Glossary

Absolute angle Angular orientation of a body segment with respect to a fixed line of reference

Acromioclavicular joint Irregular joint between the acromion process of the scapula and the distal clavicle

Active insufficiency Limited ability of a two-joint muscle to produce force when joint position places the muscle on slack

Active stretching Stretching of muscles, tendons, and ligaments produced by active development of tension in the antagonist muscles

Acute loading Application of a single force of sufficient magnitude to cause injury to a biological tissue

Agonist Role played by a muscle acting to cause a movement

Amenorrhea Cessation of menses

Anatomical reference position Erect standing position with all body parts, including the palms of the hands, facing forward; considered the starting position for body segment movements

Angle of attack Angle between the longitudinal axis of a body and the direction of the fluid flow

Angle of projection The direction at which a body is projected with respect to the horizontal

Angular Involving rotation around a central line or point

Angular acceleration Rate of change in angular velocity

Angular displacement Change in the angular position or orientation of a line segment

Angular impulse Change in angular momentum equal to the product of torque and time interval over which the torque acts

Angular momentum Quantity of angular motion possessed by a body; measured as the product of moment of inertia and angular velocity

Angular velocity Rate of change in the angular position or orientation of a line segment

Anisotropic Exhibiting different mechanical properties in response to loads from different directions

Annulus fibrosus Thick, fibrocartilaginous ring that forms the exterior of the intervertebral disc

Antagonist Role played by a muscle acting to slow or stop a movement

Anteroposterior axis Imaginary line around which frontal plane rotations occur

Anthropometric Related to the dimensions and weights of body segments

Apex The highest point in the trajectory of a projectile

Appendicular skeleton Bones composing the body appendages

Archimedes’ principle Physical law stating that the buoyant force acting on a body is equal to the weight of the fluid displaced by the body

Articular capsule Double-layered membrane that surrounds every synovial joint

Articular cartilage Protective layer of dense white connective tissue covering the articulating bone surfaces at diarthrodial joints

Articular fibrocartilage Soft-tissue discs or menisci that intervene between articulating bones

Average Occurring over a designated time interval

Axial Directed along the longitudinal axis of a body

Axial skeleton The skull, vertebrae, sternum, and ribs

Axis of rotation Imaginary line perpendicular to the plane of rotation and passing through the center of rotation

Balance Ability to control equilibrium

Ballistic stretching A series of quick, bouncing-type stretches

Base of support Area bound by the outermost regions of contact between a body and support surface or surfaces

Bending Asymmetric loading that produces tension on one side of a body’s longitudinal axis and compression on the other side

Bernoulli principle An expression of the inverse relationship between relative velocity and relative pressure in a fluid flow

Biomechanics Application of mechanical principles in the study of living organisms

Bone atrophy Decrease in bone mass resulting from a predominance of osteoclast activity

Bone hypertrophy Increase in bone mass resulting from a predominance of osteoblast activity

Boundary layer Layer of fluid immediately adjacent to a body

Bursae Sacs secreting synovial fluid internally that lessen friction between soft tissues around joints

Cardinal planes Three imaginary perpendicular reference planes that divide the body in half by mass

Carpal tunnel syndrome Overuse condition caused by compression of the median nerve in the carpal tunnel and involving numbness, tingling, and pain in the hand

Center of gravity Point around which a body’s weight is equally balanced, no matter how the body is positioned

Center of mass Point around which the mass and weight of a body are balanced, no matter how the body is positioned

Center of volume Point around which a body’s volume is equally balanced and at which the buoyant force acts

Centripetal force Force directed toward the center of rotation for a body in rotational motion

Close-packed position Joint orientation for which the contact between the articulating bone surfaces is maximum

Coefficient of drag Unitless number that is an index of a body’s ability to generate fluid resistance

Coefficient of friction Number that serves as an index of the interaction between two surfaces in contact

Coefficient of lift Unitless number that is an index of a body’s ability to generate lift

Coefficient of restitution Number that serves as an index of elasticity for colliding bodies

Collateral ligaments Major ligaments that cross the medial and lateral aspects of the knee

Combined loading Simultaneous action of more than one of the pure forms of loading

