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Oxygen Debt vs. Recovery Oxygen

Fast Component. Phosphagens (ATP

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Oxygen Debt vs. Recovery Oxygen

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    1. Oxygen Debt vs. Recovery Oxygen Oxygen Debt (AV Hill) stated most lactic acid formed during exercise was converted to glycogen (~80%), Margaria introduced concept of Alactacid and lactacid debt components Contemporary termed Recovery Oxygen or Excess post-exercise oxygen consumption (EPOC) Fast component and slow component

    2. Fast Component Phosphagens (ATP & PC) Elevated oxygen consumption during this time period fuels the bodys need for: restoring myoglobin w/oxygen restoring blood levels of O2 O2 cost of breathing Increased heart rate (myocardial O2 Replenish phosphagens Magnitude of Fast Component volume is related to previous exercise intensity Include VO2 curve for steady state and for recovery.Include VO2 curve for steady state and for recovery.

    3. Fast Component Recovery Rapid recovery of phosphagens at start of recovery & later slows down 70% - 30 seconds 100% - 3-5 minutes PC recovery 84% restored in 2 minutes 89% restored in 4 minutes

    4. Replenishment of Energy Stores Restoration of ATP + PC Half-time = 30 sec; 1 min = 3/4s; 1.5 min = 7/8; 3 min = 63/64 Muscle glycogen .7 g/kg body wt/hr, carbohydrates with high glycemic index - On average 5% of muscle glycogen used during exercise is resynthesized each hour after exercise; minimal 20 hrs to restore muscle Lactic acid removal Provided 600 grams of CHO are consumed. During successive days of competition or intense training, athletes hould consume approximately 100 g of carbohydrate within 15-30 min after exercise followed by an additional 100 g feedings every two to four hours. 60% replenished after 10 hours providing a high carbohydrate intake Liquid, solid, simple sugar, complex carbohydrate feedings appear to be equally effective. Provided 600 grams of CHO are consumed. During successive days of competition or intense training, athletes hould consume approximately 100 g of carbohydrate within 15-30 min after exercise followed by an additional 100 g feedings every two to four hours. 60% replenished after 10 hours providing a high carbohydrate intake Liquid, solid, simple sugar, complex carbohydrate feedings appear to be equally effective.

    5. O2 - Myoglobin Stores Found in skeletal muscle Store for oxygen Involved functionally in transfer of oxgyen Inside the cell to inside the mito 11.2 ml/kg of muscle or ~500 ml Functional significance related to intermittent exercise - rapidly restored following short bout of exercise

    6. Slow Component of Recovery Elevated body temperature - ? metabolic activity Oxygen cost of ventilation Oxygen cost of ? myocardial activity ? Na-K pump Glycogen resynthesis Oxidation of lactic acid Slow component is relatively unaffected by a change in exercise intensity or duration until a threshold of a combined intensity (80%) and duration (20 min) is presented Hagberg (1980) stated that 60-70% of slow component oxygen can be accounted by effect of temperature.Slow component is relatively unaffected by a change in exercise intensity or duration until a threshold of a combined intensity (80%) and duration (20 min) is presented Hagberg (1980) stated that 60-70% of slow component oxygen can be accounted by effect of temperature.

    7. Exercise Related factors that cause extra O2 consumption Temperature effects mitochondrial O2 consumption, leading to decline in energy trapping efficiency (Brooks, 2000) BMR? 13% per degree Celsius increase in body temp Sympathetic stimulation increases metabolic rate of numerous tissues

    8. Lactic Acid Removal Rest recovery - half-time = 25 min.; 75 min for near complete recovery (95%) Exercise recovery - 30-45% of VO2max untrained; 50-65% VO2max trained; Stainsby, 1970. Half-time = 10 11 minutes Complete recovery = ~ 25 minutes (Bonen & Belcastro, 1976)

    9. EPOC Slow Recovery Rest recovery - half-time = 25 min.; 75 min for complete recovery Exercise recovery - 30-45% of VO2max untrained; 50-65% VO2max trained; - Stainsby, 1970.

