Interaction between series compliance and sarcomere kinetics determines internal sarcomere shortening during fixed-end contraction

Yasuo Kawakami, Richard L. Lieber*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


The interaction between contractile force and in-series compliance was investigated for the intact skeletal muscle-tendon unit (MTU) of Rana pipiens semitendinosus muscles during fixed-end contraction. It was hypothesized that internal sarcomere shortening is a function of the length-force characteristics of contractile and series elastic components. The MTUs (n=18) were dissected, and, while submerged in Ringer's solution, muscles were activated at nine muscle lengths (-2 to +6 mm relative to optimal length in 1 mm intervals), while measuring muscle force and sarcomere length (SL) by laser diffraction. The MTU was clamped either at the bone (n=6), or at the proximal and distal ends of the aponeuroses (n=6). Muscle fibers were also trimmed along with aponeuroses down to 5-20 fibers and identical measurements were performed (n=6). The magnitude of shortening decreased as MTU length increased. The magnitude of shortening ranged from -0.08 to 0.3μm, and there was no significant difference between ΔSL as a function of clamp location. When aponeuroses were trimmed, sarcomere shortening was not observed at L0 and longer. These results suggest that the aponeurosis is the major contributor to in-series compliance. Results also support our hypothesis but there also appear to be other factors affecting internal sarcomere shortening. The functional consequence of internal sarcomere shortening as a function of sarcomere length was to skew the muscle length-tension relationship to longer sarcomere lengths. Copyright (C) 2000 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)1249-1255
Number of pages7
JournalJournal of Biomechanics
Issue number10
Publication statusPublished - 2000 Oct
Externally publishedYes


  • Contractile and elastic components
  • Frog
  • Semitendinosus muscle

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine
  • Biomedical Engineering
  • Rehabilitation


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