Flexibility

[Guest guest]

Mel Siff:

< *** Entirely! According to the standard definition as used in

biomechanics, flexibility still refers to the " functional " Range of Movement

(ROM) of a given JOINT, whether or not the tissues associated with that

joint have low or high mechanical extensibility or a high K (elasticity

constant). >

Van Mol:

Thank you for the lesson Dr Siff, but you are preaching to the choir. The

remark was merely intended to rectify your statement where you said that

muscles were not the cause of the lack of flexibility, where you yourself now

agree it does, as part of the joint. I do not doubt your expertise in the

matter one bit, just making the addition that you perhaps overlooked in your

original statement.

Mel Siff:

*** Nothing whatsoever was overlooked in my definition of flexibility - when

I wrote my original letter, I was fully aware of the nature of flexibility

and, as I again explained in my expanded definition, ROM = f (S, T, N),

which everyone in the choir knows includes implicit involvement of the soft

tissues. There is absolutely no need for " rectification " or addition -

flexibility is Range of Movement, irrespective of whether the joint is made

of muscles, ligaments, skin, rubber, or steel wire.

Mel Siff wrote:

<Note that I have chosen to use the term " extensible " instead of elastic (or

viscoelastic) here, because the length of the soft tissues associated with

the range of movement of a joint involves both contractile muscles and

non-contractile connective tissues such as ligaments and tendons (and........

>

Van Mol:

Thank you for the lesson, but I can name the all the ligaments of all major

joints off the top of my head, including origin and attachments. Like

yourself no doubt, systematic anatomy was my favorite class.

*** I was not referring to anatomy per se, but the biomechanical properties

of the tissues and how they alter in response to different conditions of

activity, with special reference to the underlying physics of the respective

materials in terms of elasticity, viscoelasticity, plasticity, Young's

modulus, Poisson's ratio and so forth - all of which can change during

muscle activity. Sadly, these topics are rarely covered in any anatomy

classes. Actually, while anatomy has always been fascinating, relativity

physics and electrodynamics were much closer to being my favourite subjects,

but eventually they took a somewhat back seat to biomechanics.

Mel Siff wrote:

<Incidentally, research indicates that the contribution to ROM due to tissue

extensibility usually is small compared with the contribution due to neural

factors (which also govern the degree of tension in any associated muscles

and therefore, the " extensibility " of the muscles). >

Van Mol

Interesting. So what you are saying is that the lack of flexibility caused

by, say a tight hamstring, would find its origin in the n. tibialis L5-S1

rather than the characteristics of the hamstring muscles, including length

and thickness ? Could you perhaps throw some of this research my way as I'm

having trouble comprehending the notion.

*** As I have stated before, the tension in any muscle is a function of

skeletal architecture, mechanical properties of all the tissues associated

with a joint and the degree of tension in any of those tissues, as

determined by neural activation and structural length. I did not state any

" either-or " scenario, as you imply, but one in which several factors can all

play a significant role. Sever all neural supply to the muscles and see how

the contractile actin-myosin structure contributes to " flexibility " - the

latter then will depend solely on passive soft tissues such as connective

tissue in the muscle complex, tendons and ligaments. No research at all is

necessary to reach this basic conclusion, but if you would like some relevant

references, begin by consulting the two books that I cite a little later on.

Mel Siff wrote:

<.... not the properties of its components. If we wished to express this in

mathematical terms:

Flexibility = ROM = f (S, T, N)

....where f (....) means " a function of " . S refers to skeletal structural

factors, T refers to tissue extensibility (including T1 = contractile........

>

Van Mol:

In mathematical terms then, the properties of a single component can alter

the outcome of the complete equation. Or am I so wrong in assuming that ?

*** That is how a mathematical " function " of several variables operates -

yes! This is no assumption; this is the basic definition of a function in

mathematics. Even without referring to the shorthand involved in that

equation, there is plenty of research which confirms that changes in any of

those three factors in parentheses will cause a change in ROM. See books

such as el & Nordin, 'Basic Biomechanics of the Skeletal System' or

Fung, 'Biomechanics: Mechanical Properties of Living Tissue'

Dr Mel C Siff

Denver, USA

Supertraining/