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SUBJECT: BIOMECHANICS

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1. LOCKING AND UNLOCKING MECHANISM OF THE KNEE JOINT

Definition

Locking Mechanism (Terminal Extension)

• As the knee approaches full extension (last 20°–30°), the medial femoral condyle is larger and has a longer articular surface than the lateral condyle.
• The lateral femoral condyle exhausts its arc of movement before the medial condyle.
• To complete extension, the tibia rotates laterally (externally) on a fixed femur (open chain) — approximately 5°–10°.
• In closed chain (weight bearing), the femur rotates medially on a fixed tibia.
• This "screw-home" rotation winds the cruciate ligaments tightly, packs the joint surfaces together, and locks the joint in a stable, close-packed position.
• The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) tighten and become taut.
• Menisci are compressed between condyles, adding to stability.
• Result: The locked knee is stable with minimal muscular energy expenditure (important during prolonged standing).

Unlocking Mechanism

• Initiated by the popliteus muscle — the "key" to the locked knee.
• Popliteus medially rotates the tibia on the femur (open chain) OR laterally rotates the femur on the tibia (closed chain), approximately 5°.
• This unwinds the cruciate ligaments and brings the joint out of close-pack, allowing flexion to begin.
• Nerve supply of popliteus: Tibial nerve (L4, L5, S1).

Clinical Significance

• Damage to popliteus → inability to unlock → difficulty initiating knee flexion from standing.
• Screw-home mechanism is used in gait during terminal stance phase.

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2. GAIT AND DETERMINANTS OF GAIT CYCLE

Definition of Gait Cycle

Phases of Gait Cycle

1. Initial Contact (Heel Strike) — 0%
2. Loading Response (Foot Flat) — 0–10%
3. Midstance — 10–30%
4. Terminal Stance (Heel Off) — 30–50%
5. Pre-swing (Toe Off) — 50–60%

1. Initial Swing (Acceleration) — 60–73%
2. Mid Swing — 73–87%
3. Terminal Swing (Deceleration) — 87–100%

Spatial & Temporal Parameters

• Step length: Distance from one heel strike to the contralateral heel strike (~70–80 cm)
• Stride length: Distance from heel strike to heel strike of the same foot (~140–160 cm)
• Cadence: Steps per minute (~90–120 steps/min)
• Walking speed: ~1.4 m/s (normal adults)
• Double support: 10–12% when both feet contact ground simultaneously
• Single limb support: 40% of cycle

Determinants of Gait (Saunders, Inman & Eberhart, 1953)

Muscles Active in Gait

Pathological Gaits

• Trendelenburg gait: Weak gluteus medius
• Steppage gait: Foot drop (tibialis anterior weakness)
• Scissor gait: Spastic adductors
• Antalgic gait: Pain-avoidance shortened stance phase

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3. FORCE — INTERNAL AND EXTERNAL COMPONENTS

Definition of Force

• SI Unit: Newton (N)
• Formula: F = m × a (Newton's 2nd law)
• Force is a vector quantity: has magnitude, direction, point of application, and line of action.

Types of Forces

External Forces

• Gravity (body weight): Acts downward through the center of gravity
• Ground Reaction Force (GRF): Equal and opposite to the force exerted on the ground (Newton's 3rd law); acts upward through the foot
• Friction: Tangential force at the foot-ground interface; prevents slipping
• External loads: Objects held, pushed, or pulled (dumbbells, resistance bands)
• Atmospheric pressure, buoyancy (in water)

Internal Forces

• Muscle force (Fm): Tension generated by muscle contraction
• Ligament/tendon force: Passive restraining forces
• Bone-on-bone force: Compressive/shear force at joint surfaces
• Joint reaction force: Net force acting at a joint due to all internal forces

Resolution of Forces (Components)

• Horizontal component: Fx = F cos θ
• Vertical component: Fy = F sin θ

Application in Human Body

• Rotary component of muscle force: Perpendicular to bone — produces rotation
• Stabilizing component: Along the bone toward the joint — compresses joint surfaces
• Dislocating component: Along the bone away from joint — distracts joint

• Maximum rotary component (perpendicular to forearm)
• At angles < 90°, significant stabilizing component; at > 90°, dislocating component

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4. LEVERS AND PULLEYS WITH EXAMPLES IN THE HUMAN BODY

LEVER SYSTEMS

• Fulcrum (F): Pivot point / axis of rotation (joint)
• Effort (E): Applied force (muscle)
• Load/Resistance (R): Weight/resistance to be moved

