Slow oxidative (SO) muscle fibers appear red mainly because of their high content of which oxygen-storing molecule?

1. SO fibers are built for long, fatigue-resistant contraction and are richly supplied with capillaries. 2. They also possess large amounts of myoglobin, an oxygen-carrying molecule similar to hemoglobin. 3. This myoglobin stores oxygen within the fibers themselves and is specifically what gives SO fibers their red color. 4. Glycogen, creatine phosphate, and troponin are all present in muscle fibers but are not the pigment-carrying molecule responsible for the red color. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 10 "Muscle Tissue", section 10.5, p. 428_