The Fitness-Fatigue Model: How You Make Progress

Key Points:

Adaptation is the process by which the body will undergo changes in order to withstand environmental pressures, allowing survival.

The key to making progress in size and strength is through forcing this adaptation process over time. This comes through more work over time (e.g. more sets, reps or weight) in response to your training.

Novices adapt quickly and since the amount of work they can cope with is SMALL, the fitness- and fatigue-after effects will be minor. This allows novices to increase workloads on a LINEAR basis EACH training session for approx. 6-12 months. 

Intermediate/advanced lifters need more workloads to stimulate further adaptations. This causes larger fitness- and fatigue-after effects. This means more experienced lifters cannot increase worloads in a linear fashion without risk of burnout. PERDIODISATION of training workloads over time will ensure optimal control of training fatigue allowing for further progressive overload over time.

Adaptation And Survival

If you were to ask what is probably the biggest most overlooked concept when it comes to making progress (in any sport!), I would have to say adaptation. Really, adaptation is what allows us to continually make progress and achieve the results we want. Without it, we simply stay in the same place forever. Is does not matter whether you want to become stronger, bigger, faster, or more powerful, adaptation is the key that is going to allow you to obtain these physical qualities over time. Not only is adaptation important for sport, but essentially, also for survival! Every living organism has the ability to adapt. Without this ability to adapt, everything would die. Not so great!

So, why does adaptation allow survival? Well, our environments are constantly changing and presenting us with new challenges to successfully overcome. If we don’t overcome these challenges, then these environments will eventually wipe us out. Maybe we find ourselves with less food and the body needs to adjust its metabolic functions to keep you functioning due to this shortage. Or imagine, maybe you are forced to live on top of Mount Everest because the whole world now finds itself under water. You know, end of the world stuff! Well, now the body has to increase its production of red blood cells in order to allow you to get enough oxygen to be so high up in the sky. If not, you would not survive. These scenarios give you a nice idea of what the body needs to do in order to survive under such circumstances. But, if you have noticed, in both these scenarios, the body just doesn’t decide to adapt randomly. It needs a good reason for doing so. Why? Simply because adaptation requires a huge amount of energy and resources! As a result, unless your body is challenged with a powerful enough stimulus, it will not commit to the adaptation process. Well, I think you can see, lack of food or a global underwater disaster probably qualify as powerful stimuli for adaptive change!

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Adaptation And Sport

In sports, the adaptation process comes at the center of all progress. If you want to get better at something, you NEED to adapt. There is no way around this fact, I can promise you. This is something you need to keep in the front of your mind if you have goals you want to achieve, otherwise, you are just spinning your wheels! When it comes to getting stronger, bigger, faster and more powerful, you need to give your body the stimuli that is going to force it to develop these qualities. For instance, say you want to develop more muscle tissue. Well, your body will only create more muscle when the current quantity of muscle you do have, cannot allow your body in its current state to support the total work you are doing. In other words, more work over time without more muscle is simply going to break your body down. The result will be that your body becomes compromised and cannot function optimally in its current environment.

However, synthesising more muscle comes at a huge energy and resource cost to the body. Something it would rather not do! Therefore, you need to train in a way that is really going to give your body the reason to commit to this process. If you walk into the gym every time and lift the same weights, for the same number of reps/sets and select the same exercises, your body stops adapting because it is no longer challenged by what you are doing. I mean, why should your body utilise extra resources when it doesn’t need to? Only when you start changing things up and increasing the total amount of work you are doing will your body perceive this as a powerful enough stimulus to change.  

The Fitness-Fatigue Model

Making progress in the gym is dependent on two things changing: fitness and fatigue. In the context of the fitness-fatigue model, we call these fitness- and fatigue-after effects. When you go to the gym and train, two things will follow: there will be an increase in both your levels of fitness and the amount of fatigue your body experiences. An increase in fitness simply means an increase in a desired physical quality (e.g. power, strength) and fatigue is simply a product of metabolic, neural and hormonal changes in response to the training session. The important thing here is to realise that both fitness and fatigue occur in response to your training sessions. But, progress will come when fitness is maximised and fatigue is minimised. How you this, depends greatly on your training experience.

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Chiu et al. (2003). The Fitness-Fatigue Model. 

An important aspect of the fitness-fatigue model in the context of training programming are the properties of the fitness- and fatigue-after effects themselves. Following training, fitness-after effects tend to rise slowly in magnitude, but exhibit a long duration. This enables you to hold onto the performance gains made over the longer-term. However, the fatigue-after effects exhibit the opposite pattern, with a sharp rise in magnitude after the training sessions and only displaying a short duration. Now, this is both good and bad! The good thing about this is that provided your recovery is on point, you can control fatigue over time appropriately, thus allowing you to reap the benefits of the fitness-after effects. However, the potential risk here is that if you train like a maniac too much without planning in recovery periods into your training, it is very easy for fatigue-after effects to quickly build up, thus preventing you from experiencing any of the positive fitness-after effects developed. However, since training fatigue builds up and dissipates fast, smart training will allow you to control this fatigue over time without the risk of losing any of the fitness-after effects gained.

