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Physiologic Flexibility – Building Human Resiliency

Performance Training Personal Training

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On the whiteboard inside the gym we’ve had an “Ask Me Anything?” section for clients to add any questions or queries they’d like to know more about the past few weeks.

There’s been some pretty far ranging questions and topics so far which has been really fun to see where people’s interest are within the fields of health, fitness and wellbeing.

A couple of the questions from this past week or so tie in nicely around the concept for todays insight, that of Physiologic Flexibility. The first of which was regarding Cold Water Immersion which seems to be a growing trend recently with many braving to cold of the seas and lakes of South Wales. The second questions was around the purpose and potential benefits of Intermittent Fasting.

In this insight I wanted to provide an overview from which we can begin to answer these types of questions collectively with a clear framework in mind. 

I owe essentially all credit to the work of Dr Mike T Nelson who’s mini-lectures, courses and podcasts I’ve followed for a few years now, and who’s responsible in bringing my attention towards the concepts of both Physiologic and Metabolic Flexibility. 

Let’s get started!

Inside our bodies we like things to be kept relatively stable. 

Our most important systems, those required for our immediate survival, work best when the internal environment is predictable. 

As such, the body has 4 major homeostatic regulators for those things that most tightly need to be kept at an equilibrium. We may be pretty familiar with these even if we may not recognise the terms specifically.

The first of these is our internal core body temperature, with normal classification commonly citied as between 36.5-37.5C. Within this range, temperature is regulated and systems are functioning optimally in response. 

However anyone who has been ill with a fever, or gone to an extremely cold part of the world, will know that core body temperature reacts in response to changing internal and external environment.

With certain types of illnesses, I may develop a fever (>37.5C), or more severe hyperthermia, in which temperature reaches above 40.0C, considered life threatening. This is an immune system response to an impending threat. Likewise if I spend too much time in an extremely warm environment without taking proper precaution, I run the risk of over-heating, again life threatening depending on severity.

Alternatively after prolonged exposure to cold conditions, which drops my core body temperature, I may potentially suffer with hypothermia (<35.0C), again life threatening.

Briefly consider just how tight a window of body temperature control that is. There’s only a few degrees difference between life threatening conditions of both under and over heating.

Yet within this window of regulatory control, we have the possibility to safely fluctuate between cold and hot, by reducing or increasing internal core body temperature through differing time-dependent exposures. 

Regular and controlled exposure to both ends within a safe zone may benefit long term in the same way in which progressively exposing yourself to resistance training can make you a stronger, more resilient human being.

The more I expose myself to either end, the greater my capacity to safely tolerate these stressors. This is no greater evidenced by those individuals who can live in countries such as Dubai, in which summer temperatures easily exceed 40C, and those in Canada in which winter temperatures can reach as low as -40C.

The next of our four homeostatic regulators is pH, the measure of how acidic or alkaline (basic) something is. 

Specifically within the human body we’re talking about the pH of both the intracellular (within a cell) and extracellular (outside the cell) spaces. The higher along the scale (0-14), the more alkaline, the lower down, the more acidic.

As with temperature, the body requires tight regulation of intra and extracellular pH for biological cells to function optimally. This range is most commonly described as between 7.0-7.4 (very slightly alkaline…) with some tissue-specific exceptions.

Within all of us, we have buffering systems that aim to keep us within the normative values for pH to enable internal systems and structures to operate smoothly.

We’re able to exposure the body to periods of more acidic conditions internally through activities that generate bi-products from energy production that decrease pH within the body. Examples would be high-intensity activities (30-120sec) with little rest periods, in which lactic acid is produced and immediately converted into lactate and hydrogen ions which the body has to buffer to return the pH to “normal” levels.

Alongside pH, we also have blood glucose. 

For us to maintain life and function as a human being, we need to produce energy. The primary ways in which we can create energy is through breakdown of food sources that we consume, or through the utilisation of stored energy found in body fat. 

