Gary Knight is a long time exercise enthusiast, exercise instructor, and online coach.  

He shows why keeping great data is so crucial to being able to gauge his and his clients' progress, by being better able to assess how to manipulate variables.

As we discuss, if you are changing more than one variable, it becomes difficult if not impossible to determine what has created either improvements or detriments to progress.

To that end, he emphasizes consistency and keeping variety to a minimum.