THE RELATION BETWEEN BIREFRINGENCE AND CONTRACTILE POWER OF NORMAL, HYPERTROPHIED, AND ATROPHIED SKELETAL MUSCLE

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Abstract
For normal, hypertrophied, and atrophied rat gastrocnemii, wt. and maximal tetanic tension were detd., their contractile power per wt. unit computed and compared with their birefringence. The latter can be regarded as a measure of the degree of completeness of the crystalline arrangement of the muscle proteins. Neither contractile power nor birefringence is altered in muscular hypertrophy produced by daily electrical training. In denervated atrophying muscles, contractile power and birefringence do not change for the first 9-11 days although the wt. losses of 30% occur. However, during the later phase of atrophy, the loss in tetanic tension surpasses distinctly the wt. loss; in consequence the contractile power diminishes. At the same time birefringence diminishes, too, and at about the same rate as the contractile power. No fixed relation between diminished fiber-diam. and loss in birefringence exists for individual fibers. For normal muscles the statistical relation between birefringence and contractile power can be expressed by the equation: birefringence = K X log. contractile power.

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