After 40 years of continuous cycling and 25 years of running until 2012 when I had a back fusion I was told no more running forever. I saw a sports medicine Doc about 6 weeks ago who said a fused back should be as strong as pre surgery and allowed me to start running again. I am curious as to whether any other geezers (I'm 77) have started running and what you went through. This reminds me of when I started cycling in my 30's and went thru a lot of pain and suffering as the muscles developed the necessary strength to ride competitively. I am now up to about 8 mi runs with about 600 feet of climbing on trails until my running legs come back. I ran this AM and sit here with pain in the calves and one upper hamstring. It is good pain as it is a sign these muscles are adapting.
I decided to add running to cycling as there are quite a few races with upper age classes. Cycling races for people over 50 are essentially nonexistent in SoCal except for State and National championships.