Aging in the saddle

I first experienced what relates to my age when I was in Thailand at age 60. I strained a muscle in my chest which effected my ability to climb hills on my bicycle. The act of standing in the saddle and pulling side to side on the handlebars hurt. I rested for a week or two. Then began recovery rides where I didn't strain myself and tried to overcome the pain. Then I had a back injury which effected me the same way. It was not a debilitating back injury but it impacted the comfort of my ride. I think between the two injuries I rode less for several months. At a younger age I wouldn't have had either injury because my upper body was a little stronger and more resilient. Now I've had another minor injury from working my upper body at the YMCA. I did various weight machines for a total of 10 minutes, very few reps with small amount of weight. The next day I had this hot dull pain in my chest. The pain was bearable but extremely irritating. Of course I was concerned that it could be the sign of a more serious diagnosis like heart something. After a week of suffering I went to the doctor. They did an EKG just to make sure. Everything was fine. When I go for rides my chest is still sensitive. I know if I ride aggressively on a tough hill I will pay for it.