BIOMECHANICS-2 MARKS-PART-1

CENTRE OF GRAVITY:

  • Center of gravity is an imaginary balancing point where the body weight can be assumed to be concentrated and equally distributed.
  • Its symbol is COG or CG. The centre of gravity (COG) of the human body is a hypothetical point around which the force of gravity appears to act.
  • In the anatomical position, the COG lies approximately anterior to the second sacral vertebra.

AXIS AND PLANES:

An axis is a straight line around which an object rotates. Movement at the joint take place in a plane about an axis. There are three axis of rotation.

  • Sagital axis – passes horizontally from posterior to anterior and is formed by the intersection of the sagital and transverse planes.
  • Frontal axis – passes horizontally from left to right and is formed by the intersection of the frontal and transverse planes.
  • Vertical axis – passes vertically from inferior to superior and is formed by the intersection of the sagital and frontal planes.

Three planes are:

  • A sagittal plane is perpendicular to the ground and divides the body into left and right.
  • A coronal or frontal plane is perpendicular to the ground and divides the body into dorsal (posterior or back) and ventral (anterior or front) portions.
  • A transverse plane, also known as an axial plane or cross-section, divides the body into cranial (head) and caudal (tail) portions.

CONCURRENT FORCES SYSTEM:

  • Concurrent forces are two or more forces whose lines of action intersect at the same point to cause rotation. The forces do not necessarily have to be applied .
  • For example: If two people stand the ends of a rope and pull on it, the forces are concurrent because the effect of the forces will intersect at the same point (presumably in the middle of the rope). A real life example of this would be a tug of war competition as shown in the image above.

ANATOMICAL PULLEY:

  • A pulley is a simple mechanical machine and consists of a wheel that turns readily on an axle.
  • A single fixed pulley:  It changes the direction of the force acting on it and its magnitude remains the same on either sides of the pulley rope irrespectively to the angle of pull of the force.
  • A single movable pulley: It acts as a second-class lever. It’s mechanical advantage is (2) as it magnifies force.
  • Pulley combination: There are many combinations and the simplest one is a combination of one fixed and one movable pulley as used in the Guthrie-Smith suspension frame.

LEVER :

  • A lever is a rigid bar that rotates around a fixed point and is used to apply force against a resistance •
  • There are 3 lever systems, each containing a fulcrum, load/resistance/weight, and effort •
  • In the body the levers are the bones, the joints are the fulcrums, the muscles act as the effort, and the weight.

MOMENT ARM:

  • It is defined as the product of the force (F) and the moment arm (d). The moment arm or lever arm is the perpendicular distance between the line of action of the force and the center of moments. Moment = Force x Distance or M = (F)(d).

CLOSED KINETIC CHAIN EXERCISES :

  • Closed kinetic chain exercises or closed chain exercises (CKC) are physical exercises performed where the hand (for arm movement) or foot (for leg movement) is fixed in space and cannot move.
  • The extremity remains in constant contact with the immobile surface, usually the ground or the base of a machine.

OPEN CHAIN EXERCISES :

  • Open chain exercises (OKC) are exercises that are performed where the hand or foot is free to move.
  • The opposite of OKC are closed kinetic chain exercises (CKC). Both are effective for strengthening and rehabilitation objectives.

MOTOR UNIT:

  • A motor unit is made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron’s axonal terminals.
  • Groups of motor units often work together to coordinate the contractions of a single muscle; all of the motor units within a muscle are considered a motor pool.

TYPES OF MUSCLE FIBERS:

  • Muscle fibers are the cells or basic building block of the muscle. There are a few different types of muscle fiber, each designed for a specific type of muscle activity.

The 3 types of skeletal muscle fibres are:

  • Red / Slow (Type I fibres, ‘slow twitch fibres’)
  • Red / Fast (Type IIa fibres, ‘fast oxidative fibres’)
  • White / Fast (Type IIb fibres, ‘fast glycolytic fibres’)

COVERING OF MUSCLE FIBERS:

The endomysium is the connective tissue that surrounds each muscle fiber (cell). The perimysium encircles a group of muscle fibers, forming a fascicle. The epimysium encircles all the fascicles to form a complete muscle.

  • Epimysium – Outermost layer. Surrounds the entire muscle.
  • Perimysium – Surrounds groups of muscle fibers called fascicles.
  • Endomysium – Deepest layer. Separates individual muscle fibers.

THE LENGTH-TENSION RELATIONSHIP :

  • The length-tension relationship is the observation that the isometric force exerted by a muscle is dependent upon its length when tested.

THE ACTIVE AND PASSIVE LENGTH-TENSION RELATIONSHIPS:

  • The active length-tension relationship reflects the degree of overlap between the actin and myosin filaments in a sarcomere.
  • The passive length-tension relationship reflects the presence of elastic elements within a sarcomere, which stretch and produce force with increasing length.

CATHERINE SHALINI RAJA
M.P.T.,MIAP.,PGDYN
CARDIO RESPIRATORY PHYSCIAL THERAPIST
FITNESS & SPORTS REHABILITATION SPECIALIST.

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