Muscle Training

How do you relieve stress? When I was in Japan, I played badminton with my friends once a week, which was a great way to relax. However, since I came abroad, I haven't had opportunities to do exercise that much. I'm worried about losing strength lately. My weight hasn't changed for ten years, but I seem to be losing muscle that was obtained when I was a high school student. So, I started muscle training such as including sit-ups and push-ups with my wife two weeks ago. There is a rule for it; First, we play cards, and then the one who lost the game has to do sit-ups and push-ups. The number of them in one cycle round is different between her and me. So far, we are having fun.