Last night I attempted some sprints, out on the middle of the road. (It was past midnight, so there were no cars on the road.) My back was bothering me, so my walk before the sprints was not so comfortable. Starting the first spring was not easy, but the second and third sprints didn't take as much willpower to commence. I felt a bit restricted in my abdominal region -- dinner? or excess fat? Still, this morning I felt rather energetic and was in the mood to sprint. I got enough sleep (a little less than 8 hours). And I did change my diet, to see if that would get rid of my sluggishness. Going primal seems to be working so far.