The lesson of this study is not that we can maximize self-efficacy, enjoyment, and improvement in our training by tricking ourselves into believing that we are performing better than we areand yet the lesson is not far off from that. What the Illinois study really tells runners is that we should feel free to arrange our training in whichever way makes our improvement most evident.
The one thing every runner must do is collect relevant objective performance feedbackmileage, pace, heart rate, and so forth. But it is up to the individual runner to determine the particular types of workouts and the ways of sequencing them that yield the best evidence of improvement. A certain amount of repetition in training is required for proof of improvement. If you never perform the same workout twiceand especially if you never perform the same hard workout twice you have no basis for apples-to-apples performance comparisons.
But if there is too much repetition in your training, there is no stimulus for improvement. Also, when the variation in training is progressive in naturefor example, your long run this week is 10 miles, and your long run next week is 12 milesthat in itself is evidence of improvement. So it is important to balance repetition and progressive variation in training.