As these food sources are broken down they enable glucose to enter the blood stream for use within the body.

Being able to regulate blood glucose levels in a time-dependent manner even in the face of large amounts of carbohydrate intake, or in periods with greater reliance on stored or consumed sources of fat, displays the capacity for resiliency and variability in energy production and blood glucose control.

Speak to anyone who suffers with diabetes and they’ll be able to describe the potential risks of when too much or too little glucose is present in the blood.

The capacity for regulation of blood glucose also adds an interesting dynamic to the timing and sources of energy intake around training. 

If carbohydrates are a more rapidly available energy source, it may benefit me to tie closely my intake of these food sources around training types of that require these more immediate form of energy such as within High Intensity Interval Training. 

Likewise with fat metabolisation being a slower rate of production but with a greater overall yield of supply it may benefit me to tie intake, or bias more stored fat usage through an approach such as fasted long-duration cardio in which very little energy is available from the intake of food sources.

Our final homeostatic regulator pertains to how oxygen (02) and carbon dioxide (C02) are balanced within the body. 

At a fundamental level, we require oxygen to live. Our cells need 02 for energy production. However the process of breathing is primarily regulated by our requirement to expel carbon dioxide, the bi-product of respiration. C02 is not so much a waste product but a crucial component that requires regulation and balance.

Anyone who has either lived or trained at high altitude, in which oxygen levels are low within the air we breathe, will attest to how greatly it impacts our ability to not only train and perform, but just simply function.

Likewise anyone who has suffered with an anxiety attack and the resulting hyperventilation that ensues, dropping C02 levels significantly due to over breathing, you’ll know how key it is to maintain the balance between 02 in and C02 out…

As you may have guessed, the easiest way we’re able to alter how we utilise 02 and C02, is through methods that impact the manner in which we breathe. 

The most obvious example here would be through exercise. As the demands of an activity increases, the requirement for 02 to the working muscles also increases. The greater the intensity, the greater 02 utilisation.

However we also have the capacity outside of exercise to alter the balance between 02 and C02 through variations in breathing techniques. 

The past few years has seen greater attention drawn to protocols such as the those described by individuals such as Wim Hof which alter this balance between the two.

Within each of these four homeostatic regulators, we have a pendulum that we’re trying to gain greater control and resiliency over; 

  • High internal temperature vs low internal temperature
  • High internal pH vs low internal pH
  • Lower blood glucose vs higher blood glucose
  • High/Low levels of 02 vs High/Low levels of C02.

The concept of Physiologic Flexibility is to develop greater robustness and anti-fragility as a human-being through pre-conditioning of these homeostatic regulators. 

Expose myself in a deliberate and controlled manner to various stressors so that I can better respond to a similar unexpected stressor when it occurs.

Within this framework lies the answers to the client questions we opened with.

What value is there of Cold Water Immersion?

Cold Water Immersion is a tool we can use to expand our capacity to tolerate changes in internal core body temperature. A contrasting example would be the use of a Sauna which can facilitate an expansion in our tolerance for increases in core body temperature. The goal here is to develop the ability over time to move between these two extremes, challenging homeostasis, so that when a true stressor arrives like a training run in a warmer climate, or exposure to freezing conditions, the body has experienced similar exposures, hot or cold, previously and developed greater resiliency along the way.

What value is there in Intermittent Fasting?

The ability to fast intermittently and maintain a stable blood glucose level represents the metabolic capacity to utilise alternate sources of fuel (i.e. stored body fat) for energy production. Likewise the ability to consume carbohydrates and manage any subsequent spike in blood glucose within a timely manner, shows the metabolic capacity to safely utilise and store carbohydrates for energy production.

Hopefully within this insight it’s provided you with an overview of basic concepts of Physiologic Flexibility, as well as potentially giving you a framework from which to begin to answer some of your own questions that may have popped up along the way.

If there’s any comments, queries or further information you’d like based on this insight, feel free to get in touch!

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