title: In Vivo Imaging of Human Sarcomere Twitch Dynamics in Individual Motor Units.
abstract: Motor units comprise a pre-synaptic motor neuron and multiple post-synaptic muscle fibers. Many movement disorders disrupt motor unit contractile dynamics and the structure of sarcomeres, skeletal muscle's contractile units. Despite the motor unit's centrality to neuromuscular physiology, no extant technology can image sarcomere twitch dynamics in live humans. We created a wearable microscope equipped with a microendoscope for minimally invasive observation of sarcomere lengths and contractile dynamics in any major skeletal muscle. By electrically stimulating twitches via the microendoscope and visualizing the sarcomere displacements, we monitored single motor unit contractions in soleus and vastus lateralis muscles of healthy individuals. Control experiments verified that these evoked twitches involved neuromuscular transmission and faithfully reported muscle force generation. In post-stroke patients with spasticity of the biceps brachii, we found involuntary microscopic contractions and sarcomere length abnormalities. The wearable microscope facilitates exploration of many basic and disease-related neuromuscular phenomena never visualized before in live humans.
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Gabriel N
authors.initials: GN
authors.lastname: Sanchez
authors.affiliation: Department of Biology, Stanford University, Stanford, CA 94305, USA; Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
authors.forename: Supriyo
authors.initials: S
authors.lastname: Sinha
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Holly
authors.initials: H
authors.lastname: Liske
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Neurology, Stanford University, Stanford, CA 94305, USA.
authors.forename: Viet
authors.initials: V
authors.lastname: Nguyen
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA. Electronic address: delp@stanford.edu.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
authors.affiliation: Department of Biology, Stanford University, Stanford, CA 94305, USA; Department of Applied Physics, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA. Electronic address: mschnitz@stanford.edu.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Schnitzer
mesh_terms: D000328:Adult; D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D004724:Endoscopy / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008859:Microscopy, Polarization / Q000295:instrumentation / Q000379:methods; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012518:Sarcomeres / Q000502:physiology*; D055815:Young Adult