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Explosive strength. SEC-series elastic component, connective tissue but mainly tendon. Muscle Spindles.
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SEC-series elastic component, connective tissue but mainly tendon
Muscle Spindles w A group of 4 to 20 small muscle fibers (intrafusal) with sensory and motor nerve endings, covered by a connective tissue sheath, and connected in parallel with extrafusal (or regular) muscle fibers. w The middle of the spindle can stretch, but cannot contract as it contains little or no actin and myosin. w When extrafusal fibers attached to the spindle are stretched, sensory neurons on the spindle transmit information to the CNS about the muscle’s length. w Reflexive muscle contraction is triggered through the alpha motoneuron to resist further stretching. w Gamma motoneurons activate intrafusal fibers, causing the middle of the spindle to stretch, making the spindle sensitive to small degrees of stretch.
Golgi Tendon Organs (GTOs) w Encapsulated sensory organs through which muscle tendon fibers pass w Located close to the tendon's attachment to the muscle w Sense small changes in tension w Inhibit contracting (agonist) muscles and excite antagonist muscles to prevent injury
Muscle and Joint Proprioceptors w Kinesthetic receptors in joint capsules sense the position and movement of joints. w Muscle spindles sense muscle length and rate of length change. w Golgi tendon organs (GTOs) detect the tension of a muscle on its tendon, providing information about the strength of muscle contraction.
Conscious Control of Movement w Neurons originating in the primary motor cortex control voluntary muscle movement (cerebro-spinal motoneurons, or “upper motoneurons”). w Clusters of nerve cells in the basal ganglia initiate sustained and repetitive movements—walking, running, maintaining posture, and muscle tone. w The cerebellum compares the actual movement with the intended movement. For this reason it is called a “comparator.” Engrams are learned motor patterns stored in the cortex.
Metabolic Specificity of Training • The use of appropriate exercise intensities and rest intervals allows for the “selection” of specific energy systems during training and results in more efficient and productive regimens for specific athletic events with various metabolic demands.
Metabolic Specificity of Training • Interval Training • Interval training is a method that emphasizes bioenergetic adaptations for a more efficient energy transfer within the metabolic pathways by using predetermined intervals of exercise and rest periods. • Much more training can be accomplished at higher intensities • Difficult to establish definitive guidelines for choosing specific work-to-rest ratios
Metabolic Specificity of Training • Combination Training • Combination training adds aerobic endurance training to the training of anaerobic athletes in order to enhance recovery (because recovery relies primarily on aerobic mechanisms). • May reduce anaerobic performance capabilities, particularly high-strength, high-power performance • Can reduce the gain in muscle girth, maximum strength, and speed- and power-related performance • May be counterproductive in most strength and power sports
Chapter 3 • Endocrine
Key Point • The specific force produced in activated fibers stimulates receptor and membrane sensitivities to anabolic factors, including hormones, which lead to muscle growth and strength changes.
Mechanisms of Hormonal Interactions • Interactions with receptors are greater when • exercise acutely increases the blood concentrations of hormones. • Receptors are less sensitive when • the physiological function to be affected is already close to a genetic maximum, • resting hormone levels are chronically elevated due to disease or exogenous drug use, and • mistakes are made in exercise prescriptions.
Hormonal Changes in Peripheral Blood • Mechanisms contributing to changes in peripheral blood concentrations of hormones: • Fluid volume shifts • Tissue clearance rates • Hormonal degradation • Venous pooling of blood • Interactions with binding proteins in the blood • These mechanisms interact to produce certain concentrations of hormones in the blood, which influences the potential for interaction with receptors.
Key Point • Hormone responses are tightly linked to the characteristics of the resistance exercise protocol.
Adaptations in the Endocrine System • Examples of the potential types of adaptation with resistance exercise: • Amount of synthesis and storage of hormones • Transport of hormones via binding proteins • Time needed for the clearance of hormones through liver and other tissues • Amount of hormonal degradation that takes place over a given period of time • How much blood-to-tissue fluid shift occurs with exercise stress • How many receptors are in the tissue
Primary Anabolic Hormones • There are three primary hormones involved in muscle tissue growth and remodeling: • Testosterone • Growth hormone (GH) • Insulin-like growth factors (IGFs)
Primary Anabolic Hormones • Testosterone • The primary androgen hormone that interacts with skeletal muscle tissue • Effects on muscle tissue: GH responses that lead to protein synthesis, increased strength and size of skeletal muscle, increased force production potential and muscle mass • Diurnal variations • Men: Exercise later in the day is more effective for increasing overall testosterone concentrations over an entire day. • Women: There are lower concentrations and little variation during the day.
