KINESIOLOGY دکترامیر هوشنگ واحدی متخصص طب فیزیکی و توانبخشی قسمت 3

Contents Terms & Concepts Kinematic Biomechanical Principles Muscle & Joint & Bone Structure and Function

Biomechanical Principles

 Biomechanical parameters 1.scalar quantities :A scalar is simply represented by its magnitude. Mass, time, and length are examples of scalar quantities. 2.vector quantities :A vector is generally described as having both magnitude and orientation  Forces and moments are examples of vector quantities.

force Force is a push or pull action. Force is a vector. Forces are vector quantities. The characteristics of force include: 1. Magnitude (each person is pulling equally in this case) 2. Direction (shown by the arrow) 3. Point of application

Weight= (mass)*(gravity) or W (m) (g) force = (mass)*(acceleration) or F (m) (a)

 Isometric – when a muscle is producing a F while maintaining a constant length (Internal T = External T)  Concentric - when a muscle is producing a F as it contracts or shortens (Internal T > External T)  Eccentric - when a muscle is producing a F while it is being elongated or lengthened (Internal T < External T) Muscle Action or Joint Action – a muscles potential to cause a torque in a particular rotation direction and plane; determined by the planes of motion available within the joint (usually multi-planar); action is in reference to the anatomic position Muscle Action or Joint Action – a muscles potential to cause a torque in a particular rotation direction and plane; determined by the planes of motion available within the joint (usually multi-planar); action is in reference to the anatomic position

Moments a moment (M) is typically caused by a force (F) acting at a distance (r) from the center of rotation of a segment. A moment tends to cause a rotation and is defined by the cross product function: M =r *F.

In general, the point of application of a force (e.g., tendon insertion) is located with respect to a fixed point on a body, usually the joint center of rotation. This information is used to calculate the moment due to that force.

Musculoskeletal Torques Forces Applied to the body either cause – Translation of a body segment – Rotation of a body segment (if F is applied at a distance from the Axis of Rotation (A of R.) Moment Arm – shortest distance between a F and the A of R Torque (T) – the product of the Force times the Moment Arm (F x M.arm); T is the rotary equivalent of F ; the vast majority of human movement is rotational Internal Moment Arm (IMA) – product of the internal F (muscle) and the M.arm. External Moment Arm (EMA) – product of the ext. F and the M.arm.

Musculoskeletal Torques Forces Applied to the body either cause – Translation of a body segment – Rotation of a body segment (if F is applied at a distance from the Axis of Rotation (A of R.) Moment Arm – shortest distance between a F and the A of R Torque (T) – the product of the Force times the Moment Arm (F x M.arm); T is the rotary equivalent of F ; the vast majority of human movement is rotational Internal Moment Arm (IMA) – product of the internal F (muscle) and the M.arm. External Moment Arm (EMA) – product of the ext. F and the M.arm.

 Torque, also known as moment of force, is the ability of force to produce rotation about an axis  Torque is the tendency of force to produce rotation about an axis The twisting force (torque) exerted by the wrench can be increased either by: 1. Increasing the force applied to the handle 2. Increasing the length of the handle

Mechanical Advantage Mechanical Advantage (MA) – the ratio of the IMA to the EMA – 1 st Class Levers – have an MA >,<, or = to 1 – 2 nd Class Levers – always have an MA > 1 (efficient) – 3 rd Class Levers – always have an MA < 1 (inefficient)  3 rd Class Levers have to produce a much greater F to overcome the external F or Resistance due to the inefficiency of the lever; however, muscle need only to contract a fraction of the distance which the limb is moved (linear displacement of the distal most segment of the lever is much greater than that of the muscle).

Musculoskeletal Levers (Cont.) First Class Lever – A of R is positioned between two opposing levers; Internal and External F typically act in the same direction, however producing opposing rotary torques Second Class Lever – A of R is located at one end of a bone & the muscle possesses greater leverage than the External F (IMA > EMA); This is the least common musculoskeletal lever system. Third Class Lever – A of R is located at one end of a bone; External F possesses greater advantage than the Internal F (muscle force); This is the least efficient, but most common lever system. F F F R R R

Mass vs. Weight Mass is the measure of the number of particles within an object, whereas Weight is the measure of the force of gravity acting on an object. Under the influence of earth’s gravitational pull, 1 kilogram (kg) mass weighs 9.8 lbs. Mass is the measure of the number of particles within an object, whereas Weight is the measure of the force of gravity acting on an object. Under the influence of earth’s gravitational pull, 1 kilogram (kg) mass weighs 9.8 lbs.

A distinction must be made between the mass and the weight of a body. The mass of an object is defined as the amount of matter composing that object. The weight of an object is the force acting on that object due to gravity and is the product of its mass and the acceleration due to gravity (g 9.8 m/s2)

Displacement, Velocity, and Acceleration  Displacement is defined as the distance travele between two locations.  Change in linear and angular position (displacement) over time is defined as linear and angular velocity  changes in linear and angular velocity over time are defined as linear and angular acceleration

work, which is defined as the force required to move an object a certain distance (work = force * distance). The standard unit of work in the metric system is a joule (J; newton* meter)

Power is defined as the rate that work is being done (power = work/time). The standard unit of power is a watt (W; watt * newton meter/second).

Energy has the same unit as work (J) and can be divided into potential and kinetic energy. While potential energy refers to stored energy, kinetic energy is the energy of motion.

Friction Frictional forces can prevent the motion of an object when it is at rest and resist the movement of an object when it is in motion.

Newton's Laws ( Laws of Motion) 1. Newton's First Law of Motion( law of inertia) : Every body continues in its state of rest or of uniform motion in a straight line unless it is acted upon by an outside force. 2. Newton's Second Law of Motion( law of acceleration) : Acceleration of a body is proportional to the force causing it. 3. Newton's Third Law of Motion( law of action reaction) : For every action there is an equal and opposite reaction.