Biomechanics: The study of the mechanical laws governing the movement of living organisms.
Kinesiology: The study of the mechanics of human movement.
Both fields are crucial for exercise selection and training execution to achieve fitness goals and prevent injuries.
Anatomical Reference Terms
Used to reference anatomical position or location.
Refers to the body in anatomical position: facing forward with arms at sides, palms and toes pointing forward.
Anatomical Location Terms
Anterior (Ventral): Front of the body or toward the front relative to a reference point.
Posterior (Dorsal): Back of the body or toward the back relative to a reference point.
Superior (Cephalic): Above a reference point.
Inferior (Caudal): Below a reference point.
Proximal: Closer to the center of the body relative to a reference point.
Distal: Farther from the center of the body relative to a reference point.
Medial: Closer to the midline of the body.
Lateral: Farther from the midline of the body.
Prone: Lying facedown.
Supine: Lying on one's backside.
Deep: Further beneath the surface relative to another reference point.
Superficial: Closer to the surface relative to another reference point.
Unilateral: Refers to only one side.
Bilateral: Refers to both sides.
Ipsilateral: On the same side.
Contralateral: On the opposite side.
Volar: Relating to the palm of the hand or sole of the foot.
Anatomical Movement
Describes how muscles act on the skeleton to generate movement.
Terms for Anatomical Movement
Abduction: Movement away from the midline.
Adduction: Movement toward the midline.
Flexion: Movement decreasing the angle between two body parts.
Extension: Movement increasing the angle between two body parts.
Lateral Flexion: Flexion in the frontal plane.
Protraction: Abduction of the scapula.
Retraction: Adduction of the scapula.
Elevation: Movement in a superior direction.
Depression: Movement in an inferior direction.
Plantar Flexion: Extension of the foot downward (inferiorly).
Dorsiflexion: Flexion of the foot upward (superiorly).
External Rotation: Rotational movement away from the midline.
Internal Rotation: Rotational movement toward the midline.
Circumduction: Circular movement of a limb extending from the joint where the movement is controlled.
Inversion: Movement of the sole of the foot toward the median plane.
Eversion: Movement of the sole of the foot away from the median plane.
Pronation: Turning the palm or arch of the foot down.
Supination: Turning the palm or arch of the foot up.
Hyperextension: Position that extends beyond anatomical neutral.
Ipsilateral: Same-side movement.
Contralateral: Opposite-side movement.
Lateral: Situated away from the midline.
Medial: Situated toward or closer to the midline.
Planes of Motion
Used to describe the direction of movement.
Frontal Plane: Divides the body into anterior and posterior halves; lateral movements like hip and shoulder abduction occur here.
Sagittal Plane: Divides the body into left and right halves; flexion and extension occur here (e.g., squat).
Transverse Plane: Divides the body into inferior and superior halves; anything requiring rotation occurs here (e.g., golf swing).
Everyday activity involves movement in all three planes.
Reduced range of motion (ROM) may occur in the frontal and transverse planes, as well as spinal extension.
Joints are healthiest when able to move through a normal ROM without restriction.
Range of Motion (ROM): The measurement of movement around a specific joint or body part.
Balance, Equilibrium, and Stability
Constantly challenged in human movement.
Maintaining optimal position reduces effort to hold position and produce/accept force.
Balance: Ability to maintain the center of gravity within the base of support.
Stability: Body's resistance to change in joint or body position.
Gravity: Attraction between objects and the Earth.
Muscular Force: Generated to move the skeleton, creating imbalance/instability.
Dynamic Balance: Ability to remain upright over a moving base of support.
Static Balance: Ability to remain upright and balanced when the body is at rest.
Center of Gravity: Hypothetical position where combined mass appears concentrated.
Base of Support: Area beneath an object or person that includes every point of contact with the supporting surface.
Mass: Amount of matter in an object.
Weight: Gravitational force of attraction on an object.
Line of Gravity: A vertical line straight through the center of gravity.
Balance and stability are maximized when the center of gravity can be determined and shifted.
Stability is easier with a larger base of support.
Training enhances awareness of the limit of stability (kinesthetic awareness).
Altered joint motions due to tight muscles can cause faulty alignment.
Kinesthesis: Awareness of the position of the joints.
Joint Mobility and Stability
Healthy joints should move through the proper ROM with control.
Collaboration between nervous system and muscles.
Joint Mobility: Degree of movement around a joint before restriction by surrounding tissues.
Joint Stability: Ability of muscles around a joint to control movement or hold it in a fixed position.
Movement dysfunctions arise from overactive (tight) and underactive (weak) musculature.
Joints typically needing greater mobility: foot/ankle, hip, thoracic spine, shoulder, and wrist
Joints typically needing greater stability: knee, lumbar spine, cervical spine, and elbow
Laws Of Motion
Laws of Motion: The laws of physics describing movement.
Explain observed phenomena in fitness and human movement.
Relate an object's motion (e.g., dumbbell) to forces acting on it (muscle actions) and gravity.
Newton's First Law: Inertia
A body in motion stays in motion, and a body at rest stays at rest unless acted on by an outside force.
Muscular contraction produces force and can change the status of movement.
Inertia: Resistance to action or change; describes 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: Acceleration
A change in acceleration occurs in the direction of the force causing it.
Change of acceleration is directly proportional to the force and inversely proportional to the mass.
a = \frac{\text{change in } v}{\text{change in } t}, where:
a = acceleration
v = velocity
t = time
Acceleration is measured in meters per second squared (m/s^2)
Velocity: The speed of an object and the direction it takes while moving.
