Kinesiology and Biomechanics

Kinesiology, Structural Kinesiology, and Biomechanics

• Kinesiology involves studying anatomy, physiology, and mechanics in relation to human movement, including active and passive structures.
• Structural Kinesiology studies muscles, bones, and joints and their involvement in the science of movement.
• Biomechanics applies mechanical principles to study living organisms, focusing on motion, equilibrium, bodies, and forces.

Linear and Angular Motion

• Linear motion occurs along a straight or curved line, with all body parts moving in the same direction and speed. This is also known as translatory motion or translation.
• Angular motion involves rotation around a central line or point, where different body parts move at different speeds.
• Rectilinear motion occurs along a straight line versus Curvilinear motion which occurs along a curved line.
• Angular motion is characterized by a center and axis of rotation, as well as a plane of motion.
• The center of rotation is the fixed point around which the body rotates.
• The axis of rotation is an imaginary line perpendicular to the plane of rotation, passing through the center.
• The plane of motion is an imaginary flat surface dividing the body along which movements occur.
• Anatomical reference position involves an erect standing position with all body parts, including supinated hands (palms facing forward).

Directional Terms

• Superior refers to closer to the head.
• Inferior refers to farther from the head.
• Anterior is toward the front of the body.
• Posterior is toward the back of the body.
• Proximal is closer in proximity to the trunk.
• Distal is at a distance from the trunk.
• Medial is toward the midline of the body.
• Lateral is away from the midline of the body.
• Superficial is toward the surface of the body.
• Deep is inside the body and away from the body surface.

Reference Planes and Axes

• The sagittal plane allows forward and backward movements around a medio-lateral or frontal axis.
• The frontal plane allows lateral movements around an anteroposterior or sagittal axis.
• The transverse plane allows horizontal movements around a vertical (longitudinal) axis.

Main Joint Movements

• Movements in the sagittal plane include flexion, which decreases the angle, and extension, which increases the angle.
• Frontal plane movements include abduction (moving AWAY from the midline) and adduction (moving TOWARD the midline).
• Transverse plane movements include internal rotation (medial rotation) and external rotation (lateral rotation).

Special Movements

• In the sagittal plane, the foot can perform dorsiflexion/plantar flexion.
• In the frontal plane, the foot can perform inversion/eversion.
• In the transverse plane, the foot can perform internal/external rotation (or adduction/abduction).
• Foot motion combinations:
• Supination is plantar flexion + adduction + inversion (foot is rigid).
• Pronation is dorsiflexion + abduction + eversion (foot is more flexible).

Scapula Movements

• Elevation involves moving upwards, while depression involves moving downwards.
• Adduction (retraction) involves moving backward, while abduction (protraction) involves moving forward.
• Upward rotation and downward rotation return to the anatomical position.

Radioulnar and Wrist Movements

• Supination is when the palm faces up, pronation is when the palm faces down/the other way.
• Wrist extension increases the angle between the palm and forearm, and flexion decreases the angle.
• Wrist abduction (radial deviation) moves in the thumb's direction.
• Wrist adduction (ulnar deviation) moves in the pinky's direction.

Trunk and Knee

• Lateral flexion involves bending to the right or left.
• Valgus: Outward angulation of the distal segment of a bone or joint, as in knock knees.
• Varus: Inward angulation of the distal segment of a bone or joint, as in bowlegs.

Bone Composition and Classification

• Bone composition includes compact, cancellous, and subchondral tissues.
• Compact tissue is harder, outer tissue making up most of the skeletal system (up to 80%) with low porosity (5-30%), found in the shafts of long bones.
• Cancellous tissue (spongy or trabecular bone) is sponge-like tissue inside bones, making up roughly 20% of the skeletal system, with high porosity (30-90%), found at the ends of long bones and vertebrae.
• Subchondral tissue is smooth tissue at the ends of bones, covered with cartilage. Cartilage is specialized, rubbery connective tissue.
• Types of bones include long, short, flat, irregular, and sesamoid.
• Long bones have a long cylindrical shaft with wide, protruding ends, and serve as levers (e.g., phalanges, tibia, femur).
• Short bones are cube-shaped, solid with large articular surfaces for articulation and shock absorption (e.g., carpals and tarsals).
• Flat bones have curved surfaces, varying in thickness for protection (e.g., ilium, ribs, sternum).
• Irregular bones serve various purposes (e.g., bones throughout the spine, ischium, pubis, maxilla).
• Sesamoid bones are embedded within the tendon of a musculotendinous unit, providing protection and improving mechanical advantages (e.g., patella).

