In economics, diminishing returns (also called diminishing marginal returns) is the decrease in the marginal (per-unit) output of a production process as the amount of a single factor of production is increased, while the amounts of all other factors of production stay constant. (from Wikipedia)
And, as much as I would like it not to, it applies to my running as well. And I know the exact point where I hit the diminishing returns.
35 miles per week. I can run 6 days a week, add speed work or hill work and my legs and body are happy. But, the week my miles get above 35, things start to fall apart.
And this is a problem when you are training for a marathon.
Have you read the book Born to Run? I have, and as much as I would like to think I was born to run, I do not think I was born to run marathons. At this point my legs are on the verge of shin splints and knee problems. I am frustrated and upset. And there are days I want to give up.
I went into this marathon training cycle fairly optimistic. This is my second marathon and I wanted to crush my last marathon time. I had a good base. Legs felt great. I had PR'd in a half marathon right at the beginning of training. But now my average pace is getting slower and slower because my legs just cannot seem to handle the faster paces right now. I am afraid that I will go into the second marathon no better off than I did in my first. I did not want to just finish another marathon. I wanted to run it well. But, at this point, I am hoping I can get to the finish uninjured.
Is this normal? Does every marathoner go through this? Am I doing something wrong? Am I just not meant to run marathons?