View Full Version : Joint forces

Paolo De Leva, P.e. Institute,rome - Sport Biom.
05-26-1993, 05:28 AM
Jesus Dapena, in his last message to BIOMCH-L, suggested the
names "active joint force" (=muscle force), and "passive joint force"
(net joint force minus muscle force) for the two main components of
the net joint force.
I agree with him that there's a need to make things simple, and
that from a practical standpoint, we really need just two components of
the net joint force, and not more.
When I wrote my previous message, I tried to find out a good
name for Rick's F2, which has been named "passive joint force" by Jesus,
but I didn't want to use the
concepts of "ACTIVE" and "PASSIVE", because they seemed too much similar
to the concepts of "ACTION" and "REACTION". Therefore, as Jesus pointed out
too, there will be always some uncertainty in using those terms,
especially when "PASSIVE" is used to describe the role of structures
like bones, ligaments, capsule, etc.. At the end of my message, I just forgot
this reasoning, and under the effect of the last minute eagerness, I used
myself the term "PASSIVE". As a second thought I wonder, again, if (e.g.) we
can call "passive" the function of a ligament who actually is in some cases,
the main "Actor", or "cause" of the motion of the segment. The example of the
baseball pitch is adequate to show this possibility. Ligaments
produce the force and the consequent angular impulse that in turn cause
the elbow extension, while the triceps is almost unactive. For other
examples, see my previous message.
Besides, even though Jesus' suggestion may be the only practical
one, the only necessary compromise to solve the problem of splitting the
joint force in two parts only, I think that Jesus' "active joint force"
should always be called with its explicit and direct name: "muscle
force". THerefore, if this form of compromise has to be done, then I suggest
to call the first component just "muscle force", and the second
"passive joint force" (clearly, muscle force means the resultant of
all muscle forces acting at a given instant on a given segment end).
When I thought about names for Rick's F2 (the net force after
removing muscle forces), I couldn't accept any of my own tentative
solutions. I discarded the term STRUCTURAL, the term NON-MUSCULAR, and
even the term PASSIVE.
Now, I think that NON-MUSCULAR could be used, although this is
a compromise too, but at least is an exact DEFINITION, though not a direct
name. The compromise is in the fact that the definition is by exclusion,
and not by direct description.
Do you listservers have any other suggestions?

Paolo de Leva
Istituto Superiore di Educazione Fisica
Biomechanics Lab
P. Lauro De Bosis, 6
00194 ROME

Tel: 39-6-5743523
FAX: 39-6-3613065

e-mail address: DELEVA@RISCcics.ing.uniRoma1.IT