Jazzy 33,
Without a pack , walk 2 hrs , just strolling, anywhere on any terrain....................6---7 km.
But you must sooner or later do the same with a pack on ........don't do any more , no need.
** As long as you start off slow on the Camino , 15-20km a day for 2 or 3 days , the rest will be enjoyable.
Pain , yes , but something that will change /stay with you forever.
You will get fit on the way, just allow 43 days to Muxia [ a must ] and enjoy.
Best wishes,
David