Biomechanics for Strength Training


Published on

This presentation describes the biomechanical basis for the expression of muscular strength and power. In it you will learn to calculate force, work, and power. You will then learn how building strength improves power and performance in sport. Finally, we will take this information and apply it to training and sports.

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Biomechanics for Strength Training

  1. 1. Biomechanics and Performance Jason Cholewa
  2. 2. What is Biomechanics • Biomechanics refers to the study of the mechanisms by which anatomical components create movements – Muscles create tension – This tension is transmitted to tendons – Tendons attach to bones – The transmission of tension through the tendons pulls on bones – Bones move through space
  3. 3. Muscles pull on bones to move us
  4. 4. • The human body is capable of moving in almost every imaginable direction at velocities ranging from joint actions that are faster than a snake’s bite to quasi-isometric slow control
  5. 5. Skeletal Muscle • Skeletal muscle is excitable tissue that contracts (shortens) via the sliding filament theory following neural stimulation • There are 2 sides to every muscle, and in almost all circumstances, both sides of a skeletal muscle attaches to bone via tendons
  6. 6. Muscle tissue merges into tendon tissue, and the tendon tissue hooks onto a knobby prominence jutting off of a bone
  7. 7. Origins and Insertions • Muscles have two attachment sites to bones • The origin of a muscle is always the part that is either – More superior (Trunk muscles/Axial skeleton) – More proximal (Limb muscles/Appendicular skeleton) • The insertion of a muscle is always the part that is either – More inferior (Trunk muscles/Axial skeleton) – More distal (Limb muscles/Appendicular skeleton)
  8. 8. Types of Muscles – Based on Involvement in Movement • We can classify muscles based on the way that they contribute to a given human movement • 1. Agonists • 2. Antagonists • 3. Synergists
  9. 9. Agonists and Antagonists • 1. Agonists – The muscle most directly involved in causing a movement – The “Prime Mover” • 2. Antagonist – A muscle that can slow down or stop a movement – The antagonist assists in joint stabilization and decreasing the velocity of a limb towards the end of a fast movement
  10. 10. Synergists • A synergist assists a movement indirectly – Often times synergists are considered to be “stabilizers” – Without synergists, prime movers would be ineffective in causing a movement • Synergists are required to control body motion when the agonist is a 2 joint muscle
  11. 11. Synergists are….
  12. 12. Multi-Joint Movements and Synergists, Part 1 • You cannot perform an effective multi-joint movement without effective synergist activity because of the dual actions of 2 joint muscles • Let’s look at the Olympic style squat – The Olympic style squat is a knee dominant exercise (Knee extension is the primary movement) – The rectus femoris is a quadriceps muscle that is considered to be a 2 joint muscle
  13. 13. Notice that Rectus Femoris Attaches to the Pelvis, The Other Quads Don’t
  14. 14. Multi-Joint Movements and Synergists, Part 2: Rectus Femoris Example • RF attachments and insertions are • The actions of the rectus femoris are the following – Knee extension (primary movement of squatting) – Hip flexion (the opposite movement that takes place during the concentric portion of the squat)
  15. 15. 321 lbs x 10 reps
  16. 16. Multi-Joint Movements and Synergists, Part 3: Rectus Femoris Example • When the rectus femoris contracts, it causes both knee extension and hip flexion • Rising from a deep squat involves both knee extension and hip extension • If the rectus femoris is to act to extend the knee as a person rises without inclining the trunk forward, then hip extensor muscles (glute max) must act as synergists to counteract the hip flexion activity of rectus femoris
  17. 17. Squatting Synergists
  18. 18. Levers • A lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force (effort) that can be applied to another object (load) • A lever has the potential to produce or resist forces – The lever acts on forces via rotation around a fulcrum/pivot point – The lever can create force or resist forces acting on it
  19. 19. Lever Systems • A lever system consists of 7 components – 1. The lever – 2. The fulcrum – 3. The moment arm – 4. Torque – 5. Force (muscular force) – 6. Resistive force – 7. Mechanical advantage
  20. 20. The Fulcrum • The fulcrum is the pivot point of the lever • The pivot point creates the central axis of rotation for a lever • All gross human movements are lever movements – The bone is the rigid body of the lever – The joint is the fulcrum
  21. 21. Types of Levers • There are 3 classes of levers – First Class Lever – Second Class Lever – Third Class Lever
  22. 22. First Class Levers • First class levers are those where the muscular force and the resistive force act on opposite sides of the fulcrum Resistive arm Muscular arm
