Meeting Abstract
The purpose of this study was to determine whether five weeks of eccentric resistance training in mice leads to an increase in whole animal performance, muscle stress, and/or an increase in stiffness of leg muscles. Twelve female mice were randomly separated into control and exercise groups. The exercise group received five weeks of downhill ladder training using a progressive overload protocol increasing from 0-15% body mass. Following training, maximum jump height was 1.5-2.5 times higher than before training. Muscles from trained mice generated ~65% greater active stress than control muscles with no difference in passive stress. In addition, on the descending limb of the force-length relationship, trained muscles exhibited ~25% greater force after stretch relative to the isometric reference force compared to control muscles. In both groups, the stress–strain relationship of elastic elements during unloading showed a 2-fold increase in the elastic modulus with activation, but elastic elements in trained muscles developed stress at 4% shorter lengths compared to control muscles. These data demonstrate that elastic properties of muscle are plastic and that eccentric resistance training leads to an increase in muscle stiffness and force enhancement with stretch. The decrease in rest length of elastic elements is consistent with the hypothesis that the elastic titin protein binds to actin upon muscle activation, decreasing titin’s free length and increasing its stiffness, potentially contributing to the increase in whole muscle stiffness and force enhancement. Future work on plasticity of titin properties is necessary for understanding how exercise and other factors influence elastic properties of muscle.
