The sarcomere length-tension relation in skeletal muscle

Area of Science:

• Muscle Physiology
• Biophysics

Background:

• Isometric tetanic contractions in muscle fibers exhibit distinct tension development phases: fast rise, slow rise, and plateau.
• Previous assumptions attributed the slow-rise phase to increasing sarcomere length dispersion.

Purpose of the Study:

• To investigate the role of sarcomere length dispersion in the slow-rise phase of tetanic tension.
• To re-evaluate the length-tension relationship during plateau phase and its consistency with cross-bridge models.

Main Methods:

• Single frog semitendinosus muscle fibers were subjected to isometric tetani.
• Sarcomere length dispersion was measured throughout different tension development phases.
• A length-tension relationship was constructed using plateau tension and sarcomere length data.

Main Results:

• Sarcomere length dispersion remained below 4% of average sarcomere length during all contraction phases.
• The slow rise in tension could not be explained by increasing sarcomere length dispersion.
• Tension was independent of sarcomere length between 1.9 and 2.6 micrometers during plateau.

Conclusions:

• Progressive increase in sarcomere length dispersion does not account for the slow rise in tetanic tension.
• The observed length-tension relationship during plateau is inconsistent with the standard cross-bridge model of muscle force generation.