A recent study showed that after a stroke, many people are unable to use the arm on the affected side and sometimes end up holding it close to their body, with the elbow flexed.
The study was published in the journal Proceedings of the National Academy of Arts and Sciences, Northwestern University and researcher Shirley Ryan AbilityLab. They found that the muscles actually lost the sarcomas – the smaller, more basic building blocks, in an attempt to adapt to this weakness.
Severe sarcoid that accumulates end to end (in series) and from side to side (parallel) forms the length and width of the muscle fiber. By imaging the biceps in three non-invasive ways, the researchers found that stroke patients had fewer sarcomas along the muscle fibers, resulting in an overall shorter muscle structure.
These findings are consistent with patients’ common experience of abnormally stiff and tense muscles that resist stretching, and suggest that changes to the muscles have the potential to amplify existing problems caused by stroke, a brain injury. The team hopes this discovery will help improve rehabilitation techniques for rebuilding sarcomas, ultimately helping to relieve tension and muscle shortening.
“This is the most direct evidence to date that chronic deformity, which places muscles in a short position, is associated with sequential sarcomere loss in humans,” said Wendy Murray, senior author of the study. “Understanding how muscles adapt after disability is critical for designing more effective clinical interventions to reduce such adaptations and to improve function after motor impairment.”
Murray is Professor of Biomedical Engineering at Northwestern University’s McCormick School of Engineering, Professor of Physical Medicine and Rehabilitation at Northwestern University’s Feinberg School of Medicine and research scientist at Shirley Ryan AbilityLab.
The research was completed in collaboration with Julius Dewald, Professor of Physiotherapy and Human Movement Science and Physical Medicine and Rehabilitation at Feinberg, McCormick Professor of Biomedical Engineering, and Research Scientist Shirley Ryan AbilityLab.
The first human demonstration
The sarcomere is only 1.5 to 4.0 m long, and is composed of two main proteins: actin and myosin. When these proteins work together, they allow muscles to contract and generate force. Although previous animal studies have found that muscle loses sequential sarcomas after fixation of the limb in a cast, this phenomenon has not previously been demonstrated in humans. In animal studies, the shortened muscles due to serial sarcoma loss became stiffer.
“There’s a classic relationship between strength and height,” says Amy Adkins, Ph.D. A student in Murray’s lab and the study’s first author. “Given that all muscles are made up of these building blocks, losing some of them affects how much force a muscle can generate.”
To conduct the study in humans, the researchers combined three non-invasive medical imaging technologies: MRI to measure muscle volume, ultrasound to measure muscle fiber bundles, and photon microendoscopy to measure microscopic sarcomas.
Photography opens up new possibilities
Combining these techniques at Northwestern and Shirley Ryan’s AbilityLab, the researchers imaged the biceps of seven stroke patients and four healthy participants. Because stroke patients were more affected on one side of their body, the researchers compared imaging of the affected side of the patient with the unaffected side as well as images of healthy participants.
The researchers found that biceps with strokes had lower volume, shorter muscle fibers, and similar sarcomere lengths. After combining data across sizes, they found that affected biceps had fewer consecutive sarcomas than unaffected biceps. The difference between the arms of the stroke patients was greater than that of the arms of the healthy participants, suggesting that the difference was related to stroke.
By combining medical imaging to better see muscle structure, this study also shows that it is possible to study muscle adaptations in the number of sarcomeres in humans. Prior to two-photon microscopy, human research was limited to examination of dissected tissue in the anatomy laboratory, which provided incomplete insight into how muscles adapt to injury and weakness, and to measurement of sarcomere length during surgery or from muscle biopsies, limiting who could participate. in research.
“In almost every aspect of our world, there is an important relationship between how something is assembled (its structure) and how it functions (functions),” the researchers said. “Part of the reason medical imaging is such a valuable resource and clinical tool is because it also applies to the human body, and imaging gives us the opportunity to measure structures.”
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