The Eagles listed just three players on their injury report ahead of their clash with the New York Giants, the lowest tally in the NFL.
Kelly told ESPN.com: "It's a combination of a lot of things, but I think part of what our sports science aspect of things is, is to make sure that time lost is the biggest thing you're trying to prevent.
"Just the little things: are we getting enough sleep, eating the right way, doing the other things. That contributes to it."
The Eagles are 1-3 going into week five of their season.