Table 1. Baseline Mechanical Variables of Papillary Muscles in Adult and Senescent Rats

Values are mean ± SD.

*P < 0.05 vs.  adult rats.

L^max= initial length; CSA = cross-sectional area; RF/TF = ratio of resting force to total force; V^max= maximum unloaded shortening velocity; ^maxVc = maximum shortening velocity; AF = isometric active force normalized per CSA; +dF/dt = peak of the positive force derivative normalized per CSA; ^maxVr = maximum lengthening velocity; −dF/dt = peak of the negative force derivative normalized per CSA; R1 =^maxVc/^maxVr; R2 = (+dF/dt^max)/ (−dF/dt^max).