How do I make inner thigh muscles not get sore?

So I ran cross-country, 2 years ago! I havnt done any exersise besides gym since then cause I moved to a new school with no cross-country.., I was really inshape by the end of the season.. But now I'm starting basketball, & when we run for messing up we run FAST, cause if we don't we just run more.. So I ran all week last week & by the end of the week I got sore in the inner thighs but after a weekend I was fine but it hurt runnin hard when I was already sore, practice is starting again this week, what can I do to make it to where I won't get sore? Cause runnin hard while bein sore hurts, but I don't wanna run more than I have to. Does it mean I'm badly outa shape??? Help!