Compression Pressing or squeezing force directed axially through a body

Compressive strength Ability to resist pressing or squeezing force

Concentric Describing a contraction involving shortening of a muscle

Contractile component Muscle property enabling tension development by stimulated muscle fibers

Coracoclavicular joint Syndesmosis with the coracoid process of the scapula bound to the inferior clavicle by the coracoclavicular ligament

Cortical bone Compact mineralized connective tissue with low porosity that is found in the shafts of long bones

Couple Pair of equal, oppositely directed forces that act on opposite sides of an axis of rotation to produce torque

Cruciate ligaments Major ligaments that cross each other in connecting the anterior and posterior aspects of the knee

Curvilinear Along a curved line

D’alembert’s principle Concept indicating a balance between applied forces and inertial forces for a body in motion

Deformation Change in shape

Density Mass per unit of volume

Dynamic equilibrium (D’ Alembert’s principle) Concept indicating a balance between applied forces and inertial forces for a body in motion

Dynamics Branch of mechanics dealing with systems subject to acceleration

Eccentric Describing a contraction involving lengthening of a muscle

Electromechanical delay Time between the arrival of a neural stimulus and tension development by the muscle

English system System of weights and measures originally developed in England and used in the United States today

Epicondylitis Inflammation and sometimes microrupturing of the collagenous tissues on either the lateral or the medial side of the distal humerus; believed to be an overuse injury

Epiphysis Growth center of a bone that produces new bone tissue as part of the normal growth process until it closes during adolescence or early adulthood

Extrinsic muscles Muscles with proximal attachments located proximal to the wrist and distal attachments located distal to the wrist

Failure Loss of mechanical continuity

Fast-twitch fiber A fiber that reaches peak tension relatively quickly

First-class lever Lever positioned with the applied force and the resistance on opposite sides of the axis of rotation

Flat bones Skeletal structures that are largely flat in shape—for example, the scapula

Flexion relaxation phenomenon Condition in which, when the spine is in full flexion, the spinal extensor muscles relax and the flexion torque is supported by the spinal ligaments

Fluid Substance that flows when subjected to a shear stress

Foil Shape capable of generating lift in the presence of a fluid flow

Force Push or pull; the product of mass and acceleration

Form drag Resistance created by a pressure differential between the lead and rear sides of a body moving through a fluid

Fracture Disruption in the continuity of a bone

Free body diagram Sketch that shows a defined system in isolation with all of the force vectors acting on the system

Friction Force acting at the area of contact between two surfaces in the direction opposite that of motion or motion tendency

Frontal plane Plane in which lateral movements of the body and body segments occur

Fulcrum The point of support, or axis, about which a lever may be made to rotate

General motion Motion involving translation and rotation simultaneously

Glenohumeral joint Ball-and-socket joint in which the head of the humerus articulates with the glenoid fossa of the scapula

Glenoid labrum Rim of soft tissue located on the periphery of the glenoid fossa that adds stability to the glenohumeral joint

Golgi tendon organ Sensory receptor that inhibits tension development in a muscle and initiates tension development in antagonist muscles

Hamstrings The biceps femoris, semimembranosus, and semitendinosus

Humeroradial joint Gliding joint in which the capitellum of the humerus articulates with the proximal end of the radius

Humeroulnar joint Hinge joint in which the humeral trochlea articulates with the trochlear fossa of the ulna

Iliopsoas The psoas major and iliacus muscles with a common insertion on the lesser trochanter of the femur

Iliotibial band Thick, strong band of tissue connecting the tensor fascia lata to the lateral condyle of the femur and the lateral tuberosity of the tibia

Impact Collision characterized by the exchange of a large force during a small time interval

Impacted Pressed together by a compressive load

Impulse Product of a force and the time interval over which the force acts

Inertia Tendency of a body to resist a change in its state of motion

Inference Process of forming deductions from available information

Initial velocity Vector quantity incorporating both angle and speed of projection

Instant center Precisely located center of rotation at a joint at a given instant in time

Instantaneous Occurring during a small interval of time

Intraabdominal pressure Pressure inside the abdominal cavity; believed to help stiffen the lumbar spine against buckling

Intrinsic muscles Muscles with both attachments distal to the wrist

Irregular bones Skeletal structures of irregular shapes—for example, the sacrum

Isometric Describing a contraction involving no change in muscle length

Joint flexibility A term representing the relative ranges of motion allowed at a joint

