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8/13/2019 Power work and energy sport biomechanics
1/23
Matt Pain
Office UU1.07
E-mail: [email protected]
Power as an Indicator of Co-ordination
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Overview
Mechanical Energy Transfer Between Segments
Passive Energy Transfer
Power Balance into and out of a Segment
Internal Work Versus External Work Some examples
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Power as an Indicator of Co-ordination
Last week we looked at energy and power calculations.
Fenn's method fractional approach
Elftmann's method joint work/power
Mechanical power is not the whole story but it can
provide lots of useful information.
Gross movement of the body occurs about the joints.
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Power as an Indicator of Co-ordination
The majority of work done by or on the body is done on or
by muscles moving limbs about joints.
Calculating the joint power histories will give an indicator
of the joint co-ordination.
Diagram 5.6 Winter 1990
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Mechanical Energy Transfer Between Segments
For a single joint with a single extensor and flexor the
joint power allows us to find the muscle power.
Humans do not have multiple joints and multiple muscles
for extensors and flexors about these joints.
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Mechanical Energy Transfer Between Segments
Two problems:
Muscle indeterminacy - more muscles across a joint than
number of joints. This is will be covered in more detail
next lecture.
Energy transfer between segments - segments that touch
will exert forces on each other, if there is motion this
means energy transfer.
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Mechanical Energy Transfer Between Segments
In its simplest form this can be considered a passive effect.
e.g. flipping book pages
rapidly move your forearm with your wrist
relaxed.
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Passive Energy Transfer
Fii
Fj
Vj
Vi
j
Energy going into segment i
Energy going out of segment j
This is in addition to active muscle forces acting across a joint.
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Power Balance into and out of a Segment
Change in energy of a segment which is made up of:
Passive power flow distal end Muscle power flow distal end
Passive power flow proximal end
Muscle power flow proximal end
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Sporting Examples
Javelin
(Menzel, 1986)
Baseball pitching
(Stodden et al., 2001)
High front kick(Sorensen et al., 1996)
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Internal Work Versus External Work
These calculations are from external measurements and
so do not give the full picture.
We are commonly interested in the work we can do on anoutside body, thrown implement, lifting weights, jumping.
But we need to do work just to make us move.
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Internal Work Versus External Work
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Internal Work Versus External Work
Hidden pow eris that which is being produced but cannot
be measured by these techniques.
To find out the actual work being done by a group of
muscles hidden power needs to be included.
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Internal Work Versus External Work
The names you give to define these is not the important
point.
Knowing that external measurements of work have to be
interpreted in light of different energy usage is.
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Internal Work Versus External Work
Some examples of hidden work:
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Examples in different sports
Consider some sports with different goals.
What are the following events trying to maximise or
minimise?
If we analyse the mechanical energy and power involved
how much help could we give the athlete?
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Ultra long distance runner
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Weightlifter
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Discus thrower
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Baseball pitcher
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Wrestler
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Synopsis
However in most sports smooth precise movements are
required to make best use of the different energy transfer
systems.
Good technique is often subjectively thought of as being
smooth or graceful and usually arises through efficient
use of energy.