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