Is senpai normal?

I'm officially a senpai now. I'm in my fourth year high school and today is the second day of school. I had P. E this morning and as soon as I came home and rest a bit, I felt like I was the little mermaid. My legs ached like crazy and I couldn't walk properly. Actually as I am writing this, it still hurts. Maybe it's because of the task I did this morning. The teacher said it's for building stamina something and the class had to run for 2 rounds around the community hall. We did it about five for each round. I guess I need to work out more.. I want to make a my diary or whatever Should I make one? Na I don't need your opinion I'll do it anyway..