I thought this was very cleverly written and very good advice. In the midst of a workout, we might get wrapped up not only in the tracks playing in our headphones, but also the "tracks" in our mind. If they are negative for any reason, push them out of your mind and focus more on your body's response to the workout, like your breathing and how you feel physically.
Then, the writer, Gregory Joujon-Roche suggests thinking back to your workout during your cool down, considering your state of mind, physical state, and if you exercised at the level you wanted to.
At times, my goal is to get in the gym, workout, and get out as soon as possible. Those days, I've mostly felt too exhausted or flustered to even go. Bringing myself into the moment, allowing my mind and body to connect in the way the writer described, seems like the perfect way to turn those workouts around for the better.