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Patrick Castagno
12-04-1998, 12:46 PM
Lee,

The answer to your question depends on what muscle and, certainly, what
action. In the example of a ballistic elbow extension or knee extension
from a flexed position, high-speed video has revealed that a joint reaches
it's greatest angular velocity at the middle of its functional range.

In the case of ballistic elbow extension during a 90mph pitch:
Regardless of how the extension velocity was generated, either by elbow
flexor concentric contraction, centrifrugal force, or momentum, in an effort
to prevent a hyperextensive type of injury, the joint must begin it's
deceleration in enough time to bring the movement of extension to a safe
stop. A self protective mechanism.. EMG signals of the elbow flexors show
that they contract to greater than 100% of their manually tested levels (in
eccentrics) during this elbow deceleration period (see DiGiovine, et al.,
1992). The peak elbow extension velocity of the elbow joint occurs well
before the ball is released.

Amazingly, the human body will only allow the extension velocity of a joint
to go to a peak level that can be safely managed by the commensurate
strength of the flexors during eccentric work. I guess this is my theory on
that.

It might be that we could extend joints at a faster rate if we had a bigger
range to accelerate into and the additional strength/power to bring that
velocity to a halt before danger.

Just one man's opinion.

Patrick Castagno
Manager/Biomechanist - Gait Analysis Laboratory
duPont Hospital for Children
1600 Rockland Road
Wilmington, DE 19899
Chestnut@udel.edu
(302-651-4615)

_______________________________________________

Lee Aylett wrote:

> Hi everybody,
>
> I'm a bit of an amateur as far as bio-mechanics is concerned so forgive
> me if this question is simple or obvious. Most of my study of this
> subjects comes directly from text books but this is a question (or
> series of questions) that I don't seem to find addressed.
>
> With concern to concentric contraction within a muscle, say the biceps
> for example, I'm interested to know at what stage within ROM does a
> muscle reach maximum speed? Does it simply continue to accelerate until
> it is inhibited and forced to decelerate by another part of the body, or
> does it accelerate until maximum contraction is achieved and then
> decelerate? Does maximum contraction equal the end of movement or simply
> the point where a muscle cannot continue to apply a force? Or, does a
> muscle reach maximum speed before it achieves maximum contraction
> perhaps because all the available fibres have been fired? If this is the
> case what happens next? Does it continue at that speed or begin to
> decelerate? If a muscle does reach maximum speed before it reaches
> maximum contraction how long would it take in the biceps for example? 30
> degrees, 60 degrees? How much does a preceding eccentric movement effect
> this process?
> Hey do I sound confused?!!
> Hope some of this is clear, I'm sure there is a simple answer to all
> this rambling.

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