KINESIOLOGY LE 1.pdf

OT 204 KINESIOLOGY displacements, and the effects of these on their I. BASIC CONCEPTS IN KINESIOLOGY: motion....

OT 204 KINESIOLOGY displacements, and the effects of these on their I. BASIC CONCEPTS IN KINESIOLOGY: motion. KINEMATICS ○ Anthropology: The study of humans, their BRIEF HISTORY societies, cultures, and development over time, encompassing both biological and social aspects ○ Physics: The science that studies matter, energy, and the fundamental forces of nature, exploring how they interact and govern the universe KINESIOLOGY CLINICAL KINESIOLOGY: study of human motion = application of kinesiology to art + science environments of the health care appreciation of professional beauty of human movement + ○ PURPOSE: understanding of scientific principles To understand the movement that provide movement & the forces acting on the theories and principles from: human body learn how to ○ Biomechanics: manipulate these forces to The application of the prevent injury, restore principles of mechanics to function, and provide optimal the living human body human performance ○ Anatomy: The study of the structure KINES: and organization of living STUDY OF HUMAN MOVEMENT organisms, focusing on the physical makeup of their Kinetics: forces bodies Kinematics: motion ○ Physiology: (types, direction, quantity) The study of the functions ○ Osteokinematics: and processes of living movements of bony organisms and their parts, partners/segments that make explaining how the body's up a joint; flex, ext, abd, add systems work. ○ Arthrokinematics: ○ Mechanics: small movements occuring The branch of physics that within the joint & between deals with the behavior of joint surfaces; physical bodies when gliding, rolling, spinning subjected to forces or  OT 204 KINESIOLOGY PLANES OF MOTION: NAMING MOVEMENTS AT JOINTS CARDINAL PLANES We name joints by using the names 3 primary planes that divide the body of the 2 bones that form the joint, and guide its movements typically by naming the proximal flat, 2D surfaces along which bone first movement occurs ○ eg: RU, AA, SI joints help describe how an object moves in relation to its orientation AXES OF MOTION An imaginary line around which the SPECIAL CASES: body or its segments rotate during Thumb movement Normal position is rotated 90° from Axes around which movement the plane of the hand occurs Motions of flexion and extension Perpendicular to the planes of occur in the frontal plane rather than motion the sagittal plane Abduction and adduction occur in the sagittal plane rather than the frontal plane Forearm: Pron & Sup As the forearm rotates, the motion no longer occurs on a longitudinal axis but on an anterior-posterior axis Hip: Med & Lat Rotation As the flexed hip rotates, the motion no longer occurs on a longitudinal axis but on an anterior-posterior axis  OT 204 KINESIOLOGY TYPES OF MOTION DEGREES OF FREEDOM The body and its segments move Number of planes within which a one of two ways: joint moves motion is either translatory or rotary Given that the body and its segments move in: 3 planes of motion, degrees of freedom (maximal) at 3° ○ maximal degrees of freedom = maximum number of different ways a body part can move A. UNIaxial a. joints that move in Linear + Rotatory movements = 1 plane around 1 axis FUNCTIONAL MOTION b. 2 types: i. Hinge Translatory ii. Pivot ○ Linear B. BIaxial ○ occurs along or a. joints that move in parallel to an axis 2 planes around 2 axes Rectilinear b. 3 types: movement in i. Condyloid a straight line ii. Ellipsoidal Curvilinear iii. Saddle movement in C. TRIaxial a curved path a. Joints that move in Rotatory 3 planes around 3 axes ○ Angular b. Ball-and-socket joints ○ occurs in a circle around an axis or a pivot point, ○ so every point on the object attached to the axis follows the arc of a circle ○ Axis of rotation pivot point for this angular or rotary motion  OT 204 KINESIOLOGY UNIaxial Hinge Saddle convex + concave surfaces Interphalangeal (IP) Humeroulnar (Elbow Joint) Tibiofemoral & Patellofemoral (Knee Joint) have greater ROM Pivot perpendicular cylindrical or conical concave + convex surfaces synovial / rotary joints Carpometacarpal (CMC) type of synovial joint Atlantoaxial (C1 and C2) TRIaxial ○ rotation of the head from side to side, shaking the head "no” Radioulnar Joint BIaxial Ball-and-socket spherical ball + concave cup Glenohumeral (Shoulder joint) Pelvic Acetabulum & Femoral Head (Hip joint) CIRCUMDUCTION VS ROTATION ○ ellipsoid joints are essentially a subtype of condyloid joints with a more specific CIRCUMDUCTION ROTATION shape. - circular or conical -turning or Condyloid movement spinning around a oval-shaped condyle + -sequential central point or elliptical cavity combination of: axis spherical convex + flex, ext, -without changing shallow concave abd & add the position of the MCP + MTP joint itself from side to side Ellipsoid Joints ovoid condyle (elongated) + elliptical cavity flattened convex + fairly deep concave Atlanto-occipital Radiocarpal (wrist)  OT 204 KINESIOLOGY JOINT STRUCTURE & FUNCTION  OT 204 KINESIOLOGY AMPHIARTHRODIAL JOINTS “on both sides” or “around” both fibrous and hyaline (or articular) cartilage & typically have a disc between the bony parts Types 1. Primary a. Immovable b. Growth plates, 1st SC joint SYNARTHRODIAL JOINTS “together” or “joined” Types of Synarthrodial Joints SUTURES SYNDESMOSIS GOMPHOSES bound connected by a peg-like 2. Secondary together by ligament or structure fits a. Limited movement connective interosseous into a socket tissue membrane b. Pubic symphysis, IV joints sutures Tibiofibular may Articulation Dento-alveolar DIARTHRODIAL JOINTS gradually Radius + Ulna joint “twice, double or two” ossify➝ -connected provides almost all of our joint fused by mobility periodontal only in the ligament joint cavity skull ○ connects distal end of one joint segment to proximal end No Very slight No movement of the other joint segment movement movement ○ maintains a small amount of synovial fluid ○ lubricates & allows wide ROM  OT 204 KINESIOLOGY Joint Capsule Joint Surfaces cartilage, ligaments, articular discs, surface of synovial joints are not the joint capsule, synovial fluid, purely geometric with flat, cylindrical, &bursae conic, or spherical designs All joint surfaces are described as either: ○ Ovoid (egg-shaped) Most synovial joints The radius of the curvature varies from point to point Convex-concave relationship ○ Sellar (saddle) TYPES OF CARTILAGE Types of Basic Motion Fibrous Rolling/Rocking ○ dense thick bundles ○ rotary, or angular, of collagen fibers motion ○ IV discs, menisci, ○ each subsequent pubic symphysis point on one surface ○ absorb shock & contacts a new point reduce friction on the other surface Hyaline/Articular Sliding/Gliding ○ MC type ○ translatory or linear ○ smooth, glassy motion appearance ○ movement of one ○ fine collagen fibers joint surface is + high water content parallel to the plane ○ ends of long bones, of the adjoining joint ribs to sternum surface ○ provides a slippery Spinning surface for joint ○ rotary, or angular, movement; reduces motion friction, supports & ○ one point of contact reinforces various on each surface structures remains in constant Elastic contact with a fixed ○ high density of elastic location on the other fibers + collagen surface ○ external ear (auricle), the epiglottis (part of the larynx) ○ provide structural support with flexibility  OT 204 KINESIOLOGY Convex-Concave Relationship Convex: surface that bulges outwards Concave: surface that curves inward GONIOMETRY Gr. gonia, angle, and metron, measure valuable clinical measurement used to define the quantity of joint motion (actively or passively) Because of individual variations in build and body type, it is useful to use the standardized ROM values as a reference, but it is most important to use the individual’s own “normal” for reliable comparison by measuring the uninvolved, or contralateral, extremity segment, assuming that it is present and unimpaired  OT 204 KINESIOLOGY TYPES OF END-FEELS Sensations experienced at the end of a joint’s ROM when it is passively stretched Resistance to further motion Abnormal/Pathological End Feels Occur either at a different place in the ROM than expected or have an end feel that is not characteristic joint  OT 204 KINESIOLOGY KINEMATIC CHAINS CLOSED & OPEN-PACKED POSITION Series of sequentially connected joints & links (bones or segments) Describes the different ways in that work together to produce which a joint can be positioned, movement in the body affecting how the bones and used to describe or analyze a surrounding structures interact with movement skill each other Open Open Closed one end of the chain is fixed, allowing for movement at one Other loose-packed , N/A end without directly affecting name/s resting the position of the other end Joint Minimal Maximal the distal segment of the Surface chain moves in space Contact reaching for an