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Evaluation of Cushioning Properties of Running Footwear

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

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Evaluation of Cushioning Properties of Running Footwear

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  1. 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

  2. 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

  3. Purpose • measure the deformation power of foot during running to determine whether the cushioning properties of footwear can be distinguished

  4. 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)

  5. 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 w

  6. Methods power deformation computed as: Pdef = DE/Dt - (Pf + Pm) • assuming no power loss/gain to/from ground • assuming non-rigid (deformable) foot

  7. Foot powers 2000. 1500. 1000. 500. Power (watts) 0. -500. -1000. Trial: F1C1T4 Force power Moment power Total power -1500. Energy rate Deformation power -2000. 0.00 0.05 0.10 0.15 0.20 Time (seconds)

  8. 1000. 500. 0. 500. -1000. -1500. -2000. Deformation powers Trial: F1C1 soft soles Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Power (watts) 0.00 0.05 0.10 0.15 0.20 Time (seconds)

  9. Mean deformation powers(subj. J1) 1000 Soft sole Hard sole 500 0 -500 Power (watts) -1000 -1500 -2000 -2500 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  10. Mean deformation powers(subj. F1) 1000 Hard sole Soft sole 500 0 -500 Power (watts) -1000 -1500 -2000 -2500 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  11. 1000 500 0 -500 -1000 -1500 -2000 -2500 Mean deformation powers(subj. L3) Hard sole Soft sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  12. 1000 Soft sole 500 0 -500 -1000 -1500 -2000 -2500 0 10 20 30 40 50 60 70 80 90 Mean deformation powers(subj. L4) Hard sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 100 Percentage of stance

  13. 1000 500 0 -500 -1000 -1500 -2000 -2500 Mean deformation powers(subj. L5) Soft sole Hard sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  14. 1000 500 0 -500 -1000 -1500 -2000 -2500 Mean deformation powers(subj. L6) Soft sole Hard sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  15. 1000 500 0 -500 -1000 -1500 -2000 -2500 Mean deformation powers(subj. L9) Soft sole Hard sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  16. 1000 500 0 -500 -1000 -1500 -2000 -2500 Mean deformation powers(subj. L10) Hard sole Soft sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  17. 1000 500 0 -500 -1000 -1500 -2000 -2500 Mean deformation powers(subj. L11) Soft sole Hard sole Power (watts) 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Percentage of stance

  18. 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

  19. 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

  20. 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

  21. 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

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