Calisthenics Instructor Certification Chapter 6: Kinesiology (continued)

Chapter 6: The Muscles of the Human Body

6.1 General Overview

Muscles are essential organs of the human body, composed of muscular tissue and connected to bones through tendons. Together, they form the systems that enable movement of the skeleton and contribute to locomotion, stability, and posture.

There are three main types of muscle in the human body:

  1. Cardiac muscle – forms the myocardium of the heart. It contracts rhythmically and involuntarily to sustain life.
  2. Smooth muscle – found in the walls of internal organs (viscera) and blood vessels, as well as in the skin and eyes. Microscopically, smooth muscle fibers lack striations. Their activity is involuntary and controlled by the autonomic nervous system.
  3. Skeletal (striated) muscle – the focus of kinesiology. These muscles form independent organs attached to bones, and their activity is voluntary, meaning they contract under conscious control.

Structure of Skeletal Muscle

Skeletal muscles are composed of multinucleated fibers (muscle cells). When observed under the microscope, they display transverse striations, hence the term striated fibers.

Each muscle fiber is wrapped in a thin membrane called the endomysium. Groups of fibers are bundled and covered by the perimysium, while the entire muscle is enclosed by a thicker membrane, the epimysium. These connective tissue layers provide protection, maintain muscle shape, and enable the transmission of force.

Muscle Fiber Types

Striated fibers are classified based on color, composition, and functional properties:

  • Red fibers (slow-twitch, Type I)
    • High content of myoglobin and mitochondria.
    • Capable of sustained, prolonged contraction.
    • Specialized for endurance activities.
  • White fibers (fast-twitch, Type II)
    • Rich in sarcoplasm and contract rapidly.
    • Generate powerful movements but fatigue quickly.
    • Specialized for speed and strength.

Both fiber types coexist within the same muscle, but their proportions differ depending on function and genetics.

The human body contains about 400 skeletal muscles, made up of approximately 250 million muscle fibers. The number of fibers per muscle varies according to its size and function.

  • Example: the biceps brachii contains ~580,000 fibers.
  • The gluteus maximus contains ~10 million fibers.
  • The tensor tympani (a tiny muscle in the ear) contains ~1,100 fibers.

Muscle Attachments

Skeletal muscles attach to bones (and occasionally to skin or fascia) via tendons. Each muscle has three main parts:

  1. Origin (proximal attachment) – the end of the muscle attached to the more fixed or less mobile part of the skeleton, usually closer to the midline.
  2. Insertion (distal attachment) – the end attached to the more mobile bone, typically further from the midline.
  3. Belly (gaster) – the thick, fleshy central portion of the muscle between origin and insertion.

All attachments are mediated by tendons, which are made of dense connective tissue.

  • In long, bulky muscles, tendons are usually cylindrical.
  • In thin, flat muscles, tendons may form broad sheets known as aponeuroses.

6.2 Classification of Muscles

Muscles can be classified in several ways, based on their shape, number of heads, location, and fiber orientation. Understanding these distinctions helps fitness professionals analyze function, design training programs, and recognize common injury risks.

By Shape

  • Long muscles: Found mainly in the limbs, designed for producing wide ranges of motion.
  • Flat muscles: Located in the trunk; many contribute to the walls of large cavities (e.g., abdominal muscles).
  • Short muscles: Smaller in size, often deeper, providing stability (e.g., spinal muscles).
  • Sphincter muscles: Circular muscles surrounding openings, essential for closure and regulation (e.g., around the mouth, anus).

By Number of Heads

  • Biceps: Muscles with two distinct origins (heads).
  • Triceps: Muscles with three heads.
  • Others: Some muscles have multiple points of origin and insertion, giving them unique functional leverage.

By Location

  • Superficial (epiploic): Situated near the surface, easily visible or palpable.
  • Cutaneous (mimetic): Found in the face, attaching to skin and controlling expressions.
  • Deep muscles: Situated beneath the superficial layers, often involved in postural control.

By Fiber Orientation

  • Parallel fibers: Fibers run directly from belly to tendon (e.g., rectus abdominis).
  • Pennate muscles: Fibers insert obliquely into the tendon, allowing greater strength:
    • Unipennate – fibers on one side of tendon.
    • Bipennate – fibers on both sides.
    • Multipennate – fibers attach in multiple directions, producing powerful contractions (e.g., deltoid, gastrocnemius).
  • Segmented muscles: Muscle bellies divided by tendinous intersections (e.g., rectus abdominis, digastric muscle).

6.3 Vascular and Nervous Supply of Muscles

Each muscle receives:

  • Arterial blood supply: A single arterial branch enters the muscle at its neurovascular hilum, then subdivides into arterioles and capillaries. Capillaries align parallel to muscle fibers, ensuring efficient oxygen and nutrient delivery. Muscle capillaries are among the finest in the body.
  • Venous drainage: Typically two accompanying veins follow the artery.
  • Nervous supply: A mixed nerve enters with the vessels and branches into:
    • Motor fibers, innervating the contractile muscle fibers.
    • Sensory fibers, monitoring position, stretch, and pain.
    • Autonomic fibers, regulating vascular tone and other involuntary functions.
      The neuromuscular junction (motor end plate) is the site where motor neurons connect with muscle fibers to trigger contraction.

6.4 Supporting Soft Structures

For stability and protection, muscles are reinforced by accessory connective tissues:

  • Fasciae: Sheaths of connective tissue that envelop one muscle, a group of muscles, or an entire body region. They prevent displacement during contraction and provide anchoring surfaces.
  • Retinacula (retaining bands): Thickened fascia that holds tendons in place, preventing bowstringing during movement.
  • Tendon sheaths: Synovial-lined tubular structures surrounding tendons, allowing smooth gliding during contraction.
  • Bursae: Small synovial sacs located between tendons, or between tendon and skin/bone. They absorb pressure, reduce friction, and protect soft tissues during repetitive movements.

6.5 Properties of Muscles

Skeletal muscles exhibit specific properties that allow them to respond to loads, stimuli, and training demands. These properties explain how muscles contract, adapt, and eventually fatigue.

Contractile Behavior

Muscles contract in response to stimuli. During contraction, they either:

  • Shorten (concentric action)
  • Lengthen (eccentric action)

At rest, muscle shape and dimensions can change actively (through contraction) or passively (through gravity or the action of antagonistic muscles). Importantly, no muscle can change shape or size entirely on its own — opposing forces are always involved.

Elasticity

Elasticity is the ability of a muscle to stretch under the influence of an external force and then return to its original length once the force is removed.

  • This property is provided by muscle fibers (which can extend up to twice their resting length) and by connective tissue fibers (which act as a brake against overstretching).
  • Elasticity is crucial for injury prevention and for storing/releasing energy during dynamic movements.

