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Quadrupedal Mechanics - Anatomy & Physiology (view source)
Revision as of 01:10, 20 June 2013
, 01:10, 20 June 2013→The force of a muscle depends on sarcomere length
==='''The force of a muscle depends on sarcomere length'''===
==='''The force of a muscle depends on sarcomere length'''===
[[File:QMFig 4.4.png|thumb|'''Fig. 4.4 Tension in muscle''']]
The dimensions of the sarcomere determine the extent to which muscle cells can be stretched or contracted. When fully stretched the sarcomere length cannot exceed 3.6 µm without the fibre losing the ability to contract again (Fig. 4.3). As the muscle contracts, more and more crossbridges are brought into use. The force produced increases (Fig. 4.4) until all the crossbridges between thick and thin filaments can be used. At this point, simply because of the dimensions of the filaments, the sarcomere length is 2.2 µm, i.e. 59% of the fully stretched length. This is the optimal length. With further contraction, no more crossbridges can be used, in fact there is interference by overlapping of thin filaments and the force produced declines. When the sarcomere length is 1.6 µm, the muscle can contract no further without penetration of the Z discs by thick filaments, and resulting damage. The sarcomere, and hence the entire muscle cell in which the sarcomeres are in series, is now 44% of the fully stretched length. These measurements made by electron microscopists can be verified by using a device as simple as a ruler, since they agree with measurements of the range of contraction of muscle fibres (and the macroscopically visible fibre bundles) in the limb muscles of animals.
The dimensions of the sarcomere determine the extent to which muscle cells can be stretched or contracted. When fully stretched the sarcomere length cannot exceed 3.6 µm without the fibre losing the ability to contract again (Fig. 4.3). As the muscle contracts, more and more crossbridges are brought into use. The force produced increases (Fig. 4.4) until all the crossbridges between thick and thin filaments can be used. At this point, simply because of the dimensions of the filaments, the sarcomere length is 2.2 µm, i.e. 59% of the fully stretched length. This is the optimal length. With further contraction, no more crossbridges can be used, in fact there is interference by overlapping of thin filaments and the force produced declines. When the sarcomere length is 1.6 µm, the muscle can contract no further without penetration of the Z discs by thick filaments, and resulting damage. The sarcomere, and hence the entire muscle cell in which the sarcomeres are in series, is now 44% of the fully stretched length. These measurements made by electron microscopists can be verified by using a device as simple as a ruler, since they agree with measurements of the range of contraction of muscle fibres (and the macroscopically visible fibre bundles) in the limb muscles of animals.
:::::'''Fig. 4.4 Tension in muscle'''
:::::'''Fig. 4.4 Tension in muscle'''
:::::Tension is maximal at a sarcomere length of 2.2 µm. A muscle, therefore, will have only one optimal length for developing tension.
:::::Tension is maximal at a sarcomere length of 2.2 µm. A muscle, therefore, will have only one optimal length for developing tension.
==='''Getting the most out of restricted muscle performance'''===
==='''Getting the most out of restricted muscle performance'''===