Flexibility

[Guest guest]

Mel Siff:

<<Note that flexibility (Range of Movement) refers to joints, not to

muscles.>>

van Mol wrote:

<Not entirely, the flexibility in the knee and hip joints are largely

dependent on the laxity or tightness of bi-articulate muscles like the

semi-tendinosus, semi-membranosus, biceps femoris (caput longum), rectus

femoris and so forth, and on the spinal erector muscles. >

*** 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).

If the tissues are very extensible, then one can proceed as far as the end of

range as decreed by the bony architecture involved. If they are not that

extensible, then the joint will not reach that ultimate structural limit. At

this limit (before the joint is damaged or dislocated), extensibility of

joint capsule and any associated ligaments may permit a slightly greater

range.

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

perimysium, epimysium, Z-bands, etc in the muscles). Thus the ROM will

depend not only on the elasticity of passive structures, but the degree to

which the associated muscles are contracted (which, in turn, depends on

neural excitation). We could also refer to the plasticity of the soft

tissues, but that refers more to the permanent deformation of those tissues

in response to more sustained loading conditions.

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). In general, flexibility

is a function of skeletal structure, tissue structure and extensibility, and

neural control - and it always refers to a range of movement, 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

tissues, T2 = non-contractile tissues) and N refers to neural factors. Of

course, we could fine-tune this to describe static, passive and dynamic ROMs

(as I do in Ch 3 of " Supertraining " 2000).

The spinal erector muscles do not directly affect the " flexibility " or range

of movement of the knee or hip joints - any specific reason why they are

mentioned in this context?

Dr Mel C Siff

Denver, USA

Supertraining/