I'm 69,have been riding 5, years riding around 150 miles a week, I have a little over 30,000 miles on my road bike. Two hours before a ride I drink an Ensure+ Protein 13g,Carbs 50g,eat a Cliff Bar Protein 9g,Carbs 42g, I try to drink water all during the day and the morning before a ride. I will usually drink 24oz of Skratch during the first half of the ride. Todays ride was 44miles I had an average HR of 123BPM,Max HR 170 BPM this includes a rest stop have way thru the ride. I ride very hard working I guess close to an all out effort. The problem I have every ride is I have very severe burn in my Quadriceps the greatest burn is when I'm doing my share of pulling. I have to really talk myself into riding at a fast pace. After a short rest stop and then when I get my legs warmed up after the half way point I'm a different person. I can push until my legs just don't have any more strength no burning, stop pedaling for a few seconds and I'm ready to go again. By the end of the second half of the ride I can completely drain my legs, with little burn nothing like the burn I have the first half. Please anyone and everyone give me your thoughts on what I'm doin wrong, no mater how crazy I will listen.