Stuart is walking past his bedroom door and accidentally slams his elbow into the door frame. The pain is sharp, immediate, and intense. The next morning his pain is a dull ache that bothers him throughout the day. The initial pain Stuart felt was caused by fibers, whereas the pain he felt the next morning was caused by fibers.

The following is missing for the question to be complete:

Slow; fast

Large; small

Fast; slow

Small; large

   Fast; slow

Explanation:  Fast-twitch muscle fibers cause sharp immediate pain and such contraction occurs, for example, in fast running or as in this case, when the elbow is slammed against the door frame. In other words, these fast-twitch fibers therefore rapidly contract, cause sharp pain due to short-term but high effort or strain.

On the other hand, slow twitch muscle fibers therefore slowly contract. The pain due to the action of these fibers occurs after some prolonged activity where like distance running and endurance is needed. Because these muscle fibers are able to withstand the long-term contractions that are necessary for stabilisation after exertion, as is the case here, the pain is felt throughout the next day.