Once again I have found interesting information found over at Ultrarunnerpodcast.com. Specifically: training harder does not lead to gains as reliably as training moderately. The following graph sums it up nicely.
Recognizing this trend in my own training, albeit on a yearly cycle instead of quarterly, has provided a new perspective on my training effort. I think I may be able to stem the tide of injury in the future, as a little knowledge goes a long way.