  23. 23. Second Class Levers • A lever where the muscle force and the resistive force are on the same side of the fulcrum – With second class levers, the muscular moment arm is longer than the resistive moment arm
  24. 24. Third Class Levers • A lever for which the muscle moment arm and the resistive moment arm are on the same side of the fulcrum – With third class levers, the resistive moment arm is longer than the muscular moment arm
  25. 25. Torque • Torque is the degree to which a force tends to rotate an object about a specified fulcrum • Torque is the magnitude of a force times the length of its moment arm – The longer the muscular moment arm, the less force required – The shorter the muscular moment arm, the more force is required
  26. 26. Longer moment arm, less force needed Shorter moment arm, more force needed
  27. 27. Muscle Force • Force generated by the sliding filament theory of muscular contraction • Muscles contract via myosin cross bridges pulling on actin – Pulls the ends of the muscle toward the center – Contraction/shortening
  28. 28. Most Muscles Operate at a Severe Mechanical Disadvantage • Most human muscles that rotate limbs operate at a mechanical disadvantage
  29. 29. Moment Arm • The moment arm describes a DISTANCE • The moment arm distance is the perpedicular distance between the object creating force and the fulcrum around which a lever moves
  30. 30. Moment Arm of Muscular Force • The muscular moment arm of the triceps is a very short distance that goes perpendicular from the elbow joint to where triceps force comes from
  31. 31. The Moment Arm of Muscular Force Length of the muscular moment arm. Direction of Muscular Force Production (Contraction) ***Notice how the muscular moment arm runs perpendicular to the direction of muscular force production
  32. 32. Moment Arm of Muscular Force & Cross-Sectional Area • The larger the cross-sectional area of a muscle, the larger the moment arm becomes – Arnold’s triceps are bigger than yours (or mine) • The mechanical advantage will increase for the muscular moment arm when the cross- sectional area increases
  33. 33. Resistive Force • The force generated by a source external to the body that acts contrary to muscle force – The 3 major types of resistive forces that muscles work against are • 1. Gravity • 2. Inertia • 3. Friction
  34. 34. Moment Arm of Resistive Force • The perpendicular distance between the resistance and the fulcrum • The resistance moment is the perpendicular distance from the resistance to the elbow joint • How does the resistance arm change as the rep progresses?
  35. 35. Moment Arm of Resistive Force This is the moment arm of resistance. Notice how it runs perpendicular to the direction of resistance Note the differences in resistance to muscle moment arms This is the direction of resistance (straight down to the center of the Earth)
  36. 36. Mechanical Advantage • Mechanical Disadvantage is… • Moment arm of resistance > moment arm of muscle force • Arnold’s triceps are at a tremendous mechanical disadvantage for the exercise pictured
  37. 37. Calculating the Mechanical Advantage • To calculate the mechanical advantage, you must measure the distance of the muscular moment arm (MM) and the distance of the resistive moment arm (RM) • Then divide the MM by the RM – MM/ RM a – > 1 mechanical advantage – < 1 mechanical disadvantage
  38. 38. Is this an advantage or disadvantage? Distance of Rm = 40 cm Distance of Mm = 5 cm -Mm = 5 cm - Rm = 40 cm - 5/40 = 0.125 -The muscle would have to generate more than 8 times the force of the resistance to rotate the elbow towards the “up” phase of the exercise
  39. 39. What about this? Resistive arm = 10 cm Muscular arm = 20 cm Mm = 20 cm Rm = 10 cm 20/10 = 2 The muscle only has to generate half the force of the resistance to rotate the joint into the “up” phase of this exercise
  40. 40. Figure 4.7
  41. 41. Tendon Insertions and Mechanical Advantage – Lets Compare Trent Richardson Silverback Gorilla Benchpress: 475 lbs ~ 4,000 lbs Top speed: 27 mph ~ 20 mph
  42. 42. Tendon Insertions and Mechanical Advantage • What are the advantages when the tendon inserts further from the joint? • Why? • If the tendons of a muscle insert farther away from the joint fulcrum, the muscular moment arm will be longer, and the mechanical advantage will be increased
  43. 43. Tendon Insertions and Mechanical Advantage • What are the disadvantages when the tendon inserts further from the joint? • Why? • If the tendon is inserted farther from the joint center the muscle has to contract more (in distance) to make the joint move through a given range of motion – A given amount of muscle shortening results in less rotation of a body segment about a joint – this translates into less speed
  44. 44. Speed of Rotation and Tendon Insertion • Get up!!!!! • We’re going to do a drill
  45. 45. Human Strength and Power
  46. 46. Identify the muscular moment arm and the resistance moment arm for the hamstrings about the hip Resistance Force Rm Mm
  47. 47. What type of lever is this? And is it working at a mechanical advantage or disadvantage?
