Homeostasis, hysteresis and you

In this post I want to talk about the principles of homeostasis, and hysteresis, and how they apply to both training, especially weight training, and dieting / losing weight.

So what are those two things? Lets look at homeostasis first. It is a general principle that states that a system adapts to external conditions until if finds an equilibrium. You might remember the phase diagram for water from high school – it shows how water reaches and equilibrium state (meaning ice, liquid, steam) depending on the temperature and the pressure. Of course for the ladies the carbon phase diagram might be more interesting: whilst on the bottom of the diagram you will find ordinary barbeque coal, on the top you will find your best friend – diamonds. And all it takes to get from one to the other is a bit of effort – some heat, some pressure. Really not much different than getting your dreambody through exercise, isnt it?

The important thing about those equilibrium processes is that – other than being potentially slow – they dont have memory: if you know the external conditions, then you know which state it is in. Or have you ever seen an ice-cube swirling in your steaming cup of tea when you were trying to make ice tea? Didnt think so.

We already mentioned memory – this is where hysteresis comes in. In fact, hysteresis is really only a fancy word for the memory of a system. Again going back to high school, you’ll see in the graph how hysteresis (for a ferromagnet) looks like. On the x-axis is the environment (magnetic field), on the y-axis is the (equilibrium!) response (magnetisation), and you see that this equilibrium response is different depending on the history of the system.

Alright, but what does it all have to do with training you might ask. I mean, I understand that you are not here to catch up on your high school physics. It is rather easy actually: the external environment is everything you do to your body, in particular your training (those 100kg+ back-squats you’ll do every other day…) and your diet (the 6000cals with 400g protein, or the 1200cals low fat as the case may be).

Now in a pure equilibrium model your body would adapt to the stimulus in a consistent manner: you eat a lot, you gain weight. If you are training hard this will be mainly muscle, it not, fat. It is funny though that people seem to only believe in this principle when it suits them: so if you lift PR’s 3 days a week you gain muscle – and if at one point the only thing you lift is yourself from the couch, then the muscle is supposed to stay magically there. Same with dieting: you starve yourself, you lose weight. You stop starving yourself – guess what? You gain it back. That’s pure homeostasis for you – a dynamic equilibrium where the body adapts itself – with a certain delay – to whatever environment you provide, upwards or downwards.

We all know that this is not the whole truth. That’s where the hysteresis comes in: the body has a memory, and what you have done in the past does impact on how it behaves now. One example is what body builders call “muscle memory”: if you had big muscles in the past, and you have lost them for the lack of exercise, you are much quicker at (re-)building  them than someone who starts from scratch. This also works the other way round unfortunately: if you have been fat in the past it is much more likely you will gain weight again if you do not pay attention.

I will come back to this concept(s) in future posts. What I want to point out here already though is that the interplay between those two concepts is pervasive at most stages of the training and nutrition process, and across many timescales. Some are obvious, some less so:

  • If you have squatted a true 1RM yesterday it is not a good idea to attempt to do the same today, unless you are a beginner (see the two timescales that come in?)
  • If you have been very fit in the past, then it is dangerous to push yourself to the max in your “comeback” workout (monster DOMS, rhabdo)
  • If you want to lose weight, then you need to reduce your calorie intake without your body switching into starvation mode (or otherwise persuade your body to be in a state where it is burning more energy than you feed it)

So what training (and dieting) is all about is to dynamically adapt the environment in which your body exists (eg training stimulus, nutrition) to the internal state in which it is in at a particular point of time (eg stage of the recovery process, metabolic parameters). Failure to do so will often result in failure. Full stop.

Now clearly, understanding this does not really bring us closer to solving the problem how to train (or eat) optimally. What it does however is to provide us with a framework for understanding different training and dieting strategies. It in particular reminds us that an overly simplistic view of the world is dangerous, and that naive application of mental model (eg of thermodynamical principles like “calories-in-calories-out”) can lead to dreaded effects, like plateaus or yoyo’s.


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