    10. Muscle Glycogen Resynthesis Full repletion of muscle glycogen requires several days and depends on: Type of exercise causing depletion Amount of dietary carbohydrate consumed during recovery period Muscle glycogen depletion can be caused by: continuous endurance-like activities & intermittent, exhaustive activities) The studies from your text tended to be of 1-hr duration. Muscle glycogen depletion can be caused by: continuous endurance-like activities & intermittent, exhaustive activities) The studies from your text tended to be of 1-hr duration.

    11. Continuous Endurance Exercise Insignificant amount of muscle glycogen resynthesized in 1st 1-2 hours of recovery Complete restoration of muscle glycogen w/ high diet of CHO requires ~46 hours W/out high CHO diet, small quantity of muscle glycogen resynthesized during 5 d Rapid replenishment occurs during first several hours of recovery When food is available and physical activity is low, the hormonal situation (elevated insulin and low catecholamines) increases the activity of the glycogen storing enzyme glycogen synthetase To speed the replenishment of carbohydrates after a hard period of training or competition, it is wise to begin consuming carbohydrate-rich foods ASAP after exercising. Recommend consuming 100g CHO within the first 15-30 minutes of recovery. Consume high to oderate glycemic carbohydrates every two hours until 500 g are consumedWhen food is available and physical activity is low, the hormonal situation (elevated insulin and low catecholamines) increases the activity of the glycogen storing enzyme glycogen synthetase To speed the replenishment of carbohydrates after a hard period of training or competition, it is wise to begin consuming carbohydrate-rich foods ASAP after exercising. Recommend consuming 100g CHO within the first 15-30 minutes of recovery. Consume high to oderate glycemic carbohydrates every two hours until 500 g are consumed

    12. Intermittent, Short Duration Exercise A significant amount of muscle glycogen resynthesized in 30 min - 2 hrs with no food Complete resynthesis of muscle glycogen does not require a greater than normal intake of carbohydrate Complete resynthesis of muscle glycogen required a 24-hour recovery period when a normal or high CHO diet is consumed Muscle glycogen is most rapid during first several hours of recovery More rapid resynthesis takes place if the person remains inactive during the recovery period. With optimal CHO intake, glycogen stores are replenished at a rate of 5-7% per hour. Therefore, under the best conditions, it will take at least 20 hours to reestablish glycogen stores after a glycogen-depleting bout of exercise Bangsbo has found similar findings regarding the partial restoration of muscle glycogen during 1st hour of recovery.More rapid resynthesis takes place if the person remains inactive during the recovery period. With optimal CHO intake, glycogen stores are replenished at a rate of 5-7% per hour. Therefore, under the best conditions, it will take at least 20 hours to reestablish glycogen stores after a glycogen-depleting bout of exercise Bangsbo has found similar findings regarding the partial restoration of muscle glycogen during 1st hour of recovery.

    13. High & Moderate Glycemic Foods High glycemic foods - contain glucose, sucrose, cane maple, corn syrup, bagel, white potato, honey, carrots Moderate glycemic foods - whole grain bread, spaghetti, oatmeal, orange Glycemic index of food is determined from the integrated rise in blood glucose following consumption of a standard amount (50-100g) compared to glucose Jenkins et al., 1981 Glycemic effect describes the effect of food on blood glucose; how quickly glucose is absorbed after a person eats, how high blood glucose rises and how quickly it returns to normal Slow absorption, a modest rise in blood glucose, and a smooth return to normal are considered desirable; Fast absorption, a surge in blood glucose, and an overreaction that forces glucose below normal are undesirable. Glycemic index provides a measure of the rapidity with which sugar enters into blood following food consumption.Glycemic effect describes the effect of food on blood glucose; how quickly glucose is absorbed after a person eats, how high blood glucose rises and how quickly it returns to normal Slow absorption, a modest rise in blood glucose, and a smooth return to normal are considered desirable; Fast absorption, a surge in blood glucose, and an overreaction that forces glucose below normal are undesirable. Glycemic index provides a measure of the rapidity with which sugar enters into blood following food consumption.