  48. 48. What lever does the gluteus maximus play in hip extension (blue)? Resistance Force Fulcrum
  49. 49. Lets get tricky… What about the external shoulder rotator, the infraspinatus? Fulcrum Force Resistance (on anterior humeral head)
  50. 50. What’s wrong here?
  51. 51. Human Strength & Power • We will now shift the focus to discussing factors related to how humans express strength and power • There are a number of variables within the strength continuum that need to be examined – Work – Power – Displacement – Velocity – Neural control – Types of muscular contractions – Types of resistances
  52. 52. What is Force? • Are these things force?
  53. 53. Force • In physics, the concept of force is used to describe an influence which causes a free body to undergo an acceleration • Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity i.e., to accelerate, or which can cause a flexible object to deform
  54. 54. Factors Related to Force • Related concepts to accelerating forces include • 1. Thrust – Any force which increases the velocity of the object • 2. Drag – Any force which decreases the velocity of any object, and • 3. Torque – The tendency of a force to cause changes in rotational speed about an axis. • Forces which do not act uniformly on all parts of a body will also cause mechanical stress, a technical term for influences which cause deformation of matter
  55. 55. Thrust Drag Torque – rotation around the hip joint
  56. 56. Question • What is strength? • Is this strength? • Is this strength?
  57. 57. Trying to Define Strength • Strength is intimately related to maximal force production • Force = mass x acceleration – Often times people forget about the acceleration component of force – Acceleration = over coming gravity • Acceleration is a change in velocity per unit time – Velocity is the rate of change in position • The best definition of strength is – The maximal force that a muscle can generate at a specified velocity
  58. 58. Force Mass = 50 kg Acceleration: Gravity = 9.8 m/s2 Force = Mass x Acceleration The force of this barbell = 50 kg x 9.8 m/s2
  59. 59. Force = 50 x 9.8 Force = 490 Velocity = constant Strength = Maximal Force Produced At a specific velocity Because the acceleration of gravity does not change on earth, then only way to change the force is by increasing the mass
  60. 60. Power • Is this power? • Is this power?
