KIN325-Scientific Principles of Strength Training-Web.ppt

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KIN325-Scientific Principles of Strength Training-Web.ppt

  1. 1. The Scientific Principles of Strength Training <ul><li>Muscular Strength : The amount of force a muscle can produce with a single maximal effort </li></ul><ul><li>Mechanical Strength: the maximum torque that can be generated about a joint </li></ul>
  2. 2. Torque about the elbow joint <ul><li>Strength determined by: </li></ul><ul><li>Absolute force developed by muscle </li></ul><ul><li>Distance from joint center to tendon insertion </li></ul><ul><li>Angle of tendon insertion </li></ul>
  3. 3. Shoulder joint torque as a function of arm position
  4. 5. Structural organization of skeletal muscle From Principles of Human Anatomy (7 th edition), 1995 by Gerard J. Tortora, Fig 9.5, p 213
  5. 6. 6-6 From Basic Biomechanics by Susan Hall (3 rd edition), Fig 6.6, page 153
  6. 7. From Skeletal Muscle: Form and Function (2 nd ed) by MacIntosh, Gardiner, and McComas. Fig 1.4, p. 8.
  7. 8. 6-5 From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.5, page 152
  8. 9. 6-3 From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.3, page 150
  9. 10. From Exercise Physiology: Theory and Application to Fitness and Performance (6 th Edition) by Scott K. Powers and Edward T. Howley. Fig 8.6 P. 147
  10. 11. A motor unit: single motor neuron and all the muscle fibers it innervates From Basic Biomechanics Instructors manual by Susan Hall (2nd edition, 1995), Fig TM 31
  11. 12. 6-7 From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.7, page 154
  12. 13. 6-8 From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.8, page 154
  13. 14. <ul><li>Types of muscle fiber: Fast twitch vs Slow Twitch </li></ul><ul><li> Type I Type IIa Type IIb </li></ul><ul><li> ST Oxidative FT Oxidative - FT Glycolytic </li></ul><ul><li> (S0) Glycolytic (FOG) (FG) </li></ul><ul><li>Contraction speed slow fast (2xI) fast (4xI) </li></ul><ul><li>Time to peak force slow fast fast </li></ul><ul><li>Fatigue rate slow inter. fast </li></ul><ul><li>Fiber diam. small inter. large </li></ul><ul><li>Aerobic capacity high inter. low </li></ul><ul><li>Mitochondrial conc. high inter. low </li></ul><ul><li>Anaerobic capacity low inter. High </li></ul><ul><li>Sedentary people – 50% slow/50% fast, whereas elite athletes may differ </li></ul><ul><li>e.g., cross country skiers – 75% slow 25% fast </li></ul><ul><li>sprinters - 40% slow 60% fast </li></ul>
  14. 15. Factors affecting force Production <ul><li>1. Cross-sectional area </li></ul><ul><li>Hypertrophy: increase in the # of myofibrils and myofilaments </li></ul><ul><li>Hyperplasia: increase in the number of fibers??? </li></ul>
  15. 16. 2. Rate Coding – frequency of stimulation From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.9, page 155
  16. 17. <ul><li>3. Spatial recruitment </li></ul><ul><li>Increase # of active motor units (MUs) </li></ul><ul><li>Order of recruitment </li></ul><ul><li>I ---> IIa -----> IIb </li></ul><ul><li>Henneman's size principle: MUs are recruited in order of their size, from small to large </li></ul><ul><li>Relative contributions of rate coding and spatial recruitment. </li></ul><ul><ul><li>Small muscles - all MUs recruited at approximately 50% max. force; thereafter, rate coding is responsible for force increase up to max </li></ul></ul><ul><ul><li>Large muscles - all MUs recruited at approximately 80% max. force. </li></ul></ul>
  17. 18. 4. Velocity of shortening: Force inversely related to shortening velocity The force-velocity relationship for muscle tissue: When resistance (force) is negligible, muscle contracts with maximal velocity. Velocity Force (Low resistance, high contraction velocity)
  18. 19. The force-velocity relationship for muscle tissue: As the load increases, concentric contraction velocity slows to zero at isometric maximum. Velocity Force isometric maximum
  19. 20. Force-Velocity Relationship in different muscle fiber types Type II fiber Type I fiber
  20. 21. Effect of Temperature on Force-Velocity relationship (22 o C, 25 o C, 31C o , and 37 o C)
  21. 22. Force -Velocity Relationship (Effect of strength-Training)
  22. 23. Force-velocity Relationship During Eccentric Muscular Contractions
  23. 24. Force/Velocity/Power Relationship Force Velocity Power 30% 30% Force/velocity curve Power/velocity curve From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.25, page 175
  24. 25. Effect of Muscle Fiber Types on Power-Velocity Relationship
  25. 26. Consequences of the force-velocity relationship for sports practice <ul><li>When training for sports that require power, train with the appropriate % of 1 RM that will elicit the most power. </li></ul><ul><li>24 weeks of: </li></ul><ul><li>a). heavy weight-training b. Explosive strength training </li></ul>From Science and Practice of Strength Training (2 nd edition) V.M. Zatsiorsky and W.J. Kraemer (2006) Fig 2.19 P. 39)
  26. 27. <ul><li>Why do elite weight lifters start a barbell lift from the floor slowly? </li></ul><ul><li>They try to accelerate maximally when the bar is at knee height. Two reasons: </li></ul><ul><li>1. At this position, the highest forces can be generated as a result of body posture </li></ul>
