“Physically valid” means herein that {TAIL ~ a muscular tension} satisfies {HEAD ~ a dynamic equation} 
“ Physically valid ” means herein that { TAIL ~ a muscular tension } satisfies { HEAD ~ a dynamic equation }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD