I am in marathon training, shooting for a 2:50-55, with a goal marathon in the winter. I have been building up my mileage to the 65-85 range. I have been doing cycles of three weeks hard (progressively) and one week easy. Over the past two cycles, I have gotten sick on each of the easy weeks. First time was a head cold. This time it was a fever, with night sweats. Each time, I recovered from the illness quickly and got right back to training. The odd thing is that I have never felt bad at all, except when I took an easy week.
Is my training schedule wrong? Mileage has been 64, 68, 72, easy week (40s), 72, 76, 80, easy week. Two hard workouts a week (intervals and hills usually). Legs feel fine, but why do I get sick on my easy week?
Should I go two weeks hard, one week easy? Skip an easy week and just back off everything? Keep doing what I am doing and be ready to feel like crap every 4 weeks?