Classes of Levers

PULLEYS IN THE HUMAN BODY

Types

• Fixed pulley: Changes direction only; MA = 1
• Movable pulley: Changes magnitude; MA = 2

Examples in Human Body

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5. EQUILIBRIUM

Definition

Conditions of Equilibrium (Newton's Laws)

• 1st condition (Translational): ΣF = 0 (Sum of all forces = 0)
  • ΣFx = 0 (horizontal)
  • ΣFy = 0 (vertical)
• 2nd condition (Rotational): ΣM = 0 (Sum of all moments/torques = 0)
  • Clockwise moments = Counterclockwise moments

Types of Equilibrium

Factors Affecting Equilibrium

1. Height of COG — lower = more stable
2. Size of base of support (BOS) — larger = more stable
3. Position of line of gravity (LOG) relative to BOS — must fall within BOS
4. Mass of body — heavier = more stable
5. Friction between foot and ground

Clinical Relevance

• Elderly patients with high COG and reduced BOS → fall risk
• Wide-based gait (ataxia) increases BOS for stability
• Walkers, canes increase BOS artificially

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6. ANGLE

Definition

Types of Angles in Biomechanics

Angle of Pull of Muscle

• Angle of insertion: Angle between muscle line of action and the bone
• At 90° → maximum rotary component (maximum torque)
• As angle decreases/increases from 90° → reduced rotary component

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7. AXIS AND PLANES (& TRIANGULAR CONCEPT)

Body Planes

Body Axes (Axes of Rotation)

Degrees of Freedom (DOF)

• 1 DOF (uniaxial): Hinge joint (elbow, interphalangeal)
• 2 DOF (biaxial): Condyloid joint (radiocarpal), Saddle joint (1st CMC)
• 3 DOF (triaxial): Ball-and-socket (hip, shoulder, glenohumeral)

Triangular (Triangle of Forces) Concept

• Used to resolve forces graphically (Lami's theorem, force polygon)
• Application: Analysis of forces at a joint — e.g., at the hip, three forces (body weight, abductor muscle, joint reaction force) form a force triangle to find the resultant joint contact force.

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8. LEVER (IN DETAIL)

Torque / Moment of Force

• T = F × d
• Unit: Newton-metre (N·m)
• Greater moment arm → greater torque for same force

Mechanical Advantage

• MA = Effort Arm / Resistance Arm
• MA > 1: Force advantage (less effort needed)
• MA < 1: Speed/range advantage (greater excursion at load end)

Why Most Body Levers Are 3rd Class

• The muscle insertion is close to the joint (short effort arm)
• Load (limb/object) is far from joint (long resistance arm)
• MA < 1 → requires large muscle force, BUT produces speed and range of motion
• Evolutionary trade-off: fast, wide-range limb movements at the cost of large muscle forces

2nd Class Lever (Most Efficient)

• Gastrocnemius/Soleus at ankle during heel raise
• MA > 1 → force advantage
• Rarest in human body

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9. STABILITY

Definition

Factors Determining Stability

1. Base of Support (BOS): Area enclosed by the outermost points of contact. Larger BOS → more stable.
2. Center of Gravity (COG)/Center of Mass (COM):
   • The point where the total body weight acts.
   • Located approximately at S2 level in anatomical position (55–57% of body height).
   • Lower COG → more stable.
3. Line of Gravity (LOG): Vertical line from COG downward. Must fall within BOS for stability.
4. Body mass: Greater mass → more inertia → more stable.
5. Friction: Between foot/support and ground — resists sliding.
6. Segmental alignment: Good postural alignment keeps LOG within BOS efficiently.

Relationship Between Stability and Mobility

• Stability and mobility are inversely related: Increasing one reduces the other.
• Wide stance = stable but less mobile.
• Narrow base = mobile (quick direction change) but unstable.

Joint Stability

1. Static stabilizers: Bony geometry (acetabulum, glenoid), menisci, labrum, capsule, ligaments.
2. Dynamic stabilizers: Muscles (rotator cuff, hip abductors, quadriceps).

Clinical Applications

• Falls in elderly → decreased BOS, raised COG, reduced muscle strength.
• Proprioceptive training improves dynamic stability.
• After ACL injury → static stability lost, dynamic stability compensates via hamstrings.

