Length sarcomere

Figure 7. Length tension relationship. A schematic diagram showing how force varies with sarcomere length, and how this is explained by the relative amount of overlap between the thick and the thin filaments, and hence the numbers of myosin crossbridges in the thick filaments that can interact with actin in the thin filaments.

Gordon, A.M., Huxley, A.F., Julian, F.J. (1966). The variation in isometric tension with sarcomere length in vertebrate muscle fibers. J. Physiol. 184, 170-192. 

Boulesteix, T., Beaurepaire, E., Sauviat, M.-P, and Schanne-Klein, M.-C. 2004. Second-harmonic microscopy of unstained living cardiac myocytes Measurements of sarcomere length with 20-nm accuracy. Opt. Lett. 29 2031-33. 

An early test of the sliding filament model was the very careful measurement by Gordon et al. (1966) of the active tension produced by the muscle at different sarcomere lengths (Fig. 7B-D). If the myosin heads or crossbridges act as independent force generators, then, as the sarcomere length... 

April, E. W., Brandt, P. W., and Elliott, G. F. (1971). The myofilament lattice Studies on isolated fibers. I. The constancy of the unit-cell volume with variation in sarcomere length in a lattice in which the thin-to-thick myofilament ratio is 6 1./. Cell Biol. 51, 72-82. 

Fig. 1. Layout of titin in the sarcomere. Center panel electron micrograph of sarcomere of stretched soleus muscle fiber, labeled with anti-titin antibodies that demarcate the tandem Ig and PEVK spring elements of titin s extensible I-band region. Superimposed are two schematic titin molecules (one for each half sarcomere). Top and bottom panels domain structure of I-band and A-band sequence of titin, respectively (from Labeit and Kolmerer, 1995). Bottom left length of tandem Ig segment (proximal + distal segment) and PEVK segment in human soleus fibers, as function of sarcomere length (based on Trombitas et al., 1998b).

In active or rigor muscle, heads that do not overlap actin filaments become disordered (Cantino et al, 2002 Padron and Craig, 1989). They therefore contribute little to the observed low-angle X-ray diffraction patterns. This population increases with increasing sarcomere length (reduced filament overlap). 

Fig. 23. Simulation of the effects of changing sarcomere length on the M3 reflection. As the sarcomere length increases from Sa in (A) to Sb in (B), the axial extent (W) of the overlapped region of A-band reduces from Wa to Wb. The effect of this on the M3 region (G) to (E) is that the peak being sampled by the interference function gradually broadens (see Fig. 6). An essentially double peak in (C) at S = 2.2 [im has two strong satellites for S = 2.8 [im (D) and becomes a set of up to six quite strong peaks at S = 3.2 [im. All simulations were carried out using MusLABEL2 (Knupp and Squire, 2005).

Linari, M., Piazzesi, G., Dobbie, I., Koubassova, N., Reconditi, M., Narayanan, T., Diat, O., Irving, M., and Lombardi, V. (2000). Interference fine structure and sarcomere length dependence of the axial X-ray pattern from active single muscle fibers. Proc. Natl. Acad. Sci. USA 97, 7226-7231. 

Other methods used for meat tenderness evaluation have included measurement of sarcomere length (Howard and Judge 1968) and determination of the amount of connective tissue present. 

Howard, R.D., and M.D. Judge. 1968. Comparison of sarcomere length to other predictors of beef tenderness. J. Food Sci. 33 456-460. 

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