Meeting Abstract

39.6  Sunday, Jan. 5 09:15  Does advanced age alter in vivo muscle operating length? HORNER, AM*; MOURADIAN, G; GROGAN, S; ROBERTS, TJ; Cal State San Bernardino; Brown University; Brown University; Brown University anghorner@gmail.com

Advanced aging is associated with muscle weakness, stiffness, and decreasing joint range of motion. The operating lengths used by aged muscle in vivo may be impacted by these sarcopenic changes. Because the proportion of passive force to total force increases in aged muscle, muscles operating at relatively longer lengths may mitigate the loss of active force by contributions of passive force. In order to test this we 1) characterized the in vivo length behavior of aged (30-32 mos) and young adult (7 mos) rat medial gastrocnemius muscles, and 2) compared in vivo lengths to in situ force-length properties of the isolated muscle. In vivo muscle lengths were measured via small (< 1.0 mm) radio-opaque beads surgically implanted into individual muscle fascicles in the medial gastrocnemius. The bead positions were determined using high-speed x-ray videography (fluoromicrometry) during locomotion across a range of speeds on level, 30 degree inclined, and 30 degree declined trackways. Directly following locomotor measurements, animals were anesthetized and the passive and active force-length properties of the muscle were recorded in situ via fluoromicrometry synchronized with a muscle ergometer. Rats in both age groups demonstrated operating lengths that crossed the plateau region of the active force-length curve.There was considerable variation in passive muscle stiffness but rats of both age groups consistently demonstrated in vivo operating lengths shorter than lengths at which passive stiffness would contribute significant force