    14. Skeletal Muscle Functional Anatomy Intact skeletal muscle organ Composed of muscle fascicles Composed of muscle fibers The intact skeletal muscle is composed of muscle fascicles or bundles, which in turn are composed of muscle fibers. Because each fiber is a single multinucleated cell, the term cell and fiber are used interchangeably. Fibers in turn, are composed of myofibrils arranged in parallel. Myofibrils are composed of sarcomeres arranged in series. Sarcomeres are the basic contractile units of skeletal muscle - composed of interdigitating thick and thin myofilaments The intact skeletal muscle is composed of muscle fascicles or bundles, which in turn are composed of muscle fibers. Because each fiber is a single multinucleated cell, the term cell and fiber are used interchangeably. Fibers in turn, are composed of myofibrils arranged in parallel. Myofibrils are composed of sarcomeres arranged in series. Sarcomeres are the basic contractile units of skeletal muscle - composed of interdigitating thick and thin myofilaments

    15. Different Kinds of Motor Units Aerobic Type Fibers Type I, red, slow-twitch (ST), or slow oxidative (SO) Anaerobic Type Fibers Type II, white, fast-twitch (FT), or fast-glycolytic (FG) IIA - fast-oxidative-glycolytic (FOG) IIB - fast-glycolytic (FG) IIC - Unclassified Myogenic factors have been found in muscle fibers that vary and affect the properties specific to the fiber. That is, fibers have different forms of myofibrillar and other proteins = isoforms Thus, fibers have different speeds and power production during contraction. One of the main differences is the myosin heavy chains. Type II fibers have a troponin with a higher Ca++ binding capacity and a faster process of cross-bridge attachment.Myogenic factors have been found in muscle fibers that vary and affect the properties specific to the fiber. That is, fibers have different forms of myofibrillar and other proteins = isoforms Thus, fibers have different speeds and power production during contraction. One of the main differences is the myosin heavy chains. Type II fibers have a troponin with a higher Ca++ binding capacity and a faster process of cross-bridge attachment.

    16. Basement Membrane Located adjacent to sarcolemma Loose collection of glycoprotein and collagen - not lipid bilayer Freely permeable to protein, solute, metabolites Wedged between B.M. and sarcolemma are cells known as satellite cells Important for growth & development Adaptive capacity to training & disuse Recovery from exercise induced damage Normally, satellite cells are dormant, but under conditions of stress or injury they are essential for the regenerative growth of new fibers. Satellite cells can migrate from one location to another area of higher need within a muscle fiber. Can undergo cell division to produce additional satellite cells. These cells migrate accross the sarcolemma into cytoplasm/cytosol, where they recognize each other, align and fuse into a myotube. Myotube is an immature muscle cell/fiber The multinucleated myotube will then differentiate into a mature fiber. In case of serious injury or neuromuscular disease, satellite cells are critical for regenerative growth What about hypertrophy of existing cells? Satellite cells are activated when muscle fibers hypertrophy. It remains to be determined how much this occur when muscles undergo resistance training.Normally, satellite cells are dormant, but under conditions of stress or injury they are essential for the regenerative growth of new fibers. Satellite cells can migrate from one location to another area of higher need within a muscle fiber. Can undergo cell division to produce additional satellite cells. These cells migrate accross the sarcolemma into cytoplasm/cytosol, where they recognize each other, align and fuse into a myotube. Myotube is an immature muscle cell/fiber The multinucleated myotube will then differentiate into a mature fiber. In case of serious injury or neuromuscular disease, satellite cells are critical for regenerative growth What about hypertrophy of existing cells? Satellite cells are activated when muscle fibers hypertrophy. It remains to be determined how much this occur when muscles undergo resistance training.