  61. 61. Defining Power • Power is intimately tied to Work – Power is work per unit time • Work refers to the force exerted on an object and the distance the object moves in the direction in which the force is exerted – Work = Force x Distance • Power is how much work was performed in a given time – Power = Work/Time
  62. 62. Force = 50 x 9.8 Force = 490 Distance = .75 m Power = Work / Time Work = Force x Distance = 490 x .75 = 367.5 In a deadlift, work does not change for a given weight. Thus, the time taken to do the work will determine power. Calculate the difference in power when the movement takes 3 sec vs. 2 sec Time taken
  63. 63. Lets Review… • Force is an influence which causes an object to undergo a change acceleration – Force = Mass x Acceleration • Strength is the maximal force a muscle can generate at a specified velocity – Strength = force x velocity • Power is the work done in a given amount of time – Work = force x distance – Power = work/time
  64. 64. Calculating Work – Knowing the Units of Measure • Without including units of measure, these calculations are meaningless • Work = Force x Distance • The unit of measure for Work that we will be using is Joules • The unit of measure for Force that we will be using is Newtons • The unit of measure for Distance that we will be using is Meters
  65. 65. Calculating Work – Gravitational Forces • Most resistance training involves gravitational forces – since gravity is a force, there are 2 variables of interest – Mass and acceleration – The mass of the resistance and the acceleration of Earth’s gravity • Mass can be represented by kilograms • The gravity of Earth pulls all objects down towards the center of the earth at the same acceleration – 9.8 meters/second2
  66. 66. Calculating Work – Determining Weight • To calculate work performed on Earth, we must determine the weight of the resistance • To calculate the weight of the resistance, the scientific community uses the unit of measure called the Newton • The Newton equals the mass of the resistance (kg) multiplied by the acceleration of gravity – Weight (Newtons) = mass x acceleration of gravity
  67. 67. Determining Work – An Example Using the Deadlift • We will say that the approximate distance traveled in the deadlift is 1 meter • The mass of the barbell being deadlifted will be 100 kg • Step 1: determine the weight/force of the bar – Mass x The Acceleration of Gravity
  68. 68. Determining Weight of the Bar – An Example Using the Deadlift • Weight/Force (Newtons) = 100 kg x 9.8 m/s2 • Weight/Force (N) = 980 N • This value in Newtons gives us our FORCE variable in the equation • Remember, Work = Force x Distance • Now we must calculate the distance traveled
  69. 69. Determining the Distance Traveled – An Example Using the Deadlift • As was previously stated, the distance covered by the barbell during the deadlift was 1 meter per repetition • You must take into account number of repetitions • If 10 repetitions are performed, then the distance traveled = 10 meters – 10 reps x 1 meter = 10 meters
  70. 70. Force = 100 x 9.8 Force = 980 Distance = 1 meter Calculating Work 10 repetitions were performed for the set, thus: 10 x 1 m = 10 m of distance
  71. 71. Determining the Work of a Set – An Example Using the Deadlift • Work (Joules) = Force (Newtons) x Distance (Meters) • For 1 repetition – Work (Joules) = 980 N x 1 meter – Work = 980 Joules • For 10 repetitions – Work (Joules) = 980 n x 10 meters – Work = 9,800 Joules
  72. 72. Calculating Power – An Example Using the Deadlift • Power = Work/Time • The unit of measure for power is the Watt • The unit of measure for time is the second • To calculate Power, divide the work by the # of seconds it took to perform the work
  73. 73. Calculating Power – An Example Using the Deadlift • Let’s say that the set of 10 deadlifts took 100 seconds to perform – Remember, the total work for the 10 deadlifts was 9,800 Joules • Power (Watts) = Work/Time – 9,800 Joules/100 seconds = 98 Watts
  74. 74. Power, a case of tall vs. short • Both athletes are bench pressing 100 kg for 5 repetitions • Athlete 1 has a ROM of .65 m and takes 7 seconds • Athlete 2 has a ROM of .5 m and takes 6 seconds • Who was more powerful?
  75. 75. Calculate Work • Force = 980 newtons ( 100 kg x 9.8 m/s2) • Work = force x distance • Athlete 1 work – 5 x .65 m = 3.25 m (distance) – Work (joules) = 3.25 m x 980 n = 3185 j • Athlete 2 work – 5 x .5 m = 2.5 m – Work = 2.5 m x 980 n = 2450 j
  76. 76. Calculate Power • Power (watts) = work/time • Athlete 1 – 3185 j / 7 s = 455 watts • Athlete 2 – 2450 j / 6 s = 408 watts • Who expressed more power? • What did we learn?
  77. 77. How Powerful are YOU?! • Based on force (subject mass x gravity) – Divide Pounds by 2.2 to = KG, multiply by 9.8 • Calculate work = Force X Distance – Distance = VJ height in Meters • Calculate power for all 5 subjects – Find the time for your VJ height – Power (watts) = Work / Time • Who was most powerful • Was this what you expected?
  78. 78. Height Inches Height Meters Time Seconds 17 0.43 0.30 18 0.46 0.31 20 0.51 0.32 21 0.53 0.33 22 0.56 0.34 23 0.58 0.35 24 0.61 0.35 25 0.64 0.36 26 0.66 0.37 27 0.69 0.37 28 0.71 0.38 29 0.74 0.39 30 0.76 0.39 31 0.79 0.40 32 0.81 0.41 33 0.84 0.41 34 0.86 0.42
  79. 79. • A more practical formula was devised by (Fox & Mathews, 1974). The Lewis formula is: • Power (watts) = • (square root of 4.9) x body mass(kg) x (square root of jump distance(m)) x 9.8 • More practical because it is difficult to accurately measure flight time by hand.
