This may be a dumb question but it seems like Romans had a long military service (25 years I think for a soldier) and the Barbarians were fighting since young teenagers. Given the nutrition of the times how muscular and in shape were these soldiers?
Did this extend into the medieval era?
Not to discourage any further answers but you may find these older posts to be interesting.
/u/Iphikrates on Greek fitness:
Did Socrates even lift? An exploration of Greek fitness?
/u/Celebreth on the Roman army:
What would "boot camp" and PT have been like for the Roman army?
What did the Roman legion's diet consist of?
I have just joined the Roman army, what is my life going to be like?