    17. A Single Multinucleated Cell Muscle Cell = Muscle Fiber Fibers composed of myofibrils Myofibrils are composed of Sarcomeres Sarcomeres are composed of thick & thin myofilaments

    18. Connective Tissue Membranes Epimysium Perimysium Basement membrane, endomysium, basal lamina The basement membrane is not a membrane in the usual sense. Rather than having the normal structure of a lipid bi-layer, the basement membrane is a loose collection of glyco-proteins and collagen network. It is freely permeable to proteins, solutes and other metabolites. An additional thin elastic membrane is found just beneath the basement membrane, and the terms plasma membrane or sarcolemma are used interchangeably. The sarcolemma is much more selective to ions, solutes and substrates crossing it. Critical for the following reasons: 1. Maintain acid - base balance in the fiber 2. Propagates the action potential/nerve impulse 3. Transports metabolites from the blood to the cytosol 4. At neuromuscular junction, a more elaborate region of functional folds The basement membrane is not a membrane in the usual sense. Rather than having the normal structure of a lipid bi-layer, the basement membrane is a loose collection of glyco-proteins and collagen network. It is freely permeable to proteins, solutes and other metabolites. An additional thin elastic membrane is found just beneath the basement membrane, and the terms plasma membrane or sarcolemma are used interchangeably. The sarcolemma is much more selective to ions, solutes and substrates crossing it. Critical for the following reasons: 1. Maintain acid - base balance in the fiber 2. Propagates the action potential/nerve impulse 3. Transports metabolites from the blood to the cytosol 4. At neuromuscular junction, a more elaborate region of functional folds

    19. Sarcomeres Mid-Portion - A-Band Outer ends - I-Bands H - Zone - bisected by M line Z - Disks or Z - Lines A-band - area that appears dark, composed of myosin. isotropic I-band - outer ends of each sarcomere appear light, primarily actin H-zone - central portion of A-band, more lightly stained - no actin associated with myosin. M - line contains proteins that keep the sarcomere in proper spatial orientation as it lengthens and shortens Z - lines - located at the end of each sarcomere The I-band and H-zone are less dense than other areas as there is no overlap of thick and thin filaments; this allows for greater penetration of light when examined with a microscope. A-band - area that appears dark, composed of myosin. isotropic I-band - outer ends of each sarcomere appear light, primarily actin H-zone - central portion of A-band, more lightly stained - no actin associated with myosin. M - line contains proteins that keep the sarcomere in proper spatial orientation as it lengthens and shortens Z - lines - located at the end of each sarcomere The I-band and H-zone are less dense than other areas as there is no overlap of thick and thin filaments; this allows for greater penetration of light when examined with a microscope.

    20. Contractile & Regulatory Proteins 20% of skeletal muscle comprised of protein 12% myofibrillar protein 8% enzymes, membrane proteins, transport channels and other proteins

    21. Myofibrillar Fraction of Skeletal Muscle Myosin Actin Tropomyosin Troponin C Protein M-line protein Alpha Actinin C protein - part of the thick filament, it is involved in holding the tails of myosin in a correct spatial agreement M - Line protein functions to keep the thick and thin filament in their correct spatial arrangement Alpha Actinin - attaches actin filaments together at the Z-disk. C protein - part of the thick filament, it is involved in holding the tails of myosin in a correct spatial agreement M - Line protein functions to keep the thick and thin filament in their correct spatial arrangement Alpha Actinin - attaches actin filaments together at the Z-disk.