  80. 80. How can we use VJ to assess power training? • If weight stays the same but VJ height increases? – If weight decreases but VJ height stays the same? • If weight increases but VJ height stays the same? – If weight increases and so does VJ height? • If both increase? • If both decrease?
  81. 81. The Interconnectedness of Strength & Power • Strength and power share these variables – Force – Acceleration – Velocity • Strength and power are what separate lesser qualified athletes from elite athletes – Genetic – Training
  82. 82. Further Discussion of the Relationship Between Strength & Power • You will often hear people describe certain exercises as strength exercises or power exercises – I.e.: Deadlift is strength because it is low speed – I.e.: Power clean is power because it is fast speed • It is not correct to associate strength with low speed and power with high speed
  83. 83. Further Discussion of the Relationship Between Strength & Power • Strength is the capacity to exert force at any given speed – IOW: most force that can be exerted in a single contraction • Power is the mathematical product of force and velocity (distance per unit time) at whatever speed is happening for the exercise
  84. 84. Muscular Power • Power = Velocity of muscular force development x amplitude of muscular force development – Velocity is how fast the fiber contracts – Amplitude is how much tension it produces
  85. 85. The Practical/Critical Component to Understand • Critical: ability to exert force at speeds characteristic with a given sporting movement – A powerlifer squatting maximal weight is producing the highest possible muscular force at low velocities • The resistance is high • A shot-put thrower is producing the highest possible muscular force at high velocities • The resistance is low
  86. 86. Force velocity relationship
  87. 87. Velocity Assessment • Training athletes who compete in different sports requires tremendous velocity assessment and training specificity – If you train an offensive lineman exclusively with high velocity training, you will not be improving the low- speed strength qualities that are so important to the sport very effectively – If you train the shot-put thrower exclusively with low velocity training, you will not be improving the high- speed strength qualities that are so important to the sport very effectively
  88. 88. So what? • A focus of work done should match the force x velocity continuum in which the athlete competes • Work outside this continuum should be geared to improve force production at competition speed
  89. 89. If we increase this curve It will push the power curve to the right
  90. 90. Strength will benefit the shot-put thrower • Higher load, moderate speed training will improve absolute tension production – More force generation per single contraction • With appropriate realization training, this means more force can be produced at higher velocities. – Which means increased power at competition speed!! • Compare the deadlift to a power clean
  91. 91. • The stronger muscle can contract faster at a given load • Relate this to loads encountered during competition – For a given tension (say… BODY WEIGHT) the stronger muscle has a greater velocity of contraction – Recall, power = tension x velocity
  92. 92. Deadlift
  93. 93. Olympic Lifts
  94. 94. The application of strength to power • Improvements in deadlift (high external load, moderate speed) must be matched by equal or greater improvements in power clean (moderate load, fast speed). • IOW: Focus should be on transforming deadlift strength to vertical jump or clean power
  95. 95. Neural Factors Related to Muscular Strength & Power • The 2 neural control factors that are intimately involved with displaying strength and power are – Recruitment – Rate Coding
  96. 96. Muscle fibers • Type I – slow twitch, fatigue resistant, low force production • Type IIA – fast twitch, high glycolytic capacity, fatigue resistant, higher force production • Type IIX – fast twitch, largest, highest force production
  97. 97. Motor unit • A motor neuron and all the muscle fibers it recruits • Muscle fibers within the MU are all the same type (I, IIA, IX, etc.) and size • The larger the muscle fiber, the more impulse needed to excite it, and the larger the motor neuron must be
  98. 98. Neural Factors Related to Muscular Strength & Power • In general, muscular force is greater when – 1. More motor units are involved with the contraction – 2. The motor units are greater in size (fast twitch motor units, which are the most difficult to recruit) – 3. The rate of neural firing increases in speed and efficiency • Rate coding – how well a message goes from your brain and down your spinal cord to eventually reach and signal the individual muscle motor units to fire
  99. 99. 1. More motor units are involved with the contraction
  100. 100. 2. The motor units are greater in size (fast twitch motor units, which are the most difficult to recruit)
  101. 101. Rate coding - speed • The repetitive firing of all available motor units occurs so quickly that there is a summation of force • The ability to produce tension is magnified beyond what you get from regular recruitment • In essence, your muscles get supercharged and are able to generate tension above and beyond what they normally would.
