Based on the context and the answer, generate a question. 

Context: I ran my five - mile rest run today and enjoyed being out . My wakeup heart rate was 55 , a bit higher than normal , but I felt fine . I was out earlier , and the temperature was 75 ( F ) when I left home . However , I spent half an hour watching two guys fly a RC dirigible , so the temperature was probably about 80 when I started running .

Answer:

They run , so their heart rate is normally lower .



What may be the reason they consider 55 beats per minute to be high for them ?