CARDIO WHITE MUSCLE VS RED MUSCLE by livestrong.com
The muscles that hold your skeleton together and allow you to move are called skeletal muscles. They work voluntarily, meaning you consciously control their movement. Skeletal muscle is divided into fast- and slow-twitch fibers; fast-twitch muscles provide short bursts of power while slow-twitch fibers endure longer use without fatigue. The fibers will appear red or white, depending on their composition. While each has its own attributes, your body needs both types for optimal function.

Skeletal Muscle Fiber
The fibers in your skeletal muscles are striated; they have alternating light and dark bands that run perpendicular to the length of the fiber itself. Muscle fibers also differ in color based on the amount of myoglobin — a substance that stores oxygen until it is needed by the cell — they contain. Fibers also have different contraction rates, based on their ability to split the energy molecule ATP. Slow-twitch fibers, or type I fibers, contract as the name suggests — slowly. Fast twitch fibers are sub-divided into type IIA and type IIB fibers, both of which split ATP quickly.

Red Fibers
Type I and type IIA fibers contain high amounts of myoglobin and are capillary-rich, making them red in color. Both fibers generate energy aerobically, or with oxygen. Aerobic respiration produces little lactic acid, which fatigues muscles, allowing these muscle fibers to withstand longer use. Type I fibers, however, contract and split ATP more slowly than type IIA fibers and have lower amounts of creatine phosphate, a molecule needed for quick, explosive movements. Slow-twitch fibers are found in muscles used often, like those in the neck. Type IIA red fibers have high amounts of creatine phosphate and split ATP faster, making them more useful during sprints or jumping to dunk a basketball.

White Muscle Fibers
Type II B fibers are considered “white” muscle fibers due to their low content of myoglobin and fewer capillaries. They contain large amounts of glycogen, a stored form of carbohydrate energy that your body depends on for intense activity. Muscles use glycogen during weight or resistance training, for instance. White muscles generate ATP anaerobically, or without oxygen; this process leads to fatigue more quickly than red muscle fibers. Type II B fibers do, however, split ATP quickly and contract rapidly. The muscles in your arms are largely composed of type II B fibers.

Balance in the Body
Both white and red muscle fibers are needed by your body. You can, however, hone the amounts of certain types to suit your athletic endeavors. Sprinters and power lifters, for instance, need higher amounts of fast — white or red — fibers, while a marathon runner benefits most from large amounts of slow-twitch fibers. For the average person, however, performing activities that target both types is beneficial. Overuse of one type can break down muscles, tendons and ligaments, leaving you prone to injury; mixing up your workouts can prevent over-training.

Read more: http://www.livestrong.com/article/466169-cardio-white-muscle-vs-red-muscle/#ixzz2PDxeQBMF