  102. 102. Rate coding – at the muscle fiber
  103. 103. Muscle force compared to simuli strength
  104. 104. At 80% all motor units have been recruited • Rate coding manifest during a lift
  105. 105. Rate coding – neural efficiency
  106. 106. Application - Maximal Effort Lifting • For the shot-put thrower – Maximal Number of motor units activated – Maximum discharge (neural stimulation) – Improve intra- and inter-muscular coordination
  107. 107. Application – The Transfer • Rate coding improves with – Practice – Stimulation • I.e.: Post activation potentiation – Perform one high tension exercise to increase CNS recruitment – After 5 min rest, perform a low tension, high speed movement to take advantage of increased CNS drive • Over time the body becomes more sensitive to the neural discharges and “learns” to accept a new level of force as being normal for a particular movement
  108. 108. Muscle CSA and Force Layne Norton Patricia Beckman
  109. 109. Muscular Cross-Sectional Area • All else being equal, the force a muscle can exert is directly related to its cross-sectional area • The large the fiber size, the more contractile proteins within in, the greater the tension development
  110. 110. Muscle CSA • Muscle “Volume” – CSA X Muscle Length • Muscle volume does not seem to be a contributing factor to the muscular force production
  111. 111. • If the CSA of the muscles of their limbs are the same • They will have the same force production capabilities 40 cm2 arm CSA 26 cm humerus length 23 cm humerus length
  112. 112. Comparing the Volume to the Cross- Sectional Area – Both individuals have the same absolute force production capabilities – Taller athlete has more muscle volume – Thus, his/her bodyweight is greater – Athlete 1: • Arm CSA 40 cm2 , arm length 26 cm • 1200 N / 1040 cm3 = 1.15 N/cm3 – Athlete 2: • Arm CSA 40 cm2, arm length 23 cm • 1200 N / 920 cm3 = 1.30 N/cm3
  113. 113. Strength-to-Mass Ratio • Strength-to-Mass ratio is intimately related to cross-sectional area and muscular volume • Most athletics involved moving the body through space • The strength-to-mass ratio directly reflects the athlete’s ability to accelerate his or her body
  114. 114. Strength-to-Mass Ratio • Strength-to-mass ratio of larger athletes is often less than smaller athletes • Greater muscle volume relative to CSA – CSA is a 2 dimensional phenomenon – Volume is a 3 dimensional phenomenon • Hypertrophy – Volume increases in greater proportion compared to CSA • Thus, when body size increases, body mass increases more rapidly than does muscular strength
  115. 115. Body Size • The reason that smaller athletes are stronger than larger athletes pound for pound is because of the fact that smaller athletes can have equal cross-sectional area of muscles as larger athletes, but the smaller athletes have less muscular volume • So what? • If an athlete increases muscle mass by 15% and force production by 10% • Reduction in ability to accelerate his/her body • More strength focus in taller athletes
  116. 116. Sliding filament theory
  117. 117. Human Strength and Power • Biomechanical Factors in Human Strength – Muscle Length • At resting length: actin and myosin filaments lie next to each other; maximal number of potential cross-bridge sites are available; the muscle can generate the greatest force. • When stretched: a smaller proportion of the actin and myosin filaments lie next to each other; fewer potential cross-bridge sites are available; the muscle cannot generate as much force. • When contracted: the actin filaments overlap; the number of cross-bridge sites is reduced; there is decreased force generation capability.
  118. 118. Figure 4.12
  119. 119. Length-tension ratio • A muscle contracts best when it is at its optimal length, which is either at resting length or slightly stretched at 1.2 times its resting length, depending on the muscle • Pennated muscles contract best when they are stretched 1.25 to 1.33 times their resting length
  120. 120. Length-tension ratio applied • Recall our vertical jump last week… • Which muscles were involved • How are they stretched when activating the jump • How would they be stretched if starting too deep or straight up?