Joint stability Ability of a joint to resist abnormal displacement of the articulating bones

Kinematics The form, pattern, or sequencing of movement with respect to time

Kinesiology Study of human movement

Kinetic energy Energy of motion calculated as 1/2 mv²

Kinetic friction Constant magnitude friction generated between two surfaces in contact during motion

Kinetics Study of the action of forces

Kyphosis Extreme curvature in the thoracic region of the spine

Laminar flow Flow characterized by smooth, parallel layers of fluid

Laws of constant acceleration Formulas relating displacement, velocity, acceleration, and time when acceleration is unchanging

Lever A relatively rigid object that may be made to rotate about an axis by the application of force

Lift Force acting on a body in a fluid in a direction perpendicular to the fluid flow

Lift/drag ratio The magnitude of the lift force divided by the magnitude of the total drag force acting on a body at a given time

Ligamentum flavum Yellow ligament that connects the laminae of adjacent vertebrae; distinguished by its elasticity

Linear Along a line that may be straight or curved, with all parts of the body moving in the same direction at the same speed

Linear acceleration The rate of change in linear velocity

Linear displacement Change in location, or the directed distance from initial to final location

Linear momentum Quantity of motion, measured as the product of a body’s mass and its velocity

Linear velocity The rate of change in location

Long bones Skeletal structures consisting of a long shaft with bulbous ends, for example—the femur

Longitudinal axis Imaginary line around which transverse plane rotations occur

Loose-packed position Any joint orientation other than the close-packed position

Lordosis Extreme curvature in the lumbar region of the spine

Magnus effect Deviation in the trajectory of a spinning object toward the direction of spin, resulting from the Magnus force

Magnus force Lift force created by spin

Mass Quantity of matter contained in an object

Mass centroid Point around which the mass and weight of a body are balanced, no matter how the body is positioned

Maximum static friction Maximum amount of friction that can be generated between two static surfaces

Mechanical advantage Ratio of force arm to resistance arm for a given lever

Mechanics Branch of physics that analyzes the actions of forces on particles and mechanical systems

Mediolateral axis Imaginary line around which sagittal plane rotations occur

Menisci Cartilaginous discs located between the tibial and femoral condyles

Meter The most common international unit of length, on which the metric system is based

Metric system System of weights and measures used internationally in scientific applications and adopted for daily use by every major country except the United States

Moment arm Shortest (perpendicular) distance between a force’s line of action and an axis of rotation

Moment of inertia Inertial property for rotating bodies representing resistance to angular acceleration; based on both mass and the distance the mass is distributed from the axis of rotation

Motion segment Two adjacent vertebrae and the associated soft tissues; the functional unit of the spine

Motor unit A single motor neuron and all fibers it innervates

Muscle inhibition The inability to activate all motor units of a muscle during maximal voluntary contraction

Muscle spindle Sensory receptor that provokes reflex contraction in a stretched muscle and inhibits tension development in antagonist muscles

Myoelectric activity Electric current or voltage produced by a muscle developing tension

Net force Resultant force derived from the composition of two or more forces

Neutralizer Role played by a muscle acting to eliminate an unwanted action produced by an agonist

Normal reaction force Force acting perpendicular to two surfaces in contact

Nucleus pulposus Colloidal gel with a high fluid content, located inside the annulus fibrosus of the intervertebral disc

Osteoblasts Specialized bone cells that build new bone tissue

Osteoclasts Specialized bone cells that resorb bone tissue

Osteopenia Condition of reduced bone mineral density that predisposes the individual to fractures

Osteoporosis Disorder involving decreased bone mass and strength with one or more resulting fractures

Parallel elastic component Passive elastic property of muscle derived from the muscle membranes

Parallel fiber arrangement Pattern of fibers within a muscle in which the fibers are roughly parallel to the longitudinal axis of the muscle

Passive insufficiency Inability of a two-joint muscle to stretch to the extent required to allow full range of motion at all joints crossed

Passive stretching Stretching of muscles, tendons, and ligaments produced by a stretching force other than tension in the antagonist muscles

