MBS 212 Human Movement

MBS 212 Human Movement Lecture 2 Biomechanical Concepts Prof. Thomas K. Monsees 2008 Prof. Monsees

Learning outcomes • Types of muscle work with reference to isotonic shortening/ lengthening static work • Levers and leverage • Centers of gravity • Bipedal erect locomotion Prof. Monsees

Muscle Tissue Types • Skeletal • Attached to bones • Nuclei multiple and peripherally located • Striated, voluntary and involuntary (reflexes) • Smooth • Walls of hollow organs, blood vessels, eye, glands, skin • Single nucleus centrally located • Not striated, involuntary, gap junctions in visceral smooth • Cardiac • Heart • Single nucleus centrally located • Striations, involuntary, intercalated disks More details in L 14/15! Prof. Monsees

Skeletal Muscles Functions • Produce body movement • Maintain posture and body position • Support soft tissue • Guard entrances and exits • Production of body heat • Store nutrient reserve Prof. Monsees

Properties of Muscle • Contractility • Ability of a muscle to shorten with force  Movement • Excitability • Capacity of muscle to respond to a stimulus • Extensibility • Muscle can be stretched to its normal resting length and beyond to a limited degree • Elasticity • Ability of muscle to recoil to original resting length after stretched Prof. Monsees

Connective Tissue, Nerve, Blood Vessels • Connective tissue • External lamina • Endomysium (inside) • Perimysium (middle) • Fasciculus (small bundle) • Epimysium (outside) • Fascia • Nerve and blood vessels • Abundant Prof. Monsees

Skeletal Muscle Structure • Muscle fibers or cells • Develop through fusion from myoblasts  • Enormous size:up to 30 cm, 100 m diaMultiple nuclei (> 100!) • striated Prof. Monsees

Tendons attach muscles to bones • Collagen fibers of endomysium, perimysium, and epimysium come together to form a bundle  a tendon, or an aponeurosis (broad sheet) • Tendons and aponeuroes attach skeletal muscles to bones • Collagen fibers extended into bone matrix •  contraction of muscle will exert a pull on attached bone More details in L 14 - 18! Prof. Monsees

How does a muscle contract? • Sliding Filament Model: • Actin myofilaments sliding over myosin to shorten sarcomeres • Actin and myosin do not change length • Shortening sarcomeres responsible for skeletal muscle contraction • During relaxation, sarcomeres lengthen Prof. Monsees

Sarcomere Shortening • During contraction: • Sliding occurs in every sarcomer  myofibril gets shorter muscle fiber contracts •  Fibers pull on attached tendon and apply tension to bone • Shortening by 30% • this process needs energy (ATP) Prof. Monsees

Tension and compression • Tension applied to an object (e.g. bone) tends to pull object toward source of tension • However, applied tension must overcome object’s resistance before movement can occur • Resistance depends on object weight, shape, friction • Compression applied to an object tends to push object away • Muscles can use energy to shorten and generate tension, but not lengthen and generate compression •  !! muscles can pull, but they cannot push !! Prof. Monsees

Neural control of skeletal muscles • Muscle contraction occurs only after activation by neurons (cell bodies in CNS) Excitation-Contraction Coupling • Neuron stimulate sarcoplasmic reticulum to release calcium ions • Ca ions trigger interaction between actin and myosin  muscle fiber contraction and consumption of energy (ATP) • filament interaction produce active tension Prof. Monsees

Neuromuscular Junction (NMJ) • Synapse or NMJ • Presynaptic terminal • Synaptic cleft • Postsynaptic membrane or motor end-plate • Synaptic vesicles • Acetylcholine: Neurotransmitter • Acetylcholinesterase: A degrading enzyme in synaptic cleft Prof. Monsees

Muscle Twitch • Muscle contraction in response to a stimulus that causes action potential inone or more muscle fibers • Phases • Lag or latent • Contraction • Relaxation Prof. Monsees

How does muscles know what is going on? Sensory receptors: • Free nerve endings (pain sensors) • Golgi tendon organs (monitors extend + force of contraction) • Muscle spindles (intrafusal fibers monitor muscle length + joint position) Golgi organ Muscle spindle Prof. Monsees

Types of Muscle Contractions • Isotonic: Change in length but tension constant • E.g. lifting object on desk, walking, running • Concentric: Overcomes opposing resistance and muscle shortens • Eccentric: Tension maintained but muscle lengthens • Isometric: No change in length but tension increases • E.g. holding baby, carry bag, holding your head up • Postural muscles of body • Muscle tone: Constant tension by muscles for long periods of time Prof. Monsees

Isotonic contraction Concentric, e.g. • skeletal muscle of 1 scm cross-sectional area can produce roughly 4 kg of tension in complete tetanus • If you hang a 2 kg weight from this muscle and stimulate it, the muscle will shorten Prof. Monsees

Isotonic contraction Concentric • muscle tension exceeds resistance  shortens • during initial period, tension rises until tension in tendon exceeds amount of resistance • as muscle shortens, tension remains constant at a value just exceeding the load ( isotonic) Prof. Monsees

Isotonic contraction • Eccentric:Muscle tension is less than load  elongates due to pull off gravity or action of another muscle • e.g. biceps curl: flexion involves concentric contractions, whereas during extension same muscles produces eccentric contractions Prof. Monsees

Isometric contraction • Muscle as a whole does not change length, tension produced never exceeded resistance • However, individual muscle fibers shorten as connective tissues stretch • Important contractions to keep your body upright to oppose force of gravity Prof. Monsees

