• Vadim Malis, Usha Sinha, Robert Csapo, Marco Narici, and Shantanu Sinha.
• Muscle Imaging and Modeling Lab, Department of Radiology, University of California, San Diego, California, USA.
• Magn Reson Med. 2018 Feb 1; 79 (2): 912-922.

PurposeThis study explores changes in strain rate (SR) (rate of regional deformation) parameters extracted from velocity-encoded MRI and their relationship to muscle force loss following 4-week unilateral lower limb suspension in healthy humans.MethodsTwo-dimensional SR maps were derived from three directional velocity-encoded MR phase-contrast images of the medial gastrocnemius in seven subjects. Atrophy-related and regional differences in the SR eigenvalues, angle between the SR and muscle fiber (SR-fiber angle), and strain rates in the fiber basis were statistically analyzed using analysis of variance and linear regression.ResultsDuring isometric contraction, SR in the fiber cross section (SRin-plane ) was significantly lower, and the SR-fiber angle was significantly higher postsuspension (P < 0.05). On multiple variable regression analysis, the volume of medial gastrocnemius, SRin-plane , and SR-fiber angle were significantly associated with force and changes in the, and the SR eigenvalues and shear SR were significantly associated with change in force with disuse.ConclusionsChanges in SR-fiber angle, SRin-plane , and shear SR as well as their ability to predict force and force changes may reflect the role of remodeling of the extracellular matrix in disuse atrophy and its functional consequence in reducing lateral transmission of force. Magn Reson Med 79:912-922, 2018. © 2017 International Society for Magnetic Resonance in Medicine.© 2017 International Society for Magnetic Resonance in Medicine.

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