Burned under a sun lamp?

This has absolutely nothing to do with the Marlins but I was wondering if someone could explain this to me.

Since his first game in the major leagues he wasn't able to play during the first two weeks of that season because his ankle had been burned under a sun lamp in the training room Joe DiMaggio has walked alone....

Red Smith - August 13, 1950.

Do we have any baseball or physical training historians who can explain why a player would be placed under a sun lamp like a bad fast food burger?

I mean sure it would provide heat to the ankle, but still, there were other ways to do that in 1950.  Or at least I think there were.

Just curious.