112.4 Saturday, Jan. 7 Correlation of bone loading and muscle function in the hindlimb of the river cooter turtle (Pseudemys concinna) AIELLO, B.R.*; BLOB, R.W.; BUTCHER, M.T.; Youngstown State University; Clemson University; Youngstown State University firstname.lastname@example.org
Limb muscles have important roles during locomotion, such as counteracting ground reaction forces (GRF) and generating propulsive mechanical work and power. Depending on the magnitude and direction of the GRF or the performance demands of locomotion, limb muscles may produce high forces that impose substantial loads on limb bones. While bone loading has been studied over a relatively broad phylogenetic and functional range of tetrapod lineages, much less is known about how muscle contractile function directly influences patterns and magnitudes of bone loading. To better understand mechanisms of limb bone loading in terrestrial locomotion, we correlated direct measurements of in vivo bone strain with muscle strain (via sonomicrometry) and EMG activation in a major hip extensor (Flexor tibialis internus) muscle of river cooter turtles (Pseudemys concinna) during treadmill walking. EMG recordings indicate activity prior to footfall that continues through approximately 60-70% of the stance phase. Large EMG bursts occur just after footfall when the muscle has reached its maximum length and is beginning to actively shorten, which it does through the first half of stance. At the time of peak bone strains (both principal and axial), the muscle fascicles are active but are no longer shortening, and remain isometric until late in stance when they passively lengthen occurs as the foot is preparing to be lifted from the tread. Peak bone loads therefore can be correlated directly with the action of limb muscles. Supported by URC #3-11.