object, bringing the hand to the Capsule & Relaxed Tight mouth, or kicking a ball Ligament all of the participating joints Tension are free to contribute any Mobility ↑ROM, ↓ ROM, number of degrees of motion to the entire unit’s movement ↓stability ↑ stability produce faster motion Closed both ends of the chain are fixed or connected to a stationary point, which means that movement at one end of the chain affects the entire chain the distal segment is fixed, and proximal parts move in relation chin-up, push-up, standing from a seated position, or a half-squat exercise movement of one segment requires all the segments to move provide more power & strength for functional activities OT 204 KINESIOLOGY  OT 204 KINESIOLOGY RATE OF MOTION II. MECHANICAL PRINCIPLES: Velocity KINETICS ○ speed of motion (m/s) Acceleration Motion – displacement of a body or one of ○ change in velocity over time its segments from one point to another (m/s2) CLINICAL RELEVANCE TYPES OF MOTION Understanding the determinants of motion is Translatory crucial for: ○ linear movement - Assessing mobility Rotary – evaluating joint ○ angular movements around range and motion an axis types in patients LOCATION OF MOTION - Planning rehabilitation – tailoring exercises Transverse that improve specific Sagittal types of motion Frontal - Preventing injuries MAGNITUDE OF MOTION – identifying Degrees – rotary (angle) abnormal motion Meter - linear patterns DIRECTION OF MOTION based on the axes FORCES - Produce, Stop, or modify motion Types of Forces: Gravity ○ the force that pulls objects towards the earth, commonly referred to as weight Muscle forces MOVEMENT POSITIVE NEGATIVE ○ generated by muscle contractions X-axis Right Left Externally applied resistance Y-axis Upward Downward ○ forces applied from external sources like weights, Z-axis Forward Backward resistance bands, or manual resistance Friction ○ resistance to movement bet 2 surfaces in contact  OT 204 KINESIOLOGY FORCE CHARACTERISTICS · Muscle forces · Magnitude – responsible for stabilizing – amount of force applied, & moving joints – measured in Newtons or – generate force to lift/resist pounds · Friction · Direction – essential for stability in – line of action of the force standing and walking – influences the resulting the · Externally applied forces motion – used to enhance or resist movements in therapeutic NEWTON’S LAW OF MOTION exercises – ex: resistance bands 1st Law: Inertia –a body at rest, stays at rest, a body in motion stays in motion unless acted upon by external force LEVERS ○ important in understanding A rigid bar that rotates around a how to initiate motion in fixed point called the fulcrum or axis patients with limited mobility COMPONENTS nd 2 Law: Acceleration Axis or fulcrum –the acceleration of a body is – pivot point (joints) directly proportional to the force Force (effort) applied and inversely proportional to – the applied force its mass: a=F/a (muscle contraction) ○ formula: F = m x a Resistance (load) ○ helps in understanding the – the weight or force to be force needed to move body moved (limb or ext weight) parts in exercises CLASSES OF LEVERS 3rd Law: Action-Reaction – for every action, Fa = Force Arm there is an equal & Ra = Resistance Arm opposite reaction ○ used in gait analysis & 1st Class improving balance in patients - Ex. head and seesaw, neck muscles balancing the head CLINICAL APPLICATION · Gravity – critical role in weight-bearing exercises & activities (body weight exercise;squats) OT 204 KINESIOLOGY 2nd Class ➔ LEVER SYSTEMS IN REHAB – ex. wheelbarrow, calf raise, 1st Class push-ups (balancing force & load ) ○ useful in balancing exercises ○ important for patients with postural instability 2nd Class (force advantage) ○ emphasizes strength in the calf muscles ○ useful in gait training 3rd Class 3rd Class – ex. bicep curl, rowing, sit up, leg (speed advantage) ext, baseball bat swing ○ focus on speed and ROM ○ important in upper limb rehabilitation TORQUE ➔ MECHANICAL ADVANTAGE OF - rotational force that acts LEVERS around an axis IN THE HUMAN BODY Arm Movement (Lifting) ○ elbow- axis (hinge) force - generated by your muscles ○ fully extended arm = harder to lift weight The farther the weight is from your elbow, - (convert to meters) the more torque your ➔ CLINICAL RELEVANCE OF muscles need to LEVERS generate to lift it. Impact on exercise design Kicking a Ball ○ Lever systems influence the ○ hip joint - axis intensity & difficulty of leg - acts like a lever