The smallest muscle component disappears in stroke patients: Studies | Health

Recent studies have shown that after a stroke, many people are unable to use their arms on the affected side and may move their arms closer to their bodies with their elbows bent.

The study was published in the minutes of researchers at the American Academy of Arts and Sciences, Northwestern University, and Shirley Ryan Ability Labs. They found that muscles actually lost sarcomere in an attempt to adapt to this disorder. This is the smallest and most basic component.

Sarcomere, stacked end-to-end (in series) and stacked left and right (parallel), constitutes the length and width of the muscle fibers. By imaging the biceps muscle in three non-invasive ways, researchers found that stroke patients had less sarcomere along the length of muscle fibers and shortened overall muscle structure. did.

This finding is consistent with the experience of common patients with abnormally tight and stiff muscles that resist stretching, and that muscle changes may amplify existing problems caused by stroke, which is a brain injury. Suggests. The team hopes that this finding will help improve rehabilitation techniques for reconstructing sarcomere and ultimately facilitate muscle tightening and shortening.

“This is the most direct evidence to date that chronic disorders that place muscles in shortened positions are associated with the loss of continuous sarcomere in humans,” said Wendy Murray, lead author of the study. I am. “Understanding how muscles adapt after a disorder is important for designing more effective clinical interventions to mitigate such adaptations and improve post-movement function. “

Murray is a professor of biomedical engineering at Northwestern University’s McCormick Engineering School, a professor of physical therapy and rehabilitation at Northwestern University’s Fineberg School of Medicine, and a research scientist at the Shirley Ryan Ability Lab.

The study was Julius Dewald, a professor of physiotherapy and human kinematics, a professor of physics and rehabilitation in Feinberg, a professor of biomedical engineering at McCormick, and a research scientist at the Shirley Ryan Ability Lab. Completed jointly with.

First demonstration in humans

Sarcomere is only 1.5-4.0 microns long and is composed of two major proteins, actin and myosin. When these proteins work together, they allow muscles to contract and produce force. Previous animal studies have shown that muscles lose continuous sarcomere after the limbs are fixed in a cast, but this phenomenon has never been demonstrated in humans. In animal studies, muscles that were shortened due to the loss of continuous sarcomere also became stiff.

“There is a classic relationship between power and length,” said Amy Adkins, Ph.D. A student in Murray’s lab and the lead author of the study. “Given that the whole muscle is made up of these building blocks, losing some of them affects the amount of force a muscle can generate.”

To conduct research in humans, researchers combined three non-invasive medical imaging techniques: MRI to measure muscle mass, ultrasound to measure muscle fiber bundles, and microscopic sarcomere measurement 2 Photon microscopic endoscopy.

Imaging opens up new possibilities

Combining these techniques at Northwestern University and the Shirley Ryan Ability Lab, researchers imaged the biceps from seven stroke patients and four healthy participants. Because stroke patients are more affected on one side of the body, researchers compared images from the affected side to the unaffected side of the patient with images from healthy participants.

Researchers have found that the biceps brachii muscles affected by stroke patients have smaller volume, shorter muscle fibers, and comparable sarcomere lengths. After combining the data across the scales, we found that the affected biceps had less sarcomere in series than the unaffected biceps. Differences in the arms of stroke patients are greater than those of healthy participants, indicating that the differences are associated with stroke.

By combining medical images to better view muscle structure, this study also establishes that it is possible to study muscle adaptation in human sarcomere numbers. Prior to two-photon microscopy, human research was limited to examining dissected tissue in an anatomical laboratory. Research.

“In almost every aspect of our world, there is an important relationship between how something is assembled (its structure) and how it works (its function),” he said. Said. “Medical imaging is an invaluable resource and one of the reasons it is a clinical tool because it also applies to the human body. Imaging gives us the opportunity to measure structure.”