Revisiting the Fitness-Fatigue Model - Lessons from the Lab

“I am fatigued.”

“Yeah, but fatigue drives fitness.”

This was an interaction between a client and I last week.  I stated it as such a matter of fact that I realized that 1) this client may have no idea what I mean when I say fatigue drives fitness, 2) he is also a coach, so if he doesn’t understand, then many of my other clients will definitely not understand 3) this model drives so much of what I think I understand about training, programming, and long term planning, that it would be worth revisiting in hopes of enlightening people as to what the fitness-fatigue model is, and how it impacts programming.  Forcing myself to put ideas in my head into words that individuals might understand, hopefully improving buy-in, effort, and training outcomes along the way. 

The Fitness-Fatigue Model is a two-factor model that tries to explain what happens to performance when we train.  I know I know, All models are wrong, but some models are useful. The Fitness-Fatigue Model is one of the useful ones. It can be applied on a daily, weekly, monthly, and even longer-term scale.  Session to session, microcycle to mesocycle to macrocycle.  The way that fitness and fatigue interact determines the level of performance expressed at any given time.  For simplicity we will assume that performance starts at some baseline level.  Whenever you train, whether it is resistance training for powerlifting, endurance running for a marathon, or sprinting for a team sport, you are doing two things.  First, you are getting better at the thing you are doing.  Your fitness is improving.  I know this seems counterintuitive. 

“I don’t feel like my fitness is improved at the end of a run.”

“My technique degrades as a squat session goes on.” 

Both statements are probably true.  Your performance is going down as the training session goes on, while I argue that your fitness is improving.  An oversimplified way of thinking about it is that your nervous system is getting better at the skill you are practicing.   The thing we all realize is that the more training we do, the more fatigue we accumulate.  You are tired at the end of a run, or after a hard training session.  If you were to squat the next day, you would likely not express improved performance due to the peripheral and central fatigue, stress, and homeostatic disruption, not being fully recovered or repaired yet. 

Fitness is driven and improved by very hard training, but hard training causes several different levels of stress and disruption.  Your nervous system's ability to express perfect technique is disrupted, even with lighter weights.  Your muscles have incurred mechanical and metabolic stress.  Your neuromuscular ability to express maximum levels of force is suppressed, usually longer than it takes for your muscles to recover physically.  All the while your connective tissues, while very robust, take the brunt of the loading in an attempt to hold your body together.  While training creates different levels and time courses for different types of fatigue, the fascinating observation is that usually fatigue seems to dissipate faster than fitness does, that with appropriate time and resources should yield improved levels of performance.  While this will not happen infinitely, you can’t maintain high levels of fitness without continuing to train, or without creating fatigue as a byproduct of training, it is valuable to understand this idea. 

Session to session

                  Intuitively we understand how this concept should be applied day to day or session to session.  If I squat 5 sets of 5 reps today, tomorrow I will probably be sore and tired from those squats, assuming those sets were sufficiently heavy or proximal to failure.  If I try to do the same workout again tomorrow, by performance will be down, because fatigue is elevated.  Again, the thing is this fatigue will dissipate faster than fitness dissipates, so if I try that squat workout 3 or 4 days later, even a week later depending on the program, I should express new levels of performance, facilitating a new overload stimulus, and repeating that process. 

Microcycle to Microcycle

If we are training sufficiently hard, our fitness should improve from week to week.  If we are recovering sufficiently well, our performance should improve from week to week.  When you first start out training, or try a new train style, or program, usually there are some noobie gains to be found, especially if we are smart enough to start light or ease our way into hard training.  Usually, we can add weight or complete more reps when we get to week 2 of a program.  We have recovered enough from the stimulus that we have adapted and facilitated some kind of improvement in performance.  Occasionally, perhaps by starting too heavy, or not being prepared for the workload presented in week one, we will see a decrease in performance in week two, lower weight, less reps, slower bar speeds, etc.  Ideally, the program has built in flexibility that allows for this reduction in performance to occur, allowing the athlete recovery to catch up to the workload presented in week 1.  Hopefully by week 3 or 4 things come around and the athlete is recovering from and adapting to the stimulus provided.  Unfortunately, this will not happen indefinitely, as loads, reps, or workloads rise, fatigue will continue to accumulate to the point where we can no longer express improved performance.  If we continue down this road performance may continue to degrade.  Again, the model would state that fitness is still improving, but fatigue is so high that we cannot dissipate enough in time to express new levels of performance by the time the next stimulus comes around. 

This is where programming strategies like deloads, reloads, washouts, come in handy.  Side note, stop straw manning deloads.  Even if you say you don’t program or believe in deloads, there is probably some form of deloading, unloading, exercise change, volume change, or some version of a volume and/or load reduction built into your program.  Telling me you don’t deload but then saying week 1 starts at RPE 6, counts as a deload.  Saying that you don’t need to deload if you use weekly undulating planning effectively, counts as a deload.  Heavier weeks have a lower number of lifts and lower volume tonnage, higher rep weeks have lower absolute loads.  The volume and/or load reduction is built into the program, they just occur in different weeks of training, the deload strategy is built into the program.  Deload weeks are not easy or low effort training weeks.  The expectation is still that you will come into the gym with high intention and execute training with a high degree of effort.  Training needs to be sufficiently hard to create a stimulus that drives growth or improvement in performance.  Deload weeks are no exception. 