exercises ○ closer to your foot = Modifying the position more torque is generated of resistance in side a strong kick with leg raises changes your foot can send the mechanical the ball flying far advantage & difficulty OT 204 KINESIOLOGY ➔ IMPORTANCE IN MOTION ➔ APPLYING TORQUE IN CLINICAL Torque is critical in joint movements SETTINGS where force is applied ○ Ex: The torque generated by the quadriceps muscle at the knee joint during a leg extension. ➔ FACTORS INFLUENCING TORQUE Therapeutic Exercises ○ Ex: Increasing the challenge by extending the moment arm, such as holding a weight farther from the body. ➔ FORCE APPLICATIONS TO THE BODY Torque= Force x d (Lever Arm) Joint reaction forces (no change) ○ exerted by the joint surfaces in response to muscle and Torque increases, external forces as lever arm distance increases ○ The compressive at the knee (lift weight- farther from your elbow) joint during a squat External Forces Torque decreases, ○ such as weights, resistance as lever arm distance decrease bands, & environmental (weight closer to your elbow) factors ○ The effect of gravity on a limb during a shoulder abduction FREE BODY DIAGRAMS A graphical representation of all forces acting on a body or segment Force Application Angle – torque is maximized when Components: the force is applied at 90° to Force vectors the lever arm – arrows representing forces, with (perpendicular to the ground) length proportional to magnitude and direction Application – used to analyze the specific joint motion OT 204 KINESIOLOGY CASE STUDIES CLINICAL APPLICATIONS OF CASE 1 CONCEPTS Scenario: You want to make Guiding Clinical Decisions a quadriceps strengthening ○ Understanding mechanical exercise more challenging for principles helps clinicians a patient without adding make informed decisions additional weight. regarding patient treatment and exercise prescription. a. Solution: Increase the length Impact on Rehabilitation of the resistance arm. ○ Ex: Adjusting exercise b. Decrease the length of the parameters based on lever force arm. arms, torque, and force c. Lower the resistance arm to application to maximize the same level as the force therapeutic outcomes and arm. minimize injury risk. CASE 2 ➔ PRACTICAL APPLICATIONS Scenario: You need to modify Applying Mechanical Principles: an exercise to reduce stress Always consider lever systems, on a patient’s knee joint torque, and force application in during rehabilitation. exercise design. Tailoring to Patient Needs: a. Increase the resistance arm. Adjust exercises based on individual b. Increase the force arm length patient’s strength, mobility, and injury while keeping the resistance status. arm the same Ensuring Safety: c. Shorten the resistance arm Minimize excessive torque and to decrease torque and forces to prevent overloading joints, reduce joint stress. particularly in patients with weakened structures or ongoing Answers to case study: rehabilitation. Why are muscle and joint reaction 1. (a) forces often larger than the external Lengthening the distance between the forces applied to the body ? knee joint (fulcrum) and the point where the resistance is applied (e.g., moving the -Because muscles must generate enough force weight farther from the knee) increases to not only overcome the external load but also the torque needed by the quadriceps to lift stabilize the joint and counteract other forces, the leg, making the exercise more such as gravity, acting on the body. challenging. What is the difference between force 2. (c) & torque? By reducing the distance between the knee joint and the point where the Force: A push or pull acting on an object, resistance is applied, the torque required causing linear motion. by the muscles decreases, leading to less joint stress. Torque: A force that causes rotation around an axis. Torque is the product of force and the moment arm (distance from the axis to the point of application of the force).  