Muscle Tone

Muscle tone refers to the constant, low-level contraction of muscles due to ongoing nerve stimulation. It plays a key role in postural control.

Types of tone:

  • Resting tone – baseline activity present even during relaxation.
  • Reactive tone – increased activity in response to cold, emotions, or cognitive effort.

Muscle tone fluctuates:

  • It increases in conditions like cold exposure, emotional stress, or mental activity.
  • It decreases with warmth (e.g., hot bath) and during sleep.

Excitability

Excitability is the muscle’s ability to respond to a stimulus by generating a contraction. This property is fundamental for voluntary movement, reflexes, and exercise responses.

Contractility

Contractility is the ability of a muscle to shorten and produce force after receiving a stimulus. The strength of contraction depends on:

  • The number of fibers activated.
  • The arrangement of fibers (e.g., pennate muscles like the quadriceps or gastrocnemius can generate great force due to their oblique fiber orientation).

Not all fibers contract at once — contractions are usually partial, but during maximal effort, a large proportion of fibers are recruited.

Fatigability (Muscle Fatigue)

Muscle fatigue is the reduced capacity of a muscle to contract after prolonged activity. Repeated contractions lead to a gradual decline in performance, eventually resulting in an inability to sustain movement.

  • Fatigue is influenced by metabolic factors, energy supply, and the accumulation of waste products.
  • Proper recovery strategies (rest, nutrition, active recovery) are essential to restore performance capacity.

6.6 Functional Classification of Muscles

Muscles of Movement (Phasic Muscles)

These are the muscles of the upper and lower limbs. They are called phasic muscles because they produce strong, rapid movements.

  • They typically have a large belly (gaster).
  • They are highly elastic and respond quickly to stimuli.
  • They feature short tendons and maintain a low resting tone.

Phasic muscles are key drivers of powerful, dynamic activities such as sprinting, throwing, or jumping.

Muscles of Posture (Tonic Muscles)

These are primarily the muscles of the spinal column. Known as tonic muscles, they are specialized for maintaining posture and stabilizing the body.

  • They contract slowly with a limited range of movement.
  • They are less elastic but possess high resistance to fatigue.
  • They maintain a high resting tone, essential for upright stance.

Tonic muscles are endurance-based and provide stability during both static and dynamic activities.

6.7 Muscle Contractions

When stimulated, a muscle contracts, and this action is called muscle contraction. There are three main types of contraction:

1. Isometric Contraction

  • The muscle contracts without changing length, meaning the insertion points do not move.
  • No external work is performed, but tension is generated.
  • Example: Holding a bucket of water steady under a tap. The elbow flexors contract isometrically to keep the load stable as the bucket fills.

2. Isotonic Contraction

During isotonic contraction, the muscle changes length. It can be:

  • Concentric (shortening) – The muscle belly shortens, overcoming external resistance.
    • Example: The biceps brachii contracts concentrically when flexing the elbow to lift a weight.
  • Eccentric (lengthening) – The muscle belly lengthens while still under tension, controlling movement against gravity or resistance.
    • Example: Lowering a dumbbell slowly during elbow extension while the biceps remain active.

3. Isokinetic Contraction

  • The muscle contracts while the joint moves at a constant speed throughout the range of motion.
  • This requires specialized equipment (e.g., isokinetic dynamometers) and is mainly used in rehabilitation and performance testing.

6.8 Roles of Muscles in Movement

Muscles rarely work in isolation. Instead, they assume different roles depending on the movement being performed:

  • Agonist (Prime Mover): The muscle primarily responsible for a movement.
    • Example: The quadriceps is the prime mover in kicking a soccer ball (knee extension).
  • Antagonist: The muscle that produces the opposite action to the agonist.
    • Example: The hamstrings oppose the quadriceps during knee extension.
  • Stabilizer: The muscle that contracts to stabilize a joint or body part, allowing the agonist to work effectively.
    • Example: The abdominals stabilize the pelvis during hip flexion.
  • Neutralizer: The muscle that cancels out unwanted movement produced by an agonist.
    • Example: When two muscles combine to abduct the arm but one also causes upward rotation, the neutralizer cancels the extra action.
  • Synergist: The muscle that assists the agonist by either neutralizing an unwanted component or helping produce the desired movement.

6.9 Muscle Receptors

Muscles contain sensory receptors that provide constant feedback to the nervous system about tension and stretch:

Muscle Spindles

  • Small spindle-shaped structures located parallel to muscle fibers.
  • Detect the rate and degree of stretch in a muscle.
  • Provide critical information for reflexes, posture, and coordinated movement.

Golgi Tendon Organs (GTOs)

  • Located at the junction between muscle and tendon.
  • Sensitive to tension produced during contraction or passive stretch.
  • Act as protective mechanisms, preventing excessive force by triggering relaxation when tension is too high (although modern research shows this function is more complex than simple inhibition).

 

6.10 The Shoulder and Shoulder Girdle

The shoulder girdle is formed by the upper thoracic vertebrae, the first two ribs, the manubrium of the sternum, the scapula, the clavicle, the humerus, and the joints between these structures.

Main Joints of the Shoulder Girdle

  1. Glenohumeral Joint
  2. Subacromial (deltoid-bursal) Joint (functional)
  3. Acromioclavicular Joint
  4. Scapulothoracic Joint (functional)
  5. Sternoclavicular Joint
  6. Sternocostal Joint
  7. Costovertebral Joint

Bones of the Shoulder Girdle

The Clavicle

  • A long, S-shaped bone with a shaft and two ends:
    • Acromial end: articulates with the acromion of the scapula.
    • Sternal end: articulates with the manubrium of the sternum.

The Scapula

  • A triangular, flat bone at the back of the thorax.
  • Features:
    • Anterior surface: subscapular fossa.
    • Posterior surface: divided by the spine of the scapula into supraspinous and infraspinous fossae.
    • Acromion: articulates with the clavicle.
    • Glenoid cavity: receives the humeral head.
    • Coracoid process: a key muscular and ligamentous attachment site.

The Humerus

  • A long bone with:
    • Head: articulates with the glenoid cavity.
    • Greater and lesser tubercles: muscle attachment points.
    • Deltoid tuberosity: for insertion of the deltoid muscle.
    • Distal end: forms part of the elbow joint with the radius and ulna.