Biosynthesis of TestosteroneFrom Cholesterol • Figure 3.8 (next slide) • The series of chemical reactions in the biosynthesis of testosterone from cholesterol
It is difficult to understand why statisticians commonly limit their inquires to averages and do not revel in more comprehensive views. Their souls seem as dull to the charm of variety as that of the native of one of our flat English counties, whose retrospect of Switzerland was that, if its mountains could be thrown into lakes, two nuisances could be got rid of at once. Sir Francis Galton. Natural Inheritance, p.62 (Macmillan, London, 1889).
Key Point • Large muscle group exercises result in acute increased serum total testosterone concentrations in men.
Primary Anabolic Hormones • Testosterone • Free Testosterone and Sex Hormone–Binding Globulin • A higher total (bound) testosterone level allows for the potential of more free testosterone. • The free hormone hypothesis states that only the free hormone interacts with target tissues. • Testosterone Responses in Women • Women have 15- to 20-fold lower concentrations of testosterone than men do, and if acute increases occur after a resistance training workout, they are small. • Training Adaptations of Testosterone
Serum TestosteroneResponses to Exercise • Figure 3.9 (next slide) • Male (green bars) and female (gold bars) serum testosterone responses to two exercise programs: • (a) a protocol entailing eight exercises using 5RM and 3-minute rest periods between sets and exercises • (b) a program that called for eight exercises using 10RM and 1-minute rest periods between sets and exercises(the total work for the second protocol was higher) • * = significantly above preexercise levels • + = significantly above the other group
Figure 3.9 Reprinted, by permission, from Kraemer et al., 1990.
Primary Anabolic Hormones • Growth Hormone • Secreted by the pituitary gland • Interacts directly with target tissues, which include bone, immune cells, skeletal muscle, fat cells, and liver tissue • Regulated by neuroendocrine feedback mechanisms and mediated by secondary hormones • GH release patterns altered by age, gender, sleep, nutrition, alcohol consumption, and exercise
Growth Hormone Cybernetics and Interactions • Figure 3.10 (next slide) • Diagram of growth hormone cybernetics and interactions
Primary Anabolic Hormones • Growth Hormone • Efficacy of Pharmacological Growth Hormone • Pharmacological use of GH has unknown and unpredictable results. • Growth Hormone Responses to Stress • GH responds to exercise stressors, including resistance exercise. • GH response depends on load, rest, and volume of exercise.
Primary Anabolic Hormones • Growth Hormone • Growth Hormone Responses in Women • GH concentrations and responses to exercise vary with menstrual phase. • Women have higher blood levels of GH than do men. • Training Adaptations of Growth Hormone • There is little change in single measurements of resting GH concentrations in resistance-trained individuals. • Training-related changes in GH include a reduction in GH response to an absolute exercise stress and alterations in GH pulsatility characteristics.
Key Point • Growth hormone is important for the normal development of a child and appears to play a vital role in adapting to the stress of resistance training. However, GH injections result in a wide variety of secondary effects not related to changes in muscle size or strength and can, in fact, result in hyper-trophy with less force production than occurs with exercise-induced hypertrophy.
Primary Anabolic Hormones • Insulin-Like Growth Factors • Exercise Responses of Insulin-Like Growth Factors • Insulin-like growth factor I (IGF-I) is most studied because of its role in protein anabolism. • Exercise results in acute increases in blood levels of IGF-I.
Insulin-Like GrowthFactor I and Exercise • Figure 3.11 (next slide) • Responses of insulin-like growth factor I to a multiple-set, heavy resistance exercise protocol on three consecutive days with and without nutritional supplementation of protein-carbohydrate (i.e., Mass Fuel) before and during the 1-hour recovery period • †p < .05 from corresponding placebo value
Figure 3.11 Adapted, by permission, from Kraemer et al., 1998.
Primary Anabolic Hormones • Insulin-Like Growth Factors • Training Adaptations of Insulin-Like Growth Factors • Changes in IGF-I appear to be based on the starting concentrations before training. • If basal concentrations are low, IGF-I increases. • If basal concentrations are high, there is no change or it decreases.