OT 204 KINESIOLOGY III. MOVEMENT SYSTEM Action Potential Nerve Impulse: PHYSIOLOGY OF EXCITABLE TISSUE: ○ an AP transmitted over a NERVE AND MUSCLE nerve fiber Muscle impulse: Nervous and Muscular Tissue ○ an AP transmitted over a Membranes are excitable muscle fiber ○ sensitive to electrochemical Neurons change ○ able to transmit electrochemical information to produce movement Cell Membrane difference in electrical potential imbalance of ions from one side of the membrane to another is called potential difference ○ 2 Factors: Selective Permeability Actively move ions ○ Resting Potential: when no action is occurring & under resting conditions Charge is negative ○ Nerve, muscle, and sensory receptors/cells need to maintain a resting potential of NERVOUS SYSTEM ANATOMY -60 to -90 mV OVERVIEW (average = -85mV) Nervous System Classification  OT 204 KINESIOLOGY Nerve Fibers Motor Unit Efferent vs. Afferent Neurons Motor neurons are located in either Nerve Fibers in the PNS: the brainstem or spinal cord Sensory nerves ○ Muscles of the face and head ○ afferent nerve fibers ○ Muscles of the neck, trunk, Motor nerve fibers and extremities ○ efferent nerve fibers Autonomic neurons ○ involuntary control of glandular activities & smooth muscles MUSCULAR SYSTEM Muscle Fibers diameter of an individual muscle fiber Motor neurons in the spinal cord are ranges from 10 to 100 micrometers located in the gray matter of the ventral/anterior horns The number of muscle fibers innervated by single motor nerve fiber varies ○ The more control required of a muscle, the fewer muscle fiber to nerve fiber ratio a muscle has. ○ The muscles that produce Epimysium large forces have much connective tissue covering larger ratios of muscle fibers keep each muscle separate from to nerve fibers adjacent muscles Perimysium In a motor unit, divides a muscle into sections within all muscle fibers act as one unit, the entire muscle contracting or relaxing nearly Fasciculus simultaneously subsection of a muscle Principle: All-or-none law Myofibrils / Myofilaments ○ If the motor unit’s nerve bundles of filaments within a muscle activates its muscle fibers to fiber contract, those fibers will composed of units & each unit is contract maximally referred to as a sarcomere Sarcolemma covering membrane of myofibril  OT 204 KINESIOLOGY Gradation of Strength Autogenic Inhibition of Muscle Contraction ○ Nonreciprocal inhibition Size Principle ○ inhibitory input to an agonist ○ the smallest motor units are muscle (prime mover) & an activated first excitatory message to the Recruitment Principles antagonist (opposing) muscle ○ increasing the number of motor units activated simultaneously increases the Muscle Spindles overall muscle tension Detect changes in muscle length Excitatory Input / 2 functions: Rate Coding Principle ○ Sensory ○ increasing the frequency of ○ Motor stimulation of individual Stretch Reflex motor units increases the The constant volley of regulatory percentage of time that each input to the muscle spindle intrafusal active muscle fiber develops fibers sets up a constant state of max tension readiness so that although the muscle is not activated, it is literally on a steady state of alert, ready to JOINT, TENDON, AND MUSCLE RECEPTORS act when needed. ○ constant state of readiness: Joint Receptors Muscle Tone**Postural Tone most of the receptors emit several AP per second as a ‘resting” output Kinesthesia & Position Sense ○ So the body always has a Consciously aware of the position of sense of position in space the various parts of the body relative to all other parts & whether a the receptor is stimulated when it is particular part is moving or still deformed ○ Dynamic motion: Kinesthesia receptors typically adapt ○ Static Motion: Position sense Golgi Tendon Organs Proprioception lie within muscle tendons more inclusive term near the point of their attachment to use of sensory input from receptors the muscle in muscle spindles, tendons, and ○ detect force/tension but not joints to discriminate joint position changes in muscle length and movement average of 10-15 muscle fibers is usually connected in direct line with each GTO  OT 204 KINESIOLOGY Integration of Motor Control MOTOR CONTROL to Produce Functional Movement Movement Musculoskeletal System Movement and posture are + exceedingly intricate and complex. Nervous System Bodily systems included in + motor control: Cognition ○ Neuromuscular = ○ Skeletal Effective Motor Control ○ Respiratory ○ Cardiovascular The more often a motor pattern is ○ Digestive learned, the less input from the ○ Neuromusculoskeletal cortical level is required Motor Control ○ regulation of Motor learning posture & movement ○ concerned with: Muscle Synergy how motor skills are ○ functional coordinated acquired muscle activation how they are made ○ proper sequence & proficient, transferred, activation/inhibition of and retained to allow muscles consistent, accurate, The systems are not arranged in a & automatic motion hierarchy but rather in a functioning heterarchy Movement