The Fitness-Fatigue Model And Training Programming

The great thing about the fitness-fatigue model is that it can be used as a framework to help optimise training (in this case for size and strength development) for both untrained (novices/beginners) and trained (intermediates/advanced) lifters. Why optimise? So that you can maximise these fitness-after effects (e.g. size and strength gains) and minimise the fatigue-after effects, ultimately allowing you to make progress over the longer-term. So, what does the model tell us?

If you are starting out in the gym for the very first time, have less than 6 months training experience under your belt or have never followed any training program in a consistent manner, then you are classed as a novice (or beginner) lifter. The advantage of being a novice is that your body is in, what I like to call, a hyper-responsive (or adaptive) state. In other words, whatever you do in terms of weight training at this point (it does not matter whether it is optimal or suboptimal), you will adapt quickly and make quick gains. It does not stay like that forever! But nonetheless, you will make progress. If you are a novice, then the chances are, your body will not be able to cope with much work to begin with (in terms of sets, reps and weights used). This of course is logical. If you have never really trained before, then your body will be lacking size and muscle mass. It is not a surprise then that you won’t be able to undertake every training session at this stage, with lots of weight, reps and sets!

However, as the total work you do will be small at this point, the fitness- and fatigue-after effects generated after each training session, will also be minor. Since fatigue rapidly dissipates over a short duration and increased fitness persists for a longer duration in comparison, novices can take advantage of this increased fitness (e.g. stronger/bigger than your previous session, thus you can do more work) every session without worrying about burning out, overtraining and under-recovering. Simply put, the fatigue you generate as a novice from one training session, will be pretty much gone within 24-48 hours, but the positive fitness-after effects will remain. By taking advantage of this, the best way of progressing as a novice lifter will be through conservative LINEAR increases in workloads for as long as possible, on a session-by-session basis (mainly through increases in weight on the bar). Typically, this you will be able to do for 6-12 months provided other aspects of your life are optimised (e.g. nutrition, sleep). However, after 6-12 months when the workloads start to become really high, you will find that you are no longer able to keep doing more work every session. At this point, linear progression is no longer a long-term option and it is time to start thinking about more sophisticated forms of training programming so that you can keep making further gains.

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Ok, so what happens if you are no longer a novice and you cannot keep increasing the total work you do on a session-by-session basis? Well, you need to start implementing some form of training PERIODISATION to your workloads. For instance, if your goal is to build more muscle, then the total training volume over time you perform will be the main driver of this (sets x reps x weight). However, as an intermediate/advanced lifter, the high workloads mean that you won’t be able to keep increasing this total training volume in a linear fashion. Since your workloads are now on average higher than as a novice lifter, the fitness-after effects and the fatigue-after effects will now be much greater. While the bigger fitness-after effects are great news, the accompanying fatigue will now be larger. This means that more time is needed between your sessions before taking advantage of this new increased level of fitness and doing even more work. Larger amounts of fatigue mean greater amounts of time are needed to allow this fatigue to dissipate. If you try and increase workloads in a linear fashion, you will simply be training each session in state of heightened fatigue. This occurs because the fatigue generated from your last session, is still too high! In this scenario, fatigue quickly builds up and your ability to use this increased fitness becomes compromised and you risk heading towards overtraining.

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If we are talking about more muscle growth over time, then typically one of the better ways of progressing in this intermediate/advanced lifting phase, is to perform short regular periods of something called functional overreaching interspersed with recovery periods. By training for short periods of time with progressively higher training volumes, you increase both the fitness-after effects as well as fatigue-after effects significantly in order to stimulate the needed adaptations. In this case, muscular growth! However, you don’t want these overreaching periods to be too long as the fatigue can quickly build up. But, as fatigue is short lasting, we can implement recovery periods following these functional overreaching periods in order to control this fatigue. Recovery periods are simply those in which normal training volumes are significantly reduced. The good thing is, you won’t lose any progress doing this. Why? Since the fitness-after effects are long in duration, we can use these recovery periods to reduce fatigue without the risk of losing any of the adaptations gained (provided the recovery periods are not too long!). Once fatigue has dissipated, you can then begin again with your new functional overreaching periods, in which you utilise your new levels of fitness to further increase workloads and make new gains! (progressive overload).

Fitness And Fatigue

Progress is all about balancing fitness and fatigue and the fitness-fatigue model explains nicely what is happening in response to training. Now that we know what is happening in terms of fitness and fatigue development, we can optimally program training to achieve maximum levels of size and strength. Now we know that fitness adaptations are actually pretty persistent in duration and fatigue is fast and short-acting in nature, we can exploit these properties to ensure that you are optimally recovering so that you can continue to progressively overload over time to stimulate further size and strength development.



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