Personal Training 7a: Skeletal adaptations to training

This post is part of an ongoing series about my learning process as I train to become a personal trainer. 

The human body is a strange and wonderful thing.  It is also remarkably responsive to activity or movement.  In this mini-series, I look at the three main types of adaptation or change that occur when we exercise.  In this first post, I look at the skeletal changes, next week I’ll look at the muscular changes and in the final week I’ll look at the cardiovascular changes. 

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Skeletal changes 

My course notes identify the adaptations by the type of exercise that causes them.  Here is a table that I have created from my notes, showing what they consider to be the skeletal adaptations and what sort of exercise (muscular strength, muscular endurance or cardiovascular) causes them: 

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Increased bone density (a rant) 

I have to start by saying that I feel that this area is poorly treated by my course notes and also by my textbook, albeit for different reasons.  That sounds fairly stroppy so let me explain. 

I think my textbook fails in that it covers over 800 pages of exercise physiology and apart from an appendix in which the “ACSM stand on physiscal activity and osteoporosis” is provided, there is no mention of skeletal adaptations to training at all.

And I think my course notes are misleading by inferring that all three types of training cause increased bone density equally.  I don’t think that this is the case at all, as only strength training really allows Wolff’s Law of Bone to work its magic.

Wolff’s Law of what?

Let me explain…

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Wolff’s Law of Bone

We all happily go along with the idea that “exercise” (whatever that is) increases bone density.  But what is actually happening and why?  In fact, the mechanism by which bone increases in density is called Wolff’s Law of Bone, which states that: 

“Bone in a healthy person or animal will adapt to the loads it is placed under.  If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.”  

In other words, if you flew off in a spaceship to live on a high gravity planet, such as Jupiter, where the gravitational pull is 2.5 times that of the earth, then your skeleton would get bigger and denser.  No squats, no milk, just gravity.

Talking about spaceships, Wolff’s law is also reversible.  It has been well observed that people who remove stressors from their bones (e.g. like astronauts or bed-ridden hospital patients) actually experience significant losses in bone mass and density.  In other words, if you don’t use it, you lose it.  So in your flight from earth to Jupiter, you would lose bone mass. 

I think Wolff’s Law of Bone is one of the most amazing and fascinating physiological adaptations that the human body is capable of.  Put another way, if you want, you can grow bone at will.  All you need is time and the appropriate application of force.  Just like The Abomination…      

Give me a real fight! 

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Decreased risk of osteoporosis 

Osteoporosis is a horrible disease that arises when bone density falls below a certain level.  However, it is not a disease like influenza, which is caused by viruses.  It is more like scurvy, which is a condition caused by the absence of enough Vitamin C.  What do I mean?

Well, Wolff’s Law of Bone doesn’t stop working when you get over a certain age.  So except for certain cases, where there are other factors causing significant hormonal problems, it seems that osteoporosis should be considered preventable.  Don’t believe me?  Check out this article on the British Medical Journal, which states: “the skeleton is mechanosensitive across the lifespan and responds and adapts to its prevailing mechanical environment.”  In other words, you can grow bone at 100 years old if you put some weight on it (see Biomarkers for further details).

I feel quite passionately that we should be doing more to educate people that they can use strength training to forestall what they see as the “inevitable” effects of ageing and osteoporosis a prime example of this.

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Increased joint strength

I’m not going to say much here other than to observe that, unless I am missing something, joints comprise mainly bone, connective tissue and muscle so are dealt with by adaptations in those areas. 

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Increased connective tissue strength

Not exactly a skeletal adaptation but my course notes clearly had nowhere else to put it.  Changes in connective tissue fall under the heading of Davis’s Law, which governs how soft tissue (tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes (connective tissue), and muscles, nerves and blood vessels (everything else)) remodels according to imposed external forces.

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Increased red and white blood cell production 

Erythropoiesis is the process by which red blood cells (erythrocytes) are produced in the red bone marrow.  White blood cells are made in a different part of the bone marrow, called the Hematopoietic stem cells.  According to my course notes, all types of exercise increase both red and white blood cell production.

I have not read anything in my course notes or my textbook about the mechanisms by which this increase occurs.  I did do some research on the internet but only really got as far as two animal studies:

• In this rather amusing study, a group of five Beagles were subjected to an hour of maximal (!) treadmill exercise for 5 days a week for 6 weeks.  The result was that no increase in red blood cell mass, serum erythropoietin concentration, or any other blood cell index measured and the researchers concluded that this type of exercise conditioning does not produce the necessary stimulus for an increase in erythropoiesis.
• And in this study, a group of 7 male horses were subjected to 272 days of consecutive hard training to assess the markers for overtraining.  The horses showed some decline in muscle ATP concentration during maximal exercise but, interestingly, plasma volume, red blood cell volume, and blood chemical variables were unchanged.

So instead of resolving the matter, I am still none-the-wiser about the mechanism by which red blood cells are increased and I am starting to doubt that they do (except in response to altitude training).  I am also quite keen to know why, if it is true that humans can increase their red blood cell production through cardiovascular exercise,  dogs and horses do not respond in the same way.  And I would really love to know how these researchers got away with doing a whole study involving letting dogs run on treadmills.  This exercise physiology research lark seems like great fun!

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Enhanced immune system

The immune system is strongly affected by the level of white blood cell production and therefore as the production of these increases, so does the efficacy of the immune system.  However, I note that there is a paradoxical effect in that the immune system is weakened directly following hard exercise, as this study shows.  Similarly, this study of IronMan competitors also showed a higher than normal level of oxidative stress among competitors.

I think I’ve probably raised more questions than given answers here but I’ll try and find time to do the research on the areas that I haven’t resolved to my own satisfaction later in the year.  As always, if you have any searing insights into the dark clouds that are hovering above my head at the moment, please do let me know.