After reaching my goal in my Senior year of track (breaking 10 min in the 3200, going to state) I immediately started looking for another goal. I'm 18, and for some reason my friend (who was also 18) and I decided to spend the summer training for a marathon in August. We gradually built up our weekly long runs from 16 miles, to 18, and eventually we did one that was 20. Two weeks later, we did the marathon with the goal of just finishing, since it was our first one. We ran together for a while up until mile 21, and my buddy told me to just go since he was dying. I pushed myself and sped up with my last 3 miles being my fastest of the race. Finished at 3:43 and was stoked just that I did it. My buddy also finished a bit later.
Recovery-wise we were both in agony for 3 days then my friend got better. I did not. My knees would randomly start buckling at random times while I was walking. I recovered from soreness after 6 days or so, but the knee buckling continued for almost a month. Now it's 5 months later and very occasionally I'll be walking and my knee will buckle, maybe once a month and it reminds me of after the marathon. Has anyone heard of this happening before and is it nothing to worry about? I'm currently training for the 5k but my friend and I are either going to train for another full or a half this summer. I've heard that people are fine running marathons when young and I've also heard it can be bad for development. Should I wait a bit before I do another full, or if I do another one, should I not speed up at the end too much? I'm 5'9 145lbs if that helps anything. I'd appreciate some wisdom on the subject. Thanks!