> This week's Case of the Week on the CGA web-site at
> 
> http://www.curtin.edu.au/curtin/dept/physio/pt/staff/kirtley/cga
> 
> is a very simple one - a classical Winterian H1 compensation for a weak A2.
> 
> It leads me to bring up the interesting debate over the importance of the
> A2 (concentric plantarflexion) action during normal walking. This power
> burst is by far the largest, and it has been suggested (by Winter) that it
> provides most (60-70%) of the forward power of the body during each cycle.
> Others (including Jackie Perry) argue that it is of lesser importance,
> providing only the power to ballistically flex the leg into swing, rather
> than moving the trunk as such.
> 
> It seems to me that this is a pretty basic component of gait, and it's
> about time we settled the dilemma. Can anyone contribute any evidence for
> or against either of these hypotheses?
> 
> Have a good weekend while you think about it!
> 
> Chris
> 
Dear Chris,
    This answer is rather late, but this has to do with my vacations 
and the enourmous bulk of e-mail that had accumulated therefter. I 
hope you are stillinterested in my opinion on the A2 work.
    I think J. Perry is right, be it on false grounds: A2 provides 
the energy for the initiation of swing (together with hip flexors).
In running the situation is completely different.
References:
-A.L. Hof et. al.
    Calf muscle work and segment energy changes in human treadmill 
walking
     J. Electromyography and Kinesiology 2: 203 - 216 (1993)
- idem
    Calf muscle work and segment energy changes in running
    XII Congress ISB, Los Angeles 1989, pp 322-333.
    
    I am forwarding the reprints, 
    Yours,
    At 




At Hof
Department of Medical Physiology    
University of Groningen
Bloemsingel 10
NL-9712 KZ GRONINGEN
The Netherlands
Phone: (31) 50 3632645
Fax:   (31) 50 3632751

Just had a look at this case this PM.
Left arm swing greater than on the right side. The right heel
prematurely leaves the ground.
It is hard to see but I believe there is probably some mid tarsal joint
pronation on the right.
The dorsiflexion lacking in the ankle is compensated for with midtarsal
joint pronation and early heel lift.
Before the left limb is about to land the right limb is starting to come
up off of the ground. This shortened stance phase on the right will not
allow the right psoas muscle to fire efficiently when it is ready to, to
pull the right limb forward.  The contra-lateral left arm must swing
further forward to help aid the psoas muscle in bringing the right limb
forward.

What do you think?

Henry

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