View Full Version : Re: 3D Joint Power

Jonas Rubenson
01-27-2004, 03:57 PM
Thanks to all those who have responded so far.

As I feared, it does not appear clear-cut how to treat the three power ‘terms’
from the different planes of the anatomical or joint coordinate system. As for
adjacent joints, however, I do not think that one should add power. This would
have a similar result as estimating power from the displacement of the center
of mass, where simultaneous positive and negative power cancel (although during
double support in walking there is also simultaneous positive and negative
power at each limb that cancel when using the center of mass approach; Donelan
et al. 2001). While some of the simultaneous positive and negative power at
adjacent joints must be the result of transfer via two-joint muscles a large
part is probably not. Isn’t the ability to detect simultaneous positive and
negative power the main reason why many feel joint power is a more accurate
estimate of muscle power than the center of mass approach?

I feel Ton’s comment about being consistent in our approach when measuring power
is important: if it is standard not to add joint power at adjacent joints why
add across planes? Maybe we do not have enough knowledge of the system to be
able to say that by adding the power terms from individual planes we are better
estimating the true muscle power anyway? The limitation of the joint power
approach in not being able to detect transfer via two joint-muscles and
transfer across planes would need to be stated of course.

Richard Baker wrote:

> It thus strikes me that the concept of
> either quantity representing power flow THROUGH a joint is highly
> mis-leading (I'm very tempted to use the term "wrong" here rather than
> "highly mis-leading").

With respect to power flow, I was under the impression that the term was used
mainly to represent the loss/gain of power of a segment due to the power of the
joint reaction force. In this sense maybe power flow ‘through’ a joint is an
ok concept??

Thanks again for all the input!


Jonas Rubenson
Dept. Human Movement and Exercise Science
The University of Western Australia

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