The Design of an Athlete-Specific Spike Plate for Skeleton

Abstract

Across all levels of high-performance sport, organisations, teams, coaches, and athletes, are always searching for an advantage to outperform their competitors, and in a sport like skeleton, even the smallest of advantages can make the difference between a podium and disappointment. Skeleton is a sport contested by individual athletes, sliding down an ice track headfirst, with the aim of achieving the quickest overall time. A key stage of the race is the push start, where the athletes have up to 65 metres to run as fast as they can and settle into a racing position on their sled. Alongside their training programmes, optimising the equipment used is an area that can be exploited to allow the athletes to perform at their maximum potential while gaining a competitive advantage. The spike plate is attached to the bottom of the shoe and its purpose is to provide traction on the ice for the push start. Through this research, an investigation into the spike plate was conducted to gain an understanding of its interactions with both the athlete and the ice to identify areas for improvement. The research aim was to investigate the current spike plate and the push start to design a novel athlete-specific spike plate through a human-centred design approach. The success of the design framework was evaluated through computational methods and qualitative feedback.

The first aspect of the research involved understanding the requirements of the athletes. Through qualitative interviews and feedback forms, the need for this research from the athlete’s perspective was established. Athletes agreed that the current equipment required improvement due to its poor durability and emphasised the importance of having confidence in their footwear. Additionally, in-shoe plantar pressure testing during a push start on a dry land push track was conducted to characterise any patterns present in the foot contact during the start. This testing found that through the start, the highest pressure region was typically along the medial edge of the forefoot and the outside foot in the push start applied greater forces than the inside foot. These investigations into the athletes’ interaction with the spike plate helped quantify the established design requirements, particularly in the required size of the spike plate based on the pressure regions recorded. This work highlighted the individual nature of each athlete, isolating the key parameters that could be modified to promote a personalised spike plate design.

Next, the mechanism of traction on ice was investigated through impact drop tests, traction testing, and computational analysis. Physical tests were designed to investigate the influence of the spike geometry and arrangement on the ice interaction. First, by modifying the spike diameter and spacing, low-velocity impact tests on both warm and cold ice showed how the peak force required to fully penetrate the spikes into the surface reacted to design changes. At the maximum specified 1.5 mm diameter, there was evidence of a potential optimum spacing at which both increasing and decreasing the spacing to the nearest spike would increase the required impact force. This was dependent on the ice temperature and was found to be in the region of 3 to 4 mm. On ice temperatures less than −10◦C, the spikes should not be less than 3 to 4 mm apart to avoid crushing the ice between the spikes and on ice temperatures warmer than −10◦C it should not be less than 2 to 3 mm to avoid crushed ice between the spikes. However, the repeatability of these tests was low due to high inter-trial variance. Finite element analysis models in ABAQUS were used to evaluate the damaged region in ice around the spikes. Two investigations were conducted, a single-impactor analysis investigating the spike diameter and a multi-impactor analysis investigating the spacing between spikes. These results highlighted a similar critical spacing range, the relationship between spacing and force within this range, and provided insight into the arrangement of the spikes. The spacing study indicated an upper limit to damage interaction between the cylindrical impactors, where spacing greater than 5 mm led to no crushed ice between the rigid bodies. Finally, small-scale traction testing investigated how the spacing and arrangement of the spikes influenced the horizontal dynamic traction force. In this investigation, spikes that were arranged perpendicularly to the direction of motion led to the greatest traction on the ice surface. These outcomes directly influenced the personalised spike plate design by informing the driving factors behind the spike plate layout.

The research culminated in a design workflow created in Rhino3D and Grasshopper to create athlete-specific spike plates. Through additive manufacturing methods, unique designs for each athlete were prototyped and attached to a shoe for use and testing through the 2021-22 skeleton season. The final personalised design framework was based on the athlete’s average plantar pressure map and the desired range of ice temperatures. The Grasshopper workflow was able to generate an optimised spike plate layout using these inputs. Through this process, novel athlete-specific spike plates for skeleton could be created for each of the given athletes on a given ice condition. The aim was to increase the theoretical traction by maximising the number of spikes and the effective surface area of the spikes placed on the shoe. With increased available traction, the spike plate could potentially provide an advantage to the athlete through increased confidence in the shoe and a greater level of available traction.

The summation of this work highlighted the potential within the sporting industry to use additive manufacturing to gain a performance advantage. Its use in this thesis demonstrated an increase in the theoretically available traction by up to 25% when compared to the existing shoes. The final results and outcomes presented in this work were demonstrated through their use at the pinnacle of the sport, in the 2022 Beijing Winter Olympics.

Date of Award	15 Nov 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	Vimal Dhokia (Supervisor), Elise Pegg (Supervisor) & Steffi Colyer (Supervisor)