  121. 121. Arrangement of Muscle Fibers • There are 2 major arrangement techniques when it comes to the direction of muscle fibers inside of a muscle – Pennate muscles – Fusiform muscles
  122. 122. Figure 4.11
  123. 123. Pennate Muscle • The word pennate traces its routes back to the Greek word for “fan” • These muscles feature fibers that “fan out” from the central aspect of the muscle belly
  124. 124. Fusiform Muscle • Fusiform muscles feature fibers that run in straight lines • There is no central region of the belly where the fibers fan out • Instead, the fibers run parallel to one another in series
  125. 125. Pennate Muscles • Pennate muscles are excellent at generating low-speed strength • Demonstrate tremendous “fiber packing” – more muscle fibers fit into the pennate arrangement vs. fusiform arrangement • Pennate muscles have a lower maximal shortening velocity compared to fusiform muscles
  126. 126. Thoughts on Hamstring Injuries Based on Fiber Arrangement • The Hamstrings are a fusiform muscle group • Fusiform muscles are great for fast contractions; • their absolute force of contraction is small compared to pennate muscle groups • The quadriceps are a pennate muscle group – Quadriceps become dominant during strength training – Quads can already be dominant in many athletes – As a result of this imbalance Q>H , the hamstrings are more likely to tear
  127. 127. Thoughts on Hamstring Injuries Based on Fiber Arrangement • Its not just Q>H that matters! • The glutei muscles are also pennate muscles – Most people have poorly developed glutei muscles!!!!!! – The glutei should be the primary hip extensors during powerful movements like sprinting – Most hamstring injuries are due to Q > G
  128. 128. Why are Hamstring Injuries Caused by Weak Glutei? • When performing powerful hip extension activities, the body will recruit whatever muscles necessary to perform action • Weak glutes = extra hamstring recruitment • Essentially, the body starts asking the hamstrings to perform a function that they are not intended to do – As a result of this, the hamstrings start working in force ranges that are above and beyond their capabilities – The connection point between the hamstring and the tendon or the tendon and the bone typically suffers some sort of injury as a result
  129. 129. Train the Glutes • With anteroposterior loading – Increases activation – Mimics hip extension during sprinting – Greater activation at full hip extension – Glutes contract best at nearly full-hip extension
  130. 130. Keep the Bar Close to the Body
  131. 131. Keeping the Bar Close to the Body: Examining the Resistive Moment Arm • When someone is lifting barbells or dumbells, the Moment Arm of Resistive Force is always oriented in the same direction – Horizontal Why? – The acceleration of gravity is always applying force in the same direction • Straight down to the center of the Earth
  132. 132. Keeping the Bar Close to the Body: Examining the Resistive Moment Arm Direction of gravity’s resistance Direction of the moment arm of resistive force If the Rm ends here, the mechanical advantage is increased because the Rm is shorter If the Rm ends here, the mechanical advantage is decreased because the Rm is longer. The longer the Rm, the greater the muscular force production required to overcome the resistive force
  133. 133. Moment Arms of the Deadlift: Mechanical Disadvantage Moment Arms of Muscular Force. Notice that with a movement like the deadlift, there are a number of muscle groups working. Despite having so many muscle groups working, all of these Moment Arms of Muscular Force are much shorter than the Moment Arm of Resistive Force Very long moment Arm of Resistive Force. The dead lift puts the muscles at the hip and back at tremendous mechanical disadvantage
  134. 134. Keep the bar close to the body
  135. 135. Keeping the Bar Close to the Body: Examining the Resistive Moment Arm • Benedikt Magnusson’s 1100 pound deadlift • From a practical standpoint, the closer to your body the bar is held, the more you reduce the moment arm of resistive force – Closer to body = decreased mechanical disadvantage – This is why good deadlifters always have scraped up shins – This is critically important for preventing back injuries
  136. 136. The Major Advantage of Standing Free Weight Exercises Machines • Standing free weight exercises are the best form of anti-gravitational resistance training available – Better than machines, better than cables • Every muscle in body must contract to stabilize body – Machines do not recruit stabilizer muscles – Machines do not mimic real world scenarios • Such weight bearing exercises promote bone mineralization, which fights against osteoporosis