    22. Myosin Thick filament Light meromyosin (LMM) Heavy meromyosin (HMM) S-1 and S-2 Subfragments Together form the crossbridge S-2 portion of HMM projects out at an angle from LMM =tail, and the S-1 portion is the globular head that can bind to actin - binding site for ATP and storage of energy S-2 portion of HMM projects out at an angle from LMM =tail, and the S-1 portion is the globular head that can bind to actin - binding site for ATP and storage of energy

    23. Myosin Myosin protein plays key role in development of muscular force & velocity of contraction Myosin is a hexameric (six-component) molecule 1 pair Myosin heavy chains (MHCs) (high molecular weight) 2 pairs of light chains (LCs) MHC protein molecules called isoforms These MHC isoforms have slight variations in their amino acid composition, particularly in the head regions (S-1 subfragment) where energy transduction processes occur during crossbridge cycle. Type 1, Type II a, Type II x and Type II b in order of their increasing ATPase activity. These different MHC isoforms provide different crossbridge turnover rates during contractionThese MHC isoforms have slight variations in their amino acid composition, particularly in the head regions (S-1 subfragment) where energy transduction processes occur during crossbridge cycle. Type 1, Type II a, Type II x and Type II b in order of their increasing ATPase activity. These different MHC isoforms provide different crossbridge turnover rates during contraction

    24. Actin Arranged in a double helix Tropomyosin Troponin Calcium binding subunit G Actin = each individual pearl F-Actin the entire string of pearls/strand of actin Each G actin contains a myosin head binding site Found at intervals along the thin filament, spaced at every seventh G actin, is the regulatory protein TROPONIN . Troponin has three subunits each with a special function 1. Troponin-T (TnT the tropomyosin-binding subunit) prevents tropomyosin from moving off actin. Loosely binds onto tropomyosin 2. Troponin I (TnI inhibitory subunit) positions tropomyosin on binding subunit. 3. Troponin C (TnC calcium binding subunit) When 4 calcium molecules bind to troponin C, the entire 3-subunit configuration changes, troponin physically moves tropomyosin to expose the myosin binding sites on actin.G Actin = each individual pearl F-Actin the entire string of pearls/strand of actin Each G actin contains a myosin head binding site Found at intervals along the thin filament, spaced at every seventh G actin, is the regulatory protein TROPONIN . Troponin has three subunits each with a special function 1. Troponin-T (TnT the tropomyosin-binding subunit) prevents tropomyosin from moving off actin. Loosely binds onto tropomyosin 2. Troponin I (TnI inhibitory subunit) positions tropomyosin on binding subunit. 3. Troponin C (TnC calcium binding subunit) When 4 calcium molecules bind to troponin C, the entire 3-subunit configuration changes, troponin physically moves tropomyosin to expose the myosin binding sites on actin.

    25. Troponin 1. Troponin-T (TnT the tropomyosin-binding subunit) prevents tropomyosin from moving off actin. Loosely binds onto tropomyosin 2. Troponin I (TnI inhibitory subunit) positions tropomyosin on binding subunit. 3. Troponin C (TnC calcium binding subunit) When 4 calcium molecules bind to troponin C, the entire 3-subunit configuration changes, troponin physically moves tropomyosin to expose the myosin binding sites on actin.

    26. Sarcoplasmic Reticulum & Relationships

    27. Sequences of events duirng contraction in striated muscle Depolarization is received at the sarcolemma & propagated down t-tubule network to sarcoplasmic reticulum (SR) Depolarization of SR in region of triad initiates the release of Ca++ from the SR and increase intracellular calcium Increased intracellular calcium increases calcium binding to troponin Troponin-calcium complex causes a structural change in position of troponin & tropomyosin on actin, enabling actin to bind to S1 units of myosin The junction of the t-tubule and sarcoplasmic reticulum (triad), calcium is released from the sarcoplasmic reticulum and increases the concentration of free calcium within the fiber. The bind of the calcium ions to the troponin molecules induces a conformational shift in the actin-troponin-tropomyosin association. This shift in three-dimensional molecular structure exposes a site that enables the noncovalent association of actin and the S1 units of myosin.The junction of the t-tubule and sarcoplasmic reticulum (triad), calcium is released from the sarcoplasmic reticulum and increases the concentration of free calcium within the fiber. The bind of the calcium ions to the troponin molecules induces a conformational shift in the actin-troponin-tropomyosin association. This shift in three-dimensional molecular structure exposes a site that enables the noncovalent association of actin and the S1 units of myosin.