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10. SHOULDER JOINT / STERNOCLAVICULAR JOINT

A. SHOULDER JOINT (Glenohumeral Joint)

Articular Surfaces

• Glenoid cavity: shallow, pear-shaped, covers only 1/4–1/3 of humeral head
• Glenoid labrum: fibrocartilaginous rim deepens the socket by 50%
• Humeral head: large, spherical, faces medially, superiorly, and posteriorly

Movements and Range

Stability Mechanisms

• Static: Glenoid labrum, capsule, coracohumeral ligament, glenohumeral ligaments (superior, middle, inferior — IGHL most important), negative intraarticular pressure
• Dynamic: SITS muscles — Rotator cuff (Supraspinatus, Infraspinatus, Teres minor, Subscapularis) compress humeral head into glenoid; long head of biceps

Bursae

• Subacromial/subdeltoid bursa (largest, most commonly inflamed)
• Subscapular bursa

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B. STERNOCLAVICULAR (SC) JOINT

Articulation

• Medial end of clavicle ↔ Manubrium of sternum + 1st costal cartilage
• An articular disc divides the joint into two synovial compartments

Movements

Ligaments

• Anterior sternoclavicular ligament — resists anterior displacement
• Posterior sternoclavicular ligament — stronger; resists posterior displacement
• Interclavicular ligament — connects both clavicles across sternum
• Costoclavicular ligament — strongest; anchors clavicle to 1st rib; limits elevation

Clinical Significance

• SC joint dislocations (rare) can compress trachea, esophagus, great vessels if posterior.
• Movement at SC joint accompanies every shoulder movement.

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11. PATELLOFEMORAL JOINT

Anatomy of Patella

• Largest sesamoid bone in the body
• Embedded within the quadriceps tendon
• Posterior surface has medial and lateral facets (7 facets described by Wiberg)
• Blood supply: Genicular anastomosis

Functions of the Patella

1. Increases mechanical advantage (moment arm) of quadriceps by ~50% (pulley function)
2. Protects the knee joint anteriorly
3. Distributes compressive forces over a wider area of femur
4. Reduces friction of quadriceps tendon over femur

Patellofemoral Mechanics

• Joint reaction force at PFJ = vector sum of quadriceps force + patellar tendon force
• At 0° extension: minimal contact force
• At 30–60° flexion: moderate force (articular contact increases)
• At 90° flexion: maximum contact area; PFJ force = 3× body weight
• During squatting: up to 7× body weight
• Contact area shifts superiorly with increasing flexion (lateral facet at deep flexion)

Q-Angle and Patellar Tracking

• Q-angle normal: 10°–20°
• Increased Q-angle (> 20°) → lateral patellar maltracking (lateral subluxation)
• Medial retinaculum + VMO (vastus medialis oblique) prevents lateral subluxation
• Iliotibial band + vastus lateralis pull patella laterally

Clinical Conditions

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12. ARTHROKINEMATICS AND OSTEOKINEMATICS OF THE KNEE JOINT

OSTEOKINEMATICS

ARTHROKINEMATICS

1. Roll (Rocking): New points on one surface meet new points on the other surface
2. Slide (Glide/Translation): One point on a surface moves across multiple points on the other
3. Spin: Rotation of one surface on a single fixed point of another

Convex-Concave Rule (Kaltenborn's Rule)

• Concave on convex: Roll and slide occur in the SAME direction
• Convex on concave: Roll and slide occur in OPPOSITE directions

Knee Joint Arthrokinematics (Tibiofemoral)

• Femoral condyles = convex; Tibial plateau = concave

• Concave tibia on convex femur
• Tibial roll: Posterior direction
• Tibial slide: Posterior direction (same direction — concave on convex rule)
• Additionally: Posterior rollback of femoral condyles increases in flexion to prevent bony impingement

• Convex femur on concave tibia
• Femoral roll: Anterior direction (same as bone movement)
• Femoral slide: Posterior direction (opposite — convex on concave rule)

• Medial femoral condyle larger → tibial external rotation at end of extension (see Topic 1)

• Medial meniscus: Moves ~5 mm posteriorly in flexion
• Lateral meniscus: Moves ~12 mm posteriorly (more mobile, thus less injured)

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13. STABILITY (Extended/Revision)

Static vs Dynamic Stability

Righting Reactions and Balance

• Righting reactions: Reflex patterns that restore upright position
• Vestibular system, visual system, and proprioception all contribute to dynamic stability
• Balance strategies: Ankle strategy (small perturbations), Hip strategy (medium), Step strategy (large)

