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Strength Training

Strength Training. Patricia A. Deuster, PhD, MPH Professor and Scientific Director Uniformed Services University. Outline of Presentation. Definitions and Healthy People 2020 ; Factors affecting force generation; Development of muscle strength; Muscular power and endurance;

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Strength Training

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  1. Strength Training Patricia A. Deuster, PhD, MPHProfessor and Scientific Director Uniformed Services University

  2. Outline of Presentation • Definitions and Healthy People 2020; • Factors affecting force generation; • Development of muscle strength; • Muscular power and endurance; • Approaches to strength training; • Benefits of strength training; • Designing a strength training program.

  3. Objectives • Identify strength training terms; • Discuss trends in the prevalence of strength training; • Discuss factors that determine muscle force development; • Identify and differentiate skeletal muscle fiber types; • Discuss strength training terms and how to develop a strength training program; • Describe benefits of strength training.

  4. Adaptation Muscular Strength Muscular Hypertrophy Muscular Power Muscular Endurance Motor Performance Functional Abilities Progressive Overload Specificity and Variation Periodization Loading Training Volume, Impulse Exercise Selection/Order Rest Periods/Frequency Muscle Action and Velocity of muscle action Strength Training Terms

  5. Healthy People 2020 Objectives and Strength Training • 2010: Increase to 30% the proportion of adults who perform physical activities that enhance and maintain muscular strength and endurance on > 2 days/wk; • 2020: Increase proportion of adults that meet current Federal physical activity guidelines for aerobic physical activity and muscle strength training. • Also recommended by the American College of Sports Medicine.

  6. Prevalence of Strength Training by Gender

  7. Prevalence of Strength Training by Ethnicity

  8. High School Students and 2020 • Among students nationwide, grades 9-12 • 15.3% met aerobic objective • 51.0% met muscle-strengthening objective • 12.2% met objective for both activities. MMWR Morb Mortal Wkly Rep. 2011 Jun 17;60(23):773-7. Physical activity levels of high school students - United States, 2010. Centers for Disease Control and Prevention (CDC).

  9. Factors AffectingForce Generation • Muscle Architecture • Muscle Mechanics • Length-Tension Relationship • Muscle Fiber Types • Force-Velocity Relationship • Electromechanical Delay

  10. Muscle Architecture • Long axis of muscle determines arrangement of muscle fibers • Reflects muscle force and power • Two basic types • Fusiform: spindle shaped • Pennate: fan-shaped

  11. Muscle Fiber Architecture

  12. Pennation Effects on Force and Fiber Packing • Pennation allows for packing more fibers into a smaller cross-sectional area than parallel fibers. •  = surface pennation angle

  13. Fusiform Fiber Arrangement Fa = force of contraction of muscle fiber parallel to long axis of muscle SFa = sum of all muscle fiber contractions parallel to long axis of muscle Fa

  14. Pennate Fiber Arrangement Fa = force of contraction of muscle fiber parallel to long axis of muscle Fm = force of contraction of muscle fiber  = pennation angle Fa = (cos )(Fm) SFa = sum of all muscle fiber contractions parallel to long axis of muscle Fa Fm 

  15. Muscle Mechanics • Active Force through contractile elements: actin and myosin mechanism; • Passive Force through elastic elements: • Series elastic elements (tendons): smooth force of contraction and reduce effects of external forces from overload. • Parallel elastic elements (fascia): absorb energy input externally, if muscle is stretched beyond normal "resting" length.

  16. The range of motion and amount of force a muscle can generate is largely determined by the arrangement of the muscle fibers Muscle Mechanics PE = Parallel elastic component (fascia) SE = Series elastic component (tendons) CE = Contractile element • Fibers in series • Force production modest, but range of shortening is large. • Fibers in parallel • Force production high, but range of shortening is minimal.

  17. Length-Tension Relationship • Force generation is optimized when muscle is slightly stretched • Due to contribution of elastic components of muscle (primarily the SEC)

  18. Human Muscle Fiber Types

  19. Human Muscle Fiber Types Characteristics Names ST/SO FTa/FOG FTdx/FG Fibers/Motor Neuron 10-180 300-800 300-800 Motor Neuron Size Small Large Large Nerve Conduction Velocity Slow Fast Fast Contraction Speed (ms) 110 50 50 Type of Myosin ATPase Slow Fast Fast SR Development Low High High Motor Unit Force Low High High

  20. Force and Types of Muscle Contractions Concentric Eccentric Isometric

  21. Isotonic Contractions • Muscle changes length (changing angle of joint) and moves a load. • Two types of isotonic contractions • Concentric: Muscle shortens as it contracts • Eccentric: Muscle lengthens as it contracts Force > Load Force < Load

  22. Isometric Contractions • Tension increases without changes in length • Occurs if the load is greater than the tension the muscle is able to develop Force = Load

  23. Force-Velocity Relationship • Maximal force developed by any muscle is governed by its shortening or lengthening velocity - holds true for all muscle types

  24. Concentric: Ability to develop force is greater at slower contraction velocities - allows greater time for cross-bridges to generate tension Force Velocity Relationships

  25. Force-Velocity Relationship • Eccentric: Greater force with velocity, due to lower metabolic cost, greater mechanical efficiency and greater contribution from SEC.