Mesocycle to Mesocycle

Depending on your programming strategy, how this concept is applied from block to block can be interesting.  At some point, it may become difficult to see significant improvements in an athlete’s fitness or performance on a weekly time scale or even over a full block.  It may take multiple blocks to yield and express any significant improvement in performance.  Creating a need for more creative training strategies and individualization.  This might mean that you use strategies where some blocks are purposefully fatiguing in different ways, in hopes that you might focus on improving different fitness qualities at different times.  This is where the block periodization concept comes from. 

Key performance indicators

We apply this information by creating some kind of key performance indicator or measurement system somewhere in the training plan.  I know some people like put their key performance measurement immediately after some kind of deload, reload, washout, volume reduction, to get an idea as to how someone is recovering from the previous block of work.  This strategy can also help dial in tapering for competition as well, in hopes of having more repeatable performance or reasonable expectations come meet day.  I know there are others who choose to have their key performance indicator measured at the end of a training block, to see how the athlete is responding when training fatigue is high, then anchoring on the idea that performance will be improved after some kind of taper, bringing fatigue down.  Others will argue that you should anchor on that performance improvement occurring by the end of the block, and train right into meet day.  I have used both strategies with clients, and while I have some biases about how much fatigue we should carry into a competition, or how much we should taper, I really think it depends on paying attention how the athlete responds to training and tapering and then individualizing and fine tuning their strategy over the long term. 

My two favourite performance indicators are AMRAP sets and estimated 1RMs derived by some kind of top set or indicator set.  I find AMRAPs to be valuable further out from a meet.  Weekly, as some kind of final set to the priority-1 SBD variations, or on a reload week to measure how stressful the block was, then comparing AMRAP performance from block to block.  If you are regularly completing 3-5 sets close enough to failure, it will be tough to match that workload using 1 AMRAP set.  While that 1 AMRAP set will be quite stressful, it will still fulfill the requirements of a deload, reduce volume and absolute intensity, in theory reducing stress and facilitating more recovery and therefore more adaptation.  Using a top set to indicate performance using an E1RM is also valuable.  This can be done using a static RPE top set, for example 1 rep at RPE 7, then holding that top set prescription static, along with the rest of the training prescription, then observing how that top set E1RM responds as people progress through training.  A Dynamic RPE system allows you to facilitate load progression of that top set, either by increasing the RPE as the block goes on, or undulating that RPE throughout the block, usually with the heaviest indicator set occurring at the end of the training block.  Then it is a matter of looking critically at the AMRAP performance or E1RM to gauge whether the training strategy is effective or not based on where someone is at in their training and then adjusting accordingly. 

Macrocycle to Macrocycle

At the highest levels of performance or at the most elevated training ages, it might take a year to express improved performance on the platform.  This can become a real slog for some people, and this is why it is important to understand and apply this model on a macrocyclic scale as well.  At the Olympic level, athletes and coaches start thinking on a quadrennial scale.  While most people, me included, find it very difficult to think and program this way; “4 years such a long time,” think about how long ago Covid was, how fast has time flown by since then?  Would you be a better lifter today if you had made a long-term training plan from that point until now.  I understand the difficulty here, things happen, life gets in the way, programs must change and adapt.  I am not saying we should plan every detail in advance.  But we could plan out competition dates, off seasons, when we will develop GPP or work capacity, what weak point training will we do in which periods and why, undulations in specificity, the list can go on and on.  Again, I am bad at this too, I struggle to even look passed the next meet.  As a Coach I am always trying to think longer term in a general sense.  I always build prehab and general hypertrophy work into powerlifting training, but could I do things better?  The idea of trying to convince athletes to step away from the powerlifts for weeks or even months at a time can be risky enough, as at the end of the day the client is trying to get better at the powerlifts, and convincing people (again, when I am pointing at you, I am also pointing at myself) to step away from the lifts for a while can be difficult.  On the other end, convincing people to go through periods of lower specificity, higher volume, growth based periods, has its drawbacks as well.  The idea of permanently being in prep has its advantages, but it comes with its longer-term disadvantages as well.  It is hard to acknowledge or even recognize those disadvantages in the moment, sometimes it takes 20+ years of resistance training and 12 years of competing to see how things could be done better, or injuries or risks could have been mitigated.  All the while being able to argue that, I might not have hit the numbers I hit if I didn’t do things the way I did, or I might not be where I am today if I didn’t follow that path.  How do I even know what I think I know?

You need to also think about the fact that we are trying to use imperfect measurements as a proxy for the stress we are placing on an athlete.  Volume, Workload, Number of Lifts, Number of Hard Sets, Intensity/Number of Lifts, Average RPE, Session RPE, Stress Index, all these things attempt to quantify the amount of stress being placed on an individual at any given time.  Then we need to factor in the fact that how someone perceives, recovers from, and adapts, to any one of these measures will change depending on where they are at in their training career.  In theory, x volume tonnage should be less stressful to an individual over time.  But if lifestyle factors change, that same workload next week might be more stressful if we aren’t recovering enough in time.  Any new father that I have worked with has experienced this, even that ones that think they are prepared. 

At the end of day, it all comes down to figuring out how much hard training is needed to drive adaptations over a certain time frame, and how much time is needed to recover from that hard training to illicit the growth we want.  Sometimes you will be fatigued, that is okay, fatigue drives fitness, and sometimes you just need to build a stronger foundation to build a bigger house. 

Addendum to the intro

The quote mentioned came the day after this client squatted 595lbsx4 at an RPE of 7.5 or so. The following week that individual squatted 633lbsx4 at an RPE of 9.5.  Fatigue Drives Fitness.