Stability in Clinical Practice

• Crutches/walkers: Increase BOS
• Low chair vs high chair: Low COG from deep hips increases stability
• Weight shifting exercises: Train dynamic stability
• Berg Balance Scale, Timed Up-and-Go test: Assess functional stability

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SUBJECT: POSTURAL UNIT

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1. MUSCLE KINESIOLOGY / FUNCTIONS

Definition of Muscle Kinesiology

Classification of Muscle Actions

Types of Muscle Contraction

Length-Tension Relationship

• Optimal muscle force is produced at resting length (sarcomere ~2.0–2.2 μm)
• Too short (overlap of actin filaments) or too long (fewer cross-bridges) → reduced force
• Clinical: Active insufficiency (muscle too short) and passive insufficiency (muscle too long)

Force-Velocity Relationship

• Concentric: Faster contraction → less force
• Eccentric: Faster lengthening → more force (up to ~1.5× isometric max)
• Isometric: Zero velocity, intermediate force

Muscle Functions in Posture

• Postural muscles (Tonic): Predominantly type I (slow-twitch); fatigue-resistant; maintain posture against gravity
  • Examples: Soleus, erector spinae, multifidus, iliopsoas, gluteus medius
• Phasic muscles: Predominantly type II (fast-twitch); produce force quickly; fatigue rapidly
  • Examples: Rectus abdominis, hamstrings, gluteus maximus, tibialis anterior

Janda's Classification (Postural vs Phasic)

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2. TEMPOROMANDIBULAR JOINT (TMJ)

Articulation

• Mandibular condyle (convex head) ↔ Mandibular fossa + articular tubercle (eminence) of temporal bone
• An articular disc (meniscus) divides the joint into two separate synovial compartments:
  • Upper compartment (temporodiscal): Translatory/gliding movements
  • Lower compartment (discomandibular): Rotary/hinge movements

Articular Disc

• Biconcave fibrocartilaginous disc (no nerve supply in central zone)
• Attached posteriorly to bilaminar zone (retrodiscal tissue — highly vascular and innervated)
• Attached anteriorly to superior head of lateral pterygoid
• Disc divides: upper = gliding; lower = rotation

Movements and Muscles

Phase of Mouth Opening

1. First 20 mm (rotation phase): Condyle rotates in lower compartment (hinge movement)
2. 20–50 mm (translation phase): Condyle + disc translate anteriorly along articular eminence (upper compartment gliding)

Capsule & Ligaments

• Lateral (temporomandibular) ligament: Primary ligament; limits posterior and inferior condylar displacement; allows rotation
• Sphenomandibular ligament: Accessory; from spine of sphenoid to lingula of mandible
• Stylomandibular ligament: Limits excessive protrusion

Nerve Supply

• Auriculotemporal nerve (branch of V3 — mandibular division of trigeminal)
• Masseteric nerve (V3)

Blood Supply

• Superficial temporal artery, maxillary artery (both branches of external carotid)

Biomechanics (Arthrokinematics)

• Lower compartment (condyle on disc): Convex on concave — spin/rotation
• Upper compartment (disc on eminence): Concave on convex — condyle-disc complex slides anteriorly

Clinical Conditions

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3. FUNCTIONS / ARTICULATION (Joints of the Shoulder Girdle)

Four Joints of the Shoulder Complex

Acromioclavicular (AC) Joint

• Type: Plane synovial joint; fibrocartilaginous articular disc (incomplete)
• Movements: Rotation, gliding, tipping of scapula
• Ligaments:
  • Acromioclavicular ligament: Horizontal stability
  • Coracoclavicular ligaments (conoid + trapezoid): Vertical stability — prevent clavicle from riding up
• AC joint separation: Graded I–VI; coracoclavicular ligament torn in Grade III+

Scapulothoracic Motion

• Not a true joint (no capsule/synovial membrane)
• Scapula moves on the thorax via SC and AC joint motion
• Movements: Elevation/depression, protraction/retraction, upward/downward rotation, anterior/posterior tipping

Scapulohumeral Rhythm

• For every 3° of arm abduction:
  • 2° at glenohumeral joint
  • 1° at scapulothoracic joint
• Ratio: 2:1 (GH:ST)
• Total 180° elevation = 120° at GH + 60° at ST (+ 30° at SC via clavicular rotation)

Articular Cartilage Functions

1. Load distribution: Spreads compressive forces over wide area
2. Shock absorption: Viscoelastic properties absorb impact
3. Smooth gliding: Reduces friction coefficient to ~0.002 (nearly frictionless)
4. Self-lubrication: Weeping lubrication under compression; boosted lubrication with synovial fluid

