Rectus Femoris Muscle

[Abdulbaset Benwali]

Good day,
I ran simulation of static optimization force as shown in the attached. I noticed that by comparing all muscle contraction I see the pink color (vastus lateralis) has higher value Approx. 75 Newton with smaller muscle and the red color (rectus femoris) has lower value Approx. 25 Newton with lager muscle. Note that all data of ground reaction force started at the same zero value as shown. My question. Should the lager muscle will have bigger value of Newton? Please advise.
Thank you in advance

[Mohammadreza Rezaie]

Hi, muscle coordination is task-specific. It's not clear from your explanations what task you are studying. Providing more info about your task and workflow could help understand the rectus femoris state. However, among the mono-articular muscles of quadriceps, vastus lateralis is the strongest one (you can compare their maximum isometric force properties) and there is no wonder it is producing more force (even if less recruited).

[Abdulbaset Benwali]

Hello Dr. Rezaie,
Thank you so much for your response.
My task is simply an isometric contraction with ground reaction force that looks like the pervious figure attached .I notices that when the external ground force is zero and there is still some force in the muscle is that excepted?
the task is isometric contraction with ground reaction force in on the horizontal direction?
I hope this will help you understand my pervious question.
Thank you very much for your time

[Mohammadreza Rezaie]

Thanks for the update. If this is a knee extension test in sitting position, I see nothing wrong with the graph actually. Because in sitting, the muscle-tendon length of rectus femoris would shorten at the hip and hence, the force-generating capacity of rectus femoris would be reduced. I believe you can easily simulate that in OpenSim GUI. Plot the total fiber force of rectus femoris against knee_angle coordinate while standing and compare it with 90 deg flexed hip (sitting position); you should get something like this:

img.png (15.19 KiB) Viewed 727 times

As you see, rectus femoris cannot generate much force when the knee is extending. So, much of the work must be done via mono-articular quadriceps muscles, and as I said earlier, vastus lateralis is the strongest one and can produce more force during knee extension, so it would be recruited more than others:

img2.png (15.4 KiB) Viewed 727 times

If you like to see all of vasti muscles are equally recruited (I would), you may want to use a custom Static Optimization in which the cost function is weighted by muscle volume, as described here: viewtopicPhpbb.php?f=91&t=14556&p=42087 ... ca46db4ca9

Hope this helps,
-Mohammadreza

[Abdulbaset Benwali]

Good afternoon, Dr. Razaie,
I thank you so much for your help. I will try that. have a great day.

[Abdulbaset Benwali]

Good morning, Dr. Rezaie,
Thank you very much for answering my questions. I will greatly appreciate if you clarify a few things for me please see below.
Figure 1: I have a few questions to help me understand this Figure.
1- Does the zero angle in this Fig correspond to the leg fully extended.
2- Does this Fig correspond to zero ground-reaction? and is gravity neglected?
3- If gravity is neglected, would the sitting and standing positions yield the same results?
4- If gravity is not neglected and for the sitting position, would gravity cause an increase in rectus femoris force as the knee extends?
The figure appears to suggest the opposite.
Comparison of my simulation and Figure1.
I compared the rectus femoris force in my simulation with the force shown in figure 1. At zero ground-reaction for my simulation, the force is about 25 Newton. But in Figure 1 the force of the same muscle at 90 degrees knee-angle is about 1250. What are the units of the y- axis? How can I relate the values of my simulation to Figure 1?
More on my simulation.
I noticed that in my simulation, the green and blue muscle forces appear to be almost the same. Does that make sense?
Sorry for the many questions, I am really trying to understand and greatly appreciate your input.
Many thanks.

[Mohammadreza Rezaie]

Hi, (I'm not a PhD)

1- Does the zero angle in this Fig correspond to the leg fully extended.

I used Rajagopal model for those graphs in which fully knee extension occurs at zero deg.

2- Does this Fig correspond to zero ground-reaction? and is gravity neglected?

The graphs are maximum force (strength) muscles can produced when they are fully activated (activation=1). So, neither gravity nor GRF is applied here. I used Built-in Curves in Plotter. Please notice that I didn't use Static Optimization or CMC tools, i.e., muscle redundancy problem has not been solved yet.

3- If gravity is neglected, would the sitting and standing positions yield the same results?

Hopefully, you can simulate that by setting gravity vector to zero [link]. There are also other forces contributing to joint moment which might not be exactly identical during testing in sitting and standing positions. Please see How Inverse Dynamics Works.

I compared the rectus femoris force in my simulation with the force shown in figure 1. At zero ground-reaction for my simulation, the force is about 25 Newton. But in Figure 1 the force of the same muscle at 90 degrees knee-angle is about 1250. What are the units of the y- axis? How can I relate the values of my simulation to Figure 1?

The muscles strength in those graphs were in Newton. As I said previously, the force curves I uploaded belong to fully activated muscles, just to give you an idea of how optimizer recruits muscles according to their strength [as well as moment arm].

I noticed that in my simulation, the green and blue muscle forces appear to be almost the same. Does that make sense?

It might happen due to differences in their moment arm at the knee. The stronger muscle might have less moment arm and hence, their moment (strength * moment arm) might become identical and the optimizer recruits them equally. I have no experience in this task and suggest reviewing the literature to see how the workflow and output curves should be.

Hope this helps,
-Mohammadreza

[Abdulbaset Benwali]

Good morning Mohammadreza,
Thank you so much again for fast response and have a great day.