Glenohumeral Joint Movements

  • Flexion: 0–180° (agonists: anterior deltoid, biceps brachii, clavicular head of pectoralis major, coracobrachialis).
  • Extension / Hyperextension: return to neutral and beyond (agonists: latissimus dorsi, teres major, posterior deltoid).
  • Abduction: 0–180° (agonists: middle deltoid, supraspinatus).
  • Adduction: return to body (agonists: latissimus dorsi, pectoralis major [sternal], teres major).
  • Internal Rotation: 0–90° (agonist: subscapularis).
  • External Rotation: 0–90° (agonists: infraspinatus, teres minor).
  • Horizontal Abduction: 0–90° (agonists: infraspinatus, teres minor, posterior deltoid).
  • Horizontal Adduction: 0–90° (agonists: pectoralis major, anterior deltoid).
  • Circumduction: a combination of flexion, extension, abduction, and adduction in sequence.

Shoulder Muscles

Muscles around the shoulder are grouped by location:

Anterior Shoulder

  • Pectoralis Major – horizontal adduction, flexion (clavicular), adduction, extension and internal rotation (sternal).
  • Coracobrachialis – flexion and adduction.
  • Subscapularis – internal rotation.
  • Biceps Brachii – elbow flexion, forearm supination, shoulder flexion.

Posterior Shoulder

  • Infraspinatus – external rotation, horizontal abduction.
  • Teres Minor – external rotation, horizontal abduction.

Superior Shoulder

  • Deltoid –
    • Anterior fibers: flexion, horizontal adduction, internal rotation.
    • Middle fibers: abduction.
    • Posterior fibers: extension, external rotation, horizontal abduction.
  • Supraspinatus – initiates abduction (0–90°).

Inferior Shoulder

  • Latissimus Dorsi – extension, hyperextension, adduction, internal rotation.
  • Teres Major – extension, adduction, internal rotation.
  • Triceps Brachii (long head) – shoulder extension.

Scapular Movements and Muscles

  • Elevation: trapezius (upper), levator scapulae, rhomboids.
  • Depression: trapezius (lower), pectoralis minor, subclavius, serratus anterior.
  • Upward Rotation: trapezius (upper & lower), serratus anterior.
  • Downward Rotation: rhomboids, levator scapulae, pectoralis minor.
  • Protraction (Abduction): serratus anterior, pectoralis minor.
  • Retraction (Adduction): rhomboids, trapezius (middle fibers).

Scapulohumeral Rhythm

The scapulohumeral rhythm describes the coordinated motion between the scapula, clavicle, and humerus. For every 2° of glenohumeral movement, there is approximately 1° of scapular rotation. This rhythm ensures full range of motion, stability, and efficiency during overhead movements.

 

6.11 The Elbow Joint

The elbow is a critical link in the kinetic chain of the upper limb. It connects the wrist and hand with the arm and shoulder, and any dysfunction here directly affects the function of the entire upper limb. Efficient hand and finger movements depend not only on local mobility but also on the functional integrity of the elbow, shoulder, and radioulnar joints.

Bones of the Elbow Joint

The elbow joint is formed by three bones:

  1. Distal Humerus
    • Capitulum (lateral condyle): articulates with the head of the radius.
    • Trochlea (medial condyle): articulates with the trochlear notch of the ulna.
    • Epicondyles: serve as attachment points for muscles (lateral and medial).
  2. Proximal Radius
    • Head of the radius: articulates with the capitulum of the humerus and with the radial notch of the ulna.
  3. Proximal Ulna
    • Olecranon process: insertion of the triceps brachii.
    • Coronoid process: forms the anterior lip of the trochlear notch.
    • Trochlear notch: receives the trochlea of the humerus.
    • Radial notch: articulates with the head of the radius.

Articulations of the Elbow

The elbow is a compound joint consisting of three articulations within a single capsule:

  1. Humeroradial Joint – between the capitulum of the humerus and the radial head.
  2. Humeroulnar Joint – between the trochlea of the humerus and the trochlear notch of the ulna.
  3. Proximal Radioulnar Joint – between the radial head and the radial notch of the ulna (allows pronation/supination).

Ligaments of the Elbow

  • Lateral (Radial) Collateral Ligament: stabilizes the lateral side; runs from the lateral epicondyle to the annular ligament.
  • Medial (Ulnar) Collateral Ligament: stabilizes the medial side; composed of three bands attaching from the medial epicondyle to the coronoid process and olecranon.
  • Annular Ligament: encircles the radial head, keeping it in position against the ulna while allowing rotation.

Radioulnar Joints and Interosseous Membrane

  • Proximal Radioulnar Joint: part of the elbow capsule, allows rotation of the radius.
  • Distal Radioulnar Joint: between the head of the ulna and the ulnar notch of the radius, stabilized by dorsal/palmar ligaments and a triangular fibrocartilage disc.
  • Interosseous Membrane: strong fibrous sheet between radius and ulna, ensuring stability and muscle attachment.

Movements:

  • Pronation: radius crosses over ulna; palm turns inward.
  • Supination: radius and ulna become parallel; palm turns outward.

Carrying Angle

When viewed with palms forward, the humerus and forearm form an angle at the elbow known as the carrying angle:

  • ~15° in men.
  • ~25° in women.
    Excessive valgus (increased angle) is called cubitus valgus.

Movements of the Elbow

  • Flexion: 0° → 150°
    • Prime Movers: Biceps brachii, Brachialis, Brachioradialis.
    • Antagonist: Triceps brachii.
    • Everyday example: lifting a bucket of water.
    • Mechanical lever: third-class lever (effort between load and fulcrum).
  • Extension: 150° → 0°
    • Prime Mover: Triceps brachii.
    • Everyday example: pushing during a push-up.
    • Mechanical lever: first-class lever (effort and load on opposite sides of fulcrum).
  • Pronation: 0° → 80°
    • Prime Movers: Pronator teres, Pronator quadratus.
    • Example: tightening a screw with a screwdriver.
  • Supination: 0° → 90°
    • Prime Movers: Supinator, Biceps brachii.
    • Example: loosening a screw with a screwdriver.

Muscles Acting on the Elbow

  • Biceps Brachii:
    • Origin: supraglenoid tubercle (long head), coracoid process (short head).
    • Insertion: radial tuberosity.
    • Actions: elbow flexion, supination, shoulder flexion.
  • Brachialis:
    • Origin: distal half of humerus.
    • Insertion: ulna (coronoid process).
    • Action: strong elbow flexor, independent of forearm position.
  • Brachioradialis:
    • Origin: lateral humerus.
    • Insertion: styloid process of radius.
    • Action: elbow flexion, especially in neutral grip.
  • Triceps Brachii:
    • Origin: scapula (long head), posterior humerus (lateral & medial heads).
    • Insertion: olecranon of ulna.
    • Action: elbow extension.
  • Pronator Teres:
    • Origin: medial epicondyle of humerus and coronoid process of ulna.
    • Insertion: lateral radius.
    • Action: pronation of forearm.
  • Pronator Quadratus:
    • Origin: distal ulna.
    • Insertion: distal radius.
    • Action: pronation.
  • Supinator:
    • Origin: lateral epicondyle of humerus and ulna.
    • Insertion: proximal radius.
    • Action: supination.

