I began a project a couple of months ago where I collected kinematics
and EMG data on an individual doing a simple bicep curl with a 5-pound
weight. I wanted to perform my own simple EMG validation, looking at
the biceps and triceps. For simplicity the individual did their best
to curl the weight at a constant (elbow) angular velocity, and
maintain a 2-D posture (in the sagittal plane). I then tried to
re-create the individual in AnyBody driving the model in two different
ways. First, I calculated the individual’s elbow joint velocity (from
3-D trajectory markers) and I drove the model with elbow angle input.
Then, using data from Vicon, I drove a second model via 3-D
trajectory points.
Re-creating my particular individual proved to be a problem at the
time, so I decided to take a step back and start with an easier model.
Before even attempting to validate the model with EMG data from an
individual, I first wanted to see if I could even get two identical
models, driven different ways, to produce the same muscle activity
outputs. Creating the model of an upper-body performing a bicep-curl
driven by elbow angular velocity is relatively easy. To create a
model driven by 3-D trajectory points which exactly mimics the
constant angular model was a little more work. What I essentially did
was I stepped through the constant-angle model analysis and took the
palm joint point at each step relative to the elbow. Then I drove the
model with all of these accumulated points. The purpose of this was
to compare the results between the two models – ideally they should be
the same regardless of whether they are driven with constant angular
velocity or 3-D trajectory points, right? Needless to say, analysis
of the two models did not result in the same muscle activities (I have
uploaded both models into the file section – they are “Mannequin – cst
arm angles.zip” and “Mannequin – vicon drive.zip”). These analyses
were all done using the simple muscle model (and the muscle activities
were different for each model), at which point I decided to try using
the more physiologically-realizable 3E muscle model. Now, however, I
can not even get the model to run. The model compiles, although when
I SetInitialConditions, I get the following for nearly every muscle in
the model:
WARNING(OBJ.MCH.MUS2) : C:\Documents and
Settings\ssullivan\Desktop\Repository.6 - Mannequin
Validation\BRep\Aalborg\Arm3D\Muscle-parameters-shoulder.any(49) :
‘biceps_brachii_caput_longum’ : Muscle without strength : The
muscle has been stretched too much
I have uploaded the two models – they run fine when the simple muscle
model (in the .Main file) is used, however the problem exists with the
3e muscle model. Is it as simple as just lengthening the Lm and Lmt?
Any suggestions would be greatly appreciated.
Thanks so much and Happy Holidays.
Sarah