See below for Phase 1 of my final project process. My research is focused on understanding the mechanics of the bare foot and the tradeoffs athletes experience with different types of footwear during strength and agility training. Enjoy!

 

5.8.2020 Traction Research

Topic: Harnessing sport-specific plantar loading patterns to develop data-driven traction designs
Villanova Wildcats guard Phil Booth (5) drives to the basket (Credit Image: © Duncan Williams/CSM via ZUMA Wire)

Advances in biomechanical analysis of plantar loading patterns can be applied to the development of traction patterns that offer zone-specific and directional traction. Analysis of the sport-specific kinematics of basketball reveal unique requirements for basketball athletes, while friction properties specific to hardcourt surfaces provide insight into the mechanisms of traction geometries. Using parametric design, we can successfully apply data from these kinematic analyses to hone traction patterns that better suit specific sports, playing surfaces, and even styles of play. 

 

I. Movement and Traction Patterns

Lateral shuffling, sidestep cutting, and frequent directional transitions are integral to both offensive and defensive techniques in basketball. Game analysis revealed that basketball players spend upwards of 31% of active play time cutting and shuffling, characterized specifically by sudden deceleration and acceleration in a new direction of movement. This study also revealed that the mean durations of activity for 11 different categories of movement were less than 3 seconds, with frequent changes in intensity and movement direction (McInnes, 1993). 

 

The loading patterns of these different movements reveal the shear stress placed on specific regions of the foot, which further informs geometries of traction patterns. During lateral shuffling, the first metatarsal head experiences the first peak of localized pressure and the largest loading rates of shear stress. The largest vertical pressure occurs at the second metatarsal head during propulsion, while during 45 degree cutting the peak loading rate occurred at the heel (Cong et al, 2014). High shear stress and peak loading of specific areas of the foot occur during the braking and propulsion associated with the rapid and frequent changes of direction endured by basketball athletes. 

A study conducted by LiNing Sports Company and Nanyang Technological University quantified the plantar pressure distribution patterns of basketball specific movements, finding the peak pressures and loading rates to be significantly higher in a variety of basketball-specific tasks (Kong et al, 2018). In sprinting and acceleration, the medial forefoot experiences the highest peak pressure and loading of all regions of the foot, followed by the hallux and second metatarsal head. During 45 degree cutting, peak pressure occurs at the first metatarsal head, hallux, and lateral heel. During layups, peak pressure and loading rates occur at the medial and lateral midfoot, and lateral heel. All peak pressures and loading rates of these basketball-specific tasks were calculated as significantly greater than the stresses recorded during running (Kong et al, 2018). 

The data gathered from these basketball-specific studies, which take into account typical athlete movements, intensities, and playing surfaces, translate well into a data-driven design system. By mapping the peak pressures and shear stresses on the shod foot during these movements, we can design a traction system to adapt seamlessly to these parameters. 

 

Existing basketball traction design takes into account the various movements of a basketball player, including pivoting and directional changes, and utilizes a “zoning” rationale that somewhat rigidly defines the purpose of each zone. A 2016 analysis of outsole pattern trends and performance outcomes revealed that 27% of basketball outsoles had a different pattern on the first metatarsal head, 43% had longitudinal traction on the lateral region of the outsole, and only 16% utilized a uniform pattern on the entire sole. Diagonal treads dominated pattern trends, occuring in 95% of outsole designs, including varieties such as herringbone and wave patterns (Van Groningen, 2016). 

While widely used and accepted as “tried and true”, these diagonal herringbone patterns leave notable room for improvement as they are not informed by the directional forces and plantar loading data observed in recent kinematic studies. 

 

 

II. Tread Form and Power Transfer

The dynamic tasks of basketball, as described above, require bilateral direction changes and rapid acceleration and deceleration. Power transfer through the outsole, though relying largely on material engineering and chemistry, can be optimized through intelligent tread form design. The shape of the individual treads, rather than the pattern as a whole, can aid in initiating and executing maximal intensity motions without loss of power or slippage. The stick-slip phenomena, a cause of the well-known squeak of basketball shoes on hardwood, results from compliance of the individual treads as they bend and vibrate across the floor. While this phenomena has been explored in the realm of frictional-adhesion, studies concur that on smooth surfaces at high velocities, stick-slip friction results in failure (Das et al, 2015). In my personal opinion, this phenomena’s relation to basketball traction garners more research, and may reveal successful applications in the future. With that in mind, note that the squeaks heard in basketball usually occur during pivoting, walking, or jogging and not at the peak velocities of competitive play. 