Patellofemoral joint Articulation between the patella and the femur

Pelvic girdle The two hip bones plus the sacrum, which can be rotated forward, backward, and laterally to optimize positioning of the hip joint

Pennate fiber arrangement Pattern of fibers within a muscle with short fibers attaching to one or more tendons

Perfectly elastic impact Impact during which the velocity of the system is conserved

Perfectly plastic impact Impact resulting in the total loss of system velocity

Periosteum Double-layered membrane covering bone; muscle tendons attach to the outside layer, and the internal layer is a site of osteoblast activity

Plantar fascia Thick bands of fascia that cover the plantar aspect of the foot

Popliteus Muscle known as the unlocker of the knee because its action is lateral rotation of the femur with respect to the tibia

Porous Containing pores or cavities

Potential energy Energy by virtue of a body’s position or configuration, calculated as the product of weight and height

Power Rate of work production, calculated as work divided by the time during which the work was done

Pressure Force per unit of area over which a force acts

Pressure drag Resistance created by a pressure differential between the lead and rear sides of a body moving through a fluid

Prestress Stress on the spine created by tension in the resting ligaments

Primary spinal curves Curves that are present at birth

Principal axes Three mutually perpendicular axes passing through the total body center of gravity

Principal moment of inertia Total-body moment of inertia relative to one of the principal axes

Profile drag Resistance created by a pressure differential between the lead and rear sides of a body moving through a fluid

Projectile A body in free fall that is subject only to the forces of gravity and air resistance

Projection speed The magnitude of projection velocity

Pronation Combined conditions of dorsiflexion, eversion, and abduction

Proprioceptive neuromuscular facilitation A group of stretching procedures involving alternating contraction and relaxation of the muscles being stretched

Propulsive drag Force acting in the direction of a body’s motion

Propulsive drag theory Theory attributing propulsion in swimming to propulsive drag on the swimmer

Propulsive lift theory Theory attributing propulsion in swimming at least partially to lift acting on the swimmer

Q-angle The angle formed between the anterior superior iliac spine, the center of the patella, and the tibial tuberosity

Quadriceps The rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius

Qualitative Involving nonnumeric description of quality

Quantitative Involving the use of numbers

Radial acceleration Component of acceleration of a body in angular motion directed toward the center of curvature; represents change in direction

Radian Unit of angular measure used in angular-linear kinematic quantity conversions; equal to 57.3˚

Radiocarpal joints Condyloid articulations between the radius and the three carpal bones

Radioulnar joints The proximal and distal radioulnar joints are pivot joints; the middle radioulnar joint is a syndesmosis

Radius of gyration Distance from the axis of rotation to a point where the body’s mass could be concentrated without altering its rotational characteristics

Radius of rotation Distance from the axis of rotation to a point of interest on a rotating body

Range The horizontal displacement of a projectile at landing

Range of motion Angle through which a joint moves from anatomical position to the extreme limit of segment motion in a particular direction

Reaction board A specially constructed board for determining the center of gravity location of a body positioned on top of it

Reciprocal inhibition Inhibition of tension development in the antagonist muscles resulting from activation of muscle spindles

Rectilinear Along a straight line

Relative angle Angle at a joint formed between the longitudinal axes of adjacent body segments

Relative projection height The difference between projection height and landing height

Relative velocity Velocity of a body with respect to the velocity of something else, such as the surrounding fluid

Repetitive loading Repeated application of a subacute load that is usually of relatively low magnitude

Resultant Single vector that results from vector composition

Retinacula Fibrous bands of fascia

Right hand rule Procedure for identifying the direction of an angular motion vector

Rotator cuff Band of tendons of the subscapularis, supraspinatus, infraspinatus, and teres minor, which attach to the humeral head

Sagittal plane Plane in which forward and backward movements of the body and body segments occur

Scalar Physical quantity that is completely described by its magnitude

Scapulohumeral rhythm A regular pattern of scapular rotation that accompanies and facilitates humeral abduction

Scoliosis Lateral spinal curvature

Second-class lever Lever positioned with the resistance between the applied force and the fulcrum

Secondary spinal curves The cervical and lumbar curves, which do not develop until the weight of the body begins to be supported in sitting and standing positions

Segmental method Procedure for determining total-body center of mass location based on the masses and center of mass locations of the individual body segments

