Muscle atrophy is a decrease in muscle mass. upon retiring, a weight lifter who works out less will likely experience atrophy of which types of muscles?

There are two types of weight lifters: endurance weightlifters and strength weightlifters. 

Endurance weightlifters use slow-twitch muscle fibers. These muscle fibers provide consistent, steady energy that allows continuous use for extended periods of time.

Strength weightlifters use fast-twitch muscle fibers.These muscle fibers contract quickly and can provide bursts of efficient energy for powerful movements. But, these muscle fibers need to be rested often because they fatigue quickly.