do hard impact contact to the ground in 5 or 6 different areas of the body ,cause changes that later turn painful ,cronic , such as parachute landing ,feet knee ,arm, shoulder in the military they teach you to land with least amount of trama to the body , this was not allways easy to do and i feel the injurys way after the service, cervical ,and lumbar and knee problems all extremly painfull and seem to be worse each year?