Lecture Notes: Biomechanics, ICF Framework, and Musculoskeletal Concepts
Resting length, excursion, and muscle elasticity
Resting length is the length of a muscle at rest. The lecture notes that a muscle can contract down to about half of its resting length and can stretch to about one and a half times its resting length. When tension is released, the muscle returns to its resting length due to elasticity, similar to a rubber band. The total range a muscle can move from its shortest to its longest length is called the excursion.
Active and passive insufficiency
A muscle that shortens to reduce ROM on a joint crossing two joints is exhibiting active insufficiency. Conversely, a muscle that cannot lengthen enough to allow full ROM at both joints it crosses is showing passive insufficiency. Passive insufficiency is discussed in the context of stretching and is especially relevant for muscles that cross two joints.
Kinematics: osteokinematic vs arthrokinematic movement
Kinematics concerns motion, and is divided into osteokinematic and arthrokinematic movement. Osteokinematic motion refers to the big-bone movements in space (flexion, extension, abduction/adduction, internal/external rotation) that occur in a specific plane around a defined axis. Arthrokinematic motion is the movement that occurs at the joint surfaces and includes roll, glide (translated as slide), and spin.
Joint positions: closed pack vs open pack
A closed-pack position yields maximum congruency between joint surfaces, providing the greatest stability and the least joint play. In contrast, an open-pack (loose-packed) position is the position of least stability, where the joint surfaces are most incongruent and there is more joint play — this is the position often sought during joint mobilization.
Mobility terminology: hypo- and hypermobility, and contracture
Hypomobility means less than normal ROM in a joint, while hypermobility means more than normal ROM. The term contracture refers to adaptively shortened muscles or connective tissue, leading to restricted movement. Contractures may fix a limb in a particular position and become resistant to stretching as they progress. Early ROM and mobility are important to prevent irreversible contracture; fixed contractures may require surgical release.
ICF framework: disease, impairment, disability, and handicap
The ICF framework links a disease (pathology) to functional outcomes. A disease or pathology (e.g., cancer, scoliosis, broken bone) may cause an impairment, defined as a loss or abnormality of structure or function (for example, decreased ROM or strength). Impairments can lead to disability, which is a restriction or lack of ability to perform activities in a normal manner (e.g., rising from a chair, walking, going upstairs). Depending on environmental and personal factors, disability can also lead to a handicap, which is the inability to perform a role in society (e.g., inability to work or shop). The model emphasizes individual variation and external factors that influence outcomes. A stroke is the disease; the resulting impairments might include decreased ROM and strength, which can lead to disability and potentially handicap depending on circumstances. The lecture also notes the relevance of cultural values, beliefs, and external supports in determining outcomes.
Chapter 1 review context: ethics, education, and practice
Session references include the APTA vision for research and evidence-based practice and the role of the ICF in PT education (entry-level PTA). The discussion touches on ethical principles, state licensure laws, departmental procedures, and the reality that patient care varies by state and setting.
Review questions and key practice concepts
Joint mobilization: Whether a PTA can perform depends on state licensure laws, which vary by state.
The Guide to Physical Therapist Practice (often referred to as the PT Bible) aims to provide a uniform description of PT practice, though its usage has decreased in some contexts.
CAPTI (Commission on Accreditation in Physical Therapy Education) is involved in accreditation of PT and PTA programs; CAPTE oversees accreditation status, and the Federation of State Boards of Physical Therapy (FSBPT) relates to the national licensure exam.
State licensing boards govern licensure.
An impairment is a loss or abnormality of an anatomical, physiological, or psychological structure or function.
The Plan of Care (POC) is based on examination, evaluation, diagnosis, and prognosis; it includes specific interventions, frequency, duration, goals, and discharge plans.
A PTA may modify interventions only within the established plan of care and in response to changes in patient status; broader changes typically require PT involvement. You may consult with a physician when appropriate.
If a patient asks about lab results (e.g., cancer findings), the PTA should inform the patient that results exist and involve the appropriate team members; a PTA should not interpret or misrepresent lab results.
Connective tissue and basic anatomy
Fibroblasts synthesize collagen, elastin, and reticulin; connective tissue is composed of these fibers. The most common fiber is collagen.
The tendon-muscle junction is the myotendinous junction, where tendon fibers integrate with muscle.
The ends of muscles attach to bones via tendons; tendons connect muscle to bone.
Ligaments connect bone to bone and serve to stabilize joints and prevent excessive motion.
Bone and skeletal anatomy terminology
Epiphysis: the ends of long bones; the growth occurs at the epiphyseal plate (growth plate). The region between the epiphysis and diaphysis includes the metaphysis. In adults, the plate is typically ossified and appears as the epiphyseal line.
Diaphysis: the shaft of a long bone.
Mature bone cells are osteocytes.
