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Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies
Published on: January 31, 2013
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On sarcomere length stability during isometric contractions before and after active stretching
Kaleena Johnston1, Eng Kuan Moo1, Azim Jinha1
1Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada, T2N 1N4.
The Journal of Experimental Biology
|November 10, 2019
Summary
Skeletal muscle force enhancement is not caused by sarcomere length (SL) instability or non-uniformity. Active stretching makes SLs more stable, not less, and does not increase non-uniformity, challenging previous theories.
Area of Science:
- Muscle Physiology
- Skeletal Muscle Mechanics
- Sarcomere Dynamics
Background:
- Sarcomere length (SL) instability and non-uniformity are proposed mechanisms for skeletal muscle properties like creep and force depression.
- Residual force enhancement (RFE) after active stretching is hypothesized to involve increased SL instability and non-uniformity.
- Previous research indicated active stretching does not increase SL non-uniformity, but its effect on SL stability remained unclear.
Purpose of the Study:
- To investigate the impact of active muscle stretching on sarcomere length (SL) stability and non-uniformity during isometric contractions.
- To determine if SL instability or non-uniformity contribute to residual force enhancement (RFE) in skeletal muscle.
Main Methods:
- Single myofibrils from rabbit psoas muscle were used.
- Sarcomere length (SL) instability and non-uniformity were measured during isometric contractions and after active stretching.
- SL instability quantified by the rate of change of individual SLs; SL non-uniformity defined as deviations from mean SL.
Main Results:
- Individual sarcomere lengths (SLs) fluctuated even during isometric contractions where the mean SL was constant.
- SLs were more stable in the post-stretch isometric state (force-enhanced) compared to the reference isometric state.
- SL instability was not correlated with changes in SL non-uniformity.
- SL non-uniformity did not differ between isometric and post-stretch isometric contractions.
Conclusions:
- Sarcomere length (SL) is more stable but similarly non-uniform in the force-enhanced state compared to the isometric reference state.
- The findings suggest that SL instability and non-uniformity are unlikely contributors to residual force enhancement in skeletal muscle.
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