Sarcomeres are the smallest contractile elements of muscle. Muscle generates force when overlapping myosin and actin filaments within the sarcomere interact to generate force. The amount of force these interactions generate depends on sarcomere length. The range of sarcomere lengths over which a muscle normally operates in the body is an important factor in analyzing a muscle’s force generating capacity. Measurement of sarcomere lengths in vivo is limited by their small size (2–4 μm) and the inability to use fluorescent dyes in humans. We recently developed a microendoscopy system to image sarcomeres in humans via Second Harmonic Generation (SHG) [1]. Here we demonstrate the use of this microendoscopy system as a robust, minimally-invasive tool for biomechanical analysis by measuring sarcomere lengths of the forearm muscle extensor carpi radialis brevis (ECRB) in 5 human subjects.

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