1. You’re overtrained, and tired – if so, reduce your training, and/or take an extra rest day.
  2. You may have chosen a goal that it too ambitions for your current ability.
  3. You may have missed some of your workouts, or not been as regular with your training.
  4. The temperature may have been above 60° F (15 ° C). Above this, you will slow down.
  5. When using different test courses, one of them may not have been accurately measured.

Learn more about  performance training in Jeff’s book  Jeff Galloway – Testing Yourself.  You will find the book at:  

https://shop.phidippides.com/collections/books-dvds