Run most days of the week, run hard all the time, and don’t take any days off when you start to experience unusual fatigue. That should do it for most runners. How do I know? Personal experience. I over-trained a few years ago, towards the end of an overly-ambitious marathon training program. High mileage, running long runs too fast, doing twice a days, too many fartlek sessions, and just too much hard running did me in.
Some of the symptoms I experienced at the time were dead legs, chronic leg muscle pain & stiffness (it is not normal to have painful calves every morning!), having to run harder to maintain usual training pace, and not being able to elevate heart rate to previous highs. My resting heart rate was also much lower than before. From what I read at the time my parasympathetic nervous system was being compromised.
I knew I was in trouble when I would go out on a short 3-mile run, try to get up to my usual pace and then check my actual pace on my Garmin. I would be way below the perceived pace, yet feel like I am running as fast as I could.
This was in early December on a marathon training program which would have culminated with a marathon in mid January. I skipped the marathon altogether, and stopped running for nearly 2 months. Eventually my resting heart rate recovered, I started feeling better & slowly worked my way back. I am much more careful now to include a range of paces in every week's running program: some easy recovery type running, some tempo/strength work etc. but no twice a days and not all of it as fast as possible...
I used to think that increased resting heart rate is indicative of over-training, and it usually is, but that is not always the case. When your parasympathetic nervous system is affected/compromised (as it can be by overtraining), your resting heart rate (RHR) can also be lower than usual. Mine was in the low 40's, usual RHR was about 58 until then. The most striking thing, though, was my inability to push my heart rate as high as previously, during exercise. I would run literally as hard as I could, and no matter what, my HR would not exceed 135 to 140. Previously, it would easily go higher than 150 and even 160+ under heavy exertion. Even when pushing myself hard on the track, my heart rate would increase by only 20 or 30 beats per minute, and drop back very quickly as soon as I stopped running. I interpreted this as a reduction in heart rate variability. It was as if my heart (controlled by the parasympathetic system which slows things down) was trying to prevent me from doing any strenuous exercise.
About 10 days ago I was starting to feel unusually fatigued towards the end of some of my runs. On a Thursday hill workout, I fell significantly behind my usual ‘rivals’. I put it down to sleep deprivation (the Olympics!) and hot humid weather. But I had my doubts. During last Saturday’s long run, I felt very sluggish. When this happened again a couple of days later, I took two days off. No running, no cross-training. Nothing. By last Thursday I had some life back in my legs, and put in my best effort on the hills so far this year.
Total mileage for the week was 41, including a 1-mile time trial () which would have been a few seconds faster but for some heavy traffic on the trail. I will continue to use the training paces based on my current VDOT of 45. Might ease off a little bit if the fatigue crops up again.