 

6.12 The Wrist and Fingers

The skeleton of the wrist and fingers is made up of 27 small bones, intricately connected to provide the hand with its remarkable functional abilities. The human hand is unique in nature, allowing precision grip, power grip, dexterity, and fine motor control — qualities that make it an essential extension of human intelligence and creativity.

Sections of the Hand

The hand is divided into three main regions:

  1. Wrist (Carpus)
  2. Metacarpus (Palm)
  3. Fingers (Phalanges)

The five fingers are named:

  • Thumb (pollex)
  • Index finger
  • Middle finger
  • Ring finger
  • Little finger

Skeletal Structure

Carpal Bones

The wrist is composed of 8 carpal bones, arranged in two rows of four:

  • Proximal row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform
  • Distal row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate

🔎 Clinical Note: The scaphoid is particularly important in sports medicine, as fractures here often heal poorly and can result in non-union (“pseudarthrosis”).

Metacarpal Bones

There are 5 metacarpals, one for each finger.

Phalanges

  • Each finger (except the thumb) has three phalanges: proximal, middle, and distal.
  • The thumb has two phalanges: proximal and distal.

Joints of the Hand

The joints of the hand allow both gross and fine motor control. They include:

  1. Radiocarpal joint (wrist joint)
  2. Intercarpal joints
  3. Carpometacarpal joints (CMC)
  4. Carpometacarpal joint of the thumb (special saddle joint)
  5. Metacarpophalangeal joints (MCP)
  6. Interphalangeal joints (proximal & distal, PIP & DIP)

Radiocarpal (Wrist) Joint

  • Formed between the distal radius and the proximal row of carpals (scaphoid, lunate, triquetrum).
  • Stabilized by collateral and palmar ligaments.
  • Classified as a biaxial ellipsoid joint, permitting flexion, extension, abduction, and adduction.

Movements of the Wrist

  • Flexion (Palmar Flexion): 0° → 80–85°
    • Muscles: Flexor carpi radialis, Flexor carpi ulnaris, Palmaris longus.
    • Synergists: Finger flexors (flexor digitorum superficialis & profundus).
  • Extension (Dorsiflexion): 0° → 65–70°
    • Muscles: Extensor carpi radialis longus & brevis, Extensor carpi ulnaris.
  • Radial Deviation (Abduction): 0° → 30°
    • Muscles: Flexor carpi radialis, Extensor carpi radialis longus & brevis.
  • Ulnar Deviation (Adduction): 0° → 30–45°
    • Muscles: Flexor carpi ulnaris, Extensor carpi ulnaris.
  • Circumduction: A combination of all above movements.

Carpometacarpal (CMC) Joint of the Thumb

The thumb’s CMC joint is a saddle joint between the trapezium and the first metacarpal, giving the thumb its extraordinary mobility.

Movements:

  1. Flexion: 0° → 50° (Flexor pollicis longus & brevis)
  2. Extension: 0° → 50° (Extensor pollicis longus & brevis)
  3. Abduction: 0° → 70° (Abductor pollicis longus & brevis)
  4. Adduction: 70° → 0° (Adductor pollicis)
  5. Opposition: Combination movement (abduction → flexion → adduction), allowing the thumb to touch the fingertips (Opponens pollicis).
  6. Circumduction: Combination of all.

👉 Clinical Note: Opposition is the most important function of the thumb, enabling grasp and fine manipulation.

Metacarpophalangeal (MCP) Joints

  • Location: Between metacarpals and proximal phalanges.
  • Movements:
    • Flexion: 0° → 90–95° (lumbricals, interossei, flexor digitorum muscles).
    • Extension: 0° → 15° (extensor digitorum, extensor indicis, extensor digiti minimi).
    • Abduction: 0° → 20° (dorsal interossei, abductor digiti minimi).
    • Adduction: 20° → 0° (palmar interossei).

Interphalangeal (IP) Joints

  • Each finger has two interphalangeal joints: proximal (PIP) and distal (DIP).
  • The thumb has one interphalangeal joint.

Movements:

  • Flexion:
    • PIP: 0° → 100°
    • DIP: 0° → 90°
    • Muscles: Flexor digitorum superficialis (PIP), Flexor digitorum profundus (DIP).
  • Extension:
    • Muscles: Extensor digitorum, Extensor indicis, Extensor digiti minimi.

Functional Considerations

  • Finger flexors (flexor digitorum profundus & superficialis) are located in the forearm, reducing muscle bulk in the hand and allowing finer motion.
  • Finger extensors form a dorsal aponeurosis across the fingers, ensuring coordinated extension.
  • Intrinsic hand muscles (lumbricals, interossei, thenar, hypothenar) allow precision grip, ab/adduction, and fine control.
  • Tendon sheaths reduce friction and nourish tendons, critical for repetitive hand use in sports and fitness.

👉 For fitness professionals:

The hand’s mobility and strength are essential for grip performance in training (pull-ups, deadlifts, kettlebell work). Knowledge of wrist and finger biomechanics helps in:

  • Designing grip-strengthening programs.
  • Preventing overuse injuries (e.g., carpal tunnel, tendinitis).
  • Understanding functional limitations when thumb or finger motion is compromised.

 

6.13 The Vertebral Column (Spinal Column)

Structure of the Vertebral Column

The vertebral column is located at the midline of the posterior aspect of the body, extending from the base of the skull to the pelvis. Its primary functions are:

  1. To support the head.
  2. To connect the upper and lower limbs.
  3. To provide support for the trunk.
  4. To protect the spinal cord and the spinal nerve roots.

The column is made up of vertebrae, the sacrum, and the coccyx, and it is divided into four regions:

  • Cervical (7 vertebrae)
  • Thoracic (12 vertebrae)
  • Lumbar (5 vertebrae)
  • Sacrococcygeal (sacrum + coccyx)

It forms four sagittal curves: cervical (convex anteriorly), thoracic (convex posteriorly), lumbar (convex anteriorly), and sacrococcygeal (convex posteriorly).

Vertebrae

There are 24 individual vertebrae, arranged one on top of the other. Each vertebra has three main parts:

  1. Vertebral foramen (central opening through which the spinal cord passes).
  2. Vertebral body (anterior, weight-bearing structure).
  3. Vertebral arch (posterior, enclosing the foramen).

The vertebral arch bears seven processes:

  • 4 articular processes (two superior, two inferior) — for vertebra-to-vertebra joints.
  • 2 transverse processes — projecting laterally, for muscle attachment.
  • 1 spinous process — projecting posteriorly, also for muscle attachment.

