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

Muscle force is dictated by micrometer-scale contractile machines called sarcomeres. Whole-muscle force drops from peak force production to zero with just a few micrometers of sarcomere length change. No current technology is able to capture adequate dynamic sarcomere data in vivo, and thus we lack fundamental data needed to understand human movement and movement disorders.

Quantification of sarcomere length distribution in whole muscle frozen sections.

Laser diffraction (LD) is a valuable tool for measuring sarcomere length (Ls), a major determinant of muscle function. However, this method relies on few measurements per sample that are often extrapolated to whole muscle properties. Currently it is not possible to measure Ls throughout an entire muscle and determine how Ls varies at this scale.

Polarization gating enables sarcomere length measurements by laser diffraction in fibrotic muscle.

Raman spectroscopy (RS) has been extensively used to characterize bone composition. However, the link between bone biomechanics and RS measures is not well established. Here, we leveraged the sensitivity of RS polarization to organization, thereby assessing whether RS can explain differences in bone toughness in genetic mouse models for which traditional RS peak ratios are not informative.

Resonant reflection spectroscopy of biomolecular arrays in muscle.

Sarcomeres, the functional units of contraction in striated muscle, are composed of an array of interdigitating protein filaments. Direct interaction between overlapping filaments generates muscular force, which produces animal movement. When filament length is known, sarcomere length successfully predicts potential force, even in whole muscles that contain billions of sarcomere units.