Mechanical Loads

• Compression: Pressing or squeezing force directed axially through a body.
• Tension: Pulling or stretching force directed axially through a body.
• Shear: Force directed parallel to a surface.
• Torsion: Load producing twisting of a body around its longitudinal axis.
• Bending: Asymmetric loading that produces tension on one side and compression on the other.
• Combined loading, which is the simultaneous action of more than one pure form of loading.

Bone Strength

• Bone compressive strength comes from minerals like calcium carbonate and calcium phosphate.
• Bone tensile strength comes from collagen.
• Bone is strongest in resisting compression and weakest in resisting shear.

Stress, Strain, and Stiffness

• Stress is the distribution of force within a body, quantified as force divided by the area (Stress = Force/Cross section area).
• Strain is the deformation or displacement of material resulting from applied stress.
• Stiffness is stress divided by the relative amount of change in shape (Stiffness = Stress/strain).

Wolff's Law

• Bone strength increases and decreases as functional forces on the bone increase and decrease.

Joint Classifications (Structural and Functional)

• Structural:
• Fibrous: Suture, Syndesmosis, Gomphosis
• Cartilaginous: Synchondrosis, Symphysis
• Synovial
• Functional:
• Synarthrodial: immovable
• Amphiarthrodial: slightly movable
• Diarthrodial: freely movable

Synovial Joint Characteristics

• A joint capsule is a sleeve-like covering of ligamentous tissue that surrounds the bony ends.
• A thin vascular synovial capsule is inside the joint capsule.
• Synovial fluid, secreted by the synovial capsule, lubricates the joint and reduces friction.
• The joint cavity is the area inside the joint.
• Hyaline cartilage covers the articular surfaces on the ends of bones inside the joint cavity. It is very elastic and helps protect the ends of the bones from wear and damage.
• Examples of synovial joints include: Ball and Socket (3 Rotations): Hip joint & Shoulder joint
• Saddle (3 Rotations): Thumb (1st carpometacarpal joint)
• Condyloid (2 Rotations): The Wrist (Radiocarpal Joint), Metacarpophalangeal 2nd, 3rd, 4th, 5th, and Metatarsophalangeal 2nd, 3rd, 4th, 5th.
• Hinge (1 Rotation): Elbow, Knee, Ankle (Talocrural)
• Pivot (1 Rotation): Proximal and Distal radioulnar joint
• Gliding (0 Rotation): Carpal bones of the wrist & Tarsometatarsal joints of the foot

Factors Affecting Joint Stability

• Bones: Anatomical configuration at joint surfaces (depth and shallowness) varies among individuals.
• Cartilage: Hyaline cartilage and specialized cartilaginous structures (knee menisci, glenoid labrum, acetabular labrum) assist in joint congruency and stability, varying in size and configuration among individuals.
• Ligaments & Connective Tissue: Ligaments connect bone to bone, resist tensile forces, and provide static stability. Differences in ligamentous tissue restrictiveness exist among individuals due to varying elastin vs. collagen amounts.
• Individuals with higher elastin to collagen ratios are hyperlax ("loose jointed"), while those with lower ratios are tighter. Collagen provides tissue strength and resilience, while elastin provides flexibility.
• Muscles: Provide dynamic stability to joints when actively contracting. Active tension provides dynamic stability, strength and endurance are significant in stabilizing joints and muscle flexibility can affect range of joint motion.
• Proprioception & Motor Control:
• Proprioception- Subconscious mechanism by which body is able to regulate posture & movements by responding to stimuli originating in proprioceptors imbedded in joints, tendons, muscles, and inner ear
• Motor Control- Process by which body actions & movements are organized and executed.

Joint Mobility and Stability

• The more mobility, the less stability and vice versa.

David's Law

• Ligaments, muscle, and other soft tissues, when placed under appropriate tension, will adapt by lengthening. They will shorten, when maintained in a loose state over a period of time.

