Anatomical Planes & Axes of Motion Explained

Apply kinetic analysis to gait by answering two questions: identify the joint movement during each phase and determine its relationship to gravity. Example 1: Ankle plantar flexion during heel strike to foot flat occurs toward gravity, requiring eccentric dorsiflexor contraction. Example 2: Knee extension during foot flat to mid stance occurs against gravity, requiring concentric quadriceps contraction. This method simplifies understanding gait biomechanics by applying consistent principles across all phases.

The gait cycle is a repetitive, cyclic pattern of walking that begins and ends with ground contact by the same foot (specifically the heel), consisting of two main phases: the support phase (approximately 60% of the cycle) when the foot is in contact with the ground, and the balance/swing phase (approximately 40% of the cycle) when the foot is off the ground; this cycle includes two key spatial parameters—the stride (distance between consecutive contacts of the same foot) and the step (distance between consecutive contacts of opposite feet)—and can be further divided into sub-phases such as initial contact, loading response, mid-stance, terminal stance, pre-swing, initial swing, mid-swing, and terminal swing, with the limbs operating in an antiphase relationship where one limb is always in support while the other is in swing.

Biomechanics applies to sports injury analysis through kinematic questions (velocity at impact, landing pattern) and kinetic questions (force absorption, stress-strain relationships). Beyond sports, biomechanics analyzes normal gait cycles, examining stride characteristics from kinematic (length) and kinetic (force production) perspectives. The field integrates with exercise physiology (muscle contraction causing force), motor control (nervous system coordination), and open/closed loop skill concepts. Open loop skills occur faster than feedback can correct them (clean and jerk within seconds), while closed loop skills allow real-time correction using proprioceptive feedback (runners adjusting stride mid-race).

The squat is a fundamental exercise that primarily trains the quadriceps, gluteus maximus, and adductor magnus, with the rectus femoris being the only quadriceps muscle capable of both knee extension and hip flexion; the gluteus maximus and adductor magnus are most effective for hip extension when the stance is wide and the squat is performed deeply, while the Valsalva maneuver (contracting the diaphragm and pelvic floor) creates intra-abdominal pressure to stabilize the spine during heavy lifts.

This extensive section details the complete gait cycle mechanics and lower extremity muscle function. Hip extensors (gluteus maximus, hamstrings) require relative hip flexion to function effectively—hip extension cannot occur from an already extended position. Primary hip external rotators include gluteus maximus, piriformis, posterior gluteus medius, lateral biceps femoris, and hamstrings. Internal rotators include inner hamstrings, anterior gluteus medius, tensor fasciae latae, and adductors. The gait cycle follows a fundamental rotation pattern: external rotation → internal rotation → external rotation. Heel strike is predominantly eccentric, requiring the body to slow itself down while transitioning toward internal rotation. Mid-stance features internal rotation of pelvis, femur, and tibia with foot pronation, requiring concentric activation of hamstrings, anterior gluteus medius, and tensor fasciae latae. Late stance returns to external rotation with concentric gluteus maximus and calf activation, eccentric hamstring slowing, and stretched psoas. The hip flexion arc shows external rotation (0-60°) transitioning to internal rotation (60-110°). A 'butt wink' in deep squats indicates inability to achieve internal rotation, forcing compensation through anterior pelvic tilt.

Goniometry is a fundamental clinical measurement technique used in physical therapy to assess joint range of motion, requiring understanding of active versus passive motion, joint end feel (soft, hard, or firm), and proper identification of bony landmarks; accurate measurement depends on proper patient positioning, proximal segment stabilization, and awareness of patient compensations, with research indicating inherent measurement errors of 4-5 degrees that make small changes potentially insignificant.

Goniometry is a clinical technique for objectively measuring joint range of motion, involving assessment of both osteokinematic (bone shaft movements) and arthrokinematic (joint surface movements including roll, spin, and slide) components; assessments can be active (revealing patient willingness, coordination, and muscle strength) or passive (revealing joint capsule, ligament, and tissue integrity), with end feel classification (hard, soft, firm, or empty) providing diagnostic information about limiting structures and pathology severity.

