The manipulation of midsole properties to alter impact characteristics in walking

Price, C; Cooper, G; Jones, R

Abstract

The midsole of footwear can provide an opportunity to attenuate the impact at the foot-ground interface. The present study was undertaken to quantify impact in walking in different footwear midsoles, comparing footwear thickness and hardness variations. Methods: Footbed thickness (28-41 mm) and hardness (30-55 Shore A) were varied independently in 7 flip-flops. Thirteen subjects walked in the footwear variations on a level walkway in the gait laboratory as lower limb kinematics, vertical ground reaction force and peak positive axial tibial acceleration were quantified. Peak magnitude and time of the acceleration were quantified and the heel-strike transient was characterised for comparison between conditions with a repeated-measures ANOVA. Thickness and hardness variations were also compared using a drop-test protocol to replicate walking. Results: Lower limb joint angles did not vary at heel-strike, however, a faster vertical heel-velocity was recorded in the softer midsoles (e.g. 55 Shore A = -0.294±0.055, 30 Shore A= -0.328±0.052, p<.001). Varying the hardness of the midsoles also significantly altered tibial acceleration and force variables, however limited significant differences existed between the thickness variations in walking. Increasing the hardness of the heel section of the footwear increased the peak positive axial tibial acceleration values, for example increasing Shore A from 30 to 40 resulted in a 35% increase in this variable. Concurrently, the occurrence of heel-strike transients increased from 5.8% in the 30 Shore A condition to 22.5%, 46.7% and 71.7% of all trials in the 40, 47 and 55 Shore A conditions respectively. The drop-test protocol replicated the differences evident in the walking protocol despite magnitudes being elevated. Conclusion: Modifying midsole properties of flip-flop footwear, particularly hardness, alters the gait kinematics and the shock experienced by the wearer in walking. This may pose benefits in terms of comfort and reduction in loading to the lower limb, however the influence on foot motion at initial contact and footwear longevity should be further quantified.

Citation

Price, C., Cooper, G., & Jones, R. (2015). The manipulation of midsole properties to alter impact characteristics in walking. Footwear Science, 7(1), 9-16. https://doi.org/10.1080/19424280.2014.983444

• Journal Article Type: Article
• Acceptance Date: Oct 30, 2014
• Publication Date: Jan 1, 2015
• Deposit Date: Dec 17, 2014
• Publicly Available Date: Jun 12, 2016
• Journal: Footwear Science
• Print ISSN: 1942-4280
• Electronic ISSN: 1942-4299
• Publisher: Taylor and Francis
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Issue: 1
• Pages: 9-16
• DOI: https://doi.org/10.1080/19424280.2014.983444
• Publisher URL: http://dx.doi.org/10.1080/19424280.2014.983444
• Related Public URLs: http://www.tandfonline.com/loi/tfws20#.VJFubqh_suc