So I've just got a one month gym membership but I'm not sure what I should work on. I would like to get my fitness at higher level for tennis, right now I consider myself reasonably fit but I could improve. I would also like to build up some muscle because right now I'm just a skinny bugger. The gym membership is for 3 nights per week for a month. So to get effective results would I be better of doing either 100% fitness work or %100 muscle work, or could I do 2 nights of one and one of the other each week?