Final answer:
Anaerobic type training typically results in a decrease in type I muscle fibers and an increase in Type IIa fibers, as the latter adapt more to high-intensity, short-duration exercises by increasing in size through hypertrophy.
Step-by-step explanation:
Skeletal muscles adapt to anaerobic type training by producing preferential transitions between type II and type I fibers in a manner such that it causes a decrease in the proportion of type I fibers and an increase in the proportion of Type IIa fibers. Anaerobic exercises are those that involve quick bursts of energy and are performed at maximum effort for a short time. This type of exercise promotes hypertrophy, which is the increase in muscle mass due to the addition of structural proteins.
Type I fibers, also known as slow-twitch or slow oxidative fibers, are more resistant to fatigue and are used for endurance activities. These fibers rely on aerobic metabolism. On the other hand, Type II fibers, particularly Type IIa, which are fast oxidative fibers, can operate under both aerobic and anaerobic conditions but are more responsive to anaerobic training, leading to an increase in these fibers. Type IIa fibers are dense in mitochondria and myoglobin, similar to slow-twitch fibers, but they can produce more power and sustain activity for longer than Type IIx or Type IIb fibers, which are more anaerobic.