KIN 365 Chp. 2
KIN 365 Chp. 2 KIN 365
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This 11 page Class Notes was uploaded by Taylor Fendley on Tuesday February 9, 2016. The Class Notes belongs to KIN 365 at University of Alabama - Tuscaloosa taught by Colleen Geary in Spring2015. Since its upload, it has received 44 views. For similar materials see Applied Biomechanics in Kinesiology at University of Alabama - Tuscaloosa.
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Date Created: 02/09/16
Chapter Two Functional Aspects of the Sensory Motor System 1/26 1. Motor Unit a. A motor nerve and all that in innervates or communicates with b. Signals the contraction of muscle fibers if stimulus is adequate for each of the fibers i. Action potential c. To produce more force, the main method is to recruit more fibers to contract, a process called recruitment d. Recruitment increases the number of muscle fibers innervated i. The main muscular response used to produce greater muscle tension ii. The more fibers recruited, the stronger the muscle action e. In review, two ways to produce more tension (two neuromuscular adaptations) in a muscle are to: i. Increase the frequency at which you send action potentials 1. Sending multiple action potentials to muscle fibers causes multiple twitches ii. Recruit more muscle fibers f. Neuromuscular adaptations are when the brain works with the muscles to produce a structural or functional change in the body g. The number of motor units responding (and number of muscle fibers contracting) within the muscle may vary significantly from relatively few to virtually all i. You can have one motor unit communicate with one or two muscle fibers, or a whole bunch of muscle fibers h. Variation depends on: i. The number of muscle fibers within each activated motor unit ii. The number of motor units activated 1. The strength of the action potential (levels of stimulus) i. All or None Principle i. Regardless of number, individual muscle fibers within a given motor unit will either fire and contract maximally or not at all 2. Fiber Composition of Muscles a. ALL muscle fibers within one motor unit are the same type of muscle fiber b. The motor nerve dictates what type of fiber the particular motor unit is i. SO, FOG, FG c. The recruitment of fiber types usually occurs in a preferential manner according to the size of the motor nerve supplying the fibers i. The smallest fibers are recruited first 1. Slow twitch fibers 2. They have the longest possibility of contracting a. Highest endurance capability b. Ex. Running and walking ii. The largest fibers are recruited last 1. Reserved until they are truly necessary d. Can have motor units with a lot or a few muscle fibers i. Very precise 1. Small motor unit 2. A small number of fibers controlled by one motor unit a. Ex. Motor units that control eye movement ii. Less precise 1. Large motor unit 2. A large number of fibers controlled by one motor unit a. Ex. Quad muscles can have about 500 fiber in motor unit 3. Muscle Fibers a. All muscle contractions / actions are caused by muscle fibers b. Two types of muscle fibers have been identified i. Slow and Fast Twitch c. Slow Twitch i. Build and decrease tension slowly 1. Takes longer for their energy supply to produce the necessary ATP 2. Only one type of slow twitch muscle fiber a. SO—slow oxidative b. The rate at which energy is produced (slow) c. Oxidative—with oxygen d. Fast Twitch i. Build and decrease tension rapidly ii. They have energy ready, and doesn’t have to go through oxidative pathways (anaerobic, or glycolytic pathways) iii. Two types 1. FOG—Fast Oxidative and Glycolytic a. Type of muscle fibers that can be changed; easily and readily available to turn into something else 2. FG—Fast Glycolytic 4. Types of Muscle Fibers a. Slow Oxidative Fibers (SO) i. Fuel Source: Oxidative Phosphorylation 1. Oxidative phosphorylation creates ATP through the electron transport chain 2. Requires oxygen to create energy ii. Aerobic fibers iii. Characteristics: 1. Low strength of contraction 2. Low anaerobic capacity 3. Small in size 4. High capillary density 5. Highly resistant to fatigue iv. Use: 1. Activities that are done over a longer period of time but don’t require a great deal of strength 2. Ex. Running a marathon, hiking, walking, swimming long distances b. Fast Oxidative & Glycolytic (FOG) i. Energy Source: Hybrid 1. Can use energy made fast without oxygen (anaerobic pathway) 2. Can use energy made slowly with oxygen (aerobic pathway) ii. Characteristics: 1. High speed and strength of contraction 2. Can use energy made aerobically and anaerobically 3. Intermediate sized fibers 4. High capillary density 5. Fatigability varies a. More fatigue than SO b. Not as fatigable as FG iii. Use: 