Why can't a girl run and study?

Just came back from the gym , I was running on the treadmill and studying my flash cards (Neuro final) this honestly helped me a lot more than sitting down and going over them , I would look up from time to time because I felt like someone was looking at me and I at least saw 6 people looking... After I was done , someone asked me if I was serious about my cards... I laughed and said " you should try it sometime" and walked away... Did I make a fool of myself?
Why can't a girl run and study?
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