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SUBJECT: KINEMATICS

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1. ARCHES OF THE FOOT

Definition

Three Arches of the Foot

A. Medial Longitudinal Arch (MLA)

• Most important and highest arch
• Bones: Calcaneus → Talus → Navicular → 3 Cuneiforms → 1st, 2nd, 3rd Metatarsals
• Keystone: Talus (at apex)
• Height: ~15–18 mm
• Static supports: Spring (plantar calcaneonavicular) ligament (key ligament — most important), long plantar ligament, plantar fascia (plantar aponeurosis)
• Dynamic supports: Tibialis posterior (main dynamic supporter), flexor hallucis longus, flexor digitorum longus, intrinsic muscles

B. Lateral Longitudinal Arch (LLA)

• Lower, less mobile
• Bones: Calcaneus → Cuboid → 4th and 5th Metatarsals
• Keystone: Cuboid
• Primarily in contact with ground in weight bearing (transmits lateral forces)
• Static support: Long plantar ligament, plantar fascia

C. Transverse Arch

• Runs across the width of the foot
• Bones: Bases of all 5 metatarsals; 3 cuneiforms + cuboid at mid-foot; heads of metatarsals (forefoot arch)
• Keystone: Middle (2nd) cuneiform and 2nd metatarsal
• Support: Peroneus longus muscle (crosses the sole — main dynamic supporter); plantar ligaments; deep transverse metatarsal ligament (at forefoot)

Functions of the Arches

1. Weight bearing and distribution: Distribute body weight across plantar surface
2. Shock absorption: Spring-like mechanism reduces impact forces (~50% of GRF)
3. Rigid lever: At push-off, arches stiffen the foot to transmit propulsive forces
4. Adaptability: Arch deforms and restores energy (Windlass mechanism)

Windlass Mechanism

• Dorsiflexion of toes at push-off tightens the plantar fascia
• This raises the medial longitudinal arch → creates a rigid lever for efficient push-off
• Described by Hicks (1954)

Clinical Conditions

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2. ELBOW JOINT

A. Humeroulnar Joint

• Type: Hinge (ginglymus)
• Articulation: Trochlea of humerus ↔ Trochlear notch (olecranon + coronoid process) of ulna
• Movements: Flexion (0–145°) and Extension (0° — some have 5–10° hyperextension)

B. Humeroradial Joint

• Type: Ball-and-socket (functionally modified)
• Articulation: Capitulum of humerus ↔ Head of radius
• Movements: Flexion/extension + pronation/supination

C. Proximal Radioulnar Joint

• Type: Pivot (trochoid)
• Articulation: Head of radius ↔ Radial notch of ulna + Annular ligament
• Movement: Pronation/Supination (with distal radioulnar joint)

Range of Motion

Carrying Angle

• Angle between humeral and ulnar shafts in anatomical position
• Normal: 5°–10° male; 10°–15° female (due to wider female pelvis / hormonal laxity)
• Cubitus valgus: Increased angle (>15°) — e.g., post-lateral condyle fracture
• Cubitus varus (gunstock deformity): Decreased angle — e.g., post-supracondylar fracture in children

Ligaments

Muscles

Brachialis: "Workhorse of Elbow Flexion"

• Pure flexor regardless of forearm position
• No supination/pronation function

Biceps Brachii: Supination Role

• Most powerful supinator when elbow is at 90° flexion

Arthrokinematics at Elbow

• Humeroulnar: Concave trochlear notch (ulna) on convex trochlea (humerus) → roll and slide in SAME direction
• Humeroradial: Concave radial head on convex capitulum → roll and slide in SAME direction
• Proximal RU joint: Radial head spins in annular ligament during prono-supination

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3. GLENOHUMERAL (GH) RHYTHM / SCAPULOHUMERAL RHYTHM

Definition

Ratio: 2:1 (GH:ST)

• 2° occurs at the glenohumeral joint
• 1° occurs at the scapulothoracic joint (scapular rotation)

Phases of GH Rhythm

1. Setting Phase (0–30°): Scapula finds its stable position on thorax; GH joint primarily active
2. Active Phase (30°–180°): Constant 2:1 GH:ST ratio maintained; scapula rotates upward 60° total

Why Scapular Upward Rotation Matters

• Keeps subacromial space open — prevents supraspinatus impingement
• Maintains optimal glenoid orientation under humeral head (prevents superior migration)
• Maximizes rotator cuff muscle length-tension relationship

