I’m not huge fan of using 21-15-9 rep schemes or very short high intensity workouts with general population CrossFit programs for a few reasons:
1. To perform a workout at high intensity, movement pattern must be adequate for all exercise that are to be performed. If there is one exercise, say pull up, the athlete is inefficient with then intensity of the decreases greatly missing the point of the stimuli
2. As exercise intensity increases, so does the risk poor movement and injury.
3. Very short, high intensity workouts don’t provide the athlete with many reps of practice to try a and hone their skills.
4. Lastly, quite often people don’t spend enough performing low intensity activity over a long duration to develop a base. This adaptation is very important because it is what allows us to recover.