View Full Version : response to: James Dowling

Jeff Mcbride
10-09-1998, 03:45 AM
James Dowling wrote:
>Without entering the weights vs machines debate, I think it is important
>to clear up a fallacy that may be widely accepted in the athletic training
>community regarding the measurement of the utilization of stored elastic
>energy in human movement.

I do not know to which fallacy you are referring in the athletic
training community (exercise science community). You are discussing two
different issues in your e-mail. The first question is that of the use of
stored elastic energy in human movement. I would refer you to a recent
investigation by Witte et al. 1997. This investigation supplies significant
evidence that human movement does involve the use of stored elastic energy.
This evidence was from in vivo measurements not computer modelling.

The second question is to why their is a difference in jump height
between a countermovement and static jump. It appears that stored elastic
energy may not be responsible for the difference observed in jump height as
supported by a recent investigation (Walshe et al. 1997). However, the
authors in this investigation still could not state with complete confidance
that stored elastic energy did not play a role. In addition, one
investigation using a musculoskeletal model has suggested that significant
levels of potential energy are stored and utilised during a countermovement
jump and that the contractile elements of the muscle perform more total work
during a static jump (Anderson and Pandy 1993).

Irrespective of this I am skeptical of computer or mathematical
models when spring constants for the elastic potential of skeletal muscle
are derived from single muscle fibres in vitro. Is this representative a
whole muscle in vivo? The muscle protein titin, which is one of the key
players in muscle elasticity was not even completely sequenced until 1995
(Labeit and Kolmerer). In addition, the elastic potential of titin was not
clearly observed until 1997 (Kellermayer et al.). Witte et al. 1997
suggests through recent analysis that the muscle tissue itself is most
likely contributing to a large portion of useable stored elastic energy in
human movement. More than ever considered in the past. Titin in cardiac
muscle has been shown to contribute up to 1% of twitch force after stretch
(Granzier et a. 1997).

I am curious as to how a computer model can determine the stored
elastic energy potential of all the skeletal muscle (for example) in the
thigh musculature. Especially when the quantity and ratio of titin (and
other possible elastic proteins) in comparison to myosin and actin has not
been clearly defined. If we do not even know the quantity of titin in the
thigh musculature then how can a computer model determine the true elastic
potential of all the muscle involved in a countermovement versus a static
jump? I do not think there is any fallacy that is widely accepted in the
exercise science community. I think this issue still needs substantial
amounts of additional investigation. The true elastic potential of muscle
of a highly trained athlete is still unknown and could contribute to
differences in countermovement and static jump performance. The adaptive
role of elastic proteins such as titin with exercise has only started to be
explored (Fry et al. 1997). It is much to early for any final conclusions
concerning this issue.

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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