202502012105
tags:

Skeletal Musculature

proximal: towards the center of body
distal: away from the center of body
agonist: muscle directly involved in bringing about a movement
antagonist: muscle that can slow down or stop a movement
synergist: muscle assists indirectly in a movement

Levers of Musculoskeletal System

first-class lever: A lever for which the muscle force and resistive force act on opposite sides of the fulcrum
fulcrum: The pivot point of a lever
lever: A rigid or semirigid body that, when subjected to a force whose line of action does not pass through its pivot point, exerts force on any object impeding its tendency to rotate
mechanical advantage: The ratio of the moment arm through which an applied force acts to that through which a resistive force acts.
moment arm: The perpendicular distance from the line of action of the force to the fulcrum
muscle force: Force generated by biochemical activity
resistive force: Force generated by a source external to the body (e.g., gravity, inertia, friction) that acts contrary to muscle force.
second-class lever: A lever for which the muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm longer than that through which the resistive force acts
third-class lever: A lever for which the muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm shorter than that through which the resistive force acts
torque: The degree to which a force tends to rotate an object about a specified fulcrum

Variations of Tendon Insertion

Anatomical Planes and Major Body Movements

sagittal, frontal, and transverse planes: slice the body into left–right, front–back, and upper–lower sections

Human Strength and Power

Basic Definitions

strength: ability to exert force
Force = Mass ∙ Acceleration

Positive Work and Power

power: the time rate of doing work
work: the product of the force exerted on an object and the distance the object moves in the direction in which the force is exerted
Work = Force ∙ Displacement
Power = Work / Time

Negative Work and Power

Angular Work and Power

angular displacement: angle through which an object rotates
Angular velocity: object’s rotational speed
rotational work = Torque ∙ Angular displacement

Strength Versus Power

Biomechanical Factors in Human Strength

Neural Control

recruitment: muscle contraction
rate coding: rate at which the motor units are fired

Muscle Cross-Sectional Area

Arrangement of Muscles

pennate muscle: has fibers that align obliquely with the tendon, creating a featherlike arrangement
angle of pennation: the angle between the muscle fibers and an imaginary line between the muscle’s origin and insertion

Muscle Length

Joint Angle

Muscle Contraction Velocity

Joint Angular Velocity

concentric muscle action: muscle shortens because the contractile force is greater than the resistive force
eccentric muscle action: muscle lengthens because the contractile force is less than the resistive force
isometric muscle action: muscle length does not change, because the contractile force is equal to the resistive force

Strength-to-Mass Ratio

Body Size

classic formula: the load lifted is divided by body weight to the two-thirds power

Sources of Resistance to Muscle Contraction

Gravity

Applications to Resistance Training

Weight-Stack Machines

Inertia

bracketing technique: the athlete performs the sport movement with less than normal and greater than normal resistance, is another form of acceleration training

Friction

Friction: the resistive force encountered when one attempts to move an object while it is pressed against another object
Friction = k∙F (k is the coefficient of friction for the two particular substances in contact)

Fluid Resistance

fluid resistance: resistive force encountered by an object moving through a fluid
surface drag: the friction of a fluid passing along the surface of an object
form drag: the way in which a fluid presses against the front or rear of an object passing through it
FR = k∙v where F is the resistive force; k is a constant that reflects the physical characteristics of the cylinder and piston, the viscosity of the fluid, and the number, size, and shape of the openings; and v is piston velocity relative to the cylinder.

Elasticity

FR = k ∙ x
where FR is the resistive force, k is a constant that reflects the physical characteristics of the elastic component, and x is the distance that the elastic component is stretched beyond its resting length.

Joint Biomechanics: Concerns in Resistance Training

Back

Back Injury

Intra-Abdominal Pressure and Lifting Belts

Shoulders

Knees

Elbow and Wrists

Reference