Type II fibers

Figure 3. Top panel Whole muscle force (x) and single fiber PCr (a, a) and ATP ( , ) concentrations at rest and after 10 and 20 sec of intermittent electrical stimulation at 50 Hz. Open symbols denote type I fibers closed symbols denote type II fibers. Bottom panel Glycogenolytic rates in type I and II fibers during the 20 sec stimulation period. The open bar denotes type I fibers the closed bar denotes type II fibers.

Some researchers reject the explanation that caffeine inhibits glycogen depletion during short term exercise54 but there is an increasing abundance of research supporting the notion of variable sensitivity to caffeine by muscle type. Muscles with higher ratios of type I fibers appear more sensitive than type II fibers, both in animal55-56 and human models.57... 

I realize that this is a side track issue, but relevant all the same. Cycle protocols were an approach intended to facilitate optimal growth of muscle tissue. Remember there are two main muscle fiber types Type I, which is endurance orientated, and Type II which is strength orientated. Type "Ha", "Hb", and Type "He" are responsible for most musculature size and have the greatest potential for growth. Testosterone increases the number of Type II fibers at the expense of the Type I transformation. Growth hormone, Insulin, IGF-1, and thyroid hormones effect growth and hyperplasia of both fiber types. This should be another key relating to protocols that were utilized and why. 

Mammalian skeletal muscle can be separated Into two distinct fiber populations, based on relative contraction characteristics, and are referred to as slow-twltch (Type I) or fast-twitch (Type II) fibers. The slow-twltch fiber type exhibits a relatively low shortening velocity (27), a low rate of tension development (27). a low myosin ATPase activity (28) and a low rate of calcium sequestration by the sarcoplasmic reticulum (29). The converse Is true for the fast-twitch fibers. Since contraction velocity highly correlates with myosin ATPase activity (30), It Is possible to easily Identify,... 

Cells from the type I fiber would be rich in mitochondria, whereas those of the type II fiber would have few mitochondria. 

Measurements of twitch contraction times reflect the rates of Ca flow into and out of the myoplasm. The time to peak twitch force is influenced by the rate of increase in myoplasmic Ca . Conversely, half relaxation time of twitch force is influenced by the rate of decrease in myoplasmic Ca " (reflecting primarily SERCA activity). Values for time to peak twitch force and half relaxation time of twitch force also vary across muscles, such that muscles composed of predominantly type II fibers have shorter times compared to those composed of predominantly type I fibers (Larsson et al, 1994 Vedsted et al, 2003). 

Carbon fibers formed at higher temperatures (>2000 C) are referred to in the literature as high modulus or type I fibers. Fibers formed at lower temperatures (1000-1600 C) are referred to as low modulus or type II fibers. Recent developments in carbon fiber synthesis have resulted in carbon fibers with a tensile modulus intermediate between type I and II but with a tensile strength similar to type II [25]. These newer fibers have been called intermediate modulus. Many improvements in the processing of PAN fibers are being made. A wide range of mechanical properties is available for specific design applications. 

The monosynaptic pathway, in which sensory input fibers synapse directly with motor output fibers, governs the primary endings (la) that mediate the dynamic stretch reflex. The type II fibers may occasionally terminate monosynaptic ally, bnt most terminate on mnltiple internenrons in the gray matter of the spinal cord. Type II fibers transmit more delayed signals to the anterior motor horn. 

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