I ahve a question,thought I'd ask it here. I like to go on runs for a few miles,I do go boxing training but only for fun.nothing serious. Anyway,when I am running,I try to include about 5 or 6 uphill sprints,for like an extra burst of energy but I find that I am absolutely exhausted afterwards! Would it be better to jog normally or should I stick with the sprinting?Also,is it better to run thinking of how many miles you have run or how long time wise.?