can be expressed from among a wide variety of movement combinations Different Centers/Regions  OT 204 KINESIOLOGY IV. MUSCLE ACTIVITY AND STRENGTH TYPE OF MUSCLE FIBERS AND SIGNIFICANCE IN MUSCLE FUNCTION TYPE I MUSCLE TYPE II MUSCLE MUSCLE ACTIVATION FIBERS FIBERS Postural Muscles- Mobility Muscles or Isometric Muscles that work Non-postural ○ No change in muscle size against gravity as we Muscles- Isotonic Contractions: sit or stand muscles that are used ○ Concentric (Shortening of the for rapid movement during explosive muscle- proximal and distal activities. segments moves closer) also referred to as “positive work” -fibers that resist These movement ○ Eccentric (Lengthening of the fatigue and are able muscles produce force to maintain sustained and power rapidly but muscle during activation- activity. have low endurance; usually during deceleration therefore, they cannot movements) also referred to sustain activity for as “negative work” (external prolonged periods. force makes a joint -soleus, peroneals, These muscles include movement and the muscle quadriceps, gluteals, the gastrocnemius, controls that movement. rectus abdominis, hamstrings, and upper Example “gravity”) upper extremity extremity flexors. extensors, erector Isokinetic spinae group, and ○ No change in the rate of short cervical flexors. movement)  OT 204 KINESIOLOGY MUSCLE FUNCTIONAL ACTIVITY MUSCLE ANATOMIC ACTIVITY Agonist Although knowledge of the anatomic ○ Primary Mover Muscle- the attachments and actions is essential one that contracts to make to the study of kinesiology, it is the movement important to recognize that these Antagonist factors can predict muscle function ○ Opposite muscle or muscle when all of the following conditions group that passively are present: elongates in a relax state to 1. The proximal attachment is allow movement produced by stabilized; the agonist muscle 2. The distal attachment moves Synergist toward the proximal ○ Muscle or muscles that attachment (concentric contracts together with the contraction); agonist muscle 3. The distal segment moves against gravity or a MUSCLE STRENGTH resistance; and 4. The muscle acts alone. Muscle Size Unfortunately, these circumstances Muscle fiber structure rarely occur in normal function. Length-Tension Relationship Once you know insertions and Moment Arm actions of muscles, you can recall Speed of Contraction other factors that affect functional Active Tension application of muscle activity. Age and Gender For example, if the proximal biceps brachii attachment is stabilized, the MUSCLE SIZE elbow will flex when the muscle activates; however, when any Muscle fibers that are long and muscle contracts, it shortens at both provides majority of the joint ends, so if neither end of the biceps movement it produces while shorter is stabilized, the shoulder flexes and muscles provide the stability of the the elbow flexes when the biceps joint movement. contracts. ○ Hypertrophy: increase in We can take this notion in another muscle size usually due to direction to better understand exercise. muscle function in a closed chain ○ Atrophy: decrease in muscle activity: If the distal segment of a size) due to inactivity. muscle’s attachment is stabilized, then the proximal segment is the moving end of the muscle.  OT 204 KINESIOLOGY MUSCLE FIBER STRUCTURE LENGTH-TENSION RELATIONSHIP In fusiform muscles, the fascicles Resting Length are parallel and long throughout the ○ Position of the muscle in muscle. which there is no tension ○ The sartorius is an example within the muscle. of a strap, or fusiform, Passive Tension muscle. These muscles are ○ Created mostly by elongation designed to produce greater of muscle tissues and the shortening distance but less connective tissue called force. “Fascia”. Pennate fascicles, on the other Active Tension hand, attach at oblique angles to a ○ Force produced by a muscle. central tendon. There are different Active tension in a muscle is pennate designs of muscles, created by activation of the depending upon the number of fiber cross bridges between the arrangements within a muscle. actin and myosin elements Unipennate muscles have one within muscle fibers. parallel fiber arrangement whereas bipennate muscles have two groups of parallel fibers running to one central tendon. Most muscles in the body are multipennate muscles with more than two pennate groups attaching to more than one centralizing tendon. Pennate fascicles are shorter than fusiform fascicles; they produce greater forces to the sacrifice of speed since their total cross section is larger. Since muscle strength is proportional to the total cross-sectional area of the muscle, strength of pennate muscles is related to the combined cross-sectional size of the pennate muscle. Therefore, total strength of pennate muscles is the sum of the cross-sectional areas of each pennate.  