I was exploring the maximum isometric force application by single hand and double hands. In AnyBody, the ratio of maximal single handed to double handed force exertion is almost always less than 0.5. This is in contradiction with literature sources which say that such a ratio is almost always greater than 0.5. That is, the literature suggests that we are less than twice as strong in double handed force application as compared to single handed force application. Instead, AnyBody seems to indicate that we are more than twice as strong in double handed force application.
I am using AnyBody version 6.0.2 with AMMR 1.6.2.
[li]Van Cott 1972 Human Engineering guide to equipment design
[/li][li]Fothergill 1991 Human strength capabilities during one-handed maximum voluntary exertions in the fore and aft plane
[/li][li]Chaffin 1983 Volitional postures during maximal push pull exertions in the sagittal plane
[/li][li]Consumer Affairs Division, DTI (Department of Trade & Industry), UK, 2002, Strength data for design safety
Could someone help me out with this?
I will need a bit more explanation about the model and the method, before I can help.
Kasper Pihl Rasmussen
I am sorry for not having written about the model earlier.
So, I start with the human standing template and use the mannequin file to input posture. The simulations are for isometric force application, so there is no motion data. Then I make a segment on which I apply a force. The segment has very low weight and inertia so as not to add its own effect on the model. The segment is oriented along z-axis and has 2 nodes around 45 cm apart for connecting the segment to the hands. The segment nodes are attached to the glove points using “anystdjoint”. The force is an increasing force with time and I note the value at the point when shoulder-arm muscle activity reaches 1 for estimating the maximal isometric force exertion.
For double handed force application, the force is applied at the centre of the segment and the segment is connected to both the hands. For single handed force application, the force is applied on the right node of the segment, which is connected to the right hand and the left hand is not connected to the segment anymore.
I checked the values for 6 directions (forward, backward, up, down, left, and right) and three postures. I have attached the 3 mannequin files for the postures and 3 text files for the force (which were interpolated using AnyFunInterpol).
Please let me know if you need some more information.
I do not have the time to build the model myself from your explanation, so I did not use your attachments. But I have some questions and comments for you.
How is torso fixed in the experimental data and your model? This will have a significant effect on the difference between one and both hands.
Which Muscle Recruitment are you using? In the case of maximum isometric force, it would be an advantage using the min/max recruitment because you want the maximum force possible the model can produce. The min/max criterion ensures that by allowing the muscles to assist each other as much as possible.
Instead of increasing the external force until the muscle activity reaches 1, you can just set the force at an arbitrary value, and then divide your external force with the maximum muscle activation which you can find in the output folder. For this to work you need to use the min/max criteria and turn off the upper bounds on for the muscle criteria (UpperBoundOnOff = Off ).
Hope this helps,
Kasper Pihl Rasmussen
I attach the model instead. You could use the mannequin files from the previous attachment.
I am not sure if I understood your comments about torso correctly. In the experimental data, there have been measurements in the free standing posture. Also, there is one case of seated measurements (which I haven’t simulated). The problem with the free standing posture is that every subject could have different postural preferences. And, I don’t have their exact posture data, so, I try to approximate it. In the model I think the torso should be free. The standing template should be fixed to the ground through the feet and that’s it, isn’t it? I haven’t changed any thing in particular about constraints of the torso or added any other support. I only input postures for the arm. In any case, my idea was to make a general comparison between different situations.
Yes, indeed, I have been using the min/max criterion. And also the 3 element muscle models except for the trunk. (I also run the calibration analysis).
Thank you for the advice. I think it is an excellent solution to save time. However, I am also interested in seeing which are the muscles at limit. I believe, if the difference from the actual value to the arbitrary value is too much, I could see more muscles reach their limit. While we are at this topic, I was wondering if there is a way to output the muscles (let’s say muscle force) that reach the limit when shoulder arm muscle activity = 1?
Thank you for your support
In my comment about the torso, I assumed all the experimental data was made with seated subjects and with the trunk fixed to increase reliability. As you mention yourself, the stance of the subject will have a significant effect on the results. The one armed trials will also recruit more muscles from the torso and lower body while the both hand trials will stabilise the balance in the body.
There is not an obvious way to output which muscles are reaching one inside AnyBody. If I were to do it, I would dump the data and write a Python or Matlab script to output which muscles are reaching one.
Kasper Pihl Rasmussen
I understand now. Thank you. However, not all the experimental data was made with seated subjects. There is data with standing postures as well. I tried to check different postures in the literature and this observation about the ratio has been true in general. That is, it’s greater than 0.5.
Meanwhile, in AnyBody, I tried to do some more simulations with trunk flexion (10° and 20°) to see how much of a difference trunk flexion makes in the simulation. There are small differences in the absolute values, but, in the end the ratio remains more or less the same. That is, it’s less than 0.5 (except for lateral directions, where different muscle groups from both the arms are used - so the contributions from the two arms are not equal).
In the next days, I would probably try to simulate the seated posture as well. So, I would see what difference does that make. But, I wonder how much of a difference would that make to the ratio itself. The posture would be common if I apply the force to 1 hand or both the hands.