Don’t chase reps, or they might case you… to the Chiro/Physio!
I treat people daily with injuries from chasing repetitions (‘reps’) and using speed and momentum (part of chasing reps) when they strength train. Speed and momentum DO allow for more reps (avoiding the hard parts of the exercise), but they do NOT necessarily recruit more fast twitch fibers than slow movements.
The ‘fast’ in fast-twitch refers to FAST-TO-FATIGUE, not the speed.
For example, the slow twitch muscle fibers of a fast-fingered piano player can move extremely quickly, but they are slow-to-fatigue (not slow to move).
Yes, fast twitch muscles recruit more muscle fibres, but studies show that enough weight (to achieve failure or close to it) in about 60 seconds will fatigue out the slow (and ‘intermediate’) twitch fibers AND do the same job of recruiting fast-twitch muscles for strength or hypertrophy purposes MORE SAFELY.
Adding speed only allows for the neurological fine-tuning of a skill and needs to be done in the exact environment required by the sport, lift or activity for practice (perfection). For example, shooting with a heavier basketball, swinging a heavier bat, hitting a heavier volleyball will all add to the injury potential and TAKE AWAY from that neurological specificity of that skill.
Therefore, you are better off doing reps slowly (4-10s/reps over 45-60+s total), with good form and to failure (or close to it) using the muscles and joints in the plane(s) required by the sport or life movement. Then, SEPARATELY, focus on the exact skill requirement.