A two dimensional model for the prediction of muscle shape and intramuscular pressure.

Traditional pennate skeletal muscle models with straight fibres and straight tendinous sheets cannot assume realistic muscle shapes and are unsuitable for predicting intramuscular pressure. The two dimensional models proposed here have flexible fibres and tendinous sheets of which the curvatures are in mechanical equilibrium with the intramuscular pressure distribution. Analytical relationships between fibre stress, pressure, curvatures and lengths of fibres and tendinous sheets have been derived based on physical laws and functional demands. These relationships were used to generate unipennate muscle shapes and to calculate pressure distributions. The results compare well with the shapes of the medial gastrocnemius muscles of man and cat and with maximum intramuscular pressures as reported in the literature.