GABALDON, Annette/M; NELSON, Frank/E; ROBERTS, Thomas/J; Oregon State Univ., Corvallis OR; Oregon State Univ., Corvallis OR; Oregon State Univ., Corvallis OR: Force-Velocity Characteristics of Ankle Extensor Muscles in Wild Turkeys During Running and In Situ
Muscles develop their highest power outputs at intermediate relative shortening velocities, i.e., approximately 0.30 V/Vmax, and near-maximal forces at V/Vmax values close to zero. Our previous studies show that ankle extensors in wild turkeys (Meleagris gallopavo) produce force with low power output during level running and increase power output during uphill running. This suggests they function at different V/Vmax values for different mechanical tasks. We made in situ and in vivo measurements of force-velocity properties of the lateral gastrocnemius (LG) and peroneus longus (PL) muscles to determine their V/Vmax values during running. Maximum unloaded shortening velocities (Vmax) measured in situ were: 13.0 L/s (LG) and 14.8 L/s (PL), and peak power output occurred at 0.32 V/Vmax for both muscles. From sonomicrometry recordings of muscle length changes during level running at 2 m/s steady-speed, we calculated stance average shortening velocities of 0.20 L/s (LG) and 0.51 L/s (PL), corresponding to V/Vmax values of 0.02 and 0.03. At these values of V/Vmax, the muscle is capable of developing 94% (LG) and 85% (PL) of maximum isometric force and 14% (LG) and 30% (PL) of peak power. When we increased the demand for mechanical power by running the birds uphill (+12 degrees), LG and PL both increased shortening to increase power output. Stance average shortening velocities were 0.05 (LG) and 0.06 (PL) V/Vmax, where the muscle is capable of developing 83% (LG) and 75% (PL) of maximum isometric force and 38% (LG) and 50% (PL) of peak power. These results suggest that turkey ankle extensor muscles can produce force economically during running even while producing significant mechanical power. Supported by NIH AR46499.
