Planes of motion Flashcards
Frontal plane
an imaginary line that divides the body into anterior and posterior halves
Example movements in this plane include lateral raises, side lunges, and lateral flexion of the spine.
Sagittal plane
an imaginary line that divides the body into left and right halves
Example movements in this plane include lunges, biceps curls, squats, flexion or extension of the hip, and walking.
Transverse plane
an imaginary line that divides the body into inferior and superior halves
Example movements in this plane are rotational, such as a golf swing or internal rotation of the shoulder.
Newton’s first law (inertia)
A body in motion tends to stay in motion while a body at rest tends to stay at rest unless acted on by an outside force.
Inertia: the resistance to action or change and describes the acceleration and deceleration of the human body
Acceleration: the rate of change of velocity
Deceleration: a special type of acceleration where a person or object is slowing down
Newton’s second law
A change in acceleration of mass occurs in the same direction of the force causing it, and the change of acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body.
a = change in v / change in t
In this equation, a is acceleration, v is velocity, and t is time.
Velocity: the speed of an object and the direction it takes while moving
F = m x a
Force = mass x acceleration
F x velocity = P
F is force, and P is power.
Force-velocity curve: a representation of the inverse relationship between force and velocity in muscle contraction
F x D = W
F is force and D is distance
W is work: the energy that is transferred when force is applied to an object
Newton’s third law
For every action, there is an opposite and equal reaction
Speed: the ability to move the body in one direction as fast as possible
Ground reaction force (GRF): the force the ground exerts on a body it is in contact with
Friction
the resistance of relative motion that one surface or object encounters when moving over another
Static friction: the friction of an object that doesn’t move
Sliding friction: the friction between two surfaces where one or both are moving against one another
Rolling friction: the force that resists a surface rolling across another surface
Compression force
the force of two surfaces pressing toward one another
Tensile force
the force when two surfaces pull apart from one another
Shear force
the force of two surfaces moving across one another
Categories of biomechanics
Stability
Maximum effort (maximum amount of force or velocity)
Linear motion
Angular motion
Stability
The ability to maintain control (i.e., resist change) of a joint or position.
Example: Maintaining the positioning of the trunk, hips, and legs during a push-up.
Maximum effort
Production of maximum force : The maximum amount of force produced by a muscle or group of muscles.
Example: Performing a one-rep maximum (1RM) for a barbell bench press.
Production of maximum velocity: The maximum movement velocity, or muscular contraction speed, for a muscle or group of muscles.
Example: Vertical jump. Throwing a baseball.
Linear
Force-velocity relationship: The greater the applied force on the same object, the greater the velocity.
Example: A larger arc of a golf swing will produce greater force and therefore move the golf ball farther.
Direction of movement: Movement occurs in the direction opposite the applied force.
Example: The body moves forward as the stroke applies force backward while swimming.
Ground Reaction Forces (GRFs): The force exerted by the ground to a body in contact with it. Because the ground does not move when applying force against a movable object, the object will move in the same direction of the force applied by the person.
Example: In a barbell squat, the bar goes up when an exerciser applies force against it because the ground won’t move. In a bench press, the bar goes in the same direction of the force the exerciser applies because the bench is solidly held by the ground. The exerciser is applying force down onto the bench rather than into the bar.
Angular motion
Angular motion: The motion of an object around a fixed point or axis. All lever actions are angular, and therefore most joint movements are angular.
Example: A figure skater spinning. Elbow motion in a biceps curl because the ulna spins on the humerus.
Conservation of angular momentum: Angular momentum is constant until an external force acts on it.
Example: A figure skater during a triple-axel jump. In the air, there is very little acting against the skater’s rotation. When gravity pulls the skater back down, the friction of the blade on the ice will stop the spin.
