Sore

I have been in the field a bunch in the last two weeks in different surveillances. Its primarily spent hunkered down in my car, sitting still watching the target for hours at a time.  I did it again today.  I have not burned any calories or moved any major muscle groups but I am sore and tired as if I had one of the 16 hour days.  I always find it surprising that I am not flying off the walls with excess energy but rather just want to go to bed early.