Muscle types

This article considers some of the properties of fast ‘twitch’ skeletal muscle. How this muscle’s structure, resting activity, electrical properties, excitation-contraction coupling, mechanical properties, metabolism, resting activity, length–tension relationship, and the ways in which its activity is controlled, suit it to the role it normally plays is discussed. Differences from the other types of skeletal muscle (slow, fatigue-resistant muscle, important in posture) are then considered. The different requirements of cardiac muscle and several types of smooth muscle are also mentioned. In all cases, differences from fast skeletal muscles are related to the different roles that these muscles normally play. The muscle types that should be regarded as most ‘primitive’ and which the most ‘advanced’ are considered. The conclusion is that the use of such terms is arbitrary and even misleading, missing the main point; namely, that each muscle type has properties that suit it to the specialized role it is required to play.