The variation in isometric tension with sarcomere length in vertebrate muscle fibres

Abstract

1. The variation of isometric tetanus tension with sarcomere length in single fibres from frog striated muscle has been re‐investigated with special precautions to ensure uniformity of sarcomere length within the part of the fibre being studied. 2. In most respects the results of Ramsey & Street (1940) were confirmed, but (a) the peak of the curve was found to consist of a plateau between sarcomere lengths of 2·05 and 2·2 μ, (b) the decline of tension above this plateau is steeper than found by Ramsey & Street, and (c) the decline of tension below the plateau becomes suddenly steeper at a sarcomere length of about 1·67 μ. 3. Many features of this length—tension relation are simply explained on the sliding‐filament theory. 4. It is concluded that, in the plateau and at greater lengths, the tension on each thin filament is made up of equal contributions from each bridge which it overlaps on adjacent thick filaments. 5. Internal resistance to shortening is negligible in this range but becomes progressively more important with shortening below the plateau.

The length–tension relationship of human dorsiflexor and plantarflexor muscles after spinal cord injury

“…At extremely short muscle lengths, thick filaments (myosin) collide with Z-lines, inhibiting adequate binding with actin (thin filaments) and thus, decreasing tension development. 6 In the SCI group, it seems that this inability to generate torque occurred at even some neutral muscle lengths, which would suggest sarcomere shortening.…”

“…This phenomenon, known as the length-tension relationship, is attributed to the degree of overlap between the actin and myosin filaments within the myofibrils. 6 A major limitation in the majority of studies that have examined various muscle property changes after SCI is the assumption that there is no change in the lengthtension relationship. A change in this relationship would not only affect muscle characteristics but would also imply a change in the optimal angle for force generation.…”

Active tension changes in frog skeletal muscle during and after mechanical extension

“…In that case the percentage excess tension would be constant over the whole range of muscle lengths. The increase in percentage excess tension comes into evidence at those muscle lengths where, by reference to the relationship between tension and actin-myosin overlap (Gordon et al, 1966b), cross bridges can be made at the mid-sarcomere terminals of the actin filaments. At shorter lengths this is excluded by the geometry of the system.…”

“…Clearly the phenomenon ofexcess tension cannot be explained in terms of actin-myosin overlap as in the sliding filament hypothesis (Gordon et al, 1966a and1966b;Huxley, 1957). Sugi (1972) suggested that, during the process of stretch, some of the cross bridges are so displaced that they are brought into a "lockedon" situation.…”

“…The sliding filament theory can be used to explain the tension-length relation under isometric conditions (Gordon et al, 1966a and1966b). The developed tension depends upon the amount of effective overlap of the thick and thin filaments and thus upon the number of cross-bridges between them.…”