#MUSCLE FIBER DESITY VS SKELETON ARMOR HOW TO#

In addition, the frequency of firing rates of the neuron also alters the muscle fiber type. If a muscle is innervated by a small neuron that muscle fiber will remain slow, whereas large myelinated fibers induce the fast isoforms. The default muscle appears to be slow, type I fibers. It appears that muscle fiber types are determined embryologically by the type of neuron that innervates the muscle fiber.

#MUSCLE FIBER DESITY VS SKELETON ARMOR HOW TO#

The Holy Grail of muscle research is to determine how to change skeletal muscle fibers from one type to another. Muscle biopsies of one world class sprinter revealed 72% fast twitch fibers and amazingly 20% were type IIB. The 'preferred' fiber type for sprinting athletes is the fast-twitch glycolytic, which is very fast, however, most humans have a very low percentage of these fibers, < 1%. In addition, women seem to have a higher ratio of slow twitch to fast twitch compared to men. As a result, the gastrocnemius muscle is used in sprinting while the soleus muscle is important for standing. On the other hand, the eye muscles are predominantly fast twitch. For example, the gastrocnemius muscle of the calf contains about half slow and half fast type fibers, while the deeper calf muscle, the soleus, is predominantly slow twitch.

In human skeletal muscles, the ratio of the various fiber types differs from muscle to muscle. For a complete list of how muscle fibers differ in their ability to resist fatigue see the table below:įast-twitch Oxidative (Type IIC, IIAC, IIA) Thus, fast-twitch fibers can complete multiple contractions much more rapidly than slow-twitch fibers. Fast-twitch fibers also pump Ca 2+ ions back into the sarcoplasmic reticulum very quickly, so these cells have much faster twitches than the slower variety. Fast-twitch fibers have a more rapid ATPase (splitting of ATP into ADP + P i) ability. Recall that it is the myosin head that splits ATP. This variability is due to different varieties of myosin molecules and how quickly they can hydrolyze ATP. How fast a fiber can contract is related to how long it takes for completion of the cross-bridge cycle. Therefore, we will refer to type X as B so that as you read other articles you can follow the nomenclature.įast-twitch (type II) fibers develop tension two to three times faster than slow-twitch (type I) fibers. It has been shown that humans do not contain the “B” isoform like animals and instead should be renamed type X but altering nomenclature can take years and is rarely successful. From slowest to fastest they are types: I, IC, IIC, IIAC, IIA, IIAB and IIB. In humans, within the above classifications, there are seven identifiable subtypes.

Fast-twitch glycolytic (Type IIB or IIX).

Fast-twitch oxidative-glycolytic (Type IIA)muscle fibers, and.Slow twitch oxidative (type I)muscle fibers,.These classifications are in the process of being revised, but the basic types include: Classically, skeletal muscle fibers can be categorized according to their speed of contraction (myosin ATPase rate) and their resistance to fatigue.

Muscle fiber desity vs skeleton armor