Vertebral Joints

  • Anterior joints (symphyses): between vertebral bodies, joined by intervertebral discs.
  • Posterior joints (facet joints): between articular processes, stabilized by capsules and ligaments.

Intervertebral Discs

Intervertebral discs represent about ¼ of the total spinal column length. They function like shock absorbers, distributing loads during daily activities.

  • In youth, discs are 80–90% water.
  • Functions:
    1. Maintain vertebral spacing.
    2. Absorb compressive loads.
    3. Facilitate mobility.
    4. Provide stability.
    5. Increase mechanical strength.
  • Structure: Nucleus pulposus (gel-like core) + Annulus fibrosus (fibrous ring).

Spinal Ligaments

Ligaments maintain stability and limit excessive movement:

  • Anterior longitudinal ligament: prevents hyperextension.
  • Posterior longitudinal ligament: prevents hyperflexion.
  • Ligamentum flavum: elastic ligaments between arches, assist in upright posture.
  • Interspinous & supraspinous ligaments: prevent excessive flexion.
  • Intertransverse ligaments: limit lateral flexion.
  • Capsular ligaments: stabilize facet joints.

Movements of the Vertebral Column

  • Flexion: Trunk bends forward in the sagittal plane, flattening cervical and lumbar curves.
  • Extension & Hyperextension: Return from flexion or moving further backward.
  • Lateral Flexion: Side-bending in the frontal plane; limited in the thoracic region due to ribs, greater in cervical and lumbar regions.
  • Rotation: Axial turning in the transverse plane, usually combined with some flexion.

Cervical Region

  • 7 vertebrae. Small bodies, large triangular foramina. Transverse processes have foramina for the vertebral arteries.
  • Atlas (C1): supports the skull, articulates with occipital condyles.
  • Axis (C2): has odontoid process (dens) acting as pivot for rotation.
  • Mobility: Greatest of all spinal regions.
    • Flexion–extension: ~140°
    • Rotation: ~153°
    • Lateral flexion: ~91°

Muscles of the Cervical Spine

  • Anterior cervical muscles: stabilize the head.
  • Prevertebral muscles: flex head and neck.
  • Scalenes: elevate ribs (assist inspiration) and flex neck.
  • Sternocleidomastoid:
    • Bilateral contraction: flexes head.
    • Unilateral: side flexion + contralateral rotation.

Thoracic Region

  • 12 vertebrae. Larger bodies, smaller foramina, spinous processes angled downward.
  • Articulates with ribs.
  • Mobility limited by rib cage.
  • Movements: mainly flexion–extension and limited side-bending with rotation.

Lumbar Region

  • 5 vertebrae. Large bodies, triangular foramina, horizontal processes.
  • Mobility:
    • Flexion: ~60°
    • Extension: ~35°
    • Lateral flexion: ~28°
    • Rotation: minimal (~5–23°).

Muscles Acting on Thoracic & Lumbar Spine

Posterior (Back) Muscles

  • Erector spinae group (iliocostalis, longissimus, spinalis): extension and lateral flexion.
  • Transversospinalis group (semispinalis, multifidus, rotatores): rotation and stabilization.
  • Accessory muscles: interspinales, intertransversarii, suboccipital muscles.

Anterior (Abdominal) Muscles

  • Rectus abdominis: trunk flexion, pelvic tilt.
  • External oblique: side flexion (same side), rotation (opposite side).
  • Internal oblique: side flexion + rotation (same side).
  • Transversus abdominis: increases intra-abdominal pressure, spinal stability.
  • Quadratus lumborum: side flexion, stabilizes pelvis and thoracic cage.

Thorax

  • Formed by 12 pairs of ribs, sternum, and thoracic vertebrae.
    • True ribs (1–7): directly attached to sternum.
    • False ribs (8–10): indirectly attached via costal cartilage.
    • Floating ribs (11–12): no anterior attachment.
  • Sternum: manubrium, body, xiphoid process.

Movements of the Thorax in Breathing

  • Anterior–posterior expansion: Sternum and ribs move upward & forward (“pump handle”).
  • Transverse expansion: Ribs rotate outward (“bucket handle”).
  • Vertical expansion: Diaphragm contracts and flattens, increasing thoracic height.

Respiratory Muscles

Primary Muscles

  1. Diaphragm: main inspiratory muscle; flattens to enlarge thoracic cavity.
  2. Intercostals (external & internal): stabilize rib cage during breathing.

Accessory Muscles

  • Inspiration: sternocleidomastoid, scalenes, pectoralis major/minor, serratus anterior.
  • Expiration (forced): abdominal muscles (rectus, obliques, transversus), internal intercostals.

👉 For fitness professionals:
Understanding spinal and thoracic anatomy is essential for:

  • Teaching correct posture and spinal alignment in exercise.
  • Preventing low back pain and injuries through proper technique.
  • Coaching breathing mechanics (diaphragmatic breathing, bracing) in resistance and endurance training.

 

6.14 The Pelvis

Structure of the Pelvis

The pelvis (also called pelvic girdle) is formed by:

  • Two hip bones (os coxae) on the sides,
  • The sacrum and coccyx posteriorly.

It has the shape of an inverted cone, with its apex pointing downward.

The pelvis serves four major functions:

  1. Supports body weight through the vertebral column and transfers it to the hips.
  2. Transmits ground reaction forces from the lower limbs upward to the spine.
  3. Provides sites for muscle attachment.
  4. Protects internal organs housed within it.

Hip Bones (Innominate Bones)

Each hip bone develops from three parts in childhood:

  • Ilium (upper portion),
  • Ischium (posterior–inferior portion),
  • Pubis (anterior–inferior portion).

These three bones fuse during adolescence into one solid structure, the os coxae.

  • On the outer surface, they form the acetabulum, the deep cavity that articulates with the head of the femur (hip joint).
  • The anterior part forms the pubic symphysis, where both hip bones meet.
  • The iliac crests end in bony landmarks important for training: the anterior superior iliac spine (ASIS) and anterior inferior iliac spine (AIIS), which serve as attachment points for muscles and ligaments.
  • Posteriorly, the ischial spine and ischial tuberosity also provide strong anchoring sites for muscles. The ischial tuberosity is the “sitting bone.”

Sacrum and Coccyx

  • Sacrum: Formed by the fusion of five sacral vertebrae. It is wedged between the hip bones, creating the posterior part of the pelvic ring. Its superior surface articulates with the fifth lumbar vertebra.
  • Coccyx: A small triangular bone, the remnant of a “tail,” formed by the fusion of 3–5 vertebrae. It articulates with the sacrum.

Pelvic Divisions

  • Greater (false) pelvis: The broad, upper region, containing digestive organs.
  • Lesser (true) pelvis: The narrow, lower region, containing urinary and reproductive organs.