Series elastic component Passive elastic property of muscle derived from the tendons

Shear Force directed parallel to a surface

Short bones Small, cubical skeletal structures, including the carpals and tarsals

Skin friction Resistance derived from friction between adjacent layers of fluid near a body moving through the fluid

Slow-twitch fiber A fiber that reaches peak tension relatively slowly

Specific weight Weight per unit of volume

Spondylolisthesis Complete bilateral fracture of the pars interarticularis, resulting in anterior slippage of the vertebra

Spondylolysis Presence of a fracture in the pars interarticularis of the vertebral neural arch

Sports medicine Clinical and scientific aspects of sports and exercise

Stability Resistance to disruption of equilibrium

Stabilizer Role played by a muscle acting to stabilize a body part against some other force

Static equilibrium Motionless state characterized by Σsf_v = 0, Σsf_h = 0

Static stretching Maintaining a slow, controlled, sustained stretch over time, usually about 30 seconds

Statics Branch of mechanics dealing with systems in a constant state of motion

Sternoclavicular joint Modified ball-and-socket joint between the proximal clavicle and the manubrium of the sternum

Stiffness The ratio of stress to strain in a loaded material; that is, the stress divided by the relative amount of change in the structure’s shape

Strain Amount of deformation divided by the original length of the structure or by the original angular orientation of the structure

Strain energy Capacity to do work by virtue of a deformed body’s return to its original shape

Stress Distribution of force within a body, quantified as force divided by the area over which the force acts

Stress fracture Fracture resulting from repeated loading of relatively low magnitude

Stress reaction Progressive bone pathology associated with repeated loading

Stretch reflex Monosynaptic reflex initiated by stretching of muscle spindles and resulting in immediate development of muscle tension

Stretch-shortening cycle Eccentric contraction followed immediately by concentric contraction

Summation Building in an additive fashion

Supination Combined conditions of plantar flexion, inversion, and adduction

Surface drag Resistance derived from friction between adjacent layers of fluid near a body moving through the fluid

Synovial fluid Clear, slightly yellow liquid that provides lubrication inside the articular capsule at synovial joints

System Mechanical system chosen by the analyst for study

Tangential acceleration Component of acceleration of a body in angular motion directed along a tangent to the path of motion; represents change in linear speed

Tensile strength Ability to resist pulling or stretching force

Tension Pulling or stretching force directed axially through a body

Tetanus State of muscle producing sustained maximal tension resulting from repetitive stimulation

Theoretical square law Drag increases approximately with the square of velocity when relative velocity is low

Third-class lever Lever positioned with the applied force between the fulcrum and the resistance

Tibiofemoral joint Dual condyloid articulations between the medial and lateral condyles of the tibia and the femur, composing the main hinge joint of the knee

Torque The rotary effect of a force about an axis of rotation, measured as the product of the force and the perpendicular distance between the force’s line of action and the axis

Torsion Load producing twisting of a body around its longitudinal axis

Trabecular bone Less-compact mineralized connective tissue with high porosity that is found in the ends of long bones and in the vertebrae

Trajectory The flight path of a projectile

Transducers Devices that detect signals

Translation Linear motion

Transverse plane Plane in which horizontal body and body segment movements occur when the body is in an erect standing position

Turbulent flow Flow characterized by mixing of adjacent fluid layers

Valgus Condition of outward deviation in alignment from the proximal to the distal end of a body segment

Varus Condition of inward deviation in alignment from the proximal to the distal end of a body segment

Vector Physical quantity that possesses both magnitude and direction

Vector composition Process of determining a single vector from two or more vectors by vector addition

Vector resolution Operation that replaces a single vector with two perpendicular vectors such that the vector composition of the two perpendicular vectors yields the original vector

Viscoelastic Having the ability to stretch or shorten over time

Viscous drag Resistance derived from friction between adjacent layers of fluid near a body moving through the fluid

Volume Space occupied by a body

Wave drag Resistance created by the generation of waves at the interface between two different fluids, such as air and water

Weight Attractive force that the earth exerts on a body

Work In a mechanical context, force multiplied by the displacement of the resistance in the direction of the force

Yield point (elastic limit) Point on the load deformation curve past which deformation is permanent