Meeting Abstract

P3.53  Tuesday, Jan. 6  Stability despite rapid large fluctuations in calculated net muscle moment at the knee during normal level running in guinea fowl. HITCHCOCK, Amanda C.*; PROPERT, Matthew W.G.; MARSH, Richard L.; Northeastern University; Northeastern University; Northeastern University hitchcock.a@neu.edu

We calculated the net muscle moments at the leg joints of guinea fowl using 2-D inverse dynamics. Birds ran along a trackway and over a force plate. Force plate data were synchronized with high-speed video recording of markers, which allowed the calculation of the joint centers. These data along with previously measured segment properties allowed the calculation of net muscle moments and powers at all of joints in the limb. Generally, peak moments at all joints were extension moments occurring during stance and were highest at the knee and hip. However, at the hip and knee relatively large moments are required in late swing due to the inertia of the limb segments. At the knee this inertial moment is in flexion and it reaches a peak near footdown, at which point it falls suddenly by 50 100% of the peak value and then rises again to approximately its former value before switching to an extension moment as stance proceeds. The sudden large drop and restoration of the flexion moment occurs in approximately 20 ms for a full cycle. During this time the knee joint angle is undergoing a stable flexion trajectory, i.e., the knee appears highly damped. We hypothesize that the large damping apparent at the knee is due to strong co-contraction occurring in knee extensors and flexors in late swing and throughout stance. Supported by NIH AR47337 and NSF IOB-0542795.