Male vs Female Pelvis

  • Male pelvis: taller, narrower, adapted for support and stability.
  • Female pelvis: wider, shallower, with greater transverse diameter, adapted for childbirth. This difference gives women a more characteristic gait due to wider hip spacing.

Pelvic Joints

1. Sacroiliac Joint

  • Between sacrum and ilium.
  • Surfaces are irregular, providing stability.
  • Function: transfer of weight from trunk to hips.
  • Highly stable, limited mobility.

2. Lumbosacral Joint

  • Between the 5th lumbar vertebra and the sacrum.
  • Same structure as lumbar joints.
  • Movements: flexion–extension and lateral flexion.
  • Has a thick intervertebral disc, allowing some mobility.

3. Pubic Symphysis

  • Cartilaginous joint between the two pubic bones.
  • Contains a fibrocartilaginous disc.
  • Normally very little movement, but becomes more mobile in women during childbirth.

Lumbosacral Angle

The lumbosacral angle is formed between the body of the first sacral vertebra and a horizontal reference line.

  • Increases with anterior pelvic tilt.
  • Decreases with posterior tilt.
  • Normal angle: ~30°.

Movements of the Pelvis

Pelvic movement occurs mainly through the hip joints and the lumbosacral joint, across all three planes.

  1. Anterior Tilt:
    • ASIS moves forward and downward relative to the pubic symphysis.
    • Lumbar spine extends, hips flex, lumbosacral angle increases.
    • Muscles: hip flexors + lumbar erector spinae.
  2. Posterior Tilt:
    • ASIS moves backward and upward relative to the pubic symphysis.
    • Lumbar spine flexes, hips extend, lumbosacral angle decreases.
    • Muscles: abdominals + gluteus maximus + hamstrings.
  3. Lateral Tilt:
    • One side of the pelvis rises while the other lowers.
    • Occurs during gait as weight shifts from one leg to the other.
    • Controlled by opposite side trunk muscles (quadratus lumborum, erector spinae) and hip abductors.
  4. Rotation:
    • One side of the pelvis moves forward or backward relative to the other.
    • Happens during walking or running.
    • Coupled with hip rotation: forward pelvic rotation = internal rotation of stance hip; backward rotation = external rotation.

Muscles Controlling Pelvic Movements

Pelvic motion always involves muscle pairs acting together:

  • Anterior tilt: hip flexors (iliopsoas, rectus femoris) + lumbar extensors (erector spinae).
  • Posterior tilt: abdominals (rectus abdominis, obliques) + hip extensors (gluteus maximus, hamstrings).
  • Lateral tilt: controlled by trunk lateral flexors on one side and hip abductors on the other (e.g., quadratus lumborum + gluteus medius).
  • Rotation: produced by coordinated action of trunk rotators and hip rotators.

👉 For fitness professionals:
Pelvic alignment is central to posture, gait, and performance.

  • Anterior tilt often accompanies excessive lumbar lordosis and must be corrected with abdominal strengthening and hamstring/gluteal work.
  • Posterior tilt can reduce lumbar curvature and affect movement efficiency.
  • Awareness of pelvic mechanics is essential when coaching squats, lunges, deadlifts, and gait retraining.

 

6.15 The Hip Joint

Structure and Function

The hip joint is a critical load-bearing joint responsible for body weight transfer and locomotion. Like the shoulder, it is a ball-and-socket joint and allows movement in multiple planes. However, unlike the shoulder, the hip is more stable because the acetabulum and femoral head fit snugly together. This stability comes at the cost of having a smaller range of motion compared to the shoulder.

The hip is a triaxial joint, allowing movement in all three planes:

  • Sagittal (flexion/extension),
  • Frontal (abduction/adduction),
  • Transverse (internal/external rotation).

Bones of the Hip

Femur

  • Head: Spherical articular surface that fits into the acetabulum.
  • Neck: Connects the head to the shaft; angled differently in men (wider) and women (narrower).
  • Greater and Lesser Trochanters: Bony prominences for muscle attachment.
  • Distal End: Forms the knee joint with medial and lateral condyles.

Acetabulum

  • Deep cup-shaped cavity in the hip bone (ilium, ischium, pubis).
  • Receives the femoral head and provides stability.

Ligaments of the Hip

The hip capsule is reinforced by strong ligaments that provide both stability and mobility:

  1. Capsular Ligament: Encloses the entire joint from the acetabular rim to the femoral neck.
  2. Iliofemoral Ligament: From the anterior inferior iliac spine to the intertrochanteric line; limits hyperextension, one of the strongest ligaments in the body.
  3. Pubofemoral Ligament: From the pubis to the lesser trochanter; limits excessive abduction and extension.
  4. Ischiofemoral Ligament: From posterior acetabulum to femoral neck; stabilizes posteriorly and limits internal rotation.
  5. Ligamentum Teres (Round Ligament): Inside the joint capsule, from acetabular notch to femoral head; provides vascular supply and minor stability.

Movements of the Hip Joint

1. Flexion

  • Movement: Lifting the thigh forward.
  • Range: 120° with knee flexed, 90° with knee extended (limited by hamstring tension).
  • Prime Movers: Iliopsoas, Rectus Femoris.
  • Assistants: Sartorius.

Key Flexor Muscles:

  • Iliopsoas: Originates from lumbar vertebrae and iliac fossa, inserts at lesser trochanter. Action: powerful hip flexor, also tilts pelvis anteriorly.
  • Rectus Femoris: Part of quadriceps; flexes hip and extends knee.
  • Sartorius: Longest muscle in the body; assists in hip flexion, abduction, external rotation, and knee flexion.

2. Extension & Hyperextension

  • Movement: Thigh moves backward.
  • Range: ~15° of hyperextension.
  • Prime Movers: Gluteus Maximus, Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus).

Key Extensor Muscles:

  • Gluteus Maximus: Primary hip extensor and external rotator.
  • Hamstrings: Assist in hip extension and knee flexion.

3. Abduction

  • Movement: Thigh moves away from the midline.
  • Range: ~45°.
  • Prime Movers: Gluteus Medius, Gluteus Minimus.
  • Assistant: Tensor Fasciae Latae (TFL).

4. Adduction

  • Movement: Thigh moves back toward or across midline.
  • Range: ~45°; can move further when combined with flexion/extension.
  • Prime Movers: Adductor group (Adductor Longus, Brevis, Magnus, Gracilis, Pectineus).

5. External (Lateral) Rotation

  • Movement: Thigh rotates outward.
  • Range: ~45°.
  • Prime Movers: Piriformis, Obturators, Gemelli, Quadratus Femoris.

6. Internal (Medial) Rotation

  • Movement: Thigh rotates inward.
  • Range: ~45°.
  • Prime Movers: Gluteus Medius (anterior fibers), Gluteus Minimus.

