The decreasing of your performance has a strong relation to your technique. In mechanics the explanation is clear “mechanical efficiency its measures the effectiveness of a machine in transforming the energy and power that is input to the device into an output force and movement” . As human beings the rules of physics is not a exception. Here I compare what happens between two points in a 10k race (km1 and km 9). If we take another human as an example of performance, like a musician, a drummer never loses the rhythm because the result can be disastrous. Musicians have to practice through repetition (technical skills) to keep the rhythm throughout the performance. There is no big difference between an athlete and a musician, both need to practice technique to achieve the best performance (both try to achieve the best results). In this video we see an elite runner who decreases his technical skills (due to different reasons) and therefore gets a worse performance. Even though he maintains his technique almost perfectly throughout the race, his output is not as good as at the beginning of the race. Are you capable of delivering your best performance throughout an entire competition?