Meeting Abstract

119.2  Tuesday, Jan. 7 10:30  Hindlimb muscle lever systems differ among joints and stride phases in basilisk lizards BERGMANN, P.J.*; HARE-DRUBKA, M.; Clark University; Clark University pbergmann@clarku.edu

Vertebrate limbs act as lever systems, and the lengths of limb bones and muscle insertion locations define the architecture of the lever systems, determining their functional properties. The gear ratio (GR) is out-lever length divided by in-lever length, and characterizes whether a lever system’s architecture is designed for high velocity movements or high force movements. The physiological cross-sectional area (PCSA) of a muscle further determines how much force a muscle can generate. We use detailed dissection and measurements of the hindlimbs of six juvenile and nine adult basilisk lizards (Basiliscus vittatus) to quantify GR and PCSA for 20 muscles, involved during stance and swing phases, and moving the hip, knee, and ankle. The hindlimb muscle architecture did not differ between juveniles and adults. However, we found that GR was highest for the knee, followed by the ankle and finally the hip. The GR was comparable between stance and swing, although it was higher for swing than stance phase muscles that move the ankle. We found that PCSA was higher in stance phase than swing phase muscles, with stance phase muscles of the knee having the highest PCSA. This is expected because the stance is the part of the stride during which propulsive force is generated. We also found that muscle fiber length decreased in more distal joints for stance phase muscles, suggesting that muscles powering proximal joints may have higher shortening velocities. For swing phase muscles, those serving the knee had the highest fiber lengths, mirroring our GR results, and indicating selection of these muscles for high velocity joint movements. Our findings illustrate the value of myological dissection for studying locomotion when physiological and in vivo studies are not practical.