Key Fitness Application

  • Hip stability is vital for standing, walking, running, and lifting.
  • Weak abductors (e.g., gluteus medius) often cause poor pelvic alignment, affecting gait and squats.
  • Tight hip flexors (iliopsoas, rectus femoris) contribute to anterior pelvic tilt and lumbar lordosis.
  • Balanced hip mobility and strength reduce injury risk and improve athletic performance.

 

6.16 The Knee Joint

Overview

The knee joint is the largest joint in the human body and is often described as a “kinesiological masterpiece.” It is designed to withstand very high loads while maintaining both stability and mobility. Structurally, it can be compared to the elbow, but it is more complex, as it must support body weight during standing, walking, running, and jumping.

The knee achieves absolute stability throughout its range of motion due to its strong bones, powerful ligaments, and the support of the quadriceps and hamstrings, two of the strongest muscle groups in the body.

Bones of the Knee Joint

  1. Distal Femur (Lower End of the Thigh Bone):
    • Contains the medial and lateral condyles, which articulate with the tibial condyles.
    • Between them lies the intercondylar notch, where the cruciate ligaments attach.
    • Anteriorly, the femoral trochlea forms a groove for the patella to glide during knee flexion.
  2. Proximal Tibia (Upper End of the Shin Bone):
    • Contains the medial and lateral condyles, covered with cartilage for articulation.
    • The intercondylar eminence lies between them, serving as an attachment site for the cruciate ligaments.
    • The tibial tuberosity (anteriorly) is the insertion point of the patellar tendon.
  3. Patella (Kneecap):
    • A triangular sesamoid bone embedded in the quadriceps tendon.
    • Its posterior surface glides within the femoral trochlea, improving the mechanical leverage of the quadriceps during extension.

Components of the Knee Joint

The knee is a compound joint, made up of:

  1. Tibiofemoral Joint:
    • Articulation between femoral and tibial condyles.
    • Includes the menisci, fibrocartilaginous discs that improve joint congruence.
  2. Patellofemoral Joint:
    • Articulation between the patella and the femoral trochlea.
    • Ensures smooth gliding of the patella and enhances quadriceps function.

Ligaments of the Knee

The knee’s stability relies heavily on its ligaments:

  • Medial Collateral Ligament (MCL): From medial femoral condyle to medial tibia; resists valgus stress.
  • Lateral Collateral Ligament (LCL): From lateral femoral condyle to fibular head; resists varus stress.
  • Anterior Cruciate Ligament (ACL): From lateral femoral condyle to anterior tibia; prevents anterior translation of tibia.
  • Posterior Cruciate Ligament (PCL): From medial femoral condyle to posterior tibia; prevents posterior translation of tibia.
  • Patellar Ligament (Tendon): Continuation of quadriceps tendon, inserting into tibial tuberosity; critical for knee extension.

Menisci

The medial and lateral menisci are crescent-shaped fibrocartilaginous discs.

  • Increase the contact area between femur and tibia.
  • Absorb shock and distribute load across the joint.
  • Enhance joint stability during dynamic movements.

Stability of the Knee

  1. Anterior–Posterior Stability:
    • Controlled mainly by ACL (anterior) and PCL (posterior).
    • Supported by patellar ligament and quadriceps contraction.
  2. Lateral Stability:
    • Controlled by MCL and LCL.
    • Supported by muscles attaching medially and laterally around the knee.
  3. Rotational Stability:
    • In full extension, the knee is “locked” and resists rotation.
    • In flexion, passive internal and external rotation is possible.
  4. Resistance to Hyperextension:
    • Prevented primarily by the ACL and posterior capsule.

Movements of the Knee

  • Flexion:
    • Range: 0°–140° (up to 150° if hip is flexed).
    • Prime Movers: Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus).
    • Functional Example: Squatting, cycling, sprinting.
  • Extension:
    • Range: 140°–0° (sometimes slight hyperextension, up to 15°).
    • Prime Mover: Quadriceps (Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius).
    • Functional Example: Kicking a ball, jumping, standing up from a squat.
  • Passive Rotation (when knee is flexed):
    • Internal rotation: ~30°.
    • External rotation: ~40°.
    • “Locking mechanism” occurs in the last 15° of extension, when the tibia externally rotates slightly to stabilize the joint.

Patellofemoral Joint and the Role of the Patella

  • Acts as a pulley, increasing the mechanical efficiency of the quadriceps by lengthening its lever arm.
  • Distributes forces across the femoral condyles, reducing wear on cartilage.
  • Stability maintained by retinacular ligaments, quadriceps muscle balance (especially Vastus Medialis vs Vastus Lateralis).

Fitness and Clinical Relevance

  • Strong quadriceps and hamstrings are critical to prevent knee injuries.
  • Weakness or imbalance (e.g., weak Vastus Medialis vs dominant Vastus Lateralis) can lead to patellar maltracking.
  • Injury-prone structures: ACL (common in pivoting sports), menisci (common in twisting under load).
  • Functional training tip: Knee stability depends not only on local strength but also on hip and ankle control.

 

6.17 The Ankle and Foot

Overview

The ankle and foot are responsible for supporting body weight and ensuring both mobility and stability during standing, walking, running, and jumping. Because they bear significant loads throughout daily activities, their structure is highly specialized to absorb impact, transfer forces, and adapt to different surfaces.

The leg connects to the foot via two long bones: the tibia (shinbone) and the fibula.

Bones of the Foot

The foot is divided into three regions:

  1. Tarsus (Hindfoot and Midfoot):
    • Composed of 7 irregular bones arranged in three rows.
    • Posterior row: Talus (ankle bone) above, Calcaneus (heel bone) below.
    • Middle row: Navicular bone.
    • Anterior row: Medial, Intermediate, and Lateral Cuneiforms + Cuboid.
    • Talus: Articulates with tibia (above), fibula (laterally), calcaneus (below), and navicular (anteriorly).
    • Calcaneus: Largest bone of the foot; posterior surface attaches the Achilles tendon.
    • Navicular: Connects talus with the cuneiforms.
  2. Metatarsus (Forefoot):
    • Five long bones (Metatarsals I–V).
    • Medially, articulate with the cuneiforms; laterally, with the cuboid.
  3. Phalanges (Toes):
    • The big toe (hallux) has 2 phalanges; other toes have 3 each (proximal, middle, distal).

