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These consist of an extensor muscle, which "opens" the joint (by increasing the angle between the two bones) and a flexor muscle, which does the opposite by decreasing the angle between two bones. However, muscles do not always work this way; sometimes agonists and antagonists contract at the same time to produce force, as per Lombard's paradox ...
The quadriceps femoris muscle (/ ˈ k w ɒ d r ɪ s ɛ p s ˈ f ɛ m ər ɪ s /, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur.
The parallel muscle architecture is found in muscles where the fibers are parallel to the force-generating axis. [1] These muscles are often used for fast or extensive movements and can be measured by the anatomical cross-sectional area (ACSA). [3] Parallel muscles can be further defined into three main categories: strap, fusiform, or fan-shaped.
It is typically used to describe the contraction properties of pennate muscles. [1] It is not the same as the anatomical cross-sectional area (ACSA), which is the area of the crossection of a muscle perpendicular to its longitudinal axis. In a non-pennate muscle the fibers are parallel to the longitudinal axis, and therefore PCSA and ACSA coincide.
The septa are formed from the fascia which is made up of a strong type of connective tissue. The fascia also separates the skeletal muscles from the subcutaneous tissue. [2] Due to the great pressure placed on the leg, from the column of blood from the heart to the feet, the fascia is very thick in order to support the leg muscles. [3]
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 pennation angle increases. [3]
These included the absence of muscles; muscles that were doubled; muscles that were divided into two or more parts; an increase or decrease in the origin or insertion of the muscle; and the joining to adjacent organs. [2] The palmaris longus muscle in the forearm is sometimes absent, as is the plantaris muscle in the leg. [5]
Henneman’s size principle describes relationships between properties of motor neurons and the muscle fibers they innervate and thus control, which together are called motor units. Motor neurons with large cell bodies tend to innervate fast-twitch, high-force, less fatigue-resistant muscle fibers , whereas motor neurons with small cell bodies ...