Longitudinal Growth a N D Rate of New Sarcomere Formation in Porcine Muscle 1

Fascicular length and muscle length were measured in sartorius and peroneus longus muscles of 34 pigs from 10 to 304 days postnatal. Mean sarcomere length was measured from myofibril lar fragments examined in polarized light. Fascicular and muscle lengths were adjusted to a resting length proport ional to a sarcomere length of 2 .5 / lm in order to compensate for differences in degree of contraction occurring during sampling. The two muscles examined were known to differ in their fascicular structure with the sartorius but not the peroneus longus having intrafascicularly terminating myofibers. In both muscles the measured fasciculi were approximately parallel to the long axis of t h e muscle. Muscle weights and animal live weigh~sl were considered as cubic roots in order to ~nable a linear regression~of length against weight. Longitudinal growth: of whole sartorius (r ~ .90) and peroneus longus (r = .92) muscles was closely related to ~ive weight. Longitudinal growth of fasciculi was less~ closely related (r = .85 and r = .80, respectively). This difference was ~considered to be:flue partly to variation in fascicular arrangemerit within muscles. One example:of this was identified in the sartorius where the fascicular/ whole muscle length fraction was proport ional to the degree of contraction as judged from sarcomere length. The correlation between whole muscle length and muscle weight was higher in the sartorius (r = .91) than in the peroneus longus (r = .82). The correlation between fascicular length and muscle weight was also higher in the sartorius than in the peroneus longus (r = .87 and r = .44, respectively). Despite these differences and a relatively low correlation between the weights of the