    28. Sequences of muscle contraction Actin-myosin binding enables the S1 (head) units to move immediately to relaxed position, causing movement of attached actin toward central region of sarcomere; ADP and Pi are released from S1 unit during this process. Actin connected to Z-lines, actin movement results in the shortening of each sarcomere with the fibers of stimulated motor unit Provided continual ATP replenishment at myosin-actin sites of sarcomere, ATP molecules bind to myosin S1 units, causing release of S1 units from actin At the conclusion of the previous crossbridge cycle, the ATP that was bound At the conclusion of the previous crossbridge cycle, the ATP that was bound

    29. Sequences of muscle contraction During release of actin and myosin, ATP is hydrolyzed to ADP and Pi, causing S1 units to change conformation to a vertical strained position If increased intracellular Ca++ is maintained (continued neural stimulation), myosin S1 units continue cyclical attachment and detachment to actin Relaxation occurs when nerve impulses not received by neuromuscular junction and Ca++ actively pumped back into the SR It is believed that ATP hydrolysis provides the free energy needed to move the S1 units to the strained position Referred to as contraction cyclingIt is believed that ATP hydrolysis provides the free energy needed to move the S1 units to the strained position Referred to as contraction cycling

    30. Sliding Filament Theory Actin + Energized Myosin + ADP + Pi = actin binding Actin + Energized Myosin + ADP + Pi = actin binding = crossbridge movement Actin + Myosin + ATP = crossbridge dissociation from actin Actin + Myosin + ATP = ATP hydrolysis Stored energy is released and ADP and Pi are released from myosin during the crossbridge movement Actin and myosin have a strong attachment. The linkage is broken when ATP binds to myosin. Following the dissociation of actin and myosin, the ATP bound to myosin is hydrolyzed. The free energy from ATP is bound to the myosin.Stored energy is released and ADP and Pi are released from myosin during the crossbridge movement Actin and myosin have a strong attachment. The linkage is broken when ATP binds to myosin. Following the dissociation of actin and myosin, the ATP bound to myosin is hydrolyzed. The free energy from ATP is bound to the myosin.

    31. Sequence of Events

    32. Animated Sarcomere

    33. Analogy: ATP Activating Myosin Head Visualize spring - loaded mousetrap - takes energy to set the trap - much like splitting ATP to set or activate the myosin Once set, the trap releases energy when it is sprung, similar to myosin head possessing stored energy which will be released when the myosin heads bind to actin and swivel Plowman & Smith (1997)

    34. Distribution of FT and ST Fibers Generally, majority of muscles contain mixture of FT and ST fibers Soleus - 25-40% more ST than other leg muscles Triceps - 10-30% more FT than other arm muscles Composition varies between regions of same muscle, between different muscles in same person and among the same muscles of different people

    35. Structural & Functional Characteristics of Type I & II Muscle Fibers Generally, Type II > Type I in size Type I fibers have >? mitochondrial density & myoglobin content; greater capillarization Type I & IIA have higher quantities of stored triglycerides Increase in Type II size: allows for more contractile filaments resulting in higher force production - More developed sarcoplasmic reticulum - Troponin has a higher Ca++ binding capacity - Faster process of cross-bridge attachment (due to Myosin ATPase activity level) Increase in Type II size: allows for more contractile filaments resulting in higher force production - More developed sarcoplasmic reticulum - Troponin has a higher Ca++ binding capacity - Faster process of cross-bridge attachment (due to Myosin ATPase activity level)

