Muscle impairment is common in a wide range of disorders, including
stroke, traumatic brain injury, spinal cord injury, Parkinson's disease,
and cerebral palsy. Currently, the gold standard for diagnosing
neuromuscular problems involves clinical exams or painful and sometimes
impossible muscle biopsies.
The most direct and highest-resolution
approach for characterizing human muscle health is to measure the
movements of sarcomeres, which are responsible for generating muscle
‘A minimally invasive, fiber-optic technique accurately measures the sarcomere length to quickly diagnose and treat a wide range of movement disorders.’
While a couple of tools are available to measure sarcomere length in
patients, they are not suitable for common clinical evaluation of
For example, laser diffraction requires surgery, damages
tissue, and is not compatible with movement. Meanwhile, microendoscopy
does not rapidly collect simultaneous, real-time, high-resolution
samples across a large amount of muscle tissue.
A minimally invasive, fiber-optic technique that accurately measures
the passive stretch and twitch contraction of living muscle tissue could
someday be an alternative to the painful muscle biopsies used to
diagnose and treat a wide range of movement disorders, researchers
report in Biophysical Journal
In a fraction of a
millisecond, the tool measures the length of thousands of sarcomeres -
the contractile units of muscle tissue - making it possible to quickly
identify issues and develop personalized treatment plans for patients.
"This approach enables measurement of previously unobtainable muscle
properties by combining advances in telecommunications technology with a
deep understanding of muscle structure, biomechanics, and pathology,"
says senior author Richard Lieber, a physiologist at the Rehabilitation
Institute of Chicago.
"This bioengineering innovation will permit new
studies of human muscle function and pathology and permit efficacy
testing of muscle treatments." His group has applied for a patent on the
To address these shortcomings, Lieber and his collaborators recently
developed a technique called resonant reflection spectroscopy (RRS).
Here's how it works: a laser source continuously sweeps across and
illuminates muscle through a very thin (1/4 millimeter) fiber optic
probe, which is inserted directly into the muscle belly and positioned
parallel to sarcomeres. The same optical probe collects reflected light
from the muscle, and these data are then used to calculate sarcomere
In the new study, the researchers applied this method to living
muscle tissue for the first time. They demonstrated that RSS could
simultaneously sample 4,200 sarcomeres spanning millimeters of muscle
tissue in one-tenth of a millisecond, capturing nanometer-scale changes
in sarcomere length during passive stretch and electrically stimulated
twitch contractions of lower leg muscles in rabbits. In theory, the
technique could enable the complete 3D reconstruction of sarcomere
proteins for studying muscle diseases.
"Our findings demonstrate a new method to measure protein-scale
interactions during muscle movement," Lieber says. "To our knowledge,
this method achieves sample sizes, resolutions, and compatibility with
human movements that no other current or proposed technique can match."
To make the tool suitable for routine clinical use, Lieber and his
collaborators are currently addressing technical challenges, such as
developing a new optical source and optical probe, and they will also
work on making the method more affordable. "We plan to use this
technology in both fundamental and clinical studies of human movement
and movement disorders," Lieber says. "We hope that these new
experiments lead to better understanding and maintenance of human muscle