OT 204 KINESIOLOGY MOMENT ARM The maximum number of crossbridges that can be formed The moment arm of a muscle is the occurs at slow speeds. The more lever arm that produces rotation rapidly the actin and myosin around a joint. filaments slide past each other, the The muscle’s moment arm is the smaller is the number of links that length of a perpendicular line from are formed between the filaments in the joint’s axis of motion to the a unit of time so less force is muscle’s force vector or line of pull. developed. You may recall from previously HOWEVER, this is opposite during presented information that all of the eccentric contraction. muscle muscle’s force rotates the joint strength actually increases as speed (produces torque) when the muscle increases during eccentric is aligned perpendicularly to the long contraction until the speed reaches a axis of the body segment. point at which the muscle is unable Torque is the measure of the force to control the load. that can cause an object to rotate about an axis. SPEED OF CONTRACTION As the speed of a concentric contraction becomes slower, the muscle’s force development increases. When there is no motion, this is a maximum isometric contraction, or zero-velocity, contraction. A muscle’s decreased ability to produce a contraction force with increasing speed of shortening is based on the number of links between the actin and myosin filaments that can be formed per unit of time.  OT 204 KINESIOLOGY ACTIVE TENSION STRESS-STRAIN CURVE The force produced by a muscle. Stress is a force or load that the Active tension in a muscle is created body or its parts resist. by activation of the cross bridges How well those structures are able between the actin and myosin to resist stress is dependent upon elements within muscle fibers. their ability to deform. This is a strain Motor units are recruited in an order of a structure: the amount of according to the size of the motor deformation it is able to tolerate unit (smaller ones are recruited first), before it succumbs to the stress. the size of the muscle cells (smaller (factors that affect strain: Viscosity, ones are recruited before larger Elasticity, and Extensibility) ones), and the type and speed of ○ Viscosity is the resistance to conduction of the muscle fibers an external force that causes (slower type I are recruited before a permanent deformation. faster type II). The smaller motor ○ Extensibility is the ability to units are slower to respond but last stretch, elongate, or expand. longer than the larger ones which ○ Elasticity is the ability to respond quickly with strong bursts. succumb to an elongating Therefore, type I motor units are force and then return to recruited for posture. normal length when the force is released. AGE AND GENDER All structures, natural and Males are generally stronger than man-made, have their specific females. In both genders, however, relationship between stress and muscle strength increases from birth strain. This is called the stress-strain through adolescence, peaking curve or stress-strain principle. between the ages of 20 and 30 The initial section of the stress-strain years, and gradually declining after curve is the toe region. In a resting 30 years of age. state, tissue has a crimped or wavy After puberty, however, the muscle appearance. When stress is applied mass of males becomes as much as to the tissue, this slack is taken up 50% greater than that of females, within the toe region of the and the ratio of lean body mass to stress-strain curve. Once the tissue whole body mass also becomes is elongated to the point at which the greater. On the other hand, muscle slack is taken out of the structure so strength per cross-sectional area of it becomes taut, the stress force muscle is similar in males and moves the tissue into the elastic females. range. But of course, muscle strength This elastic range is the point at varies in each individual due to other which the tissue’s elastic properties factors (genetics, lifestyle, rate of are stressed. The tissue strain and biological maturation, etc.) the amount