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The Scientific Principles of Strength Training

The Scientific Principles of Strength Training. Muscular Strength : The amount of force a muscle can produce with a single maximal effort Mechanical Strength: the maximum torque that can be generated about a joint. Torque about the elbow joint. Strength determined by:

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The Scientific Principles of Strength Training

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  1. The Scientific Principles of Strength Training • Muscular Strength: The amount of force a muscle can produce with a single maximal effort • Mechanical Strength: the maximum torque that can be generated about a joint

  2. Torque about the elbow joint • Strength determined by: • Absolute force developed by muscle • Distance from joint center to tendon insertion • Angle of tendon insertion

  3. Shoulder joint torque as a function of arm position

  4. Structural organization of skeletal muscle From Principles of Human Anatomy (7th edition), 1995 by Gerard J. Tortora, Fig 9.5, p 213

  5. From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.6, page 153 6-6

  6. From Skeletal Muscle: Form and Function (2nd ed) by MacIntosh, Gardiner, and McComas. Fig 1.4, p. 8.

  7. From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.5, page 152 6-5

  8. From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.3, page 150 6-3

  9. From Exercise Physiology: Theory and Application to Fitness and Performance (6th Edition) by Scott K. Powers and Edward T. Howley. Fig 8.6 P. 147

  10. 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. From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.7, page 154 6-7

  12. From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.8, page 154 6-8

  13. Types of muscle fiber: Fast twitch vs Slow Twitch Type I Type IIa Type IIb ST OxidativeFT Oxidative - FT Glycolytic (S0)Glycolytic (FOG) (FG) • Contraction speed slow fast (2xI) fast (4xI) • Time to peak force slow fast fast • Fatigue rate slow inter. fast • Fiber diam. small inter. large • Aerobic capacity high inter. low • Mitochondrial conc. high inter. low • Anaerobic capacity low inter. High Sedentary people – 50% slow/50% fast, whereas elite athletes may differ e.g., cross country skiers – 75% slow 25% fast sprinters - 40% slow 60% fast

  14. 1. Cross-sectional area Hypertrophy: increase in the # of myofibrils and myofilaments Hyperplasia: increase in the number of fibers??? Factors affecting force Production

  15. 2. Rate Coding – frequency of stimulation From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.9, page 155

  16. 3. Spatial recruitment • Increase # of active motor units (MUs) • Order of recruitment I ---> IIa -----> IIb • Henneman's size principle: MUs are recruited in order of their size, from small to large • Relative contributions of rate coding and spatial recruitment. • Small muscles - all MUs recruited at approximately 50% max. force; thereafter, rate coding is responsible for force increase up to max • Large muscles - all MUs recruited at approximately 80% max. force.

  17. (Low resistance, high contraction velocity) Force Velocity 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.

  18. isometric maximum Force Velocity The force-velocity relationship for muscle tissue: As the load increases, concentric contraction velocity slows to zero at isometric maximum.

  19. Force-Velocity Relationship in different muscle fiber types Type II fiber Type I fiber

  20. Effect of Temperature on Force-Velocity relationship (22oC, 25oC, 31Co, and 37oC)

  21. Force -Velocity Relationship (Effect of strength-Training)

  22. Force-velocity Relationship During Eccentric Muscular Contractions

  23. Force/Velocity/Power Relationship Force/velocity curve Power/velocity curve Force Power 30% From Basic Biomechanics by Susan Hall (3rd edition), Fig 6.25, page 175 30% Velocity

  24. Effect of Muscle Fiber Types on Power-Velocity Relationship

  25. Consequences of the force-velocity relationship for sports practice • When training for sports that require power, train with the appropriate % of 1 RM that will elicit the most power. 24 weeks of: a). heavy weight-training b. Explosive strength training From Science and Practice of Strength Training (2nd edition) V.M. Zatsiorsky and W.J. Kraemer (2006) Fig 2.19 P. 39)

  26. Why do elite weight lifters start a barbell lift from the floor slowly? They try to accelerate maximally when the bar is at knee height. Two reasons: 1. At this position, the highest forces can be generated as a result of body posture

  27. 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. From Science and Practice of Strength Training (2nd edition) V.M. Zatsiorsky and W.J. Kraemer (2006) Fig 2.20 P. 40)

  28. Adaptations associated with strength training 1. Activates protein catabolism. This creates conditions for enhanced synthesis of contractile proteins during the rest period (break down, build up theory) From R.L. Leiber (1992). Skeletal Muscle Structure and Function. Fig 6.1, p. 262.

  29. 2. Neural adaptations occur to improve intra-muscular and inter-muscular coordination. • Intra-muscular coordination – affects the ability to voluntarily activate individual fibers in a specific muscle • Inter-muscular coordination – affects the ability to activate many different muscles at the appropriate time

  30. Intra-muscular coordination changes with training • Untrained individuals find it difficult to recruit all their fast-twitch MUs. With training, an increase in MU activation occurs • Strength training also trains the MUs to fire at the optimal firing rate to achieve tetany • MUs might also become activated more synchronously during all out maximum effort

  31. Consequently, maximal muscular force is achieved when: 1. A maximal # of both FT and ST motor units are recruited 2. Rate coding is optimal to produce a fused state of tetany 3. The MUs work synchronously over the short period of maximal effort.

  32. Psychological factors are also of importance • CNS either increases the flow of excitatory stimuli, decreases inhibitory stimuli, or both • Consequently, an expansion of the recruitable motor neuron pool occurs and an increase in strength results • Hidden strength potential of human muscle can also be demonstrated by electrostimulation • Muscle strength deficit (MSD) = (Force during electrostimulation-Maximal voluntary force) x 100 Maximal voluntary force • Typically falls between 5-35%

  33. Electrostimulation • Possibility exists to induce hypertrophy through electrostimulation • However, does not train the nervous system to recruit motor units • Bilateral Deficit • 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 • Bilateral training can eliminate this deficit, or even allow bilateral facilitation

  34. Other benefits of strength training • Increase in resting metabolic rate • Each additional pound of muscle tissue increases resting metabolism by 30 to 50 calories per day = 10,950 to 18,250 calories a year = 3-5 lb of fat • Increase in bone mineral content and, therefore, bone density • Increases the thickness and strength of the connective tissue structures crossing joints such as tendons and ligaments – helps prevent injury • Increased stores of ATP, Creatine Phosphate (CP), and glycogen • Aids rehabilitation from injury • Aging gracefully! Less falls in latter years • Looking better, feeling better. Greater self-esteem

  35. Metabolic stress of resistance training • Classed as only light to moderate in terms of energy expenditure per workout • Standard weight-training does not improve endurance or produce significant cardiovascular benefits like aerobic type activity does • Circuit-training increases metabolic stress

  36. Delayed onset of muscle soreness (DOMS) • The intensity and the novelty of a workout influence how sore you become • Lactate does not cause muscle soreness due to: • 1. Lactate returns to baseline within an hour of exercise • 2. After exercise, lactate is in equal amounts within the muscle and the blood • 3. DOMS is specific, not generalized • Muscle soreness is due to the physiological response to muscle fiber and connective tissue damage (microtears) • White blood cells enter the muscle tissue, clean up the debris of broken proteins, and then initiate the regeneration phase

  37. Muscle Soreness (continued) • Edema (increase in fluid) to the area accompanies the above response • The pressure from edema is thought to produce the sensation of soreness • Also, metabolic by-products released from the macrophages may sensitize pain receptors • Next stage is the proliferation of satellite cells - help form new myofibrils • Eccentric contractions cause the greatest amount of soreness

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