evaluation of cushioning properties of running footwear
DESCRIPTION
Evaluation of Cushioning Properties of Running Footwear. D. Gordon E. Robertson, Ph.D.* Joe Hamill, Ph.D.** David A. Winter, Ph.D.# * School of Human Kinetics, University of Ottawa, Ottawa, CANADA ** Dept. of Exercise Science, University of Massachusetts, Amherst, USA - PowerPoint PPT PresentationTRANSCRIPT
Evaluation of Cushioning Properties of Running Footwear
D. Gordon E. Robertson, Ph.D.*
Joe Hamill, Ph.D.**
David A. Winter, Ph.D.#
* School of Human Kinetics,
University of Ottawa, Ottawa, CANADA
** Dept. of Exercise Science,
University of Massachusetts, Amherst, USA
# Kinesiology Dept., University of Waterloo,
Waterloo, CANADA
Introduction
• most mechanical analyses assume rigid body mechanics
• during initial contact and toe-off the foot may not act as a rigid body especially if footwear is worn
• modeled as a deformable body, cushioning properties of foot/shoe can be evaluated under ecologically valid conditions
Purpose
• measure the deformation power of foot during running to determine whether the cushioning properties of footwear can be distinguished
Methods
• nine runners (seven male, two female) having men’s size 8 shoe size
• video taped at 200 fields/second
• five trials of stance phase of running
• speed: 16 km/h (4.4 m/s, 6 minute/mile)
• ground reaction forces sampled at 1000 Hz
• two conditions:
– soft midsole (40-43 Shore A durometer)
– hard midsole (70-73 Shore A durometer)
Methods
• foot’s mechanical energy and rate of change of energy computed (E/t)
• inverse dynamics to calculate ankle force (F) and moment of force (M)
• ankle force power:Pf = F . v
• ankle moment power: Pm = M
Methods
power deformation computed as:
Pdef = E/t - (Pf + Pm)
• assuming no power loss/gain to/from ground
• assuming non-rigid (deformable) foot
Foot powers
0.00 0.05 0.10 0.15 0.20
Time (seconds)
-2000.
-1500.
-1000.
-500.
0.
500.
1000.
1500.
2000.
Pow
er (
wat
ts)
Trial: F1C1T4Force powerMoment powerTotal powerEnergy rateDeformation power
Deformation powers
0.00 0.05 0.10 0.15 0.20
Time (seconds)
-2000.
-1500.
-1000.
500.
0.
500.
1000.
Pow
er (
wat
ts)
Trial: F1C1 soft solesTrial 1Trial 2Trial 3Trial 4Trial 5
Mean deformation powers(subj. J1)
Percentage of stance
Pow
er (
wat
ts)
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100-2500
-2000
-1500
-1000
-500
0
500
1000
Soft sole
Mean deformation powers(subj. F1)
0 10 20 30 40 50 60 70 80 90 100Percentage of stance
Pow
er (
wat
ts)
Hard sole
0 10 20 30 40 50 60 70 80 90 100-2500
-2000
-1500
-1000
-500
0
500
1000Soft sole
Mean deformation powers(subj. L3)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100
Soft sole
Mean deformation powers(subj. L4)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
1000 10 20 30 40 50 60 70 80 90
Soft sole
Mean deformation powers(subj. L5)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100
Soft sole
Mean deformation powers(subj. L6)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100
Soft sole
Mean deformation powers(subj. L9)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100
Soft sole
Mean deformation powers(subj. L10)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100
Soft sole
Mean deformation powers(subj. L11)
Percentage of stance
Pow
er (
wat
ts)
-2500
-2000
-1500
-1000
-500
0
500
1000
0 10 20 30 40 50 60 70 80 90 100
Hard sole
0 10 20 30 40 50 60 70 80 90 100
Soft sole
Results
• in all nine subjects there was an initial period of negative work
• in six subjects a brief period of positive work followed
• in seven subjects a period of negative work occurred in midstance
• in eight subjects there was a period of positive work immediately before toe-off
Discussion
• the initial negative work was assumed to be due to energy absorption by the materials in the heel of the shoe and/or the tissues in the heel
• the subsequent positive work was likely due to energy return from, most likely, the shoe
• negative work during midstance may be due to midsole deformation or work by moment at metatarsal-phalangeal joint
• the final burst of power was assumed to be due to work done by the muscle moment of force across the metatarsal-phalangeal joint
Conclusions
• there was no significant difference between the impact characteristics of the two types of shoe durometer
• assumption of rigidity of foot-shoe is not appropriate
• power deformation patterns were consistent within subjects but varied considerably across subjects
• subjects probably adapted to the shoe impact characteristics to mask the differences in the shoe’s durometer
Hypotheses
• subjects probably adapted to the shoe impact characteristics to mask the differences in the shoe’s durometer
• need to test methodology on a mechanical analogue that can consistently deliver a footfall to a force platform