Overestimating How Hard We Exercise

I'm more used to write content instead of simply pasting links, but I just stumbled on an article published today in the blog section of the New York Times: "Overestimating How Hard We Exercise", by Gretchen Reynolds.
Some of you could find it an interesting read (follow the link to the article).

This relates to some reflections I have been having about the Freeletics method.

Having a fixed workout content and only completion time as a variable, is a great way to ensure high intensity.
Each time that I have a meeting with Aphrodite or one of the gods, I try to setup a new PB. I don't always succeed and sometimes it's mission impossible (bad day, sickness, doing several workouts in a row, etc.). But missing the PB is not that important. What matters most is how far I am from my peak performance.
If I finish in 20:00 instead of 19:00, I still got a good sweat in the process. But if I finish near 30:00, no matter how good my explanation, the clock doesn't lie: I am back to were I was 8 months ago. Hard to pretend that I was at maximum intensity...