On 3/30/00, S.......?<[log in to unmask]> wrote:
<< An answer to this puzzle may be found in this extract taken from the
nursing
spectrum website (http://nsweb.nursingspectrum.com/ce/ce123.htm). Although
there is no graph (the Starling Curve) included it clearly states that in the
left ventricle the maximum muscle force is produced under conditions of
maximal prestretched muscle length to a point and that stretching the muscle
fibres beyond this reduces the force of contraction. I think the definition
of maximal should not be taken to be the same as maximum. Taking this into
consideration the two statements can be seen to concur. >>
***Your web search has put you on the right track, though we have to move
away from one type of muscle to another. Starling's Law is based upon
studies of heart contraction and, for the sake of deeper analysis, I simply
extrapolated that work to the case of skeletal muscle, which is involved more
with linear contraction across a joint than with the more volumetric contracti
on of cardiac muscle. Thus, we might examine if this sort of extrapolation to
striated muscle is accurately justified.
For one thing, how can we relate the different mode of reflexive and
voluntary neural excitation of skeletal muscle contraction to that of cardiac
rhythmicity? Are we stretching the theories and scope of laws a bit?
We also have to look carefully at concepts of muscle contraction, range of
joint movement and the degree of actomyosin overlap at different joint
angles, and then to move on from that point. For example, is it really
impossible for there to be significant actomyosin overlap even near full
range of joint movement? Does all of this mean that maximum actomyosin
overlap should be most likely when the muscle is most relaxed?
For those who wish to read more information on the biomechanics of muscle
action, then books or articles by authors such as Fung (Biomechanics:
Mechanical Properties of Living Tissue) and Frankel & Nordin (Basic
Biomechanics of the Skeletal System) can be very helpful.
Back to the rest of you!
Mel Siff
Dr Mel C Siff
Denver, USA
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