SLOW-TWITCH MYOSIN. “There are several types of myosin proteins but the most abundant and best understood for mammalian skeletal muscle physiology are type I (slow-twitch) and type II (fast-twitch) myosin. Type I fibers take more time and more energy to contract. As a trade-off, they are slow to fatigue and hold the contraction longer. In humans, these types of fibers tend to dominate in muscles of the limbs (except for the hand) and spine.“
http://onlinelibrary.wiley.com/doi/10.1111/joa.12440/full