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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).
It was shown that the use of electrical stimulation of muscles for motor control would stimulate large, fatigable motor unit first. [14] For many years it has been believed that the use of electromyostimulation (EMS) to stimulate muscle contraction creates a reversal of the general size principle recruitment order, due to the larger motor unit ...
In vertebrates, the force of a muscle contraction is controlled by the number of activated motor units. The number of muscle fibers within each unit can vary within a particular muscle and even more from muscle to muscle: the muscles that act on the largest body masses have motor units that contain more muscle fibers, whereas smaller muscles ...
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.
Resistance training has been shown to dramatically increase performance of motor units of the larger muscle groups. [2] Motor unit plasticity of the larger muscle groups is extremely important for athletes, especially those participating in high impact and fast pace sports such as track and field, martial arts, and American football.
The SI unit for specific strength is Pa⋅m 3 /kg, or N⋅m/kg, which is dimensionally equivalent to m 2 /s 2, though the latter form is rarely used. Specific strength has the same units as specific energy, and is related to the maximum specific energy of rotation that an object can have without flying apart due to centrifugal force.
[5] Muscle contraction ends when calcium ions are pumped back into the sarcoplasmic reticulum, allowing the contractile apparatus and, thus, muscle cell to relax. Upon muscle contraction, the A-bands do not change their length (1.85 micrometer in mammalian skeletal muscle), [5] whereas the I-bands and the H-zone shorten. This causes the Z-lines ...
The strength-duration time constant (chronaxie) and rheobase are parameters that describe the strength-duration curve—the curve that relates the intensity of a threshold stimulus to its duration. As the duration of a test stimulus increases, the strength of the current required to activate a single fiber action potential decreases.