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A better solution to power transfer can be found in form studies of screw threads in clamps and vices. Various thread types are used in industrial screws, each with specific advantages and disadvantages. Most applicable to the challenge of power transfer in traction design is the ACME thread. ACME threads have a thread angle of 29 degrees on either side, taking the shape of a trapezoid when viewed in section. Due to the larger cross section at the base, this thread form is significantly stronger and more resistant to shear stress than a traditional square thread (Singh et al, 2017). This feature applies well to the kinematic data collected regarding the shear stresses and loading during basketball-specific tasks. When applied to traction, the tread will not comply but rather transfer the power back into the foot for a more explosive “bite”. In addition, the ACME thread forms symmetrical shape, when compared to other industrial threads such as the buttress, transmits powers in both directions, a key application for the directional changes experienced during basketball. Though a traditional square thread may be marginally more efficient in scenarios where normal, or perpendicular, stress is applied, the ACME thread is far more applicable to scenarios of shear stress, such as basketball (Singh et al, 2017).

   

 

III. Prior Art

a. US20160095384A1: Sole for a shoe

Ulrike Elisabeth Kraft; Adidas AG

 

Described are soles for shoes, in which the sole includes a porous mesh and a continuous first layer arranged at least partially on a first side of the porous mesh, wherein the first layer penetrates the porous mesh at least partially to form a tread structure on a second side of the porous mesh opposite the first side, and wherein the first layer and the porous mesh are bonded at least in an area where the tread structure is formed.

 

b. US8322049B2: Wear resistant outsole

Frederick J. Dojan; Nike Inc. 

 

An article of footwear may have an outsole with multiple contact zones. Each of those contact zones may include perimeter regions formed from a harder elastomeric material and traction elements formed from a softer elastomeric material. The traction elements within a particular contact zone may be generally planar in shape and aligned in parallel along on orientation direction for that contact zone. When undeformed, the traction elements in a contact zone may extend outward from the outsole beyond the perimeter regions of that same contact zone. In response to a shear force resulting from activity of a shoe wearer, the traction elements may be deformable so as to rest within a volume formed by the perimeter regions.

 

c. US20190328087A1: Article of footwear having a polygon lug sole pattern

Eric P. Avar, Kevin W. Hoffer, Tobie D. Hatfield; Nike Inc. 

 

an outsole (300) engaged with the midsole, the outsole including a plurality of lugs (310) extending from a base surface, the lugs being polygonal and uniform in shape and arranged to form a ground contacting surface of the outsole, and wherein the lugs are sized, shaped or spaced from one another to provide regions of the outsole with different impact-attenuation characteristics, including the following regions: (a) a high pressure or force bearing region including a first plurality of lugs (310a, 410a) located at a central portion of the outsole expending at least from a heel region to a ball of the foot region and (b) a low pressure or force bearing region including a second plurality of lugs (310b, 410b) located at a periphery of the central portion, wherein at least some of the second plurality of lugs in the low pressure or force bearing region are smaller in size, have a smaller wall thickness, and/or are more spaced apart from other lugs as compared with at least some of the first plurality of lugs in the high pressure or force bearing region.

 

d. US9510645B2: Article of footwear with multi-directional sole structure

Eric P. Avar, Aaron A C Cooper, David J. Dirsa, Thomas Foxen, Tom Luedecke; Nike Inc. 

 

An article of footwear with a multi-directional sole structure including a flex groove system is disclosed. The flex groove system includes a plurality of longitudinal flex grooves and lateral flex grooves that divide the sole structure into a plurality of segments. The flex groove system also includes a plurality of diagonal flex grooves that intersect the corners of the plurality of segments. The flex grooves system can provide enhanced flexibility for the sole structure and can enhance multi-directional flexing.

e. US9854871B2: Sole structures that include portions with different herringbone traction pattern arrangements

Justin r. Taylor; Nike inc. 

 

Sole structures for articles of footwear include herringbone type contact surface portions wherein at least two of the herringbone contact surface portions include herringbone traction element components that are oriented in different directions and/or two herringbone contact surface portions separated from one another by an arch area of the sole.

 

Sources:

Cong, Y., Lam, W. K., Cheung, J. T.-M., & Zhang, M. (2014). In-shoe plantar tri-axial stress profiles during maximum-effort cutting maneuvers. Journal of Biomechanics, 47(16), 3799–3806. doi: 10.1016/j.jbiomech.2014.10.028

Das, S., Cadirov, N., Chary, S., Kaufman, Y., Hogan, J., Turner, K. L., & Israelachvili, J. N. (2015). Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces. Journal of The Royal Society Interface, 12(104). doi: 10.1098/rsif.2014.1346

Kong, P. W., Lam, W. K., Ng, W. X., Aziz, L., & Leong, H. F. (2018). In-Shoe Plantar Pressure Profiles in Amateur Basketball Players. Journal of the American Podiatric Medical Association, 108(3), 215–224. doi: 10.7547/16-123

McInnes, S. E. (1993). The Physiological Load Imposed on Basketball Players During Game Play (dissertation).

Singh, V., Singh, V., Srivastav, V., Sunva, D., & Singh, S. K. (2017, October 27). PDF.

Van Groningen, D. (2016). Effects of Outsole Shoe Patterns on Athletic Performance (dissertation).