Meeting Abstract

40.1  Friday, Jan. 4  Intrinsic and neural contributions to muscular control of stable running in the guinea fowl (Numida meleagris) DALEY, M.A.; University of Michigan mdaley@umich.edu

Terrestrial animals move through complex environments with awe-inspiring agility and dynamic stability. Yet, little is known about muscle dynamics and neuromuscular control in rapid non-steady locomotion. Recent studies of avian limb mechanics suggest that distal muscles mediate rapid stabilization through interplay among feedforward, intrinsic dynamic, and reflex feedback mechanisms. Here I investigate the specific muscular control mechanisms involved in running stability through in vivo measures of lateral gastrocnemius (LG) force, length and activation (EMG) as guinea fowl encounter and recover from a sudden drop in terrain. The LG exhibits posture-dependent changes in force and work output that help return the bird to a steady gait. Multiple regression analysis suggests that muscle force and work in the perturbed step depend primarily on intrinsic length and velocity factors, which explain 72 and 67% of the total variance, respectively, whereas EMG intensity explains only 9 and 5%. In the 1st stride following the perturbation, EMG intensity is a larger factor in force and work (explaining 47 and 41%). Within the 2nd stride following the perturbation, all significant muscle performance factors have returned to within the 95% c.i. for the control mean. These results confirm the role of intrinsic muscle dynamics in rapid stabilization and reveal that neural factors contribute to complete recovery within two strides. Future work will test whether a Hill-type muscle model can predict muscle dynamics in these high-strain non-steady conditions, or whether alternative simple models can do better. Computationally intensive neuromechanical models require the simplest model that predicts muscle dynamics over a wide range of animal behavior.