Axial skeleton includes the skull, ribs, and vertebrae. The appendicular skeleton includes the bones of the upper and lower extremities.
Cartilage types and joints
Hyaline cartilage covers the ends of long bones in synovial joints and provides a smooth surface for articulation.
Fibrocartilage provides shock absorption and helps deepen a socket (e.g., labrum, intervertebral discs, menisci).
Elastic cartilage is found in the ears and nose (and the larynx); it is more flexible.
There are several types of synovial joints (diarthrodial joints) with different shapes, including ball-and-socket, pivot, and hinge joints. These joints allow varying ROM depending on shape and constraints.
Synovial joints involve synovial fluid; this fluid reduces friction between articulating surfaces.
Bursa are small synovial membrane-lined sacs that reduce friction, usually named based on their location (e.g., prepatellar bursa).
Fascia is connective tissue surrounding muscles; it is typically not dense regular as some sources state; fascia is better characterized as dense irregular connective tissue in many regions.
The living skeleton supports tissues, facilitates movement, stores minerals, and provides a framework for the body; it does not determine an individual’s somatotype.
The vascular supply is a key factor in healing; fibrocartilage has limited vascular supply, which slows healing (e.g., the menisci often require removal rather than repair due to limited blood flow).
Muscle tissue and contraction basics
Three types of muscle tissue: skeletal, cardiac, and smooth. This course primarily addresses skeletal muscle.
The endomysium surrounds individual muscle fibers; it is part of the connective tissue layers within muscle.
The smallest organized unit of the contractile mechanism in skeletal muscle is the sarcomere, which is delimited by Z-lines.
Muscle mechanism is commonly described by slow-twitch (Type I) and fast-twitch (Type II) fibers; Type I is slow-twitch, oxidative, and fatigue-resistant; Type II is fast-twitch, more suited to power and rapid force production.
In a typical muscle: the proximal attachment is the origin, the distal attachment is the insertion. The muscle most directly responsible for movement in a given direction is called the agonist; the antagonist performs the opposite action; synergists assist the agonist; neutralizers cancel out specific actions of another muscle; stabilizers fixate a joint to enable efficient movement.
A straight-leg raise example illustrates concentric contraction of hip flexors as the leg rises, followed by eccentric contraction as the leg lowers (the hip flexors lengthen while generating less force). The knee extensors (quadriceps) stabilize the knee to keep it extended during this movement (isometric contraction).
For two-joint muscles, active and passive insufficiency can limit simultaneous cross-joint movements, as previously described.
Levers, balance, and locomotion
The body uses lever systems: first class lever (effort-fulcrum-load in a line), second class lever (fulcrum-load-effort; MA > 1; built for power), and third class lever (fulcrum-effort-load; MA < 1; built for range of motion).
In the human body, the third-class lever is the most common configuration.
Mechanical advantage is achieved when the force arm is longer than the resistance arm (MA > 1); balance occurs when MA ≈ 1 (first-class example).
Balance requires keeping the center of gravity within the base of support. To improve balance, you can lower the center of gravity and widen the base of support. To challenge balance, raise the center of gravity.
Practical considerations: healing, blood supply, and clinical notes
Vascular supply is crucial for healing; tissues with poor vascular supply (e.g., fibrocartilage) heal more slowly, which is why certain structures (like parts of the meniscus) are difficult to repair and are often removed surgically.
The thyroid cartilage, like other avascular or poorly vascularized tissues, has limited healing potential.
Important reminders for exam preparation
Revisit chapter material, compare notes to textbook content, and ensure chapter comprehension and correct capitalization and terminology.
Be prepared to discuss the differences between planes and axes, and how they relate to osteokinematic vs arthrokinematic motions, as well as the implications for joint mobilization and therapy.
Review the terminology around tissue types (bone, cartilage, connective tissue), joint types, and the functional roles of ligaments, tendons, fascia, and bursae.
Quick reference: key terms and concepts summarized
excursion, resting length, elasticity, contracture, active insufficiency, passive insufficiency
osteokinematic motion, arthrokinematic motion, roll, glide, spin
closed pack position, open pack position
hypomobility, hypermobility, plan of care (POC)
ICF: disease, impairment, disability, handicap
origin, insertion, agonist, antagonist, synergist, neutralizer, stabilizer
concentric, eccentric contractions; isometric contraction
first/second/third class levers; mechanical advantage; base of support; center of gravity
axial vs appendicular skeleton; epiphysis, epiphyseal plate, metaphysis, diaphysis
hyaline cartilage, fibrocartilage, elastic cartilage; synovial (diarthrodial) joints; bursa; fascia
endomysium, sarcomere, Z-lines; slow-twitch (Type I) vs fast-twitch (Type II)
myotendinous junction; tendon function; ligament function; bone vascularity and healing
practical clinical care considerations, including the role of licensure and accreditation bodies (state licensure laws, CAPTE, CAPTI, FSBPT)