Discovered in the pinacoteca at Castello Sforzesco

As I mentioned in the mummified crocodile post, we ventured to the Castello Sforzesco on Saturday to visit its museums. In reality, there's one big museum with many themes, and one ticket gets you into all of them. We missed the musical instruments this time, but I'm sure we'll be returning.
I've posted photos of the castle before, but this is the courtyard from inside the building. It's pretty cool.
In the pinacoteca is this Mantegna, Madonna in gloria e santi Giovanni Battista, Gregorio Magno, Benedetto e Girolamo. Laura's name for it: Mary and Jesus in a Tree of Floating Baby Heads. She has a point, I suppose.
I didn't have time to dwell on that, though, because I was distracted by the question of the day: Did Jesus lift weights in utero? If you take a look at this detail of Giovan Battista Trotti's Adoration of the Shepherds with St. Clare and St. Francis of Assisi, you'll see what I mean.I mean, he's both chubby and buff at the same time. Is that possible? (I don't seem to have taken a picture of the whole painting, but you can see it here.)