Analysis of Contraction of Skeletal Muscle

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Abstract
The ultimate unit of the contractile machinery is likened to a linear high polymer having e =2.718 . . reactive groups/cm of length which, when stimulated with no load, react irreversibly and at random statistically similar to the polymers discussed by P. J. Flory, J. Am. Chem. Soc. 64: 177 1942 and F. T. Wall, ibid, 64:269, 1942 in which l/2e or 18.4% of reactive groups are left isolated when the reaction (shortening) is complete. Under load, only those sites whose activation energies were increased at the expense of the total energy initially present can react. The original number of reactive sites at zero load will be reduced by the factor exponent (-P/0.33 Po) where P =Load, Po = maximum isometric tension at rest length (Lo), 1/0.33 has the dimensions of length and 0.33 Po = average heat of shortening from Lo to 0.184 Lo. The activated energy is degraded as heat, stored in the load and reserved as potential energy in the structure. In the reversible range of shortening sufficient activated energy is reserved as potential energy to restore that fraction stored in the load. The system is restored in relaxation by acceleration of an isothermal reaction whose outward manifestation during contraction is activation heat. If shortening exceeds 1/3 Lo insufficient potential energy is reserved to restore that fraction of energy stored in the load and the fiber goes into the delta-state. The series elastic component arises as a consequence of isolation of reactive sites during shortening. The analysis is extended to stretched muscle and the delta-state. The repeating subunit will be a multiple of 1/e or 0.368. With reasonable assumptions the activation energy is calculated as 7000 cal/M.

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