Biomechanics and Levers Quiz

Levers

• First Class: Load → Fulcrum → Effort; Advantage: Force + Distance
• Second Class: Effort → Load → Fulcrum; Advantage: Force
• Third Class: Fulcrum → Effort → Load; Advantage: Distance
• If unsure, assume Third Class.

Basic Movement Analysis Rules

• Action + Concentric = Muscle Group (e.g., flexion + concentric = flexors)
• Action + Eccentric = Muscle Group (e.g., flexion + eccentric = extensors)
• Isometric = Muscle group working against gravity

Bone Remodeling

• Wolff's Law: Bone responds to stress.
• Examples: Increased humerus width in tennis players, larger metatarsals/tarsals/phalanges in ballet dancers.
• Bone resorption: Bone breakdown.
• Example: Reduced bone density in astronauts due to lack of gravity.
• Adult bone maintenance stage lasts 7-10 years.

Biomechanics of Bone

• Loading Modes & Descriptions:
  • Tension: Pulled at ends, elongates (e.g., Calcaneal tensile fracture)
  • Compression: Gravity puts pressure on body, widens in the middle (e.g., vertebral compressive fracture)
  • Shear: Horizontally opposing forces (e.g., leg extension machine)
  • Torsion: Twisting, fracture line diagonal; (e.g., 3-point or 4-point fracture of the tibia)
  • Bending: 3-point or 4-point fracture, (e.g., 3-point tendon fracture of the tibia)
• Muscle Activity Influence on Bone Loading:
  • Tibia falling forward
  • Ski boot in the way
  • 3 point bending
  • Bone is weaker under compression
  • Soleus muscles compress the tibia
  • Reduces damage in falls

Bones and Articulations of the Shoulder Complex

• Shoulder Girdle: Scapula + clavicle (sternoclavicular + acromioclavicular)
• Movements: Protraction/Retraction, Elevation/Depression, Upward/Downward Rotation
• Scapulo-humeral Rhythm: 2º glenohumeral abduction = 1º of upward scapular rotation
• Glenohumeral Joint: Scapula + humerus
• Movements: Flexion/Extension, Adduction/Abduction, Horizontal abduction/adduction, Internal/External rotation, Circumduction
• Glenoid Labrum: Fibrocartilage, increases glenoid depth by 50%

Strength to Balance Ratio Between Internal and External Rotators

• 3:2 ratio (internal: external)
• Rotators: Infraspinatus, Teres Minor, Supraspinatus, Subscapularis, Deltoid.

Shoulder Girdle Actions

• Elevation/Depression
• Retraction/Protraction
• Upward/Downward Rotation

Spinal Contributions to Shoulder Movement

• Trunk extension & flexion
• Lateral flexion & rotation

Range of Motion (ROM)

• Flexibility of a joint
• Measured in degrees using a goniometer.
• Active ROM: Muscle contraction
• Passive ROM: External force

The Elbow Complex

• Synovial joints:
  • Humeroulnar: Hinge
  • Humeroradial: Plane
  • Proximal Radioulnar: Pivot
• Ligaments: Annular, Radial collateral, Ulnar collateral
• Valgus: Distal end of limb more lateral
• Varus: Distal end of limb more medial

The Wrist

• Triangular Fibrocartilage Complex (TFCC): Load-bearing structure, pulley for wrist movements
• Wrist Movements: Flexion, extension, abduction, adduction
• Palmar Intercarpal Ligament, Ulnotriquetral, Radiocarpal.
• Arches of the hand are Proximal Transverse (carpals to metacarpals), Distal Transverse (Metacarpals to phalanges), Longitudinal.

