Final answer:
In box-to-box plyometric drop jumps that require quick force generation, the slow-twitch Type I muscle fibers are bypassed in favor of fast-twitch Type II fibers, especially Type IIx, due to their ability to contract quickly and produce a greater amount of force in a short amount of time.
Step-by-step explanation:
When one is performing a box-to-box plyometric drop jump, the principle of selective recruitment typically bypasses the slow-twitch muscle fibers, known as Type I fibers. These Type I fibers are dense with capillaries and rich in mitochondria and myoglobin, which supports sustained aerobic activity, making them insufficient for explosive movements that require rapid force generation.
The muscle fibers recruited during these high-intensity, short-duration jumps are Type II fibers, specifically Type IIx and possibly Type IIa fibers, which can contract quickly and generate more force than oxidative muscle. Type IIx fibers are the fastest muscle type in humans and primarily utilize anaerobic glycolysis, allowing for quick, powerful contractions but with a limited duration before fatigue sets in. Type IIa fibers, while also fast, are more oxidative than Type IIx fibers and can switch to anaerobic metabolism when necessary.
Therefore, for box-to-box plyometric drop jumps requiring significant force in less than 200 ms, the Type IIx and Type IIa fibers are preferentially recruited over Type I fibers to maximize performance.