Meeting Abstract

P2.73  Friday, Jan. 4  Don’t call me a stiff: changes in performance and histology with age BURNETTE, MF*; MONROY, JA; LINDSTEDT, SL; NISHIKAWA, KC; Northern Arizona University morgan.burnette@nau.edu

As many of us can feel, muscles get stiffer and weaker as we age. Stiffness is dependent on the force generated by the muscle as well as the external load. This is true for muscles during both active shortening and lengthening. Our study investigates the histology underlying changes in stiffness and force during active shortening. Mouse soleus and EDL muscles were serially sectioned and stained for ATPase activity and oxidative capacity. We measured whole muscle cross-sectional area, fiber cross sectional area, fiber density, fiber-type (fast or slow), fiber-type ratio and distribution. Relative to old muscles, young muscles are larger in cross-sectional area and mass. In young EDL and soleus muscles, low oxidative fibers have greater cross-sectional area and diameter than high oxidative fibers. Furthermore, the ratio of fast to slow fibers was 60:40 in EDL and 50:50 in soleus. Preliminary results indicate that old EDL and soleus muscles have relatively fewer high oxidative fast fibers. As such, muscles that produce less force have increased stiffness. These results suggest an increased importance of maintaining muscle force to ensure more compliant muscles as we age.