Kinematic Analysis of Running Gait

1
Kinematic Analysis of Running Gait

• Angular displacement of the hip, knee and ankle
  vs. time was digitalized, and the angle of the
  foot above the ground during any period of time
  was calculated from this data.
• Slope calculated between consecutive points in
  order to determine velocity during each period of
  time in gait.

?F Resulting Angle of Foot Above Ground
http//www.viconstandard.org
2
Results from Digitalized Data

• Healthy, male runner
• Velocity at Footslap 7.08rad/s

velocity data points v/(natural frequency)
3
Ankle Dynamics

• Ankle characterized as a Single Degree of Freedom
  Oscillator rotated about ankle joint from the
  saggital plane
• Muscle control mainly from the tibialis anterior,
  the gastrocnemius, and the soleus provide
  stiffness and damping in the ankle
• Free Vibration of SDOF Oscillator characterized
  by the following equations of motion

Tibialis anterior
Soleus
Gastrocnemius
http//www.exrx.net/Muscles.html
4
Purpose of Simulation Tests

• The main objective of the simulation was to
  evaluate the severity of the footslap velocity
  for a patient with no ankle stiffness, and to
  develop an appropriate ankle stiffness that would
  most closely resemble the functioning of an ankle
  in a healthy, male runner.
• The simulated ankle stiffness could then be
  translated into the appropriate spring type
  needed to be implemented into the artificial
  ankle joint.
• Simulation set up to evaluate the position and
  velocity of the foot at any period of time from
  the heelstrike to the footslap portion of the
  running gait.

5
Model Setup

• ?F angle of the foot measured from the ground
  to the bottom of the shoe
• LH length of foot from heel to ankle pivot
• Ka and Ca spring stiffness and damping

Sum of Moments about the Heel
6
Analysis

• Runge-Kutta-Nystrom Method used to calculate
  numerical solution of second order differential
  equation
• Spring Neutral Position set at offset 19
• Simulation Tests

7
Simulation Results

• Ankle Stiffness 80 Nm/rad
• ? 0.35
• Ia 0.105 kgm² If 0.1064 kgm²

Simulation Velocity at Footslap 7.09 rad/s
8
Simulation Results, cont.

• Zero Ankle Stiffness Jason Williams Injury
• ? 0.35
• Ia 0.105 kgm² If 0.1064 kgm²

Simulation Velocity at Footslap 15.2 rad/s
9
Non-Linear Spring

• Simulation performed of a non-linear spring that
  varied with the angle of foot deflection from
  ground.
• Non-linear model adjusted so the velocity at
  footslap would remain equivalent to that of a
  normal runner at 7.09 rad/s
• Purpose of non-linear spring is to make the brace
  more adaptable for jumping.

10
Conclusion of Simulation

• Presently, footslap of Jason Williams is nearly 2
  times that of normal runner ( 15.2 rad/s)
• Brace designed to bring footslap back down to
  normal velocity of 7.01 rad/s.
• Spring Design for Brace (linear spring)
• Torsional Spring Stiffness 80 Nm/rad
• Equivalent linear spring stiffness
• Moment Arm ½ KL 3.15 kN/m
• Moment Arm ¾ KL 2.1 kN/m
• Moment Arm 1 KL 1.57 kN/m

11
REFERENCES

• Cavanagh, Peter R. Biomechanics of Distance
  Running Human Kinetics Books, Champaign, Il.
  1990.
• Weiss, P.L., Hunter, I.W., and Kearney, R.E.
  Human Ankle Joint Stiffness Over the Full Range
  of Muscle Activation Levels Journal of
  Biomechanics, v21, pg 539-544
• Williams, Kieth R., Biomechanics of Running
  Exercise and Sports Reviews, v13 pgs 389-420.
• Ankle and Foot Biomechanics and Gait Cycle
  http//www.orthoteers.co.uk/Nrujpij33lm/Orthfootm
  ech.htm