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>On Fri, 16 Oct 1998, James Dowling wrote:
>
>No. I only discussed one issue which was the attribution of extra
>potential energy achieved in a counter movement jump over that achieved in
>a squat jump to the utilization of stored elastic energy. If you re-read
>my posting more carefully you should see that I stated that SOME of that
>extra energy IS probably due to the utilization of stored elastic energy
>but there are other contributing factors not related to either stored
>energy or to neural facilitation. Unless you are willing to form the
>contrary argument that you CAN quantify the amount of stored elastic
>energy recovered in human movement with the method proposed by Komi and
>Bosco (1978), I fail to see the point of your posting.
You stated that more work is produced in the concentric phase of a
stretch-shorten cycle even without storage of energy in elastic elements as
found from a computer simulation of the elbow joint (Dowling, Human Movement
Science 11:273-297, 1992). Therefore, you indicated that Komi and Bosco
(1978) were incorrect in attributing differences in changes in positive
energy between a drop jump and a static jump purely to stored elastic
energy. I do not agree with your conclusion. It has been suggested that an
increase in mechanical work performed by a stretched muscle fibre may be the
result of an increased excitation state (potential energy) of cross-bridges
or increased cross-bridge interaction (Cavagna et al. 1986). However, a
recent study could not confirm this theory (Cavagna et al. 1994). Morgan
(1990) has indicated that even when there is no filament overlap in a
sarcomere after fast stretching there is still an increased ability to do
work from the fibre (these studies have looked just at muscle tissue, no
tendons or ligaments). Cavagna et al. (1994) stated that passive
visco-elastic components of muscle tissue during stretching increase the
ability to do work during subsequent shortening. However, they could not
confirm cross-bridge contribution to increased work after stretch. If
cross-bridges are not responsible for increased work then where is the
ability to perform more work after stretch coming from?
Very little difference was found between the amount of work
performed in the concentric phase between a static (concentric only) and
countermovement squat if the static squat was preceded by an isometric
preload (Walshe et al. 1998). Therefore, more work isn't achieved in a
countermovement squat over a static squat if a pre-force is added. Cavagna
et al. (1985) reported storage of elastic energy after both stretch and
isometric contraction. So where is the increased work coming from if
cross-bridge interaction is not a factor? This would only leave the elastic
structures within the muscle tissue itself (titin). Do you have additional
evidence (other than your computer model of the elbow joint) that more work
can be performed during the concentric phase of a stretch-shorten cycle
WITHOUT the usage of stored elastic energy from the visco-elastic components
of the muscle? I know some evidence supporting the role of cross-bridge
potentiation after stretch exists but this area is still unclear.
>Again, if you read my posting more carefully you will notice the the
>mathematical model that I referred to had NO ELASTICITY! In laboratory
>experiments involving biological tissues you cannot eliminate elasticity
>completely and this is the beauty of a mathematical proof. If you can
>prove that the counter movment produces more energy in the complete absence
>of strain energy then one cannot attribute ALL of the energy to
>elasticity. At least one additional factor exists and this
>level of proof (mathematical) is unattainable in traditional experiments.
If a muscle fibre produces more work after stretch with no filament
overlap (no cross-bridge interaction) (Morgan 1990) and can also produce
more work, as you have stated, with no elasticity then I am at a loss.
Where is the ability to do additional work coming from?
>This is in total agreement with my posting. Incidentally, I Emailed both
>Marco Cardinale and Jerry Telle asking them to estimate how widespread the
>practice of estimating utilization of stored elastic energy in athletes
>was. At the time of this posting, I have not received a response from
>either of them. Given the problems with the measurement of this
>phenomenon, I hope the practice is not very common and the only purpose of
>my original posting was to alert those that may using the method of its
>potential errors.
I will finish with a statement from Cavagna et al. (1994).
"Stretching a contracting muscle leads to greater mechanical work being done
during subsequent shortening.... the mechanism of this enhancement IS NOT
KNOWN." There is not a problem with measuring differences in changes in
positive energy between countermovement and static jumps which has been done
for years by exercise scientist. One must be careful when supplying reasons
for this difference, however, I do not think it is unreasonable to speculate
that the difference between changes in positive energy during a
countermovement jump (or drop jump) and static jump could be due purely to
stored elastic energy.
