Question

fast fibers
○ have many mitochondria.
○ rely on aerobic metabolism.
○ have low resistance to fatigue and quick twitches.
○ have twitches with a very brief contraction phase.
○ have low resistance to fatigue.

Explanation:

Fast - twitch muscle fibers are characterized by quick contractions and low fatigue - resistance. They have a brief contraction phase, rely more on anaerobic metabolism, and have fewer mitochondria compared to slow - twitch fibers.

Answer:

have low resistance to fatigue and quick twitches; have twitches with a very brief contraction phase; have low resistance to fatigue.