A few days ago I believe you had your model uploaded. I downloaded it and played around a little bit. I believe if you change your thorax joint to a weld joint that it will work.
<Body name="thorax">
<mass>15.6903353239452</mass>
<mass_center> -0.12797 -0.13354 0.0115064</mass_center>
<inertia_xx>0.270280513098911</inertia_xx>
<inertia_yy>0.123967353014763</inertia_yy>
<inertia_zz>0.218867763026006</inertia_zz>
<inertia_xy>0.02441147645256</inertia_xy>
<inertia_xz>-0.008948253626665</inertia_xz>
<inertia_yz>-0.003326809054344</inertia_yz>
<!--Joint that connects this body with the parent body.-->
<Joint>
<WeldJoint name="ground_thorax">
<parent_body> ground </parent_body>
<location_in_parent> 0.000000000000 0.000000000000 0.000000000000 </location_in_parent>
<orientation_in_parent> 0.000000000000 0.000000000000 0.000000000000 </orientation_in_parent>
<location> 0.000000000000 0.000000000000 0.000000000000 </location>
<orientation> 0.000000000000 0.000000000000 0.000000000000 </orientation>
</WeldJoint>
</Joint>
Running it with a few of my own kinematics files from a similar model gave exceptional results and actually helped to fix a problem of my own. Thank you!!