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David Egan
04-03-1997, 04:16 PM
I tried to post a message yesterday, and for some unknown reason only half
the message made it to the list. Here is the full posting, and thanks to
those of you that have replied so far.

As part of an undergraduate sports biomechanics project, I am investigating
injury potential in netball.

The rules of netball require players to halt suddenly as soon as they receive
the ball. This means that ground reaction forces on landing after catching
the ball are relatively high compared to other activities. Netball has a
high injury rate (when compared with basketball, for example), with most
injuries occurring at the ankle and knee. Our experiment has attempted to
evaluate the injury potential for two conditions: catching a ball aimed at
chest level, and catching a ball aimed 2.5 m high. In both cases, the
subject landed on a force plate and took no more than one and a half steps
after landing. Ground reaction forces were plotted against time. Approach
speed was controlled.

Steele and Milburn (1988a) found that on landing after high passes compared
with chest level passes there was: a lower magnitude of initial peak vertical
ground reaction force (VGRF), greater attenuation of peak VGRF, and lower
horizontal braking forces. They recommended the promotion of a high passing
game style to reduce injuries. In their 1989 study, Steele & Milburn
suggested that this greater dampening of landing forces after high passes was
because subjects tended to land on their forefoot, allowing an additional
body segment to play an active role in force attenuation. Neal and
Sydney-Smith (1992) pointed out that approach speed was not controlled in
Steele and Milburn's work. They concluded that the modulating effect of a
high pass is related to lower approach speeds, and suggested that jumping to
catch a high pass may negate the attenuating effects of a forefoot landing on
peak VGRF

[Steele, J.R., Milburn, P.D. Reducing the risk of injury in netball:
changing rules or changing techniques? NZ journal of health physical
education and recreation 21 (1): 17-21. Steele, J.R., Milburn, P.D. A
Kinetic Analysis of Footfall Patterns at Landing in Netball. Australian
Journal of Science and Medicine in Sport. 21 No.1 March 1989. Neal RJ,
Sydney Smith M The effects of footfall pattern and passing height on ground
reaction forces in netball. Australian Journal of Science and Medicine in
Sport. September 1992.]

Does anyone know of any studies pertaining to any jumping sports which have
controlled horizontal speed experimentally prior to landing? Have any
studies linked horizontal braking forces on decelerating from a run with
injury potential? I have already searched medline and sport discus with few
results.

In addition, I am interested to know why the magnitude of the initial peak
VGRF (which is a transient peak superimposed on the rising phase of the VGRF
time trace) on landing in netball or in any jumping sport is related to
injury potential. I have heard that this represents force experienced
before the musculoskeletal system has had a chance to react to impact, but I
have no references. The magnitude of this initial force is typically lower
than peak VGRF. Are greater stresses experienced during this initial peak
than when VGRF has reached maximum? Is this because the musculoskeletal
system has not yet aligned properly at this point?

Why is it assumed that GRF magnitudes, loading rates etc. are correlated with
injury potential, which is surely determined by a multitude of factors?

Any ideas or references would be gratefully accepted, and I will post a
summary of replies.

David Egan

Sports Studies Undergraduate, Brunel University College

DEgan69484@aol.com