Carpal Tunnel

• Retinaculum completes tunnel
• Median nerve involved
• Phalen's Test: Wrist flexion for 30-60 seconds
• Prehension: Grasping objects (Power grip, Pinch grip)

Pelvis, Hip and Knee

• Acetabular Labrum: Cartilage ring that deepens the acetabulum.
• Transverse ligament: Stabilizes hip.
• Ligamentum Teres: Intra-articular structure, supports & lubricates hip joint.
• Acetabular alignment: Centre-edge (Wiberg) angle; acetabular anteversion angle
• Hip extension and internal rotation will tighten the ligaments
• Types of prehension are Tip pinch, Lateral pinch, Pulp pinch, Palmar pinch

Active Range of Motion (ROM)

• Hip Flexion: Supine position, to prevent hamstring stretch.
• Hip Hyperextension: Supine position, keep knee joint extended, avoid lumbosacral motion

Assessing Leg Length Discrepancy

• True leg length: Bone length measured using anterior superior iliac spine (ASIS) and medial malleolus (MM).
• Apparent leg length: Pelvic rotation, sacroiliac dysfunction, foot pronation/supination
• Measure from umbilicus to medial malleolus

Surface Motion of the Knee

• Sagittal plane motion (flexion & extension):
• Example: flexion 15 degrees

Patella Mechanism

• Functions: Protection, leverage, shock absorption, reducing friction
• Tracking: Medial/lateral tracking in flexion

Foot and Ankle

• Windlass mechanism: Plantarflexion increases arch height.
• Gait cycle:
  • Stance Phase: Heel strike, foot flat, heel rise, push off, toe off
  • Swing Phase: Acceleration, toe clearance

Biomechanical Assessment of Foot and Ankle

• Knee to wall test assesses dorsiflexion ROM

Spine and Posture

• Ligaments: Anterior longitudinal ligament, Posterior longitudinal ligament, Ligamentum flavum,.
• Spinal curvatures: Normal (lordosis, kyphosis) & Abnormal (hypo/hyperlordosis, hypo/hyperkyphosis)
• Normal line of gravity passes anterior to spinal column if kyphosis exists

Pelvic Tilt

• Anterior tilt increase load on lumbar spine.
• Erector spinae control posture.
• Lying down and raising legs helps reduce load.

Spinal Nerves

• Nerve plexus: 5 main (Cervical, Brachial, Lumbar, Sacral, Coccygeal)
• Spinal nerves: 31 pairs total

Spinal Nerve Diagram

• Dorsal root: Sensory neurons
• Ventral root: Motor neurons
• Reflex arc: Unconscious response loop.

Components of a Reflex Arc

• Receptor: Receives stimulus
• Sensory neuron: Transmits signal
• Integration centre: Relays signal
• Motor neuron: Carries signal to effector
• Effector: Carries out response

Brachial Plexus

• Spinal nerves C5-T1 (superior to clavicle).
• Innervates upper limbs and associated dermatomes.

Lumbar Plexus

• Spinal nerves L1-L4
• Innervates anterior and medial thigh, associated dermatomes
• Also innervates some hip muscles

Sacral Plexus

• Spinal nerves L4-S4
• Longest, thickest plexus
• Pain along sciatic nerve, possible numbness/shooting pain/leg pain.

Innervation of Skin

• Dermatomes: Areas of skin innervated by a specific spinal nerve.

Somatotyping

• Quantifies body shape and composition.
  • Endomorphy: Fatness
  • Mesomorphy: Musculoskeletal robustness
  • Ectomorphy: Linearity/slenderness

Measuring Somatotypes – Heath Carter Method

• Body measurements for somatotyping (height, weight, skin folds, bone breadth, girth).
• Measurements are taken on the Right side of the body to avoid left-right asymmetry.
• Skinfolds: Triceps, Subscapular, Supraspinale, Medial Calf
• Bone Breadth: Humerus, Femur
• Girth: Arm, Calf

Plotting Somatotypes

• Plotting methods: Determining body type from measurements.

Test your understanding of the biomechanics of levers, muscle movements, and bone remodeling. This quiz covers first, second, and third class levers, as well as the effects of stress on bone structure. Dive into the fundamental principles that govern human movement and skeletal adaptation.