Pennate muscle
This article may require cleanup to meet Wikipedia's quality standards. The specific problem is: infobox is misleading; references 1 and 2 are broken. (April 2015) |
Rectus femoris | ||
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Antagonist Hamstring | | |
Identifiers | ||
TA98 | A04.0.00.016 | |
TA2 | 1989 | |
FMA | 74993 | |
Anatomical terms of muscle] |
A pennate or pinnate muscle (also called a penniform muscle) is a type of skeletal muscle with fascicles that attach obliquely (in a slanting position) to its tendon. This type of muscle generally allows higher force production but a smaller range of motion.[1][2] When a muscle contracts and shortens, the
Etymology
The term "pennate" comes from the Latin pinnātus ("feathered, winged"), from pinna ("feather, wing").
Types of pennate muscle
In skeletal muscle tissue, 10-100
Consequences of pennate muscle architecture
Physiological cross sectional area (PCSA)
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.[4][5] 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 (an alternative definition is provided in the
where ρ is the density of the muscle:
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.
Relationship between PCSA and muscle force
The total force exerted by the fibers along 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:[9]
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[8]), is exerted along the direction of action of the muscle:[8]
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 (
Lower velocity of shortening
In a pennate muscle, as a consequence of their arrangement, fibers are shorter than they would be if they ran from one end of the muscle to the other. This implies that each fiber is composed of a smaller number N of sarcomeres in series. Moreover, the larger the pennation angle is, the shorter are the fibers.
The speed at which a muscle fiber can shorten is partly determined by the length of the muscle fiber (i.e., by N). Thus, a muscle with a large pennation angle will contract more slowly than a similar muscle with a smaller pennation angle.
Architectural gear ratio
Architectural gear ratio, also called anatomical gear ratio, (AGR) is a feature of pennate muscle defined by the ratio between the longitudinal strain of the muscle and
AGR = εx/εf
where εx = longitudinal strain (or muscle-shortening velocity) and εf is fiber strain (or fiber-shortening velocity).[10]
It was originally thought that the distance between aponeuroses did not change during the contraction of a pennate muscle,[5] thus requiring the fibers to rotate as they shorten. However, recent work has shown this is false, and that the degree of fiber angle change varies under different loading conditions. This dynamic gearing automatically shifts in order to produce either maximal velocity under low loads or maximal force under high loads.[10][11]
References
- ^ Frederick H. Martini, Fundamentals Of Anatomy And Physiology Archived 2006-11-14 at the Wayback Machine.
- ^ "Jacob Wilson, Abcbodybuilding, The Journal of HYPERplasia Research". Archived from the original on 2008-12-05. Retrieved 2006-12-01.
- PMID 9763648.
- PMID 6749514.
- ^ S2CID 46565389.
- ^ Alexander, R. McN.; Vernon, A. (1975). "The dimension of knee and ankle muscles and the forces they exert". Journal of Human Movement Studies. 1: 115–123.
- S2CID 19747247.
- ^ ISBN 978-0-471-49238-2.
- S2CID 20263826.
- ^ PMID 17397068.
- PMID 18230734.