When Jesus is portrayed in older paintings and art he is portrayed as well toned? Was this the norm at the time from more physical labor or is this just an invention of Renaissance artists?
There are no descriptions of Jesus' muscle tone in any of the near-contemporary literature, so there is no answer to this question.
Early iconography did not focus on his physique.
Can you provide an example? Even among the well trained legionaries only an extremely few number would be described as well muscled by today's standards due to their emphasis on endurance training. Protein rich diets were and would remain a possibility only for the very wealthy up until the 19th century.