial process that extends beyond the feelings of exhaustion and tiredness.”


Mike made a great point; it does not always decrease performance. Adding in after the decreased performance; decreased motivation, and/or increases in pain sensitivity is important. We can be fatigued and still driving progress forward, but for how long?  In these situations we see a loss of motivation and increases in pain sensitivity.  Often these issues are due to factors outside of the gym, and not the training itself.



Having a better definition of fatigue can allow for more productive conversations regarding the subject matter.  I think many coaches view fatigue as being tired and needing to pull back.  I think this definition highlights how complex fatigue is and how we do not always need to pull back when a lifter is fatigued. However, sometimes we do need to pull back.


This is just a start on the topic.  More to come.

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