Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + A Download Section PDF Listen + 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 + B Download Section PDF Listen + 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 + C Download Section PDF Listen + 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 Download Section PDF Listen + 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 + E Download Section PDF Listen + 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 + F Download Section PDF Listen + 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 + G Download Section PDF Listen + 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 + H Download Section PDF Listen + 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 + I Download Section PDF Listen + 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 + J Download Section PDF Listen + 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 + K Download Section PDF Listen + 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 + L Download Section PDF Listen + 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 + M Download Section PDF Listen + 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 + N Download Section PDF Listen + 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 + O Download Section PDF Listen + 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 + P Download Section PDF Listen + 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 Download Section PDF Listen + 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 + R Download Section PDF Listen + 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 + S Download Section PDF Listen + 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 Σsfv = 0, Σsfh = 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 + T Download Section PDF Listen + 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 + V Download Section PDF Listen + 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 + W Download Section PDF Listen + 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 + Y Download Section PDF Listen + Yield point (elastic limit) Point on the load deformation curve past which deformation is permanent