Ran a marathon last weekend and was surprised by quad muscle depletion. I was feeling very good and keeping my heart rate down the first part of the race. Started to pick up the pace around 10 miles because it felt good. I tried to slow down a couple of time but my pace kept creeping so I went with it. My max HR is about 175 and I was running at about 155 to 160 when my quads started to cramp. I was using GU 15 before 45 into the race and 30 minutes after. Drank at all aid stations alternating Gatorade and water. I did not feel thirsty until after the race. At 18 miles I started to feel the cramps and tried to relax, but could not get them to recover. I tapered for three weeks, and ran very little the week prior. Is this a fueling issue or is this a hydration issue or a downhill muscle strength issue?? My feet felt great, my hammies and my glutes all good. IT band started hurting the last mile because I was determined to finish. Is there any damage that can be done by running with cramped muscles. Quads cramped in unison,,,middle then...outside....then inside and finnally all. Any suggestions would be great.