weak muscles-need info for marathon tomorrow!

My husband is running a marathon tomorrow, he's staying with family in another state (Florida) and has been loading up on bananas and oranges thinking this would be good for the race. He normally eats these foods but has been eating more the past few days. Now he says his upper leg muscles feel weak and in general feels slow. I think he has too much potassium and now needs more sodium but I'm not sure. We live in the northwest so the weather is quite a change for him. Oh and he also took a few packets of the emergn-C drink mix (not sure what other minerals are in it just know it has vitamin C.
Any suggestions for him? Thanks so much