1. Depends on energy source 2. Can be trained to be more oxidative in nature and act more like a SO, but will never be as effective in their actions 3. Can be trained to be more anaerobic in nature and act more like a FG, and can be pretty good in their actions c. Fast Glycolytic (FG) i. Energy Source: Glycolysis 1. Glycolysis is an energy pathway with twelve steps that gives off a lot of ATP quickly but also runs out quickly 2. No oxygen is required to create energy (anaerobic) ii. Characteristics: 1. Highest speed and strength of contraction 2. High anaerobic capacity 3. Largest of the three types of muscle fibers 4. Low capillary density 5. Low aerobic capacity 6. Most easily fatigable iii. Use: 1. Activities that are forceful and quick a. Require a “big burst” 2. Ex. Sprints, quick strong reflexes d. SO, FOG, FG 5. Fiber Composition and Training a. Cannot change fiber composition of: i. Fast twitch fibers to slow twitch fibers ii. Slow twitch fibers to fast twitch fibers b. Can change fiber composition of: i. FG fibers into FOG fibers 1. Ex. Distance training 2. Shift produced through endurance training ii. FOG fibers into FG fibers 1. Ex. Weight training 2. Shift produced through short-duration training iii. This is possible because they are both within the fast twitch category iv. The aerobic capacity and glycogen content of the muscle can be improved with training 1. Done through specific training 2. Most of the change will come from the FOG fibers (hybrid fibers) because they can pull from both energy sources c. Selective recruitment i. Neurons tend to recruit smaller fiber types than larger fiber types 1. Smallest output force—slow oxidative 2. Slightly larger output force—fast oxidative and glycolytic 3. Largest output force—fast glycolytic 6. Muscle Action a. If summation/tetanus is reached, the force of the muscle contraction of fiber will increase accordingly, because of increased calcium available and a muscle contraction will occur b. Contractions occur when tension is developed in a muscle as a result of a stimulus i. The term contraction may be confusing because in some contractions the muscle doesn’t shorten in length c. As a result, it has become increasingly common to refer to the various types of muscle contractions as muscle actions/joint actions instead d. All muscle contractions are either isotonic or isometric 7. Types of Muscle Action a. Isometric Contraction i. Active tension is developed within muscle but joint angles remain constant ii. Static contractions that prevent motion iii. Significant amount of tension may be developed in muscle to maintain joint angle in a relatively static or stable position iv. May be used to prevent a body segment from being moved by external forces b. Isotonic Contraction i. Involves muscle developing active tension to either cause or control joint movement ii. Dynamic contractions iii. The varying degrees of tension in muscles result in joint angles changing iv. Either concentric or eccentric depending on whether the muscle shortens or lengthens 8. Proprioceptors a. Mechanism by which the body is able to regulate body position and movement by responding to stimuli subconsciously and sending that information back to the brain b. These internal receptors are located in the skin, the inner ear, and in and around the joints, muscles, and tendons c. Respond to changes in the position and acceleration of body segments i. Provide feedback relative to the position of the body and limbs, and the movement of the joint d. There are multiple types i. The two types stimulated during muscle actions are called musculotendinous receptors 9. Musculotendinous Receptors a. Used in muscular control and coordination b. Provide feedback relative to the movement of the joint, specifically: i. Tension within the muscles ii. Length of muscles iii. Rate-of-change in length of muscles iv. Contraction state of muscles c. Two types of musculotendinous receptors: Golgi tendon organs (GTOs) and muscle spindles 10. Golgi Tendon Organs a. Located in the tendons b. Sensitive to tension development in tendons i. Due primarily to muscle contraction, and passive stretch of tendon c. Keeps muscle from excessively contracting by inhibiting the motor nerve (protective effect) d. Tension in tendons and GTO increases as muscle contracts, activating GTO i. GTO stretch threshold is reached ii. Impulse sent to CNS iii. CNS send signal to muscle to relax iv. Facilitates activation of antagonist as a protective mechanism e. Signals: i. Afferent signals sent up spinal cord in response to excessive contraction or passive stretch of tendons ii. Responding effect signal has two purposes: 1. Inhibition (relaxation) of the contraction of the associate muscle (agonist) a. Relaxation of agonist (working muscle) 2. Excitation (contraction) of the opposing muscle, the associated muscles’ antagonist a. Contraction of antagonist (associated muscle) f. Example i. A weight lifter attempting an extremely heavy resistance in biceps curl ii. Lifter reaches a point of extreme overload 1. GTO activated iii. Biceps suddenly relaxes/triceps suddenly contract iv. Appears as if lifter throwing weight down 1. Really, GTO has caused inhibition of biceps and contraction of triceps 11. Muscle Spindle a. Located in muscles between the fibers b. Sensitive to the rate and degree of muscle strength c. As you stretch a muscle: i. Stretch of muscle spindles ii. Excites sensory nerves to send signals up spinal cord iii. CNS sends motor signal to cause a reflexive contraction of the associated muscle (agonist contracts) occurs 1. Called the myotatic or stretch reflex d. Signals: i. Afferent signal sent up spinal cord in response to excessive stretch or rapid stretch ii. Efferent signal sent in response to “stretch” has two purposes: 1. Excitation and contraction of the associated muscle (agonist) a. Agonist contracts 2. Inhibition and relaxation of the associated muscles’ antagonist a. Antagonist prevented from contracting e. Example i. Patellar tendon reflex 1. Sudden tap on patellar tendon causes a quick stretch of musculotendinous units of quads 2. Quick quad stretch activates muscle spindle 3. Information is sent to the CNS to quickly contract quads 4. Causes knee jerk 12. Reciprocal Inhibition a. Two things can happen when a muscle contracts b. Sensory nerve excites agonist and inhibits antagonist i. Caused by: Muscle spindles c. Sensory nerves excite antagonist and inhibit agonist i. Caused by: Golgi tendon organs (GTOs) d. GTOs vs. Muscle Spindles e. Either one occurring is called reciprocal inhibition 13. Fiber Length a. Another factor that affects the contraction of the muscle is the length of the muscle fiber before it is stimulated i. Resting length b. This length before stimulation and subsequent tetanic tension development is called the length-tension relationship c. For each muscle, an optimal length exists for developing tetanic tension (maximal tension development during the contraction) i. This optimal length corresponds with maximum overlap of thick myosin filament and thin actin filament d. Development of tension is optimized when maximal number of active actin sites are available for attachment of myosin cross bridges e. If a sarcomere is stretched beyond its optimal length, force output steadily declines i. Decline occurs because thin filaments pulled away from thick filaments, preventing myosin heads from binding to active actin sites f. If a sarcomere is not stretched to its optimal length, force output is virtually zero i. Lack of force production is due to actin sites being blocked by previously attached myosin heads physically preventing new myosin cross bridges from binding g. The theoretical optimal length of an intact muscle corresponds to muscle’s resting length, however… i. The elastic force contributed by elastic components changes this optimal length for optimal force production 1. Elastic components are non-contractile components of muscle, and are stretched passively rather than by muscle contraction 2. Help produce tension by storing energy as the muscle lengthens during a passive stretch h. The relationship between muscle length and muscle tension, at time muscle is stimulated to contract is as follows i. Shorter muscle= less tension 1. If you don’t stretch beyond 70-80% of resting length, the ability to develop contractile tension and exert force is essentially reduced to zero ii. Longer muscle=more tension 1. But if muscle is too long=less tension 2. If stretched beyond 120-130% of resting length, there’s a significant decrease in the amount of tension a muscle can develop and the amount of force a muscle can contract iii. Muscles generate the greatest amount of tension when stretched between 70-80% and 120-130% of its resting length 1. 120-130% is with elastic components iv. Comparison 14. Active and Passive Insufficiencies a. Cannot contract (active) the same amount of muscle tension or stretch (passive) with the same amount of flexibility across two joints at the same time b. These insufficiencies ONLY apply to two joint muscles 1. Two joint muscles cross more than one joint 2. Even if they cross more than two joints, they still suffer from insufficiencies c. Active Insufficiency i. The point reached when a muscle becomes shortened to the point it can no longer generate/maintain active tension 1. Ex. Hamstring muscle a. If shortened, contract across one joint, ex. Hip i. It cannot keep shortening (contracting) across other joint, knee ii. Failure to produce force at