L23 - Angular Kinetics: Fast Running Facts

• Sprinting Phases - looking at 100 m:

  • For any type of sprint length (100 m to 400m etc) have sprinting phases
  • Speed changes over course of sprint
  • 4 phases
• Sprinting Phases - looking at 100 m:

  1. Drive phase (0-10 m)
  2. Transition phase (turning point)
  3. Maximal Velocity phase
  4. Maintenance phase
• Sprinting Phases - looking at 100 m:

  1. Drive phase (0-10 m) - initiating movement
  2. Transition phase (turning point) from hz drive & become upright into maximal speed, change in stride, speed etc & how develop force
• Sprinting Phases - looking at 100 m:

  • 3. Maximal Velocity phase - where start to reach peak velocity; constant increase until reach max, more upright posture, change of flexion & extension of hips & drive of force
• Sprinting Phases - looking at 100 m:

  • 4. Maintenance phase - acceleration reached = no longer accelerating just trying to maintain as much as possible (60 m - 100 m → but normally slowing down before 100 m)
• Starting blocks:

  • Blocks set up that way to have CoM to drive forward, to supply reaction forces in hz direction make initial hz phase faster (automatically in direction want) = propulsion force (as much as possible)
• Sprinting Phases:

  • Acceleration phase (20-30 m)
  • Maximal velocity (~60 m)
  • Maintenance of velocity
• Sprinting Phases:

  • Phases of movement
  • Red line = speed curve
  • Green = acceleration over 100 m (changes in velocity)
  • Initially changes drastically in drive phase
  • Transition maintain acceleration (plateau but still increase in velocity)
  • Maximal velocity acceleration decreases as rate of change decreases
  • After peak accelerating no longer increasing at 0 = maintain speed (below 0 = decelerating)
• Sprinting Phases:

  • Transition CoM still forward to propel forward
  • Upright to drive force downward for reaction force
  • Braking phase = decelerating
• Sprinting Phases - What makes a good sprinter?

  • Blue = quick explosive acceleration typically seen in elite sprinters (LJ, hurdles, 100 m)
  • Green = acceleration = middle distance runners
  • Red = not as explosive, peak later, seen in high school athletes
  • Light blue = long distance doesn't really need explosive
• World Record 100 m Sprint Profiles:

  • What makes sprinters different
  • Ben reached peak early then started decelerating (= unusual)
  • Carl - drive phase shorter, 2 transition phase, up & down (training issue should be maintaining not going up and down in acceleration) - also unusual
  • Mo - good
  • Mo - burnt self out in drive, maintenance stage quite early (worse time)
• World Record 100 m Sprint Profiles:

  • Tim - smooth transition phase, good maintenance
  • Asafa - less sharp deceleration, really long maintenance
  • Bolt - similar drive phase, 2 transitions points, takes longer to get to maximal (starts at back), its max while others in maintenance, maintenance start later well everyone is slowing down + for longer (see why he is faster), then sharps deceleration
• Acceleration phase is about propulsion:

  • GRF during acceleration phase of a sprinter
  • Peak hz pretty high initially, then very little neg hz (means next to no braking, 0 = no braking) → bc/ really leaned over directing drive backwards to drive self forward keeping CoM ahead
  • As strides elongate and velocity increase more braking force come in and more vt component (starting to stand upright)
  • Neg hz still gonna be + (propulsive) over all
  • Maintain good hz propulsive force
  • Almost 50/50 hz/vt at start of drive phase
• Reaching Peak Velocity:

  • Hz forces begin to decrease
  • Propulsive & braking forces begin to equalise
  • Speed = ([F vt / FBW] x distance) x (t stance + t aerial)^-1
  • Hz & vt component over full 100 m
  • More hz at start then then vt for majority of it
• Reaching Peak Velocity:

  • After 40 m - hz force is less important
  • Why?
  • As becomes less efficient because
  • Faster go longer (greater ROM) takes to swing leg
  • Limiting factor to muscle performance = velocity of contraction (has a max)
  • Where doing hz becomes less efficient as takes more time - relying on contractile components
• Reaching Peak Velocity:

  • As becomes less efficient because
  • Time is not friend, so if can't rely on hz force (muscle shortening to provide force) - muscle tendon units (not active can't contract but can) transfer energy to system through elastic recoil
  • Stretch tendon as release put energy back into system
  • So we can increase force production by using this elastin recoil
  • Store energy, when contract, force of muscle with stored energy in tendon = greater force production
• Reaching Peak Velocity:

  • Hz = contractile components
  • Vt = elastic components
  • More force in shorter time
• Reaching Peak Velocity:

  • As velocity increases:
  • Decrease ground contact time (faster move longer flight phase)
  • Step frequency and length increasing → step length comes with flight phase
• Reaching Peak Velocity:

  • Average reflex time for a muscle = 50ms
  • 100-75 not a lot of time to apply force (during ground contact)
  • Greatest force in shorter amount of time = fastest runner
• The Biomechanics of Maximal Speed (cont.):

  • How can the athlete increase GRF in a shorter time?
  • How can they cycle the limb through the recovery phase quickly in order to apply forces in the next stride?
  • Cycle limb thru faster increase time component limited due to contractile components
• The Biomechanics of Maximal Speed (cont.):

  • To better understand let's compare a sprinter to a long distance runner
  • Marathon runner: 5.7 m/s ~20.5 km/h
  • Sprinter: 10.2 m/s ~36.7 km/h
  • Speed = sum of force z * distance stance / change in time
• The Biomechanics of Maximal Speed (cont):

  • Get narrower & compresses
  • Impact peak hz = braking, foot in front of CoM, further ahead more braking applied (sprinting)
  • Sprinter stepping close to CoM minimise braking (ground contact almost directly under body)
• The Biomechanics of Maximal Speed (cont):

  • To better understand compare a sprinter to a long distance runner:
  • Marathon runner
  • 5.7 m/s ~20.5 km/h
  • Longer duration, foot contact time
  • Similar to walking (separation bw/ 2 peaks)
  • Walking impact component lower & active (propulsive) component larger in marathon runner
  • Sprinter
  • 10.2 m/s ~36.7 km/h
  • Peak force = 4000 N = 400 kg
  • When walking curve as impact peak & active peak (propulsive)
  • Time shorten bw/ them so much that 2 peaks come together (still there)
• They need to cycle the limb quicker:

  • H tot = ICMω + mk^2ω
  • Look at recovery leg position
  • Kick but in sprinting, increases flexion of knee and decreases length of moment arm which
  • Bc/ angular moment and mass moment of inertia
  • Knee closer = less resistance to rotate - increases speed of leg spin
  • As get recovery inertia force moves quickly as lags behind, ROM for free, as move faster get more of it, some have to do work for
• Point of application of the force:

  • Marathon = Left; Sprinter = Right
  • Marathon = soft knee and hip
  • Absorbing energy of contact
  • Reduce impact force
  • Accumulative effect (as to do for ages)
  • Athletic tracks tuned to give energy back to athletes; would also make faster but increase risk
• Point of application of the force:

  • Sprinter: hip and knee almost fully extended
  • Transfer energy of contact into next stride
  • Stimulate muscle tendon to go into next stride
  • Not as beneficial to have soft knee to absorb
  • To run faster: ground contact closer/under CoM, makes more efficient as not absorbing any energy
  • Would cause injury if constantly did this (body can't stand this over time)
• What about the hip ROM?

  • Greater hip ROM for sprinter
  • Driving knee up (vt distance giving vt force production )
  • Greater extension because moving forward face (inertia reaction = reaction force)
  • Greater extension in recovery, greater flexion in drive (of sprinter)
• What do the arms do?

  • H sag = ICM.ω + mk^2ω
  • H long = (ICMω + mk^2ω)upper + (ICMω + mk^2ω)lower
  • Arms help by counterbalancing
  • If didn't would be walking like penguin
  • Splitting long axis in half - to 0 out rotation in long axis
• Other things to consider:

  • The action of biarticular muscles
  • Contribute free energy to lower segments and the action of monoarticular muscles
  • Law of action reaction means the faster we move our hip the greater counter rotation at the knee which will increase knee ROM for free
  • Greater hip and knee motion will place high strain or tension on the hamstring muscles
  • Hamstring must be compliant
  • High GRF forces mean Gastrox must be stiff to transfer force through the chain without attenuating
• Reaching Peak Velocity:

  • Initial 10 m large hz component
  • As move thru hz component drops off and vt component picks up
  • Relates to position of body posture
  • Changing force application of where CoM is
  • Must be greater than 0 to be propulsive
  • Want to maintain 0 hz in terms of velocity (check)
• Acceleration phase is about propulsion:

  • l Fprop * dt + l Fret * dt > 0
  • Acceleration phase = drive + transition phase
  • Hz force profile (braking & propulsive impulse)
  • If want to change velocity need greater propulsive impulse than braking (can't be 0 and should be positive)