  27. 28. <ul><li>2. Because force decreases when velocity increases, barbell must approach the most favored position at a relatively low velocity to impart maximal force to the bar. </li></ul>From Science and Practice of Strength Training (2nd edition) V.M. Zatsiorsky and W.J. Kraemer (2006) Fig 2.20 P. 40)
  28. 29. Adaptations associated with strength training <ul><li>1. Activates protein catabolism. This creates conditions for enhanced synthesis of contractile proteins during the rest period (break down, build up theory) </li></ul>From R.L. Leiber (1992). Skeletal Muscle Structure and Function. Fig 6.1, p. 262.
  29. 30. <ul><li>2. Neural adaptations occur to improve intra-muscular and inter-muscular coordination. </li></ul><ul><ul><li>Intra-muscular coordination – affects the ability to voluntarily activate individual fibers in a specific muscle </li></ul></ul><ul><ul><li>Inter-muscular coordination – affects the ability to activate many different muscles at the appropriate time </li></ul></ul>
  30. 31. <ul><li>Intra-muscular coordination changes with </li></ul><ul><li>training </li></ul><ul><li>Untrained individuals find it difficult to recruit all their fast-twitch MUs. With training, an increase in MU activation occurs </li></ul><ul><li>Strength training also trains the MUs to fire at the optimal firing rate to achieve tetany </li></ul><ul><li>MUs might also become activated more synchronously during all out maximum effort </li></ul>
  31. 32. <ul><li>Consequently, maximal muscular force is achieved when: </li></ul><ul><li>1. A maximal # of both FT and ST motor units are recruited </li></ul><ul><li>2. Rate coding is optimal to produce a fused state of tetany </li></ul><ul><li>3. The MUs work synchronously over the short period of maximal effort. </li></ul>
  32. 33. <ul><li>Psychological factors are also of importance </li></ul><ul><li>CNS either increases the flow of excitatory stimuli, decreases inhibitory stimuli, or both </li></ul><ul><li>Consequently, an expansion of the recruitable motor neuron pool occurs and an increase in strength results </li></ul><ul><li>Hidden strength potential of human muscle can also be demonstrated by electrostimulation </li></ul><ul><li>Muscle strength deficit (MSD) = </li></ul><ul><li>( Force during electrostimulation-Maximal voluntary force ) x 100 </li></ul><ul><li>Maximal voluntary force </li></ul><ul><li>Typically falls between 5-35% </li></ul>
  33. 34. <ul><li>Electrostimulation </li></ul><ul><ul><li>Possibility exists to induce hypertrophy through electrostimulation </li></ul></ul><ul><ul><li>However, does not train the nervous system to recruit motor units </li></ul></ul><ul><li>Bilateral Deficit </li></ul><ul><ul><li>During maximal contractions, the sum of forces exerted by homonymous muscles unilaterally is typically larger than the sum of forces exerted by the same muscles bilaterally </li></ul></ul><ul><ul><li>Bilateral training can eliminate this deficit, or even allow bilateral facilitation </li></ul></ul>
  34. 35. Other benefits of strength training <ul><li>Increase in resting metabolic rate </li></ul><ul><ul><li>Each additional pound of muscle tissue increases </li></ul></ul><ul><ul><li>resting metabolism by 30 to 50 calories per day = 10,950 to 18,250 calories a year = 3-5 lb of fat </li></ul></ul><ul><li>Increase in bone mineral content and, therefore, bone density </li></ul><ul><li>Increases the thickness and strength of the connective tissue structures crossing joints such as tendons and ligaments – helps prevent injury </li></ul><ul><li>Increased stores of ATP, Creatine Phosphate (CP), and glycogen </li></ul><ul><li>Aids rehabilitation from injury </li></ul><ul><li>Aging gracefully! Less falls in latter years </li></ul><ul><li>Looking better, feeling better. Greater self-esteem </li></ul>
  35. 36. Metabolic stress of resistance training <ul><li>Classed as only light to moderate in terms of energy expenditure per workout </li></ul><ul><li>Standard weight-training does not improve endurance or produce significant cardiovascular benefits like aerobic type activity does </li></ul><ul><li>Circuit-training increases metabolic stress </li></ul>
  36. 37. Delayed onset of muscle soreness (DOMS) <ul><li>The intensity and the novelty of a workout influence how sore you become </li></ul><ul><li>Lactate does not cause muscle soreness due to: </li></ul><ul><ul><li>1. Lactate returns to baseline within an hour of exercise </li></ul></ul><ul><ul><li>2. After exercise, lactate is in equal amounts within the muscle and the blood </li></ul></ul><ul><ul><li>3. DOMS is specific, not generalized </li></ul></ul><ul><li>Muscle soreness is due to the physiological response to muscle fiber and connective tissue damage (microtears) </li></ul><ul><li>White blood cells enter the muscle tissue, clean up the debris of broken proteins, and then initiate the regeneration phase </li></ul>
  37. 38. Muscle Soreness (continued) <ul><li>Edema (increase in fluid) to the area accompanies the above response </li></ul><ul><li>The pressure from edema is thought to produce the sensation of soreness </li></ul><ul><li>Also, metabolic by-products released from the macrophages may sensitize pain receptors </li></ul><ul><li>Next stage is the proliferation of satellite cells - help form new myofibrils </li></ul><ul><li>Eccentric contractions cause the greatest amount of soreness </li></ul>

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