Muscles Producing GH Rhythm

Force Couple for Scapular Rotation

• Upper trapezius: Pulls superiorly on lateral clavicle/acromion
• Lower trapezius: Pulls inferior angle medially/downward
• Serratus anterior: Pulls inferior angle laterally/anteriorly
• These three form the scapular force couple — produce pure upward rotation

Clinical Relevance

• Altered GH rhythm → subacromial impingement, rotator cuff pathology
• Scapular dyskinesia: Abnormal scapular motion (winging, anterior tipping) disrupts rhythm
• Serratus anterior weakness (long thoracic nerve palsy): Winging of scapula → disrupted GH rhythm
• Ratio disturbance → reduced subacromial space → impingement syndrome

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4. PREHENSION

Definition

Classification of Prehension (Napier, 1956)

A. POWER GRIP (Palmar Grasp)

B. PRECISION GRIP (Pinch)

Muscles in Prehension

• Flexors: FDP, FDS — finger flexion
• Intrinsics (interossei, lumbricals): Balance MCP/IP joint positions
• Thumb opposition: Opponens pollicis, FPB, abductor pollicis brevis
• Wrist extensors stabilize the wrist (synergists)

• Intrinsic muscles dominate — interossei, lumbricals
• FPL: Flexes IP joint of thumb
• APB: Abducts thumb
• Requires MCP flexion + IP extension (lumbrical-interosseous action)

Wrist Position in Prehension

• Wrist in extension (20°–30°) maximizes grip force by placing finger flexors at optimal length
• Wrist flexion significantly reduces grip strength

Thumb's Role

• The thumb provides 40–50% of total hand function
• Opposition of thumb is the key movement for precision grip
• Requires: Palmar abduction + Flexion + Rotation of CMC joint

Kinematics

• Power grip: MCP 70°, PIP 40°, DIP 10° (approx.) flexion
• Precision grip: MCP 50°, PIP 30° (variable by task)

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5. POSTURE (KINESIOLOGY)

Definition

Ideal Posture — Plumb Line Test

• External auditory meatus
• Through cervical vertebral bodies
• Anterior to thoracic vertebral bodies
• Through lumbar vertebral bodies
• Slightly posterior to hip joint (resting iliofemoral ligament)
• Slightly anterior to knee joint axis
• Slightly anterior to lateral malleolus (through cuboid)

• Midway between occipital protuberance and C7
• Midline of spine
• Gluteal cleft
• Midway between medial malleoli

Curves of the Spine

Common Postural Deviations

Postural Muscles

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6. TWO-JOINT MUSCLES AND ONE-JOINT MUSCLES

One-Joint (Monoarticular) Muscles

• More specific action, easier neural control
• Force relatively constant throughout range of the joint they cross

Two-Joint (Biarticular) Muscles

• Subject to active and passive insufficiency
• Produce coordinated multi-joint movements

Active Insufficiency

• A two-joint muscle becomes actively insufficient when it is fully shortened over both joints simultaneously
• It cannot generate adequate force because it is on the descending limb of the length-tension curve
• Example: Hamstrings — difficulty generating strong knee flexion when hip is also fully flexed (as in kicking while lying prone at full hip extension the hamstrings are stronger)

Passive Insufficiency

• A two-joint muscle becomes passively insufficient when it is fully stretched over both joints simultaneously
• The muscle cannot lengthen further; motion at one joint is limited by the taut muscle at the other
• Example: Hamstrings — straight leg raise limited by hamstrings being stretched at both hip (flexed) and knee (extended)
• Example: Gastrocnemius — dorsiflexion limited with extended knee; more range available with knee flexed (isolates soleus)

Clinical Relevance

• Tight rectus femoris: Limits knee flexion when hip is extended (Ely's test positive)
• Tight hamstrings: Limits SLR; causes lumbar flexion in bending
• Thomas test: Assesses hip flexor tightness
• Gastrocnemius vs Soleus differentiation: Dorsiflexion ROM with knee straight tests gastrocnemius; with knee bent tests soleus---

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QUICK REFERENCE SUMMARY — RUHS EXAM

BIOMECHANICS

POSTURAL UNIT

KINEMATICS

All answers are structured for 16-mark RUHS exam format with definitions, classification, tables, clinical relevance, and examples. For each topic write approximately 1.5–2 pages in your answer booklet to achieve full marks.