Anatomy and Biomechanics of Cycling

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Anatomy and Biomechanics of Cycling
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Danielle Stoll
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Overview

• Anatomy
• Muscles
• Bones
• The Pedal Stroke and forces
• Static Equilibrium of a Cyclist
• Joint Reaction Forces

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Introduction

• Biomechanics is applying mechanical principles to
  living organisms
• Further our understanding of how the human body
  reacts during movement
• Helps identify reasons for injuries
• Helps athletes to maximize muscle power

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Lower Body Anatomy
Angle from horizontal (deg)
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Lower Body Anatomy
Angle from vertical (deg)
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Changes in Seat Height

• Greater saddle height allows cyclists to pedal
  with greater ease especially at high work loads
• Changing saddle height alters
• joint angles of muscles
• lengths of muscles
• amount of force a muscle can produce
• Optimal saddle height 105 107 of leg length

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Changes in Seat Height
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Bones of the Lower Body

• Tibia is the shin bone
• Fibula attaches to the Tibia on the outside (or
  laterally)
• tarsals are the ankle bones
• Phalanges are the toes

Right Leg
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ogy/Skeletal/lower_extremity.jpg
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2-D Model of Cyclist Leg

• Human Leg
• 3 rigid link system
• Hip joint
• Knee joint
• Ankle joint

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Joints

• Knee joint
• Hinge joint
• Allows for slight internal and external roatation
• Ankle joint
• Simple pin joint
• Foot
• 26 different bones
• Can absorb shock

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Movement of the Legs

• Power phase 0-180
• Recovery phase 180 -360
• At comfortable seat height
• ROM of thigh 45 from max flexion to max
  extension
• ROM of knee 75 from max flexion to max
  extension
• ROM ankle 20 between max dorsiflexion and max
  planterflexion
• Hip joint never moves into full extension
• Only full extension when thigh moves behind
  center of trunk

(A) minimum hip flexion (B) maximum hip
flexion (C) maximum knee extension (D) maximum
knee flexion
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Bones of the Lower Body
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• The acetabulum articulates with the femoral head
• The hip joint is a ball and socket joint

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The Sit Bones

• Sit bones Ischial Tuberosity

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Gender Differences in the Pelvis

• Figure A shows a typical male pelvis
• Notice the V shape at the pubic arch
• Narrower Ischial tuberoisity
• Figure B shows female pelvis
• Notice the U shape at the pubic arch
• Wider ischial tuberosity

FEMALE
MALE
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The Pedal Stroke
Ankling Angle (deg)

• Location of foot during a pedal stroke
• (A) accepted literature
• (B) study of 7 elite riders
• Ankling angle versus crank angle of 7 elite
  riders

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Pedal Reaction Forces

• Pedal Reaction Forces- when a foot applies a
  force to a pedal, it is met with a reaction force
  equal and opposite magnitude
• Peak pedal force
• Normal force Fz60 bodyweight or 350 N for
  avgerage cyclist
• Shear forces
• Medial and lateral (Fx)
• Anterior and Posterior (Fy)

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Pedal Reaction Forces

• Resultant Pedal Reaction Force for right lower
  extremity
• Force vector in front Center of Rotation (COR) of
  hiphip extensor muscles activated
• Force vector behind (COR) for kneeknee extensor
  muscle activated
• Force vector in front of ankle joint plantar
  flexor muscles activated

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Pedal Reaction Forces

• Pedal Reaction Forces
• Does not exceed body weight unless standing
• Resultant force vector changes magnitude and
  direction throughout pedal stroke

Pedal Reaction Force
90 180 270 360
Pedal Cycle (degrees)
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Pressure Distribution on Shoe

• Almost all pressure us located under big toe
• Little pressure exerted at arch and heal
• Pattern of pressure distribution on the sole of
  the shoe

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Static Equilibrium of a Cyclist

• A cyclist balancing on the cycle
• C cyclist propelling bike forward
• Major forces
• G1 and G2 are ground reaction forces at front and
  rear wheels
• P1 and P2 left and right pedal forces

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Static Equilibrium of a Cyclist

• Wr force due to weight of rider
• Wb is the weight of the cycle
• R is drag due to air resistance
• H is the force exerted by hands of handle bars
• G1G2P1P2WrWbH

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Joint Reaction Forces

• Power phase
• compressive joint reaction force by distal end of
  femur on tibial plateau
• Anteriorly directed joint reaction force during
  the power phase
• Laterally directed joint reaction force at the
  knee
• Peak joint reaction forces have highest values at
  90 of pedaling cycle

http//www.treehugger.com/Norwegian20cyclist.jpg
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References

• Burke, Edmund R. Science of Cycling. Human
  Kinetics, 1986.
• (2002). Cycling Styles Techniques. Retrieved
  February 17, 2009, from North Lanarkshire
  Council Web site http//www.northlan.gov.uk/lei
  sureandtourism/sportsactivities/cycling/cycling
  styles andtechniques.html
• Gregor, Robert J., and Francecso Conconi. Road
  Cycling - Hanbook of Sports Medicine and
  Science. OxfordMalden,Mass Blackwell Science,
  2000.
• Lee, C. (2008). Updates Log. Retrieved February
  17, 2009, from Calvin Lee Web site
  http//www.risingpianofire.com/updates.htm
• Potter, J. J., J. L. Sauer, et al. (2008).
  "Gender differences in bicycle saddle pressure
  distribution during seated cycling." Medicine
  and Science in Sports and Exercise 40(6)
  1126-1134
• (2009). Semimembranosis. Retrieved February 17,
  2009, from Club Physio Plus Web site
  http//www.clubphysioplus.com/Myofasial_stretches
  /semimemb.htm
• University of Southern Calafornia. Retrieved
  February 17, 2009, from Pelvic Anatomy Web site
  http//radiology.usc.edu/Presentations/SaddlePros
  thesis/PAGE2_ANAT_FINAL2.HTM
• Wilson, C. and T. R. Bush (2007). "Interface
  forces on the seat during a cycling activity."
  Clinical Biomechanics 22(9) 1017-1023.

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Muscle Activity

• Peak muscle activity during pedal stroke (0 is
  top)
• Gluteus Maximus 55
• Rectus Femoris drops off at 90
• Soleus and Gastrocnemius just before 90
• Gastrocnemius peaks at an average of 107 and
  ends at 270
• Hamstrings active during entire down stroke
  (power phase)
• Semimembranosus Semitendinosus 0-90 peaks
  at 90
• Quadriceps activity ceases at 90