What is the main effect of chronic resistance training on Type II muscle fibers?

Chronic resistance training primarily leads to a greater increase in the size and strength of Type II muscle fibers, which are also known as fast-twitch fibers. These fibers are responsible for generating quick and powerful muscle contractions but fatigue more quickly than Type I fibers.

When an individual engages in regular resistance training, the mechanical tension and metabolic stress on the muscle fibers stimulate adaptations such as muscle hypertrophy (an increase in muscle fiber size). This effect is particularly pronounced in Type II fibers, as they have a greater capacity for growth in response to strength training stimuli compared to Type I fibers.

The increase in Type II fiber size contributes to improved performance in activities requiring strength, power, and sprinting, which are characteristic functions of these fibers. Thus, the main effect of chronic resistance training is indeed a greater increase in the size and functional capacity of Type II muscle fibers.