I never was into sports but after high school I went to the gym and did for about 20 years. I got out of the habit when I started shift work and never got back

I never was into sports but after high school I went to the gym and did for about 20 years. I got out of the habit when I started shift work and never got back except some cycling in the summer. I miss the feeling after I pushed myself the warm feeling and the total relaxation no aches no stress. I hated the feeling of missing the gym I could feel the tendons in the back of my knees and crooks of my arms (inner elbow?) ache. The problem was I never made any progress I must be what is called a non-responder. If I tried to do more I got tired and took more time off. Often I found I did better after taking a three or four days off. But any exercise is like medicine you're only there you only exercise because you have to. I want to be active but not a march forced by the fear of death I want to be there because it's fun.