Physical Therapy/Study Notes/Kinesiology & Biomechanics

Kinesiology & Biomechanics

Understanding human movement through the study of muscle contractions, joint mechanics, gait analysis, and functional anatomy essential for physical therapy practice.

1. Types of Muscle Contractions 2. Joint Movements & Terminology 3. Lever Systems 4. Upper Extremity Kinesiology

5. Lower Extremity Kinesiology 6. Spine & Core 7. Gait Analysis 8. Posture & Balance

1. Types of Muscle Contractions

Concentric

• Muscle shortens
• Overcomes resistance
• "Positive" work
• Example: Bicep curl lifting phase

Eccentric

• Muscle lengthens
• Controls movement
• "Negative" work
• Example: Bicep curl lowering phase
• Produces more force than concentric

Isometric

• No length change
• Static hold
• Force equals resistance
• Example: Wall sit, plank

Kinetic Chain Concepts

Open Kinetic Chain (OKC)

• Distal segment free to move
• Isolated joint motion
• Example: Leg extension, bicep curl
• Higher shear forces

Closed Kinetic Chain (CKC)

• Distal segment fixed
• Multi-joint motion
• Example: Squat, push-up
• More functional, less shear

Muscle Roles

Role	Function	Example
Agonist (Prime Mover)	Primary muscle for movement	Biceps during elbow flexion
Antagonist	Opposes the agonist	Triceps during elbow flexion
Synergist	Assists the agonist	Brachialis during elbow flexion
Stabilizer	Stabilizes a body part	Rotator cuff during arm movement
Neutralizer	Cancels unwanted action	Pronator teres canceling supination of biceps

2. Joint Movements & Terminology

Movement Terms

Primary Movements

Flexion: Decreasing joint angle
Extension: Increasing joint angle
Abduction: Away from midline
Adduction: Toward midline
Internal Rotation: Rotate inward
External Rotation: Rotate outward

Special Movements

Pronation: Palm down / foot eversion + abduction
Supination: Palm up / foot inversion + adduction
Dorsiflexion: Ankle - toes up
Plantarflexion: Ankle - toes down
Circumduction: Circular movement
Protraction/Retraction: Forward/backward

Planes of Motion

Sagittal Plane

Divides left/right

Axis: Frontal (medial-lateral)

Movements: Flexion, extension

Frontal (Coronal) Plane

Divides front/back

Axis: Sagittal (anterior-posterior)

Movements: Abduction, adduction, lateral flexion

Transverse (Horizontal) Plane

Divides top/bottom

Axis: Vertical (longitudinal)

Movements: Rotation, pronation, supination

Arthrokinematics

Joint surface movements during osteokinematic motion:

Roll: New points on both surfaces contact each other
Glide (Slide): Same point on one surface contacts new points on other
Spin: Rotation around a stationary axis

Convex-Concave Rule:

• Convex moves on concave: Roll and glide in opposite directions
• Concave moves on convex: Roll and glide in same direction

3. Lever Systems

First Class Lever

Fulcrum between effort and resistance

F-A-R or R-A-F

Example: Head on atlas (neck extension)

Like a seesaw

Second Class Lever

Resistance between fulcrum and effort

A-R-F

Example: Standing heel raise (ankle plantarflexion)

Like a wheelbarrow - favors force

Third Class Lever

Effort between fulcrum and resistance

A-F-R

Example: Elbow flexion (biceps)

Most common in body - favors speed/ROM

Mechanical Advantage

MA = Force Arm / Resistance Arm

• MA > 1: Favors force production (2nd class)
• MA < 1: Favors speed and range (3rd class)
• Most body levers have MA < 1 (designed for speed, not force)

4. Upper Extremity Kinesiology

Shoulder Complex

Scapulohumeral Rhythm

For every 3° of shoulder abduction: 2° at glenohumeral joint, 1° at scapulothoracic

Ratio: 2:1 (GH:ST)

Rotator Cuff (SITS)

Supraspinatus: Initiates abduction (first 15°)
Infraspinatus: External rotation
Teres minor: External rotation
Subscapularis: Internal rotation

Force Couples

Upward rotation: Upper trap, lower trap, serratus anterior
Downward rotation: Rhomboids, levator scapulae, pec minor
Rotator cuff depresses humeral head during deltoid abduction

Elbow & Forearm

Movement	Prime Movers	Normal ROM
Elbow Flexion	Biceps, brachialis, brachioradialis	0-150°
Elbow Extension	Triceps, anconeus	0°
Forearm Supination	Biceps, supinator	0-85°
Forearm Pronation	Pronator teres, pronator quadratus	0-75°