F = m \times a, where:
F = force
m = mass
a = acceleration
Force-Velocity Curve: Representation of the inverse relationship between force and velocity in muscle contraction.
F \times \text{velocity} = P, where:
F = force
P = power
Momentum: The quantity of motion of a moving body, measured as a product of its mass and velocity.
Newton's Third Law: Action and Reaction
For every action, there is an opposite and equal reaction.
The body provides the force to move, and the surface provides a reactionary force.
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 in contact with it.
Force
Interaction that creates work or physical change.
Components: magnitude, direction, point of application, and line of action.
Types:
Compression: Two surfaces pressing toward one another.
Tensile: Two surfaces pulling apart from one another.
Shear: Two surfaces moving across one another.
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
Muscular Contraction and Motion
Muscular Contraction: The shortening or resistance to lengthening of a muscle fiber.
Muscles can only pull to create movement.
Types of motion:
Linear: Straight or curved line.
Angular: Rotation around an axis.
Linear Motion: Movement along a line, straight or curved.
Angular Motion: Rotation around an axis.
Axis: Point of rotation around which a lever moves.
Joint movement is almost always angular motion.
Displacement: The distance an object is displaced from a starting point.
Distance: The total or sum of the length an object travels.
Angular Displacement: The change of location of an object that is rotating about an axis.
Linear Displacement: The distance an object moves in a straight line.
Friction
The force created by the resistance between two surfaces of two objects moving across one another.
It is the force that allows the body to walk forward
Static Friction: Friction of an object that does not move.
Sliding Friction: Friction between two surfaces where one or both are moving against one another.
Rolling Friction: The force that resists a surface rolling across another
Principles of Biomechanics
Explained by laws of motion and kinetics.
Kinetics: The study of forces acting on a mechanism.
Categories of Biomechanics:
Stability
Maximum effort (maximum amount of force or velocity)
Linear motion
Angular motion
Principles of Biomechanics Overview
Stability: The ability to maintain control (i.e., resist change) of a joint or position.
Production of Maximum Force: The maximum amount of force produced by a muscle or group of muscles.
Production of Maximum Velocity: The maximum movement velocity, or muscular contraction speed, for a muscle or group of muscles.
Force-Velocity Relationship: The greater the applied force on the same object, the greater the velocity.
Direction of Movement: Movement occurs in the direction opposite the applied force.
Ground Reaction Forces (GRFs): The force exerted by the ground to a body in contact with it.
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.
Conservation of Angular Momentum: Angular momentum is constant until an external force acts on it.
Angle of Muscle Pull
Strength varies throughout ROM based on the angle the muscle is pulling.
Mechanical Advantage: The ratio of force that creates meaningful movement compared to the force applied to generate the movement.
Work
Moving the body and exercising are examples of measurable work
W = F \times D, where:
W = work
F = force
D = distance or displacement.
Work: Force times distance measured in foot-pounds.
900 \text{ feet/pound} \div 3 \text{ seconds} = 300 \text{ feet/pound of work per second}
900 \text{ feet/pound} \div 2 \text{ seconds} = 450 \text{ feet/pound of work per second}
Power: The combination of strength and speed-the ability for a muscle to generate maximal tension as quickly as possible.
Levers
The most common mechanical machines within the human body.
A lever consists of a rigid bar and an axis or point of rotation the lever moves around.
Levers: A rigid or semirigid bar rotating around a fixed point when force is applied to one end.
Fulcrum: The point on which a lever rests or is supported and on which it pivots.
Lever Components
Bones: levers
Joints: axis (fulcrum)
Muscles: contract to apply force
Effort Arm: The portion of the lever arm between the applied effort and the axis.
Lever Arm: The rigid bar portion of a lever that rotates around the fulcrum.
Resistance Arm: The portion of the lever arm between the load and the axis.
Moment Arm: The perpendicular distance between the fulcrum and the line of the force being applied.
Three Classes of Levers
Differentiated by the location of the fulcrum, resistance, and effort.
First-Class Lever: Fulcrum is between the effort and load (e.g., neck extension).
Second-Class Lever: Load is between the fulcrum and effort (e.g., plantar flexion).
Third-Class Lever: Effort is between the fulcrum and load (e.g., elbow flexion).
Torque
Force applied rotationally.
Torque is force applied that results in rotation about an axis.
Torque: Force applied that results in rotation about an axis.
Rotary Motion: The movement around a fixed axis moving in a curved path.
Force Arm: The distance between the fulcrum and the force or load application in a lever.
Determined by multiplying force by the length of the force arm.
Muscles as Movers
Create movement by generating force and transferring it to bones via tendons.
Origin: The proximal muscular attachment point to a bone.
Insertion: The distal muscular attachment point to a bone.
Agonist: The primary muscle used for a mechanical movement.
Synergists: Muscle(s) supporting the mechanical movement of a prime mover.
Antagonist: Muscle(s) opposing the mechanical movement of a prime mover.
Sherrington's Law of Reciprocal Inhibition: A law that states that for every muscle activation, there is a corresponding inhibition of the opposing muscle.
Stabilizer Muscles: The muscles playing the role of stabilizing or minimizing joint movement.
Muscle Relationships
An example of a group of muscles working together in this fashion is a dumbbell curl. The biceps brachii is the agonist, the brachioradialis is a synergist and the triceps are the antagonist.
A single muscle may act as agonist, synergist, or antagonist depending on movement.
Length-Tension Relationship: The amount of tension a muscle can produce with respect to its length.
Force-Couple Relationship: Two or more muscles acting in different directions that influence the rotation of a joint in a specific direction.
Muscle Synergies: The activation of a group of muscles to generate movement around a particular joint.
Innervation: The distribution or supply of nerves.