So i just got back to my school last week and we started practice this past monday. We've just been doing some 45-60 minute runs the past 3 days before we start workouts on saturday. But for some reason like today for example i was gonna go for 50 minutes and we were running around 6:10-6:20 pace after about a 7 min fist mile. By twenty minutes I was barely hanging on, then by thirty minutes I had to back off and jog extremely slow. But two weeks ago this would have been no problem for me. I mean I was running 90 minutes at around 630-640 pace.I felt fine last friday. But all of the sudden I can barely jog 45 minutes. What could the problem be? Burnout? We run trail loaded with wood chips and back home I run on dirt roads. Could I just not be used to that? I don't know. Any help would be great. Thanks a lot.