Stretch Tension Research Articles

Extensibility of gastrocnemius muscle at rest and during contraction.

The medial head of rat gastrocnemius shows greater static and semidynamic passive tension (per cm2 cross-section area) than the lateral head. Regarded as two resistances in parallel, resistance of lateral and medial heads together (1.16 and 4.71 mm/sec., 1–5 mm stretch) approximate resistance of whole muscle. Resting muscle shows a slow rise and low tension at 0.29 mm/sec., a rapid rise and higher tension at 1.16 mm/sec., and declining tension rise and level with faster stretches. The lateral head yields more readily than the medial head. The lateral head controls whole muscle's reaction to stretch at rest. Tetanized (15 cps) muscle shows a linear, faster tension rise with faster stretches. Excess (over isometric) tension, related to resting stretch tension, shows a decline with stretch (yielding). The amount of excess tension increases with speed of stretch. The lateral head shows less excess tension rise than the medial head. The medial head controls whole muscle's reaction to stretch during isometric tetanus.

Finite strain in elastic problems—II

In a recent paper one of the authors has developed the theory of finite strain in elastic problems on the hypothesis that the second order terms in the components of strain may not be neglected. Owing to the magnitude of the displacements considered, it has been necessary to use throughout the coordinates of the points of the body after strain instead of those before strain, as is always done in the theory of small strains. The method has already been applied, in the paper mentioned above, to a few particular cases, viz., (i) a cylinder subjected to uniform tension; (ii) a rectangular plate bent into the form of a right cylinder; and (iii) the torsion of a right circular cylinder. As may be expected, the tension stretch curve is not now a straight line as in the ordinary theory, but is more like that found in practice for some materials. The object of present paper is to apply the hypothesis to the following further problems:— (i) a thick spherical shell subjected to uniform, but not necessarily equal, normal tractions on the inner and outer surfaces; (ii) a thick cylindrical shell or tube under the same type of internal and external tractions as in (i), but which is constrained by end tractions to remain in a state of plane strain; (iii) a thick cylindrical tube turned inside out under the same types of traction as in (ii); (iv) a thick cylindrical tube turned inside out under no surface tractions; (v) the particular forms of problems (i) and (ii) arising when the shells are thin.