Simon,

Thanks for the physics lesson. You are obviously better at this than I am.
(I actually had to cram to bring my grade up to a C).

But I am still a little confused.

You wrote:


>Force=mass x acceleration
>
>body weight = mass x acceleration due to gravity


I remember this. This was before we were taught about torque which is RXF.
In the body, wouldn't  F be body weight (mass times gravity) and R the
distance of F from the joint axis?


>Try standing on some bathroom scales, then bend your knees to squat or jump
>up and down, you will find that the force measured changes so that sometimes
>you will be "heavier", this is because your acceleration changes. This
>explains why we see the classic double hump for vertical load in force plate
>data during walking, i.e. force is not constant but dependent upon
>accelerations. The first hump occurs because the CoM is accelerating
>downwards (this hump is usually greater than body weight), the trough that
>follows occurs because the CoM is accelerating upwards away from the ground,
>force is reducing, the second hump occurs during propulsion because the CoM
>is once again accelerating downwards. Any biomechanics text will explain
>this.

Isn't the first hump related more to momentum (I think this was M V), and
since the acceleration is constant at 32 ft/sec/sec, the higher we drop
from the more the velocity and the greater the force required to stop the
downward progression (hence the greater compression of the spring and the
greater weight being shown.
Isn't the trough related to the fact that there is no Momentum, and the
force is reducing towards body weight.
Isn't the second hump related to the reactive force of the Center of Mass
going upwards?

As you can see, I was not a good student, so I hope you can help me see
this correctly.


>Moreover, the position of the centre of force and it's line of action on the
>foot changes with time during the gait cycle. Both the magnitude and
>position of the centre of force appear to be influenced by FFO's. Thus
>moments about the joints of the foot may also be altered.


This is something that I really can't understand. How does the position of
the center of force change if we do not change any position of the joints?
I see that your research shows that these moments are altered by FFO's, I
just don't understand how, unless you are getting more in motions somewhere
that you are not observing.


Kind regards,

Stanley

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