Assuming we want the muscle to contract rapidly and quickly pull the skin away f

Question

Assuming we want the muscle to contract rapidly and quickly pull the skin away from the pin we know multiple variables affect how much force and velocity a muscle can contract at and a joint can rotate at. Describe the following variables affect muscle force and / or velocity. Please note that some variables affect both force and velocity and some will affect only force or only velocity. A. Muscle fiber type, b. muscle fiber shortening velocity (both positive and negative velocity ), c. Muscle length – consider an increase in length as well as a decrease, d. Muscle architecture, e. Moment R/r=gear ration ( relate this torque and rotation at the joint instead of muscle velocity and muscle force)

Explanation / Answer

A) Muscle fibre type: Different types of muscle fibers possess different contractile properties. Broadly human muscle fibers are categorized as type I, type IIa, or type IIb fibers. Fibre affect both the force as well as contractile velocity. In general, the contractile force of a type IIb fiber is greater than that of a type I fiber. Thus muscles composed of more type IIb fibers are likely to generate larger contractile forces than a comparable muscle consisting of mostly type I fibers. With respect to muscle velocity,  Type II muscle fibers display a faster shortening velocity than type I muscle fibers. A higher proportion of type II muscle fibers may therefore be beneficial for strength and power sports. Type IIb fibers exert larger forces at higher velocities, while type I fibers have slower maximal contractile velocities as well as lower peak forces.

B) Muscle fibre shortening velocity: The maximal force that a muscle can develop is governed by the velocity of the muscle’s shortening or lengthening. A plot of a muscle’s force of contraction over contractile velocity for isometric and concentric contractions reveals that contractile force is maximum when contraction velocity is zero (isometric contraction) and decreases as contraction velocity increases. The reverse holds true for when the muscle is stretched-force increases above isometric maximum, until finally reaching an absolute maximum.

C) Muscle Length: The force-length relationship in muscle indicates that muscles generate the greatest force when at their resting, or ideal length, and the least amount of force when shortened or stretched relative to the resting length.

D) Muscle Architecture: The functional effect of muscle architecture can be simply stated as: muscle force is proportional to physiologic cross-sectional area (PCSA), and muscle velocity is proportional to muscle fiber length. PCSA is the sum of the areas of each fiber in the muscle. Fiber arrangements have different names but fall into two major categories, parallel and pennate. The muscle with parallel fibers has longer fibers than those found in the pennate muscle. Because the amount of shortening that a muscle can undergo depends on the length of its fibers, the muscle with parallel fibers is able to shorten more than the pennate muscle. The angle at which the fibers insert into the tendon also influences the total force that is applied to the limb by a pennate muscle. This angle is known as the angle of pennation. Greater pennation angles are associated with greater muscle tension.

E) Moment= Moment arm of a muscle is the perpendicular distance between the muscle and the point of rotation. This moment arm depends on the location of the muscle’s attachment on the bone and on the angle between the line of pull of the muscle and the limb to which the muscle attaches. Muscles with shorter anatomical moment arms are capable of producing greater angular excursions of a joint than muscles of similar fiber length with larger anatomical moment arms. The muscle’s moment arm is maximum when the muscle’s angle of application is 90°, since the sine of 90° equals 1.

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