I have started training for my first half marathon which is in september and really enjoying it, for now I can only get 3-4 days in a week as I seem to get DOMS after most sessions (not on my easy run) as I am still at the early stages of training.Today I went for a 6 mile run and even though my legs were recovered as I had 2 days off, my legs were aching and prevented me going faster, I didnt feel that out of breath but more fatigued on my legs. Then it crossed my mind that maybe I should be lifting weights to increase leg muscle strength? If so, Should I be weight lifting my upper body too or just focus on my legs and stomach? Then how often should I be weight lifting on my legs... could leg weight lifting be replaced by hill sprints? A lot of my runs involve hills which get the legs muscles working hard.