In Vivo Sarcomere Length Measurement in Whole Muscles during Passive Stretch and Twitch Contractions

Area of Science:

• Biophysics
• Muscle Physiology
• Medical Technology

Background:

• Muscle force generation relies on sarcomeres, which are micrometer-scale contractile units.
• Whole-muscle force drastically decreases with minimal sarcomere length changes.
• Current in vivo technologies lack the precision and scope to capture dynamic sarcomere data, hindering research into human movement and disorders.

Purpose of the Study:

• To develop and validate a novel in vivo method for dynamic sarcomere length measurement.
• To overcome limitations of existing invasive or imprecise techniques for muscle analysis.
• To enable fundamental data acquisition for understanding muscle function and movement disorders.

Main Methods:

• Combined resonant reflection spectroscopy with optical frequency domain interferometry.
• Utilized a 250-μm-wide fiber optic probe for in vivo measurements.
• Captured sarcomere length changes at the sub-millisecond timescale.

Main Results:

• Achieved dynamic sarcomere length measurement in vivo.
• Demonstrated the ability to capture nanometer-scale changes in thousands of sarcomeres.
• Successfully recorded data during whole-muscle stretch and twitch contraction.

Conclusions:

• This study presents the first large-scale sensing of in vivo sarcomere dynamics.
• The developed method is essential for advancing the understanding of human movement and movement disorders.
• This technology paves the way for patient-specific surgical interventions and rehabilitation strategies.