of stretch move through a linear relationship when there is a OT 204 KINESIOLOGY direct relationship between the amount of stress applied to the tissue and the tissue’s ability to stretch. If the force or load is released at any time during either of these two ranges, the tissue returns to its normal length. On the other hand, if the force applied continues to increase, the tissue moves from its elastic range into its plastic range. In this range, there is microscopic damage to the structure; some of the tissue ruptures because it is unable to withstand this amount of stress. It is at this point that permanent change in the tissue’s length occurs. If the force is released at this point, the tissue is elongated compared to what it was prior to the stress application. Videos of Injuries as an example of the If the amount of stress continues to stress-strain curve increase past the plastic range, the https://www.youtube.com/watch?v=H tissue moves into the necking range. Z2957l4r4U At this point, more and more https://www.youtube.com/shorts/qxIa microscopic ruptures occur until the b6Ln7jw tissue becomes macroscopically damaged. It is at this time that the force or load required to create tissue damage is less than previously because the tissue is weakening. If the stress increase continues, immediately before the tissue ruptures entirely, a give in the structure is felt and then the tissue rips apart, moving into the failure range. The continuity of the tissue is lost when tissue failure occurs. OTHER MECHANICAL FACTORS THAT  OT 204 KINESIOLOGY Another unique way the body avoids AFFECT MUSCLE STRENGTH the weakness caused by active insufficiency is by changes in the Passive Excursion mechanical leverage that occurs Active Excursion throughout the joint’s range of Leverage and Length-Tension motion. Interactions In the example of the biceps brachii Open Kinematic/kinetic Chain (OKC) muscle (Fig.4.17), the physiologic vs Close Kinematic/kinetic Chain length-tension factor is most (CKC) favorable when the elbow is in full PASSIVE EXCURSION extension, and the maximum tension that can be produced during muscle The functional excursion of a muscle contraction decreases as the elbow is the distance to which the muscle approaches and passes 90º of is capable of shortening after it has flexion. To compensate for this loss been elongated as far as the joint(s) in physiologic muscle tension, the over which it passes allows. muscle’s leverage (moment arm Passive excursion or passive length) increases to its maximum at insufficiency: When muscles 90º. This increase in moment arm become elongated over two or more length provides the muscle’s joints simultaneously, they may greatest mechanically-produced reach the state of passive torque at a point in the range of insufficiency. This full elongation of a motion which is important for holding muscle prevents further shortening heavy objects. by its opposite muscle. In this instance, the torque that the ○ Passive tension of muscles muscle can produce actually that cross two or more joints increases because of a mechanical may produce passive change, even though the physiologic movements of those joints. muscle tension decreases. This effect is called tenodesis action of muscle. Active Excursion or active insufficiency: Active insufficiency occurs in multijoint muscles when the muscle is at its shortest length when its ability to produce physiologic force is minimal. LEVERAGE AND LENGTH-TENSION INTERACTIONS  OT 204 KINESIOLOGY In closed chain activities, compression of the joints occurs, providing stabilization through joint approximation and coactivation of opposing muscle groups. OPEN KINEMATIC/KINETIC CHAIN (OKC) vs CLOSE KINEMATIC/KINETIC CHAIN (CKC) A common specification for a closed kinetic chain condition is that it is essentially weight-bearing. In contrast, an open kinetic chain condition is a non-weight bearing position. Although both open and closed chain conditions occur in functional upper and lower extremity activities, the upper extremity is more often used in open kinetic chain activities whereas the lower extremity functions primarily in closed kinetic chain activities. It should be kept in mind that open chain activities often facilitate rapid movements whereas closed chain functions are used to develop force and power. In functional upper extremity open chain activities such as throwing, the proximal portion of the extremity initiates the movement for the distal joints.