Situation in body is more complex • Normal daily activities involve a combination of isotonic and isometric muscle contractions • Muscles are not always positioned directly above the resistance and attached to bones, not to static weights • Changes in relative positions of muscles and articulating bones, effects of gravity, mechanical and physical factors interact to increase or decrease amount of resistance the muscle must overcome as movement proceeds Prof. Monsees

Situation in body is more complex (cont..) • Eccentric contractions (triceps) normally occur as a braking force in opposition to a concentric contraction (biceps) to protect joints (elbow) from damage. • During virtually any routine movement, eccentric contractions assist in keeping motions smooth, but can also slow rapid movements such as a punch or throw. Prof. Monsees

Levers Muscle contractions are a pull or force by relative positions of • Lever: Rigid shaft or bone • Fulcrum: point around which lever rotates. Pivot point or joint • Load: body weight or external resistance • Force: produced by muscular effort seesaw Prof. Monsees

3 Classes of Levers Weight, Fulcrum, aPplied force • Class I • Fulcrum between force and weight • Seesaw or head movement • Class II • Weight is between fulcrum and pull • Wheelbarrow, standing on toes: (F, metatarsal heads; P, calf muscles; W, body) • Class III • Pull located between fulcrum and weight • Person using a shovel: F, elbow; P, biceps; W, forearm • Most common Prof. Monsees

Leverage • 2nd class lever • force is farther away from fulcrum than resistance small force can move heavy weight effective force increases at expense of speed and distance Prof. Monsees

Leverage (cont…) 3rd class lever= opposite of 2nd class lever • force between fulcrum and resistance speed and distance travelled increased at expensive of effective force • E.g. elbow: resistance 6 times farther from fulcrum than applied force, i.e. effective force is reduced to same degreeForce decreases: muscle must generate 180 kg of tension to support 30 kg held in hand. Speed/distance increases: load will travel 45 cm when point of attachment moves just 7.5 cm Prof. Monsees

General principles of muscles • Origin or head: Muscle end attached to more stationary of two bones (or more proximal) • Insertion: Muscle end attached to bone with greatest movement (or more distal) • Belly: Largest portion of the muscle between origin and insertion • Synergists: Muscles that work together to cause a movement • Prime mover: Plays major role in accomplishing movement • Agonist: Muscle causing an action when contracts • Antagonist: A muscle working in opposition to agonist • Fixators: Stabilize joint/s crossed by the prime mover Prof. Monsees

Components of muscle action Head Belly Insertion Prof. Monsees

Center of mass/gravity Definition • Center of mass of a system of particles is a specific point at which the systems mass behaves as if it where concentrated • The center of mass is a function only of the positions and masses of the particles that comprise the system • Often also called as center of gravity – the point where gravity can be said to act Prof. Monsees

Center of gravity in human body Center of gravity is posterior to hip joint Prof. Monsees

Center of gravity alters during exercises Vertical shift lateral shift Prof. Monsees

Bipedal erect locomotion Definition • Bipedalismis standing or moving on two legs • Animal moving in bipedal manner = biped • E.g. human, primates, birds, kangaroos etc. • In contrast: the great majority of living vertebrates are quadrupeds Prof. Monsees

Bipedal erect locomotion • Most bipedal animals move with their backs close to horizontal, using a long tail to balance the weight of their bodies. • The primate version of bipedalism is unusual because the back is close to upright (completely upright in humans) and, among primates that move bipedally, only the lemurs have tails. • Humans and large birds walk by raising one foot at a time. • On the other hand macropods (e.g. kangaroos), smaller birds and bipedal rodents move by hopping on both legs simultaneously. Prof. Monsees

Advantages of bipedal locomotion • Bipedalism raises the head; this allows a greater field of vision with improved detection of distant dangers or resources. • While upright, non-locomotory limbs become free for other uses, including manipulation (in primates and rodents), flight (in birds), digging or combat (bears). • Upper limbs get free for other functions than locomotion  one reason for enlargement and development of the brain Prof. Monsees

Forms of bipedal movements • Standing  L 20 • Walking  L 20 • Running  L 21 Prof. Monsees

Biomechanics Wikipedia definition: Biomechanics is mechanics applied to biology. This includes research and analysis of the mechanics of living organisms and the application of engineering principles to and from biological systems. This research and analysis can be carried forth on multiple levels, from the molecular all the way up to the tissue and organ level. Some simple applications of Newtonian mechanics can supply correct approximations on each level, but precise details demand the use of continuum mechanics. Prof. Monsees

Gait analysis • Gait: is a particular way or manner of moving on foot, e.g. human gait (walking vs running), horse gait • Gait analysis: study of locomotion. Gait analysis is commonly used to help athletes run more efficiently and to identify posture-related or movement-related problems in people with injuries. • The study encompasses quantification, i.e., introduction and analysis of measurable parameters of gaits, as well as interpretation, i.e., drawing various conclusions about the animal (health, age, size, weight, speed, etc.) from its gait Prof. Monsees

Gait analysis • Gait is composed of periodic cycles, with a gait cycle time representing the time between two successive occurrences of the same event in gait. • We will do a video analysis in Prac 6 Prof. Monsees

Gait cycle for running body Prof. Monsees

Horse gaiting diagrams Prof. Monsees

Thank you for your attention! Next lecture is on Upper limb movements 1/2 Prof. Monsees

MBS 212 Human Movement