Meeting Abstract
Dynamic coordination of animal motion depends on the interaction between the neuromuscular system and body mechanics. An open challenge is whether one can predict muscle length changes from the electrical activation patterns (electromyogram: EMG) in fully intact animals. This challenge arises from the myriad forces acting on any contracting muscle. We asked if we can predict the magnitude and time course of muscle length changes induced from measured EMGs in Manduca sexta where there is a one-to-one relationship between the timing of muscle electrical activation and length-wise contraction. During flight, the dorsal longitudinal muscles (DLMs) the antagonist dorsal ventral muscles (DVMs) deform the thorax, indirectly powering wing flapping. We recorded DLM and DVM EMG activity during in vivo tethered flight. Simultaneously, we used 3D high-speed video of thorax deformation to measure the change in length of the DLM muscles. Using Fourier transform methods, we confirmed that the primary frequency of our two signals matched, consistent with previous work demonstrating the synchronous activation of this muscle group. The average percent length change on the dorsal aspect of the thorax was 0.76 % (SD 0.72%) suggesting large variability in muscle shortening across trials and individuals. We also found large variation in the phase between length change and electrical activation. Preliminary results show a frequency dependent increase in the phase of muscle length change relative to activation. The one-for-one correspondence between muscle activation and shortening in M. sexta allows us to decipher the relationship between activation and functional outcome.
