When I was growing up did Judo and goto Brown belt before giving it away in late high school, played Football (Aussie Rules) since I was 8 till about 7yrs ago when I did my right knee and had a to have a full reco then came back and did it again, so gave it away else I think I would still be playing, and much the same for Cricket I played since I was 8 and gave it away about the same time as I did my knee, just couldn't be bothered with cricket, plus now having kids it makes it a bit harder to find the time...
I think over all the discipline from martial arts and training for footy certainly helps in the gym and in some ways you already know how far you can be pushed and push yourself.