Hand & Wrist

Functional position of hand: Wrist 20-30° extension, MCP 45° flexion, IP slight flexion, thumb opposed
Grip types: Power grip (cylindrical, spherical, hook), Precision grip (tip, lateral, palmar)
Intrinsic muscles: Lumbricals flex MCP, extend IP

5. Lower Extremity Kinesiology

Hip Joint

Movement	Prime Movers	Normal ROM
Flexion	Iliopsoas, rectus femoris	0-120°
Extension	Gluteus maximus, hamstrings	0-30°
Abduction	Gluteus medius, gluteus minimus	0-45°
Adduction	Adductor magnus, longus, brevis	0-30°
Internal Rotation	TFL, gluteus medius (anterior)	0-45°
External Rotation	Deep rotators, piriformis, gluteus maximus	0-45°

Knee Joint

Movements

Flexion: Hamstrings, gastrocnemius (0-135°)
Extension: Quadriceps (0°)
Screw-home mechanism: External rotation of tibia on femur during terminal extension

Key Structures

ACL: Prevents anterior tibial translation
PCL: Prevents posterior tibial translation
MCL: Resists valgus stress
LCL: Resists varus stress

Ankle & Foot

Talocrural Joint

Dorsiflexion: Tibialis anterior (0-20°)
Plantarflexion: Gastrocnemius, soleus (0-50°)

Subtalar Joint

Inversion: Tibialis posterior
Eversion: Peroneals

Arches of the Foot:

• Medial longitudinal arch (highest)
• Lateral longitudinal arch
• Transverse arch

6. Spine & Core

Spinal Curves

Cervical: Lordosis (secondary curve)
Thoracic: Kyphosis (primary curve)
Lumbar: Lordosis (secondary curve)
Sacral: Kyphosis (primary curve)

Core Stabilization

Local Stabilizers

• Transverse abdominis
• Multifidus
• Diaphragm
• Pelvic floor

Global Movers

• Rectus abdominis
• External obliques
• Erector spinae
• Quadratus lumborum

7. Gait Analysis

Gait Cycle Phases

Stance Phase (60%)

Initial Contact (Heel Strike)
Loading Response (Foot Flat)
Midstance
Terminal Stance (Heel Off)
Pre-swing (Toe Off)

Swing Phase (40%)

Initial Swing
Mid-swing
Terminal Swing

Common Gait Deviations

Deviation	Cause	Appearance
Trendelenburg	Hip abductor weakness	Pelvis drops on swing side
Compensated Trendelenburg	Hip abductor weakness	Trunk leans toward stance leg
Steppage (Foot Drop)	Dorsiflexor weakness/peroneal nerve	Excessive hip/knee flexion to clear foot
Circumduction	Hip flexor weakness or stiff knee	Leg swings outward in arc
Antalgic	Pain	Shortened stance on painful side
Vaulting	Leg length discrepancy or stiff knee	Rising on toes of stance leg

Gait Parameters

Step length: Heel to heel of opposite foot (~72 cm)
Stride length: Heel to heel of same foot (~144 cm)
Cadence: Steps per minute (~113 steps/min)
Velocity: Distance / time (~82 m/min or 1.4 m/s)

8. Posture & Balance

Ideal Posture (Plumb Line)

Lateral view alignment:

• Through external auditory meatus
• Through shoulder (acromion)
• Through greater trochanter
• Slightly anterior to knee axis
• Slightly anterior to lateral malleolus

Postural Deviations

Kyphosis-Lordosis

• Increased thoracic kyphosis
• Increased lumbar lordosis
• Forward head posture

Flat Back

• Decreased lumbar lordosis
• Posterior pelvic tilt
• Flexed trunk

Sway Back

• Long kyphosis
• Posterior pelvis displacement
• Hip hyperextension

Scoliosis

• Lateral spinal curvature
• Named by convex side
• Structural vs functional

Balance Systems

Visual: Eyes provide spatial orientation
Vestibular: Inner ear detects head position/movement
Somatosensory: Proprioceptors in joints, muscles, skin

Key Takeaways for the Board Exam

Muscle Contractions

• Concentric: Muscle shortens
• Eccentric: Muscle lengthens (controls)
• Isometric: No length change

Convex-Concave Rule

• Convex on concave: Roll/glide opposite
• Concave on convex: Roll/glide same

Gait Deviations

• Trendelenburg: Hip abductor weakness
• Steppage: Foot drop (peroneal nerve)
• Antalgic: Pain avoidance

Shoulder

• Scapulohumeral rhythm: 2:1
• SITS: Rotator cuff muscles

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