  26. Force-Velocity Relationship

  27. Development of Muscle Strength • Maturation • Training

  28. Maturation and Strength Factors contributing to muscle strength during maturation 100% Adult potential Lean body mass Theoretical fiber type differentiation Testosterone Neural myelination development Birth Puberty Adult Strength primarily via motor patterns Consolidation of strength factors Optimal strength potential Kraemer, 1989

  29. Adaptations to Strength Training • Physiological Adaptations •  muscle fiber size and strength; • connective tissue density and bone integrity. • Muscle fiber type conversion? • Neural Adaptations •  recruitment of motor units; •  in firing rate of motor neurons; • Improved synchronization in motor neuron firing; • Counteraction of autogenic inhibition to allow greater force production.

  30. Muscle Fiber Hypertrophy • Increase in numbers of myofibrils and actin and myosin filaments • Allows more cross-bridges. • Increases in muscle protein synthesis during post-exercise period • Testosterone serves a role in promoting muscle growth • High intensity training may promote greater fiber hypertrophy than low intensity training.

  31. Muscle Fiber Hyperplasia • Muscle fibers may split in half with intense weight training. • Each half may then increases to size of parent fiber. • Satellite cells may also be involved in skeletal muscle fiber generation. • Clearly shown in animal models, but in only a few human studies. • 1996: Resistance training resulted in hypertrophy of total muscle CSA and fiber areas with no change in estimated fiber #.

  32. Satellite Cells • Quiescent mononucleated myogenic cells located between the sarcolemma and basement membrane of terminally-differentiated muscle fibers; • Normally quiescent in adult muscle; • Proliferate in response to injury and give rise to regenerated muscle and more satellite cells; • Repair and maintain skeletal muscle.

  33. Cross section of muscle fiber Longitudinal section

  34. Early strength gains influenced by neural factors Long-term strength gains due to muscle hypertrophy Process of Strength Gains

  35. Mechanisms of Strength Training Adaptations • Mechanical stimuli • CON-only training equally effective as ECC, despite mechanical advantage of ECC (greater forces, muscle damage, etc) • Metabolic Stimuli • Greater metabolic costs with CON • Build-up of metabolic by-products may enhance release of anabolic hormones and lead to greater motor unit activation.

  36. Muscular Power • Power = Work/Time = • (Force X Distance)/Time = • Force X Velocity • Maximal power occurs at: • ~ 1/3 max velocity • ~ 1/3 max concentric force • Affected by muscular strength and movement speed; • Main determinant of performance for throwing, jumping, changing direction, and striking activities.

  37. Force-Power Relationship • Power generated is greater in muscle with a high % of fast-twitch fibers at any given velocity of movement; • Peak power increases with velocity up to movement speeds of 200-300º•sec-1 • Force decreases with increasing movement speed beyond this velocity

  38. MaximumPower Muscle lengthening -10 -20 Muscle Load and Shortening Velocity • Max velocity at minimum load • Max load at velocity 0 30 • Power (force x velocity) • Power = 0 at 0 load and max load • Maximal power of muscle occurs at 1/3rd max load, or where Velocity X Load is greatest. 20 Velocity of Contraction (cm/s) 10 0 0.33 0.66 max Load opposing contraction

  39. Force-generating capability of neuromuscular system under maximal voluntary or involuntary activation depends on movement velocity.

  40. Fiber Recruitment as a Function of Power

  41. Muscular Endurance • Ability to exert tension over a period of time • Constant: gymnast in iron cross • Varying: rowing, running, cycling • Length of time dramatically affected by force and speed requirements of activity. • Training involves many repetitions with light resistance.

  42. Approaches to Strength Training • Static (isometric) actions • Dynamic actions • Free weights • Gravity dependent • Variable resistance • Isokinetic actions • Plyometrics • Other • Neuromuscular electrical stimulation • Activated isolated strength training

  43. Plyometrics • Used to develop jumping, sprinting and explosive power; • Muscle is contracted eccentrically then immediately concentrically (muscle is lengthened before it is contracted); • Should not be done more than 2x/wk; • Requires 100% effort for all movements; • Need adequate rest time between exercises to recover: 1 to 5 work:rest ratio.

  44. Other Devices • The body – pushups, sit-ups, pull-ups • Pushup variations • Sit-ups, curl-ups - changing resistance • Pull-ups – pronated vs. supinated grip

  45. Neuromuscular Electrical Stimulation • Characterized by low volt stimulation targeted to stimulate motor nerves to cause a muscle contraction. • Brain sends a special signal via a nerve impulse to muscle "motor point" causing muscle to contract and exercise just as if it had received a signal from the brain. • TENS is designed to stimulate sensing nerve endings to help decrease pain. 

  46. Activated Isolated Strengthening: The Mattes Method • Highly specific; • Exercises that maximize brain-muscle connection; • Two controlled contractions performed slowly with precision and accuracy - concentric and eccentric; • Intended to develop specific muscle support and acquire local joint stamina.

  47. Strength Training Benefits • Reduces: • # of injuries • Severity of injuries • Rehabilitation time • Increases and Maintains: • Strength and power • Endurance and stamina • Lean body mass • Develops: • Mental focus & toughness

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