Muscle Force Production and Range of Motion

• Force: The ability of a muscle to exert force, related to muscle cross-section area. The bigger the muscle cross-section diameter, the increased ability to produce force.
• Range of Motion: The ability of a muscle to move a joint through a large range of motion (ability to shorten), the longer a muscle, the greater range of motion it provides.

Muscle Fiber Arrangement

• Parallel: Parallel muscles have their fibers arranged parallel to the length of the muscle and produce a greater range of motion compared to pennate muscles of similar size. Types: Flat, Fusiform, Strap, Radiate (triangular, fan-shaped, convergent), & Sphincter (circular)
• Pennate: Pennate muscles have shorter fibers arranged obliquely to their tendons, resembling a feather, which produces in an increased cross section area of the muscle, enabling an increased force production capability. Types: Unipennate, Bipennate, Multipennate

Muscle Tissue Properties

• Contractility: The ability of muscle tissue to shorten or contract forcefully when stimulated.
• Excitability (Irritability): The ability of a muscle or nerve cell to detect and respond to a stimulus.
• Extensibility: The ability of muscle tissue to be stretched or extended without being damaged.
• Elasticity: The ability of muscle tissue to return to its original shape after being stretched or contracted.

Types of Muscle Contraction

• Isometric: No change in muscle length.
• Eccentric: Muscle length increases (lengthening).
• Concentric: Muscle length decreases (shortening).

Roles of Muscles

• Agonist: Muscle that produces the main/desired movement, usually through concentric contraction.
• Antagonist: Acts against the main mover, by either relaxing or eccentric action.
• Stabilizers (Fixators): Contract to fixate or stabilize an area to enable another limb or body segment to exert force and move.
• Synergist: Assists in the action of an agonist but are not necessarily prime movers for the action.
• Neutralizers: Counteract or neutralize the action of other muscles to prevent undesirable movements.

Muscle Spindles and Golgi Tendon Organs

• Muscle Spindles: Concentrated primarily in the muscle belly between fibers. They are sensitive to Stretch & Rate of Stretch. Rapid stretch causes muscle to contract; this is known as a myotatic or stretch reflex.
• Golgi Tendon Organs (GTOs): Located in the tendon near the muscle-tendon junction. They are sensitive to extreme stretch. Muscle contraction leads to tendon and GTO stretch. Extreme muscle contraction extreme stretch of tendon and GTOs activates GTO which leads to muscle relax + activates the antagonist (protective mechanism).

Muscle Force-Length and Force-Velocity Relationships

• As the length increases, the amount of active tension that can be developed increases until approximately 130% of the muscle's resting length is reached. After this point, further increases in length result in decreased ability to generate active tension.
• Passive tension begins to increase on the muscle lengthened beyond its resting length.
• Eccentric means lengthening of muscle
• Isometric means no change in length of the muscle
• Concentric means shortening of muscle

Linear Kinematics

• Kinematics describes motion, while kinetics finds the origin of motion. E.g., Displacement, velocity, acceleration v. Forces & Torques
• Scalar has only magnitude, such as distance, speed, time, and mass.
• Vector has magnitude + direction, such as displacement, velocity, acceleration, force, and weight.
• Linear Displacement is change in position of an object (usually in meters).
• Linear Distance is the total amount an object has moved.
• Velocity is displacement divided by time (m/s).
• Speed is distance divided by time (m/s).
• Acceleration is the rate of change in velocity. Acceleration due to gravity is -9.8 m/s/s.

Angular Kinematics

• Relative Angle represents the angle between two segments, also known as a joint angle.
• Absolute Angle is the angle between a segment and a fixed horizontal or vertical plane.
• Angular Displacement is the change in angles (final - initial angles), measured in degrees or radians (vector, counterclockwise (+), clockwise (-)).
• Angular Distance is the total amount of angular motion, measured in degrees or radians (scalar).
• Angular Velocity is angular displacement divided by changes in time (units: deg/s, rad/s, rev/s, rpm) (vector).
• Angular Acceleration is angular velocity divided by changes in time (units: deg/s^2, rad/s^2, rev/s^2).
• Instantaneous center of rotation is the center of rotation at a specific instant in time during movement.

