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[[Image:Fiederung.svg|thumb|right|300px|'''Figure 1''' Pennate muscle fiber arrangements. The green lines represent PCSA; the blue lines represent ACSA]]
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In [[pennate muscle]]s, the '''physiological cross-sectional area''' (PCSA), as opposed to the anatomical one (ACSA), is the  total area of the cross-sections perpendicular to the muscle fibers.
 
== Definition ==
 
One advantage of pennate muscles is that more muscle fibers can be packed in parallel, thus allowing the muscle to produce more force, although the fiber angle to the direction of action means that the maximum force in that direction is somewhat less than the maximum force in the fiber direction.<ref name = Gans>
C. Gans (1982). Fiber architecture and muscle function. Exercise & Sports Science Reviews. 10:160–207.</ref><ref name = Otten>
E. Otten (1998). Concepts and models of functional architecture in skeletal muscles. Exercise & Sports Science Reviews. 16:89–137.</ref>
 
The muscle cross-sectional area (blue line in figure 1, also known as anatomical cross-section area, or ACSA) does not accurately represent the number of muscle fibers in the muscle. A better estimate is provided by the total area of the cross-sections perpendicular to the muscle fibers (green lines in figure 1). This measure is known as the physiological cross-sectional area (PCSA), and is commonly calculated and defined by the following formula, developed in 1975 by Alexander and Vernon:<ref>
R. McN. Alexander, A. Vernon (1975). The dimension of knee and ankle muscles and the forces they exert, Journal of Human Movement Studies, 1:115–123.</ref><ref name="Narici">
Narici M.V., Landoni L., Minetti A.E. (1992). Assessment of human knee extensor muscles stress from in vivo physiological cross-sectional area and strength measurements. European Journal of Applied Physiology & Occupational Physiology. 65(5):438–444.</ref><ref name="Maganaris">
Maganaris C.N., Baltzopoulos V. (2000). In vivo mechanics of maximum isometric muscle contraction in man: Implications for modelling-based estimates of muscle specific tension. In Herzog W. (Ed). Skeletal muscle mechanics: from mechanisms to function. Wiley & Sons Ltd, p.267-288.</ref>
 
:<math>\text{PCSA} = {\text{muscle volume} \over \text{fiber length}} =
                    {\text{muscle mass}  \over {\rho \cdot \text{fiber length}}},</math>
 
where ρ is the density of the muscle:  
:<math>\rho = {\text{muscle mass} \over \text{muscle volume}}.</math>
 
PCSA increases with pennation angle, and with muscle length. In a pennate muscle, PCSA is always larger than ACSA. In a non-pennate muscle, it coincides with ACSA.
 
=== Estimating muscle force from PCSA ===
The total force exerted by the fibers in their oblique direction is proportional to PCSA. If the ''specific tension'' of the muscle fibers is known (force exerted by the fibers per unit of PCSA), it can be computed as follows:<ref name="Sacks">R.D. Sacks, R.R. Roy (1982). Architecture of The Hind Limb Muscles of Cats: Functional Significance. Journal of Morphology, 185–195.</ref>
 
:<math>\text{Total force} = \text{PCSA} \cdot \text{Specific tension}</math>
 
However, only a component of that force can be used to pull the tendon in the desired direction. This component, which is the true ''muscle force'' (also called ''tendon force''<ref name="Maganaris" />), is exerted along the direction of action of the muscle:<ref name="Maganaris"/>
 
:<math>\text{Muscle force} = \text{Total force} \cdot cos \Phi</math>
 
The other component, orthogonal to the direction of action of the muscle (Orthogonal force = Total force × sinΦ) is not exerted on the tendon, but simply squeezes the muscle, by pulling its aponeuroses toward each other.
 
Notice that, although it is practically convenient to compute PCSA based on volume or mass and fiber length, PCSA (and therefore the total fiber force, which is proportional to PCSA) is not proportional to muscle mass or fiber length alone. Namely, the maximum ([[tetanic contraction|tetanic]]) force of a muscle fiber simply depends on its thickness (cross-section area) and [[Skeletal muscle#Muscle fibers|type]]. By no means it depends on its mass or length alone. For instance, when muscle mass increases due to [[Human development (biology)|physical development]] during childhood, this may be only due to an increase in length of the muscle fibers, with no change in fiber thickness (PCSA) or fiber type. In this case, an increase in mass does not produce an increase in force.
 
Sometimes, the increase in mass is associated with an increase in thickness. Only in this case it will have some effect on fiber force, but this effect will be proportional to the increase in thickness, not to the increase in mass. For instance, in some stages of physical development, the increase in mass may be due to both an increase in PCSA and in fiber length. Even in this case, muscle force does not increase as much as muscle mass does, because the mass increase is partly produced by a variation in fiber length, and fiber length has no effect on muscle force.
 