second joint when muscles are contracted across first joint 1. Decreased ability to form a fist in wrist flexion is an example of active insufficiency d. Passive Insufficiency i. The state reached when a muscle becomes stretched to the point where it can no longer lengthen and allow movement 1. Ex. Hamstring muscle a. If lengthened across one joint, ex. Hip i. It cannot keep lengthening (stretching) across other joint, knee ii. Restriction of second joint range of motion when muscles are full stretched across first joint 1. Decreased range of movement for wrist extension with the fingers extended is an example of passive insufficiency e. A muscle can only shorten/contract so much 15. Force-Velocity Relationship a. The final player affecting force production during muscle action is the velocity of the contraction, called the Force-Velocity Relationship i. The greater the load against which a muscle must contract, the lower the velocity of that contraction will be b. At a 90 degree angle, 100% of muscle force contributes to movement of the bones i. Muscle is strongest at 90 degrees ii. Muscle is weaker at either end of 90 degrees c. But, most actions do not require you to hold muscle at 90 degrees, so what happens to force production during different types of muscle contractions? d. One of two situations can occur when tension is produced in a muscle: i. A segment moves 1. Dynamic tension—isotonic contraction ii. A segment does not move 1. Static tension—isometric contraction e. A muscle can adjust the force of its contraction to match the resistance that it experiences during a contraction, at the cost of the speed of the contraction i. The greater the load against which a muscle must contract, the lower the velocity of that contraction f. The amount of force exerted then depends on the length of time the muscle has to contract, describing the Force-Velocity Relationship 16. Dynamic Tension a. Isotonic contraction i. When the segment (body part) moves in the direction or opposite to the direction of applied muscular tension b. Concentric tension i. Contraction of a muscle during which the muscle shortens and causes movement towards the midline of the body 1. Ex. Up movement of push-up for triceps 2. Ex. Down movement of push-up for biceps c. Isotonic contractions i. Least amount of force of ALL three contractions d. Slower speed (velocity) of concentric contraction – more force e. Faster speed (velocity) of concentric contraction – least force i. Probably due to: 1. High metabolic cost 2. The faster the contraction, the fewer cross-bridge interactions a. Due to the inability of some myosin cross-bridges to bind with active actin sites b. Results in the loss of force production f. Eccentric tension i. Contraction of a muscle during which the muscle lengthens and causes movement away from the midline of the body 1. Ex. Down movement of push-up for triceps 2. Ex. Up movement of push-up for biceps ii. Slower eccentric contraction—not as much force iii. Faster eccentric contraction—more force iv. No matter the velocity, eccentric contractions can develop more force than ANY velocity concentric contraction, and even more than static contractions 1. Probably due to: a. Low metabolic cost b. Elastic component assistance c. Some cross-bridges remaining bound, increasing the total number of active cross-bridges 17. Static Tension a. Isometric contraction i. When a muscle produces tension or force against an opposing force or resistance and the segment of muscle does not move ii. Because static contraction occurs without muscle movement, velocity is not an issue iii. Produces more force than ANY CONCENTRIC contraction 1. Probably due to: a. Maximal cross-bridge interaction maximum force output b. Myosin cross-bridges, without time constraints, attach freely to active actin sites b. Isometric tension i. Muscular contraction during which no discernible segmental movement is taking place ii. Muscles develop tension with no visible change in muscle length iii. Ex. Plank, wall squats iv. Ex. Arm wrestling someone with exactly equal strength 18. In Review a. Amount of force generated listed from least to greatest i. Faster concentric contraction ii. Slower concentric contraction iii. Static/isometric contraction iv. Slower eccentric contraction v. Faster eccentric contraction 1. Up to a point at which force production levels off b. Maximum amount of force generation is achieved at approximately 30% of maximal contraction velocity i. Beyond 30% of maximal velocity, force production decreases with increasing velocity ii. Slows down the amount of time spend on contraction (velocity of shortening) with any amount of force in order to produce the greatest amount of power
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