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Document Title: Livesay-AJSM-Mar06.shtml
Article Title:
Peak Torque and Rotational Stiffness Developed at the Shoe-Surface Interface: The Effect of Shoe Type and Playing Surface
Authors: Glen A. Livesay, PhD, Dawn R. Reda, MS and Eric A. Nauman, PhD
Publication: American Journal of Sports Medicine, Baltimore, Maryland
Date: March 2006.
Volume 34, pages 415-422
Keywords: Twisting-type injuries, pivoting, plant-and-twist injury, non-contact injury, ACL tearing via twisting, shoe-surface interface, grip, peak torque, shoe type, playing surface, biomechanics, friction coefficient, rotational stiffness, Astroturf, Astroplay, FieldTurf, artificial turf, infill-type synthetic turf, natural grass.
(Reference-denoting numbers appear in the same font and point size as the document text. As with all Knee Library documents, this article is provided in full-text form, complete with all figures and tables.)
Comments: This intriguing study looks at the peak torque, hence maximum torque attained prior to slippage, developed with different combinations of shoe type (large-cleated standard grass shoes, as common for outdoor soccer for decades, versus the newer small-cleated turf shoes) and playing surface (natural grass versus traditional Astroturf, versus the newer artificial surfaces [FieldTurf and AstroPlay, which utilize sand and/or crumb-rubber infill]). Ten different shoe-and-surface combinations were tested. The highest peak torques arose with the grass shoe–FieldTurf tray and turf shoe–Astroturf combinations, whereas the lowest peak torques consistently appeared with the grass surface; however, certain combinations of shoe and infill-type synthetic surfaces brought peak-torque values very similar to those of the natural-grass surface. It would seem reasonable to conclude that a thick, healthy natural grass (which unfortunately is difficult to maintain on a heavily-used field, especially in arid and hot climates) would be most conducive to low twisting-type knee-injury rates. Natural grass also appears to be the most forgiving in terms of shoe type: grass shoe or turf shoe can be used without engendering worrisome increases in peak torque. Meanwhile, the infill-type synthetic surfaces are a good substitute for natural grass, but only if used with the appropriate footwear (i.e. small-cleated turf shoes). Using traditional large-cleated grass shoes on artificial surfaces (including the newest infill types) appears to be risky. The authors note that although the testing loading was a mere 511 N (much less than the weight of the average football player), there is a linear relationship between peak torque and compressive loading, and so the results could be scaled up. The authors also note that because human reaction time must be taken into account when analyzing injury situations, the rate at which the torque rises to its peak value also merits consideration. Finally, other factors play a role too; these include attributes of the athletes themselves, for example training, muscle strength, knee anatomy, knee alignment, and vestibular/proprioceptive/neuromuscular firmware aspects. Given that twisting-type knee injuries occur on all playing surfaces, it is also clear that the athlete's pivoting technique plays a major role in these injuries. For this reason, regardless of the playing surface used, the athlete would be well-advised to practice knee-friendly pivoting techniques, in particular pivoting only on the front portion of the foot (instead of planting the entire shoe sole prior to pivoting).
ABSTRACT
Background: Shoe-surface interactions have been implicated in the high number of noncontact knee injuries suffered by athletes at all levels.
Purpose: To examine shoe-surface interactions on newer field designs and compare these with more traditional shoe-surface combinations. The peak torque and rotational stiffness (the rate at which torque is developed under rotation) were determined.
Study Design: Controlled laboratory study.
Methods: A device was constructed to measure the torque versus applied rotation developed between different shoe-surface combinations. Data were collected on 5 different playing surfaces (natural grass, Astroturf, 2 types of Astroplay, and FieldTurf), using 2 types of shoes (grass and turf), under a compressive load of 333 N.
Results: The highest peak torques were developed by the grass shoe–FieldTurf tray and the turf shoe–Astroturf field combinations. The lowest peak torques were developed on the grass field. The turf shoe–Astroturf combination exhibited a rotational stiffness nearly double that of any other shoe-surface combinations.
Conclusion: The differences in the rotational stiffness across all 10 shoe-surface combinations were greater than those of the peak torques. It is possible that rotational stiffness may provide a new criterion for the evaluation of shoe-surface interface.
Clinical Relevance: An improved understanding of shoe-surface interactions remains a critical need to improve the design of shoe-surface combinations with the goal of meeting player needs while minimizing injury potential.
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