== Alternative definition ==
In 1987 a different definition of PCSA, herein denoted PCSA<sub>2</sub>, to facilitate comparison with the previous definition, was introduced by Sacks & Roy:<ref name="Sacks"/>
 
:<math>\text{PCSA}_2 = {\text{muscle volume} \cdot cos \Phi \over \text{fiber length}} =
                      {\text{muscle mass}  \cdot cos \Phi \over {\rho \cdot \text{fiber length}}},</math>
 
The comparison shows that
:<math>\text{PCSA}_2 = \text{PCSA} \cdot cos \Phi.</math>
 
in a pennate muscle, since cosΦ is always smaller than 1, PCSA<sub>2</sub> is always smaller than PCSA. Hence, it cannot be described as the total area of the cross-sections perpendicular to the muscle fibers (green lines in figure 1). It can be interpreted two ways:
# Projection of PCSA (green line in figure 1) on the anatomical cross-section plane (blue line).<ref>This is because the angle between the anatomical and physiological cross-section planes (angle between blue line and green line in figure 1) coincides with &Phi;, by definition.</ref>
# ACSA of a non-pennate muscle with the same force as the pennate muscle.<ref>In a non-pennate muscle, ACSA = Muscle force / Specific tension, and Muscle force = PCSA<sub>2</sub> × Specific tension, hence PCSA<sub>2</sub> = Muscle force / Specific tension = ACSA.</ref>
 
This implies that, in a muscle such as that in figure 1A, PCSA<sub>2</sub> coincides with ACSA. The disadvantage of this definition is its more complex interpretation, its advantage is that muscle force can be computed more directly:
 
:<math>\text{Muscle force} = \text{PCSA}_2 \cdot \text{Specific tension}</math><ref name="Sacks"/>
 
Currently, some authors keep using the original definition of PCSA,<ref name="Narici" /><ref name="Maganaris" /> probably because of its intuitively appealing geometrical interpretation (figure 1).
 
== References ==
{{reflist}}
 
{{Muscle tissue}}
 
[[Category:Muscular system]]
[[Category:Physiology]]

Latest revision as of 01:03, 4 May 2014

Most people select a backpack to hold their gear in. A correctly fitted pack should experience mostly unnoticed on the hunter's again. One made out of quiet fleece or canvas is important. There's nothing worse than a department scratching across noisy nylon when sneaking through the woods. The pack doesn't need to be large. It simply needs to be large enough to your essentials, along with somewhat meals and a pair quarts of water. A substitute for a backpack is what is known as a strap vest. The strap vests, also known as skeleton vests, will be purchased at out of doors retailers corresponding to Filson and Cabelas.

The Gerber 06 Fast is built on the same platform because the totally automated Gerber 06. The knife is so widespread that Gerber resolve to offer this assisted opening version of the knife. This Gerber 30-000118 is opened by the ambidextrous thumbstuds on both aspect of the blade. The Gerber 06 Fast has a partically serrated tanto blade that is held in place by a piston lock within the handle. To close the blade simply push on the piston lock. A pocket clip is included for easy carrying. However there is a drawback additionally – a ceramic blade is susceptible for fracture, if utilized to the facet of the blade.

The Knife and Device Sharpener is a small one hundred twenty volt7 amp motor that runs the sanding belt used for sharpening that runs from the drive shaft on the motor to 2 other ball bearing wheels. The belt runs along the drive shaft to a hard and fast wheel after which to a wheel on a spring shaft to stress the belt that adjusts with a knob on the aspect Kershaw Breaking Knife Review. Origami is the Japanese artwork of paper folding and kirigami is the artwork of reducing paper to create arise, pop up or three dimensional figures. Here are free printable origami and kirigami patterns and template so that you can minimize, fold and create.

The lockside is precision CNC manufactured from 6AL4V titanium that includes our Hinderer Lockbar Stabilizer The knife might be set up for either tip up or tip down carry. The non-lock side has a050' titanium liner with a G-10 or Carbon Fiber deal with scale. These high energy materials combined with the total titanium liner add power and rigidity. The handle scales can be simply changed by the tip user if another color is desired. The standard end on all XM folders is a highly sturdy tumbled/stonewash that will stand up to hard use in all environments. The deal with development is an open again design using large standoffs.

Mounted blade knives would not have a hinge to fold with, so they are normally stronger below disturbing conditions. The blade is made out of a stable piece of metal that extends into the deal with. Always being in the open position can increase pace and ease of use when working with only one hand. Mounted blade knives are carried in a belt, leg, boot, or generally a lower arm sheath. Which sheath works one of the best for you'll depend upon the particular sort of recreation you are hunting, and the type of clothing worn. Fixed blade knives are almost always your best option for hunting larger sport and deep woods tenting.

As with every assortment, accumulating Case knives is a interest which might very simply get out of control. Knowing easy methods to properly value Case knives can assist you to build a better collection which can have considerable residual worth in the future. Simply keep in mind to always purchase the Case knife that you just like earlier than shopping for one which's expensive simply because it's a collector piece. I desire my sheaths to sit lower, so this was less than optimum for me. I was in a position to fix the issue by adding a $5 dangler

Whittling has been round for many hundreds of years. All the best way again to the days of cavemen. One may say that it is as a result of we began to whittle that know-how started. It was the shaping of wooden, after all-after the discovery of sharp edges-that sparked human creativeness to make carts, cooking implements and garments, weapons for hunting and methods of food gathering. Who would've thought? So that you need to whittle wooden. Good for you. Whittling is the easy removing of pare shavings or slicing small bits from a bit of wooden with a knife No more, no less. So what does it take to become a good whittler?

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