    36. Nerve and Recruitment Characteristics Instigating Movement Initiating Movement Motor cortex ---> corticospinal tract Cerebellum --->correcting rapid motor patterns Basal ganglia & several nuclei inform motor cortex Motor Cortex--->Corticospinal tract---> Other connections from the Red Nucleus, Cerebellum and basal ganglia are important for the refinement of the patterns or action potentials from motor cortex. Cerebellum-coordinating and correcting rapid motor patterns, for preparing future motor patterns and for storing correct movement sequences. Neural output from the cerebellum is responsible for exciting agonist muscles and inhibiting antagonist muscles. As the cerebellum receives afferent input from peripheral mechanoreceptors, it immediately adjusts errors to make the completion of the motor pattern smoother. Basal ganglia-several nuclei within the mid brain and lower brain that receive nerves from the motor cortex and primarily return nerves back to the cortex. In other words, it receives input from regions of the brain and informs the motor cortex of appropriate movement pattersn or of the appropriate speed at which movement patterns should occur. Red Nucleus-is responsible for assisting the motor cortex in causing refined movement of the distal muscles of the body (forearm, lower leg) All components of motor control regions of the brain operate together in a complex manner that results in the controlled and precisely orchestrated series of action potentials propagated to the appropriate alpha motor nerve.Motor Cortex--->Corticospinal tract---> Other connections from the Red Nucleus, Cerebellum and basal ganglia are important for the refinement of the patterns or action potentials from motor cortex. Cerebellum-coordinating and correcting rapid motor patterns, for preparing future motor patterns and for storing correct movement sequences. Neural output from the cerebellum is responsible for exciting agonist muscles and inhibiting antagonist muscles. As the cerebellum receives afferent input from peripheral mechanoreceptors, it immediately adjusts errors to make the completion of the motor pattern smoother. Basal ganglia-several nuclei within the mid brain and lower brain that receive nerves from the motor cortex and primarily return nerves back to the cortex. In other words, it receives input from regions of the brain and informs the motor cortex of appropriate movement pattersn or of the appropriate speed at which movement patterns should occur. Red Nucleus-is responsible for assisting the motor cortex in causing refined movement of the distal muscles of the body (forearm, lower leg) All components of motor control regions of the brain operate together in a complex manner that results in the controlled and precisely orchestrated series of action potentials propagated to the appropriate alpha motor nerve.

    37. Size Principle of Motor Unit Recruitment Motor unit use (recruitment) is directly related to the size and ease of triggering an A.P. (nerve impulse) Smaller the soma (cell body), the easier the motor unit can be recruited Motor units with large cell bodies (fast-fatiguable and fast fatigue-resistant) will be used last during recruitment For example, when one walks slowly, the movement is supported primarily by slow motor units. When one breaks into a sprint, the slow units are still recruited, but in addition, the fast units are recruited.For example, when one walks slowly, the movement is supported primarily by slow motor units. When one breaks into a sprint, the slow units are still recruited, but in addition, the fast units are recruited.

    38. Wave Summation Two stimuli in rapid succession Asynchronous summation of motor unit = smooth contraction.(some units contract/twitch and some relax) During submaximal efforts , some motor units contract and summate asynchronously while others relax As each motor unit comes into play, one sees a fusing with prexisting twitches of already contracting units this produces a continued contraction of any given level of strength that is smooth and nonjerkyAsynchronous summation of motor unit = smooth contraction.(some units contract/twitch and some relax) During submaximal efforts , some motor units contract and summate asynchronously while others relax As each motor unit comes into play, one sees a fusing with prexisting twitches of already contracting units this produces a continued contraction of any given level of strength that is smooth and nonjerky

    39. Types of Contractions Isometric no change in muscle length; and/or if external load applied to muscle is equal to the amount of force being developed Concentric-external force is less than the force the muscle is generating = shortening Eccentric-external force is greater than the force the muscle is generating=lengthening

    40. Muscle Relationships Length-tension relationship Force-velocity relationship

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