This comprehensive introduction covers goniometry fundamentals for PTA students. Three types of range of motion exist: Active Range of Motion (AROM) is patient-initiated movement; Active Assisted Range of Motion (AAROM) involves external assistance like walls; Passive Range of Motion (PROM) requires patient relaxation with external force. End feel reflects tissues limiting joint motion and can be physiological or pathological. Contraindications include absolute contraindications (movement disrupting healing, joint subluxation/dislocation/fracture, myositis ossificans, post-fusion) and precautions (severe pain, acute inflammation, osteoporosis, hypermobile joints, acute soft tissue injuries, prolonged immobilization). The universal goniometer is the primary tool, with small versions for small body parts and larger versions for large body parts. Tape measures are preferred for trunk motions for greater accuracy.

Seven points ensure accurate ROM measurement: joint relaxed, proper starting position, stable proximal segment, fixed moving arm with distal segment, stable arm with proximal segment, neutral joint position, and comfortable patient position. Contraindications include joint dislocation, fracture, and soft tissue surgery. Precautions cover acute inflammation, osteoporosis, hemophilia, and hematoma. Eight factors affect ROM: soft tissue tightness, scar formation, muscle bulk, gender, age (children > adults), UMN lesions (decreased ROM from spasticity), LMN lesions (increased ROM from flaccidity), and joint pathology.

This video demonstrates proper goniometric measurement techniques for assessing upper extremity joint range of motion, including shoulder movements (flexion 0-170°, extension 0-60°, abduction 0-70°, horizontal abduction 0-40°, horizontal adduction 0-130°, internal rotation 0-60°/70°, external rotation 0-80°/90°), elbow flexion (0-135-150°), and forearm rotation (supination 0-80-90°, pronation 0-80-90°), with specific instructions on patient positioning, goniometer axis placement, and alignment of stationary and movable bars relative to anatomical landmarks and planes of movement.

Injuries are categorized into two types: pathomechanical (caused by inefficient movement patterns building up over time) and pathological (caused by acute trauma). Pathomechanical injuries result from microtraumas accumulating due to poor movement mechanics, eventually causing macrotrauma. Examples include Achilles tendon ruptures from years of improper landing mechanics or ACL injuries from repeated poor cutting movements. Pathological injuries result from acute trauma like collisions or falls. Understanding this distinction is crucial for rehabilitation - pathomechanical injuries require addressing underlying movement patterns, while pathological injuries focus on healing the acute damage. Most chronic back and joint problems fall into the pathomechanical category.

Pathomechanics refers to the changes in normal movement and function of body parts resulting from injury or disease, derived from Greek words meaning 'suffering' and 'movement'; it affects bones, muscles, joints, tendons, ligaments, and cartilage, and can be caused by trauma, disease, or aging, with examples including flat feet, scoliosis, and rotator cuff tears, diagnosed through physical examination and imaging tests, and treated through methods such as rest, ice, heat, medication, braces, exercises, or surgery.

The ankle complex contains three muscle compartments: the lateral compartment (peroneus longus and brevis) serves as weak plantar flexors and strong inverters/evertors, with peroneus longus uniquely plantar flexing the first metatarsal and facilitating weight transfer from lateral to medial foot during gait; the anterior compartment (tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius) acts as primary dorsiflexors, where tibialis anterior additionally functions as a supinator while the others serve as pronators, with muscle weakness causing specific deformities like foot drop, calbatoe, and claw toe.

Pathomechanics explains how injuries occur through the principle that the chain is only as strong as its weakest link. Injuries in the back, shoulders, and knees often result from insufficient movement, improper movement patterns, or inadequate training. Repetitive postures and movements, such as sitting for extended periods, can lead to pain and functional limitations. Movement variability and proper loading are essential for preventing these issues. Quality of movement is crucial—how one moves is as important as building up movement progressively.

This segment covers anatomical planes, axes, and musculoskeletal anatomy. The three body planes are: Sagittal (divides left/right), Frontal/Coronal (divides front/back), and Transverse/Horizontal (divides upper/lower). Each plane has a corresponding perpendicular axis. For movement analysis, viewing from the side reveals sagittal plane movements and frontal axis, while viewing from the front reveals frontal plane movements and sagittal axis. Lean body mass includes muscles, bones, and non-fat tissues, excluding body fat. Tennis elbow (lateral epicondylitis) is an overuse injury affecting the elbow, common in tennis, golf, and badminton players, involving inflammation of tendons attaching to the lateral epicondyle of the humerus.