--
Jeffrey M. McBride, MS, CSCS
School of Exercise Science and Sport Management
Southern Cross University
PO Box 157
Lismore, NSW 2480, Australia
Telephone: Int + 61 2 6620 3763 Facsimile: Int + 61 2 6620 3880
Email: jmcbri10@scu.edu.au
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>
>No. I only discussed one issue which was the attribution of extra
>potential energy achieved in a counter movement jump over that achieved in
>a squat jump to the utilization of stored elastic energy. If you re-read
>my posting more carefully you should see that I stated that SOME of that
>extra energy IS probably due to the utilization of stored elastic energy
>but there are other contributing factors not related to either stored
>energy or to neural facilitation. Unless you are willing to form the
>contrary argument that you CAN quantify the amount of stored elastic
>energy recovered in human movement with the method proposed by Komi and
>Bosco (1978), I fail to see the point of your posting.
You stated that more work is produced in the concentric phase of a
stretch-shorten cycle even without storage of energy in elastic elements as
found from a computer simulation of the elbow joint (Dowling, Human Movement
Science 11:273-297, 1992). Therefore, you indicated that Komi and Bosco
(1978) were incorrect in attributing differences in changes in positive
energy between a drop jump and a static jump purely to stored elastic
energy. I do not agree with your conclusion. It has been suggested that an
increase in mechanical work performed by a stretched muscle fibre may be the
result of an increased excitation state (potential energy) of cross-bridges
or increased cross-bridge interaction (Cavagna et al. 1986). However, a
recent study could not confirm this theory (Cavagna et al. 1994). Morgan
(1990) has indicated that even when there is no filament overlap in a
sarcomere after fast stretching there is still an increased ability to do
work from the fibre (these studies have looked just at muscle tissue, no
tendons or ligaments). Cavagna et al. (1994) stated that passive
visco-elastic components of muscle tissue during stretching increase the
ability to do work during subsequent shortening. However, they could not
confirm cross-bridge contribution to increased work after stretch. If
cross-bridges are not responsible for increased work then where is the
ability to perform more work after stretch coming from?
Very little difference was found between the amount of work
performed in the concentric phase between a static (concentric only) and
countermovement squat if the static squat was preceded by an isometric
preload (Walshe et al. 1998). Therefore, more work isn't achieved in a
countermovement squat over a static squat if a pre-force is added. Cavagna
et al. (1985) reported storage of elastic energy after both stretch and
isometric contraction. So where is the increased work coming from if
cross-bridge interaction is not a factor? This would only leave the elastic
structures within the muscle tissue itself (titin). Do you have additional
evidence (other than your computer model of the elbow joint) that more work
can be performed during the concentric phase of a stretch-shorten cycle
WITHOUT the usage of stored elastic energy from the visco-elastic components
of the muscle? I know some evidence supporting the role of cross-bridge
potentiation after stretch exists but this area is still unclear.
>Again, if you read my posting more carefully you will notice the the
>mathematical model that I referred to had NO ELASTICITY! In laboratory
>experiments involving biological tissues you cannot eliminate elasticity
>completely and this is the beauty of a mathematical proof. If you can
>prove that the counter movment produces more energy in the complete absence
>of strain energy then one cannot attribute ALL of the energy to
>elasticity. At least one additional factor exists and this
>level of proof (mathematical) is unattainable in traditional experiments.
If a muscle fibre produces more work after stretch with no filament
overlap (no cross-bridge interaction) (Morgan 1990) and can also produce
more work, as you have stated, with no elasticity then I am at a loss.
Where is the ability to do additional work coming from?
>This is in total agreement with my posting. Incidentally, I Emailed both
>Marco Cardinale and Jerry Telle asking them to estimate how widespread the
>practice of estimating utilization of stored elastic energy in athletes
>was. At the time of this posting, I have not received a response from
>either of them. Given the problems with the measurement of this
>phenomenon, I hope the practice is not very common and the only purpose of
>my original posting was to alert those that may using the method of its
>potential errors.
I will finish with a statement from Cavagna et al. (1994).
"Stretching a contracting muscle leads to greater mechanical work being done
during subsequent shortening.... the mechanism of this enhancement IS NOT
KNOWN." There is not a problem with measuring differences in changes in
positive energy between countermovement and static jumps which has been done
for years by exercise scientist. One must be careful when supplying reasons
for this difference, however, I do not think it is unreasonable to speculate
that the difference between changes in positive energy during a
countermovement jump (or drop jump) and static jump could be due purely to
stored elastic energy.
--
Jeffrey M. McBride, MS, CSCS
School of Exercise Science and Sport Management
Southern Cross University
PO Box 157
Lismore, NSW 2480, Australia
Telephone: Int + 61 2 6620 3763 Facsimile: Int + 61 2 6620 3880
Email: jmcbri10@scu.edu.au
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To unsubscribe send UNSUBSCRIBE BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://www.bme.ccf.org/isb/biomch-l
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