Back to the Basics!

Hello readers!

This week I met with Uzma, who is a PhD candidate in the lab. Muscles are activated depending on what we are doing; that is, only muscles that are needed for a task as on. Muscles are not just on and off, they have various levels of activation, like pressing down on the accelerator in a car. It is very important that the correct activations are used in the prosthesis control program, so as to feel comfortable and safe for the user. This is what Uzma spends most of her time achieving. More activation is required for lifting heavy objects (since more work needs to be done to move the objects certain distance) and vise versa.  In the past, the lab originally just had the muscle 100% on or completely off. This was OK for a first approximation to test out the software capability, but now they are ready to fine tune the activation levels.

What makes this fine tuning procedure difficult is that most of what we understand about muscles properties come from maximum stimulation (100% activation) experiments. In fact, the BiOM has torque equations based off of these maximal stimulations but they don't always match up to how much activation is actually needed. We need to make sure that the equations match the various levels of activation required during various activities.

Uzma works with real mouse muscles at a lower activation to understand their properties. She removes muscles from mice, and puts them on a “Force Lever”, which can change the length of the muscle, and is a representation of the muscle still in the mouse. It measures how much force the muscle produces when activated to a certain level. When muscles are activated, they want to shorten. The lever uses electrodes to shock the muscle, which makes it shorten, producing a force that is recorded. It is also used to measure how much force the muscle is producing. One way scientists are making this more like it is in the mouse, is by shortening and lengthening the muscle periodically, as happens in our leg muscles as we walk. We use the data found from this experiment to derive equations when the muscle is cyclically activated.

Now, their muscle models work better than others because they incorporate one extra muscle protein, titin, into their calculations. Titin is the largest protein in our bodies and works as a giant string. For the purpose of this project, it stores energy in muscles and the muscle stretches, which can be used to shorten. The crazy thing about this spring protein is that it is much stiffer in active muscles than passive. Understanding how this affects body movement is under intense investigation in the lab. That's all I have for today. Next week, I will meet with Dr. Tester who is one of the research advisors for the project.

Until next time,

Krishna Patel