Joints of the Foot

  1. Ankle Joint (Talocrural Joint):
    • A uniaxial hinge joint formed by the talus, tibia, and fibula.
    • Supported by a fibrous capsule and collateral ligaments:
      • Medial (Deltoid) ligament
      • Lateral collateral ligaments
    • Movements: Plantarflexion (30°–50°) and Dorsiflexion (20°).
  2. Subtalar (Talocalcaneal) Joint:
    • Between talus and calcaneus.
    • Allows gliding and contributes to inversion/eversion.
  3. Transverse Tarsal Joint (Talonavicular + Calcaneocuboid):
    • Works with subtalar joint for complex movements.
  4. Metatarsophalangeal Joints:
    • Between metatarsals and proximal phalanges.
    • Movements: flexion, extension, hyperextension, abduction, adduction.
  5. Interphalangeal Joints:
    • Between phalanges.
    • Movements: flexion, extension, hyperextension (big toe).

Movements of the Ankle and Foot

Plantarflexion

  • Movement of the foot downward (toward the sole).
  • Prime Movers: Gastrocnemius, Soleus, Plantaris.

Muscles:

  • Gastrocnemius: From posterior femur → Achilles tendon → calcaneus.
  • Soleus: From posterior tibia/fibula → Achilles tendon → calcaneus.
  • Plantaris: From posterior femur → Achilles tendon → calcaneus.

Dorsiflexion

  • Movement of the foot upward (toward the shin).
  • Prime Mover: Tibialis Anterior.

Muscle:

  • Tibialis Anterior: From lateral tibia → medial cuneiform + 1st metatarsal.
  • Also assists inversion.

Inversion (Medial Lift / Supination)

  • Inner border of foot lifts.
  • Prime Movers: Tibialis Posterior (plantarflexion + inversion), Tibialis Anterior (dorsiflexion + inversion).
  • Helps maintain the medial longitudinal arch.

Eversion (Lateral Lift / Pronation)

  • Outer border of foot lifts.
  • Prime Movers: Peroneals (Fibularis Longus, Brevis, Tertius).
  • Work together to stabilize lateral ankle.

Toe Movements

  • Flexion: Flexor Digitorum Longus, Flexor Hallucis Longus.
  • Extension: Extensor Digitorum Longus, Extensor Hallucis Longus.
  • Intrinsic Foot Muscles: Small muscles of sole and dorsum (lumbricals, interossei, flexors, abductors, adductors) stabilize the arches and assist fine motor control.

Arches of the Foot

  1. Medial Longitudinal Arch
  2. Lateral Longitudinal Arch
  3. Transverse Arch

Function:

  • Absorb shock, distribute weight, and provide elastic spring during gait.
  • Maintained by bone shape, ligaments, plantar fascia, and intrinsic/extrinsic muscles.

Fitness and Clinical Relevance

  • Proper foot mechanics are essential for balance, posture, and injury prevention.
  • Weak arches (flat feet) or excessive arches can affect gait and cause knee/hip strain.
  • Achilles tendon injuries and ankle sprains are common in sports — strengthening the calves, tibialis anterior, and peroneals is key.
  • Barefoot or unstable-surface training (e.g., balance boards) can activate intrinsic muscles of the foot, improving overall stability.

 

6.18 Gait

Definition

Gait refers to the process of moving the body from one location to another through a coordinated sequence of steps. A step is the movement that occurs when one foot contacts the ground until the same foot contacts the ground again in the same way.

Every person’s gait is unique. It can vary depending on body type, health, psychological state, personality, and activity. For example:

  • A person with poor health may walk without coordination.
  • A confident person may walk with stability.
  • Emotional state can influence posture and pace.

Walking requires continuous balance and coordination between the central nervous system, muscles, and joints.

Phases of the Gait Cycle

Each gait cycle is divided into two main phases:

  1. Stance Phase (≈60% of cycle):
    Begins with heel strike and ends when the toes leave the ground. It involves supporting the body’s weight while the foot is in contact with the ground.
  2. Swing Phase (≈40% of cycle):
    Begins when the foot leaves the ground and ends with the next heel strike of the same foot.

During walking, there are two brief periods of double support, when both feet are in contact with the ground. This occurs twice in every cycle, each lasting about 10% of the gait cycle at normal walking speed.
In running, double support disappears — there is instead a flight phase.

Subdivisions of the Stance Phase

  1. Heel Strike (Initial Contact): The heel touches the ground.
  2. Foot Flat (Loading Response): The entire foot comes in contact with the ground, weight begins to transfer.
  3. Mid-Stance: Body weight is directly over the supporting foot; the opposite foot lifts off.
  4. Heel Off: The heel rises, shifting weight to the forefoot.
  5. Toe Off (Pre-Swing): Only the toes remain in contact with the ground before lifting.

Subdivisions of the Swing Phase

  1. Acceleration (Initial Swing): The toes leave the ground and the foot swings forward.
  2. Mid-Swing: The swinging foot passes under the body.
  3. Deceleration (Terminal Swing): The leg extends forward, preparing for the next heel strike.

Joint Movements During Gait

  1. Heel Strike:
    • Hip: ~25–30° flexion
    • Knee: ~5° flexion
    • Ankle: Neutral
  2. Foot Flat:
    • Hip: ~25–30° flexion
    • Knee: Flexion increases
    • Ankle: Moves into plantarflexion
  3. Mid-Stance:
    • Hip: Extension begins
    • Knee: Extension
    • Ankle: Dorsiflexion begins
  4. Heel Off:
    • Hip: Extension continues
    • Knee: Slight flexion
    • Ankle: Plantarflexion begins
  5. Toe Off:
    • Hip: Flexion begins
    • Knee: Flexion increases
    • Ankle: Plantarflexion
  6. Acceleration (Swing Start):
    • Hip: Flexion
    • Knee: Flexion
    • Ankle: Dorsiflexion
  7. Mid-Swing:
    • Hip: Flexion maintained
    • Knee: Extension begins
    • Ankle: Dorsiflexion
  8. Deceleration (Swing End):
    • Hip: Flexion → extension preparing for contact
    • Knee: Extension then slight flexion
    • Ankle: Dorsiflexion

Muscular Activity in Gait

  • Hip flexors (Iliopsoas, Rectus Femoris, Sartorius, Tensor Fasciae Latae) → active during swing to advance the leg.
  • Hip extensors (Gluteus Maximus, Hamstrings) → control forward motion at heel strike, extend hip during stance.
  • Knee extensors (Quadriceps) → stabilize the knee during stance and extend it at terminal swing.
  • Knee flexors (Hamstrings) → flex the knee during swing and decelerate the leg at terminal swing.
  • Plantarflexors (Gastrocnemius, Soleus, Tibialis Posterior, Peroneals) → provide push-off at toe-off.
  • Dorsiflexors (Tibialis Anterior, Extensor Digitorum Longus, Extensor Hallucis Longus) → lift the foot during swing, prevent toe drag.

Muscles work concentrically (to accelerate movement), eccentrically (to control and decelerate movement), or isometrically (to stabilize joints and maintain posture).

 

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