Does the X3 target fast or slow twitch muscles?
The training applied to stimulate fast vs slow twitch is turning out to be conflicting. The most conclusive evidence shows that momentary fatigue using resistance stimulates growth of both types the same. See this meta-analysis study:
Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res. 2010 .