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Updated: Aug 1, 2026
09:49
Procedures for Rat in situ Skeletal Muscle Contractile Properties
Published on: October 15, 2011
Cross-bridge cycling theories cannot explain high-speed lengthening behavior in frog muscle
J D Harry1, A W Ward, N C Heglund
1Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138.
Biophysical Journal
|February 1, 1990
Summary
The Huxley model accurately predicts muscle shortening but fails during forced lengthening. Modifications to the model for forced lengthening require unrealistic cross-bridge properties, suggesting sarcomere inhomogeneities are key.
Area of Science:
- Muscle Physiology
- Biophysics
Background:
- The Huxley 1957 model precisely describes striated muscle shortening.
- The model's predictions diverge from experimental data during forced lengthening.
Purpose of the Study:
- To evaluate modifications of the Huxley model for forced lengthening.
- To investigate the mechanical properties of cross-bridges, including maximum strain.
- To acquire new force-velocity data for comparison with model predictions.
Main Methods:
- Used isolated frog sartorius muscles at 2°C.
- Stretched active muscle at speeds up to and exceeding 2 Vmax.
- Acquired new force-velocity data during rapid stretches.
Main Results:
- Muscle force during stretch exceeded peak isometric force, even at high velocities.
- Force was largely independent of velocity for stretches faster than 0.5 Vmax.
- Model modifications required unreasonable cross-bridge extensibility.
Conclusions:
- The Huxley model requires significant, potentially unrealistic, adjustments to match forced lengthening data.
- Sarcomere inhomogeneities may significantly influence muscle force-velocity characteristics.
- Further research into sarcomere inhomogeneities is warranted.
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