Drawing off Claire Wendling again I notice;
1) really gestural drawing, where there’s an overall rhythm rooted in how body parts interlock
2) heads and torsos can be analyzed as three interlocking parts
3) muscles especially aren’t symmetrical and will bulge or flatten depending on activity and viewer angle
4) everything else is technical knowledge of muscles, bones and joints. And these are always homologous to human structures (with the exception of pectorals as quadrupeds lack collar bones).