Trevor Allen is a researcher at the School of Physiotherapy, The 
University of Melbourne, who lectures our post-graduate physiotherapy 
students in muscle physiology - forwarded by Liz Williams, Lecturer
>------------------
>
>Response from Trevor Allen:
>
>Sorry for butting in here folks, but I have to respond to the email by Dr.
>Mel Siff.  I do not want people to walk away from this with a
>misunderstanding of muscle physiology.  Firstly I am not a physio, I am a
>muscle physiologist, having recently completed a PhD on eccentric
>contractions and muscle damage.  Also I have missed the earlier posts so I
>don't know what has gone on before this (or if there have been any more
>recent posts).
>
>
>>>Date: Tue, 28 Mar 2000 15:56:05 -0500 (EST)
>>>From: [log in to unmask]
>>>Subject: PILATES & PHYSIOLOGY
>>>Sender: [log in to unmask]
>>>To: [log in to unmask]
>>>Reply-to: [log in to unmask]
>>>X-Unsub: To leave, send text 'leave physio' to [log in to unmask]
>>>
>>>Ond 3/28/00, Simon Mesner<[log in to unmask]> wrote:
>>>
>>><< I am suprised that you are slagging off the muscle physiology behind
>>>Pilates when you are unable to adequately describe muscle contraction.
>>>Muscles activate both when shortening and lengthening, the latter being
>>>eccentric muscle contraction.   >>
>>>
>
>[log in to unmask] wrote:
>>>***I am not quite sure whether your comment is a comic response or not, so I
>>>shall start by assuming that it is serious. If so, then it is your
>>>understanding of muscle physiology that needs major re-examination.
>>>
>
>Simon was pretty much correct in saying that "Muscles activate both when
>shortening and lengthening", although I would prefer to change "muscles
>activate" to "muscle can be active".   An eccentric contraction is a
>contraction in which the external force is greater than the isometric force
>of the contracting muscle, so that the muscle is forcibly lengthened while
>generating tension.
>
>
>[log in to unmask] wrote:
>>>You have
>>>fallen for the very common misunderstanding that a muscle lengthens during
>>>ecccentric joint action relative to its resting state.   A muscle, whether
>>>acting concentrically, eccentrically or isometrically, always has a shorter
>>>length than in its resting state.
>
>What do you mean by "resting state"?  Are you talking about muscle length,
>limb position or level of activity?  For a given limb position yes the
>muscle will be shorter while it is "active" compared to when it is not.
>But this is not necessarily the case if the limb is then moved in a
>direction that increases the length of the muscle-tendon unit.  We are
>talking about dynamic muscle activity here (eccentric, concentric) the
>limbs are moving, not in a static position.  Simon's above reference to
>lengthening (eccentric) contractions made no reference what the muscle
>length was to start with, or what length the muscle may be stretched to.
>Neither does mine or any other definition I've seen, so why are you
>bringing in a separate topic about whether the muscle is stretched beyond
>what you call the "resting state"?
>
>[log in to unmask] wrote:
>>>Every textbook on physiology will tell you that muscle can only relax or
>>>contract.
>
>This statement makes it sound like muscle activation is an all-or-nothing
>phenomenon.  This is the case for a single fibre, but not whole muscle.
>What is a "relaxed" muscle?  I would say that you can relax a muscle (ie.
>reduce the neural drive to it) but it can still be contracting.  Many
>muscles of the body have some resting activity even when they appear to be
>relaxed.  Only when there is almost complete inhibition of motorneurones at
>the spinal cord level (eg. REM sleep) could you safely say that a whole
>muscle is no longer contracting.  Also, the term "contract" in muscle
>physiology should not be associated with "shortening", or we all get very
>confused.  We know a muscle can contract while being lengthened (ie.
>eccentric), which from our dictionary definition of "contract" is a
>contradiction in terms, so it is better to consider that a "contracting
>muscle" is one which is "active" or "generating tension" (ie. the
>crossbridges within the sarcomeres are cycling).
>
>[log in to unmask] wrote:
>>>If muscles is stimulated by nervous excitation, it can NEVER
>>>lengthen relative to its unactivated state.
>
>Wrong.  An external force such as gravity can forcibly stretch a muscle to
>beyond its resting length while contracting, as long as anatomical limits
>allow it to do so.
>
>[log in to unmask] wrote:
>>>If you examine a full back and
>>>forth repetition of every exercise, the muscle shortens over its resting
>>>length during its concentric phase, then, during the eccentric phase, the
>>>muscle lengthens towards its original resting state length.  It never
>>>lengthens beyond its resting state length.
>>>
>
>What if your "resting state length" of the muscle happens to be relatively
>short before you start the movement?  For example, if the "resting state
>length" of quadriceps is close to full knee extension, the quads are almost
>at their shortest length in this position (ignoring hip angle for the
>moment).  Any flexion of the knee will stretch these muscles, so if you
>walk down a steep hill, the quads are undergoing eccentric contractions and
>they will be stretch to a length greater than when they are at "resting
>state length".   Sure the tendons will take up some of the lengthening, but
>not enough to stop active stretching of the muscles beyond their "resting
>length".  This is especially the case for two joint muscles such as
>gastrocnemius, hamstring, biceps brachii etc etc.
