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‚On April 6th I sent the following question to Biomech©l. After the query
is a summary of the replies.
I'm looking for studies investigating the influence of resistance
and flexibility exercises on the resting length of muscle, its stiffness
and resting tonicity. My question concerns the clinical
practice of correcting an anterior pelvic tilt which results in icreased
lordosis via a strengthening regime of Rectus Abdominis. This practice
would suggest that by strengthening a muscle its resting length or its resting
tonicity would change to result in an alteration in the pelvic
posture. The reverse of this is to stretch the hip flexors resulting in a
decreased "pull" on the pelvis and a subsequent decrease in the anterior
pelvic tilt. A parallel to this example is the theory that strengthening
the chest muscles without concommitant strengthening of the back
musculature will result in rounded shoulders. I can not find
any support for this in the literature. I
would appreciate any relevant sources that address these issues directly
or indirectly.
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I am not sure if you are referring to resting sarcomere length or measureable
length of muscle fibers. In regards to stretching, the literature is
controversial but it appears that sarcomere length tends to adapt to prolonged
tensions by the addition of sarcomeres so as to maintain the optimal sarcomere
lengths. As you probably know passive extensibility of a muscle is limited
mostly by its connective tissue. The jury is out as to what are the long term
adaptations to passive stretching so you may want to do some basic literature
reviews before you assume you can directly influence muscle extensibility
through basic stretching techniques. There are numerous studies on the short
term effects but I assume you are looking towards more lasting changes. You
can certainly demonstrate changes in range of motion in muscles with specific
stretching but some recent studies are suggesting that this increase is due
to an increase in stretch tolerance and probably not a change in muscle
stiffness. I would assume you would be trying to influence muscle stiffness
in order to make any lasting changes in pelvic girdle posturing. You might
read research by Jan P. Halberstma or S. Peter Magnusson on the effects of
stretching on passive extensibility and stiffness in hamstrings. Both of
these have written quite a few articles on the subject. You might consider
mobility not only of the hip flexors but also of the posterior lumbar soft
tissues, intervertbral disc. and other muscle groups i.e. rectus Femoris and
probably the anterior portion of the TFL . There are studies suggesting that
isometric exercise may influence soft tissue extensibility similiar to passive
stretching but unfortunately I dont have them in front of me right now but if
you need them let me know and I will get them for you.
ŒSteve Laslovich
slaslovich@aol.com
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Steve Laslovich also replied;
The problem comes when you are directly relating maximum measures of static
ROM with muscle stiffness. Rarely do we function at the maximum measurable
range of motion so the question becomes, is stiffness a better measure of
function than static maximal ROM? In your study, in what range are the hip
flexors functioning to control pelvic rotation would be something to answer.
No one has come up with the exact mechanism for stiffness other than
descriptive parameters of stiffness. The question you have is whether you
want to influence stiffness or do you want to influence max ROM. If you look
at the numerous studies on flexibility of the
musculotendon unit you will notice that not only or results variable and
mostly temporary but there are limits. Hamstring flexibility, which is the
most commonly used group, tends to have finite improvements in ROM across most
studies. This makes sense when you consider that collagen orientation and
chemistry are fairly stable entities. Studies on prolonged immobilization in
lengthened (or shortened) positions point to adaptations in sarcomere number
but may not necessarily relate to increases, (decreases) in resting muscle
fiber length. Look at studies by PE Williams and then read RD Herbert, J
Crosbie 1997 Eur J Appl Physiol. It becomes apparent that the numbers of
sarcomeres in series may be dictated by the tensile stress over time.
Preliminary studies even on eccentric contractions show a possible adaptation
may be the addition of sarcomeres in series.
In regards to exercise and changes in muscle tension look at Dean C Taylor et
all 1997 on their study of passive stretching vs muscular contractions for
some insight into the role of exercise, in this case isometric, on passive
tension.
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á á
In reference to the subject of Strength vs Flexibility y would like to say
that basically there is no relationship between these two parameters.
In order to shorten a muscle we have to put it into a "shortened
mechanical position". Studies show that after 4 days of immobilization a
muscles shows increase in the quantity of colagen which increases its
"stifness".
In a study that we did on the effect of strength training with various
ranges of motion on the flexibility we found that the flexibility was notŒaffected by neither of the regimes.
This is consistent with what we found in the literature at the time.
I remember one study that reported a decrease in flexibility as results of
strength training and this study trained the elbow flexors. People that
train the elbow flexors usually adopt a "flexed elbow posture".
The reason of the shortening of the elbow flexors is not the fact that they
become stronger but the fact that they are most of the time in a shortened
position.
In regards to the comment about Round shoulders and Lordosis I would like
to tell you that human beings do not behave in a mechanistic way.
It is nice to think that if we stretch a muscle group and strengthen the
antagonists we will improve posture.
I work with postural problems for more than 30 years and this approach does
not work.
Sincerely yours
Alberto Ayalon, Ph.D.
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Gregory J Lehman
M.Sc. Candidate--Spine Biomechanics
University of Waterloo
(519) 885-6652
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