Hey /fit/, I'm perplexed.Since I've moved back to college, I've been getting infinitely more exercise (I basically did nothing but vegetate at home over the summer). Im already a healthy weight, but Ive wanted to build up my endurance. I decided that instead of jumping on the treadmill as soon as I got here, I'd gradually get back into exercising by first walking up and down all the stairs and hilly paths of the campus in my daily school routine. I figured that once I got used to that, I would be ready to start jogging or running.The first few days I was sore as hell, but I never really felt tired. Now, my muscles are fine, but I find myself out of breath just going up three flights of stairs when I was totally fine with it before. My weights the same, too. Why does it seem like my endurance is getting worse?