>
>[log in to unmask] wrote:
>>>You also need to understand that muscle action is determined by its active
>>>contractile component (CC) and its two passive connective tissue components
>>>(SEC - Series Elastic Element and PEC - Parallel Elastic 
>>>Component), with all
>>>contraction being undertaken by the CC and any passive stretching involving
>>>the connective tissue components.
>>>
>
>It is important to also say that the contractile components often make a
>contribution to tension during passive stretching, either due to some
>resting activity of the muscle, or the formation of what are called "stable
>crossbridges" within sarcomeres.  Filament overlap within sarcomeres can
>also change (decrease) during passive stretching.
>
>[log in to unmask] wrote:
>>>Thus, if there is an element of stretching, it is due to the small 
>>>elongation
>>>of these components.  In this regard, the degree of stretch is determined by
>>>the magnitude and rate of loading (since all of the tissues are
>>>viscoelastic), so that ballistic, suddenly terminated or rebound activities
>>>will induce a greater lengthening than slow activities.
>
>Ballistic or high velocity stretches will not induce a greater lengthening
>of the muscle-tendon unit (as a whole) than slow stretches if they occur
>over the same anatomical range.
>
>[log in to unmask] wrote:
>>>However, since the
>>>mechanical stiffness of the active soft tissues and the passive tendons  is
>>>so large, even this amount of lengthening is small relative to the 
>>>changes in
>>>length of the muscle complex associated with muscle contraction.
>>>
>>>If you would like to study the biomechanics of muscle action in greater
>>>depth, you may refer to Ch 1 of our textbook, Siff & Verkhoshansky,
>>>"Supertraining" (1999).  There you will also find out how the behaviour of
>>>the different components of muscle explain the stretch-shortening 
>>>phenomenon,
>>>transient lengthening of the muscle complex and so-called 
>>>plyometric training
>>>(Ch 5), plus how this relates to PNF in physiotherapy.
>>>
>>>You will also discover that there is a process that may be called explosive
>>>isometrics, a coupling phase between sequences of explosive eccentric and
>>>concentric joint actions, and that it is during this phase, not during
>>>eccentric action that tension in the muscle complex reaches its greatest
>>>value.
>
>
>How does this explain Hill's Force-Velocity curve which we see in every
>muscle physiology text?  According to that, the highest tensions occur
>during high velocity eccentric contractions.  There are also numerous
>papers which show that muscle can generate more force during an eccentric
>than either a concentric or isometric contraction.  It may be that for
>stretch-shortening, in the preceding eccentric contraction the muscle is
>sub-maximally activated.  If you have the data, to be honest I can't think
>of another explanation.
>
>
>>>
>>>Simon Mesner again:
>>>
>>><<I also believe that when the Pilates people refer to longer muscles they
>>>are describing muscles that are worked through out range rather than only at
>>>inner range, something which weight training programmes
>>>
>>>do not identify with regard to abdominal training at least.>>
>>>
>
>[log in to unmask] wrote:
>>>***In physiology there is no such thing as working the"inner 
>>>range" or "outer
>>>range" of a muscle. However, if you have come across a suitable reference to
>>>prove how defective my muscle physiology is in this department as well, I
>>>would really appreciate being re-educated.   Joints may act over differing
>>>ranges, a process that is orchestrated by muscle action, but muscles don't
>>>have an inner part and an outer part which lengthen or contract differently
>>>during Pilates work.
>>>
>
>I find this inner and outer range thing a bit confusing, but probably
>because I am not a Physio.  I also know nothing about Pilates so I will
>stay out of that.  Physiologists prefer to talk about the ascending and
>descending limbs of the muscle length-tension (or angle-torque) relation.
>All mammalian skeletal muscles show an ascending limb (where isometric
>force increases as with muscle length) and a descending limb (where
>isometric force begins to decrease with increasing muscle length.  When
>muscles are connected to the skeletal system we have to talk about
>angle-torque relation of muscles since the muscles are attached across
>bones (usually via tendons), and muscle length ranges are limited by the
>range of motion of the joint(s).  In this case muscle length is altered by
>movement of a limb(s) about a joint(s), which will also alter moment-arm at
>the same time.  For some muscles the angle-torque relation is similarly
>shaped to the length-tension relation (ie. there is still both an ascending
>and descending limb), and although not always the case, many muscles are
>stretched onto their descending limb within the anatomical range of the
>joint.  Repeated active stretching (eccentric contractions) of muscle onto
>the descending limb is often responsible for the sensation of delayed
>muscle soreness we feel after unaccustomed exercise.
>
>[log in to unmask] wrote:
>>>
>>>Resting muscle length is determined in any individual by the 
>>>distance between
>>>the sites for its two bony attachments (often called its origin and
>>>insertion), i.e., genetically inherited joint architecture, and has nothing
>>>to do with Pilates exercises.
>
>What about tendon length and compliance?  What about muscle fibre pennation
>angles?  What about resting muscle activity?  What about length,
>architecture and activity of other muscles working across the same
>joint(s)? (agonist and antagonist).
>
>I think you need to clearly define some of the terms you throw into the
>discussion.  If anyone would like to read a quality muscle physiology text
>I would recommend "Muscle Structure and Function - Implications for
>Rehabilitation and Sports Medicine" by R. Lieber (1992).
>
>
>Trevor Allen
>
Elizabeth Williams
Lecturer in Paediatrics
School of Physiotherapy
The University of Melbourne
Telephone + 61 3 9344 7924
Fax + 61 3 9344 4188
email [log in to unmask]


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