Kinetics

• First law (Law of Inertia): A body will maintain a state of rest or constant velocity unless acted on by an external force that changes the state.
• Second Law (law of acceleration): A force applied to a body causes an acceleration of that body of a magnitude proportional to the body's mass. Formula: Force (N)= mass (kg) x acceleration (m/s^2).
• Third law (Law of Reaction): For every action there is an equal and opposite reaction.
• Weight is a vector and is a type of force, body force as a result of gravity. Mass is a scalar and is not a force.
• Ground Reaction Force is the force exerted by the ground on a body in contact with it.
• Center of Mass (COM) is the point where the mass and weight of a body are balanced in all directions.
• Balance occurs when the COM is (line of gravity) is inside the base of support.
• Torque (or Moment) is the tendency of a force to rotate the body to which it is applied. Formula: Force * distance. Unit of measure is the Newton meter. Vector quantity.
• Moment Arm is the perpendicular distance between the force application axis and the center of rotation.

Static Equilibrium

• Static Equilibrium is a state characterized by balanced forces and torques (no net forces and torques).

Shoulder Girdle Joints

• Sternoclavicular (SC) Joint: Gliding (arthrodial) joint & Includes Anterior sternoclavicular ligament, Posterior sternoclavicular ligament, Costoclavicular ligament, interclavicular ligament
• Acromioclavicular (AC) Joint: Gliding (arthrodial) joint. Ligaments include The superior acromioclavicular ligament, inferior acromioclavicular ligament, Coracoclavicular ligament: Conoid and Trapezoid.
• Scapulothoracic Joint: NOT a true synovial joint. Lacks ligamentous support.

Shoulder Girdle Muscles

• Trapezius (Upper fibers): Origin: Base of skull, occipital protuberance, and posterior ligaments of neck Insertion: Posterior aspect of the lateral third of the clavicle Action: Elevation, Upward Rotation, Extension and rotation of the head at the neck
• Trapezius (Middle Fibers): Origin: Spinous processes of seventh cervical and upper three thoracic vertebrae (C7 & T1-T3) Insertion: Medial border of the acromion process and upper border of the scapular spine Action: Elevation, Upward rotation, and Adduction (Retraction)
• Upper Fibers act in Elevation, Upward Rotation, Extension and rotation of the head at the neck
• Middle Fibers act in Elevation, Upward rotation, and Adduction (Retraction)
• Serratus Anterior acts in Abduction (protraction), Upward Rotation.
• Subclavius Muscle: Origin: Superior aspect of the first rib at its junction with its costal cartilage, Insertion: Inferior groove in the midportion of the clavicle. Action: Stabilization and protection of the sternoclavicular Joint, Depression, Abduction (protraction)
• Pectoralis Minor: Origin: Anterior surfaces of the third to fifth ribs and Insertion: Coracoid process of the scapula. Action: Abduction (protraction), Downward Rotation as it abducts, it draws the scapula downward, and Depression.

Shoulder Joint Muscles

• Deltoid (Anterior Fibers): Origin: Anterior lateral third of the clavicle, Insertion: Deltoid tuberosity on the lateral humerus, Action: Abduction, Flexion, Horizontal adduction, and Internal Rotation
• Deltoid (Middle Fibers): Origin: Lateral aspect of the acromion, Insertion: Deltoid tuberosity on the lateral Humerus, Action: Abduction and Horizontal Adduction
• Pectoralis Major (Upper & Lower Fibers): Insertion: Medial lip of the intertubercular groove of the humerus. Action: Internal Rotation, Horizontal Adduction, Flexion, Adduction and Extension.
• Latissimus Dorsi: Origin: Posterior crest of the ilium, back of the sacrum, also Insertion: Medial lip of the intertubercular groove of the humerus, Action: Adduction, Extension, Internal Rotation, and Horizontal Abduction
• Teres Major Origin: Posteriorly on the inferior third of the lateral border of the scapula & Insertion: Medial lip of the intertubercular groove of the humerus, Action: Flexion, Adduction, and Horizontal Adduction
• Rotator Cuff Muscles are composed of: Subscapularis, Supraspinatus, Infraspinatus, Teres Minor
• Subscapularis: insertion is the Lesser tubercle of the humerus, Action: Stabilizes the humeral head in glenoid fossa and does internal rotation.
• Supraspinatus: insertion is the greater tubercle of the humerus, Action: Stabilizes the humeral head in glenoid fossa and does abduction.
• Infraspinatus and Teres Minor: insertion is the greater tubercle of the humerus, Action: Stabilizes the humeral head in glenoid fossa and does external rotation.