No really, it isn't intensive at all, for that human body a 486 would be more than enough if coded in C for example. If you have for example 14 solids, in 2D that means 14x3=42 variables, after applying the boundary conditions you have only 42-26=16 variables. The kind of problems that can be solved with computers nowadays may have millions of variables.
http://upload.wikimedia.org/wikipedi...ualization.jpg
It's not like in real life, it's an approximation, you define the precission with the method (first, second... order, etc.) and the step size (in time). Every instant you estimate the 16 position variables from their values one step before.
http://upload.wikimedia.org/wikipedi..._rectangle.png
Assembly is for programmers,
you can't ask an engineer to code in assembly. Most will even use Matlab, Maple or Mathematica most times instead of a generic compiled language.