do you have check if you have any self-intersection between your muscle in each frame?
you can do it with this part of script
copy this in script editor mel, select your muscle, set the selfIntersectAnalyser(frameInput,frameOutput); and lauch the script as mel :
global proc selfIntersectAnalyser(int $frIn,int $frOut)
{
string $sel[] = `ls -sl`;
int $i = $frIn;
while($i <= $frOut)
{
currentTime $i;
if (`progressWindow -q -isCancelled`)
break;
select $sel;
string $return[] = `zFindSelfIntersections ($sel)`;
progressWindow -isInterruptable 1;
if (size($return)>0)
{
print("\n FRAME : " + $i + "\n");
print($return);
}
$i = $i+1;
}
progressWindow -endProgress;
}
selfIntersectAnalyser(990,1128);