  137. 137. Most Common Back Injuries • Between 85 to 90% of all intervertebral disk herniations occur at either – The junction of L4 & L5 or – The junction of L5 & S1 • Factors that lead to injury – 1. The tremendous mechanical disadvantage imposed upon the spinal musculature during 2 foot barbell lifts – 2. When people allow their lumbar and thoracic spine to move into kyphosis
  138. 138. Moment Arms of the Deadlift: Mechanical Disadvantage Moment Arms of Muscular Force. Notice that with a movement like the deadlift, there are a number of muscle groups working. Despite having so many muscle groups working, all of these Moment Arms of Muscular Force are much shorter than the Moment Arm of Resistive Force Very long moment Arm of Resistive Force. The dead lift puts the muscles at the hip and back at tremendous mechanical disadvantage
  139. 139. Kyphotic Back: Absolute Disaster • The primary way that people hurt themselves during 2 foot barbell lifts is by moving the lumbar and thoracic spine into a kyphotic position • The cardinal rule to follow in any weight room is to never let the back roll over
  140. 140. Disk Injuries • Kyphosis sets the stage for possible vertebral disk injuries • Bulges or herniations of the disk always occur on the posterior aspect of the vertebrae
  141. 141. Disk Injuries • The anterior portion of the spinal discs DECREASE in space upon flexion. • Both the anterior and posterior aspects of the discs INCREASE in space upon extension.
  142. 142. Protecting the Disk • The lower back should be moved into lordosis during 2 foot barbell lifting – An arched back position • It has been shown that the muscles of the low back are capable of exerting considerably higher forces when the back is arched rather than rounded
  143. 143. Proper Back Positioning • You’ll see how the lifter in this picture has her lumbar vertebrae moved into lordosis • Anytime you see an experienced individual training with barbells, you will see them making sure the low back is arched with all major lifts
  144. 144. Abdominal Tension and Pressure – The Fluid Ball • The contents of the abdomen include – Abdominal muscles – Parts of the digestive tract – Parts of the diaphragm • The most abundant substance in the abdomen is fluid – The majority of mass in the abdomen is water • Contract the abdominal muscles forcefully during 2 foot barbell lifts pressurizes the fluids in the abdomen • Increased abdominal pressure significantly reduces the forces imposed on spinal erector muscles, and significantly reduces compressive forces on the disks
  145. 145. Figure 4.15
  146. 146. The Valsalva Maneuver • Probably every competitive strength athlete utilizes the Valsalva Maneuver during the execution of 2 foot barbell lifts – The Valsalva significantly increases intrabdominal pressure • The Valsalva Maneuver involves attempting to forcibly exhale against a closed glottis • The Valsalva Maneuver significantly increases blood pressure in the chest and reduces venous return to the heart • Blackout is associated with prolonged Valsalva
  147. 147. Friction Resistance • ALL GRAVITATIONAL FORCES ARE ENTIRELY VERTICAL IN NATURE • FRICTIONAL RESISTANCE TRAINING IS ENTIRELY HORIZONTAL IN NATURE • Athletes encounter horizontal/frictional forces during competition, therefore, not training these forces is a mistake
  148. 148. Friction Resistance/Horizontal Force Production • The best way to get frictional resistance/horizontal force production in during the training process is through the use of sled work – Dragging sleds and pushing sleds is a tremendously challenging form of exercise • The limitation to sled work is that it is always harder to get the sled moving, and it is always easy to keep the sled moving once it starts
  149. 149. Sled work, all invited
  150. 150. Coefficients of Friction • The coefficient of static friction is always greater than the coefficient of sliding friction – This is why it is hard to start a sled, but easy to keep it moving • Once the sled is moving, the resistance stays the same, so the resistance does not change as the speed increases – The faster the sled goes, the greater the power output
  151. 151. Sled Work is a Killer! • 88E • sg&feature=related • Don’t believe me, check this out
  152. 152. So, Have We Learned Anything? • Tell me anything that you think you have learned thus far from our biomechanics discussions – Now tell me if you can think of any way that you can apply this new found knowledge
  153. 153. Questions ? "Two!" "Mmnn, actually Homer that's just one. See, each pushup includes both an up part and a down part."