Steroid injection - advice please

Let me state clearly that I am not a medical person, I am an engineer. Steroid injections can reduce inflammation, swelling and I suppose hence also reduce pain and discomfort and stiffness. The effects are temporary. I believe that one of the worst things that you can then do is to over-exercise, thinking that the magical steroid injection has fixed everything. The benefits of a steroid injection can wear off, they are not a cure. I am now in my late 60s. At age 21 while at university I injured my knee playing rugby. At the time is was disgnosed as a "bad knee". At the end of the season we staged a 700 mile run for charity - it involved 15 of the club running in relay, 700 miles around the roads of Warwickshire over 3 or 4 days. After my first day where I had run about 20 miles in 2-mile legs, my knee was killing me. I went to the GP on the campus surgery, he was a strong supporter of the rugby club and often helped out with popping-back dislocated fingers and similar on match days. He understood that I wanted to continure, so he gave me a steroid injection into my knee. I continued running for the next few days. Once I finished and the stroid wore off - I was in agony. I later discovered that I had damaged my knee severely. Now, with maturity and appreciation of my physical mortality and limitations (something I ignored at age 21) I understand that after a steroid injection then gentle excercise and gentle physiotherapy might be beneficial, but you should not simply resume your previous regimes befoe the steroid wears off. . You can do further damage that only becomes obvious when the effects of the steroid wear off.