FAST-TWITCH MYOSIN. “Type II fibers consist of a number of isoforms (different sub-types) but overall they are able to contract more quickly than type I fibers and use less energy. As a trade-off, they are quick to become fatigued and cannot hold the contraction as long as type I fibers.”
http://onlinelibrary.wiley.com/doi/10.1111/joa.12440/full