How might we enable precise speedskating control for athletes with limb loss?

Prosthetic Speed Skate

Overview: For my undergraduate senior capstone design project, my team and I sought out to improve an existing prosthetic speed skate design by making it lighter and allowing for optimized ankle flexion features.

Role: Team Co-Leader (organized meetings, delegated roles, investigated ankle elastomer component).

Skills: Stakeholder Engagement, CAD, 3D Printing (FDM & SLA), Project Documentation

Background

For my senior design project, I joined the Mines Human Centered Design Studio (HCDS), where students develop devices to empower individuals with disabilities in a variety of innovative ways.

Our primary client, Caitlin, has a transtibial amputation and was eager to try out speedskating. However, due to the dynamic ankle motions required for proper speedskating technique, traditional prosthetic feet do not work well in a traditional speed skate boot.

A prior HCDS team had made this prosthetic speed skate design that utilizes a bike shock to enable customizable ankle flexion. However, Caitlin reported that this design was incredibly bulky and too difficult to compress. With this in mind, our team set out to create a lightweight design that enabled more fluid ankle movement.

Background Research

Since nobody in my team had any experience with speedskating, the first step was to learn as much as possible. We began by asking Caitlin questions about her current prostheses—what did she like about them? What did she dislike? What was the experience like utilizing them in athletic settings? We took as many notes as possible to approach the problem by addressing her needs rather than our ideas.

The next step was to get on the ice ourselves! We connected with the Colorado Gold Speedskating team to try out speedskating for ourselves and to better understand the movements required that our prostheses would need to replicate.

Speedskating proved to be incredibly difficult, with more precision and balance required than I had originally expected. The key component we were looking for was how much ankle dorsiflexion was required, since this was the primary motion our prototype sought out to replicate.

Working with local skating professionals, we took some measurements and determined that our design needed to provide up to 35 degrees of ankle dorsiflexion to effectively imitate anatomical motions during speed skating.

Initial Prototyping

Initial prototypes of our design were modeled after a prosthetic rollerblade developed by a prior HCDS team. This team utilized a 3D-printed carbon fiber frame and an interchangeable rubber elastomer to enable mild ankle dorsiflexion.

However, this design wasn't optimized for use with common prostheses and the elastomer was too stiff to provide the 35 degrees of dorsiflexion we were looking for.

This image depicts an early CAD model for the design created by my team member. I added these notes for ideas to improve upon.

We 3D-printed an updated design out of carbon fiber nylon filament for optimal strength-to-weight performance. However, this design ended up shearing in-between the front and back sections due to repeated stress, so we needed to add more support.

A crucial component of our initial prototypes involved utilizing SLA 3D printing to develop a variety of resin-based elastomer designs that would sit in-between the front and rear ends of the prosthesis and compress during use. Varied geometries allowed for customizations in ankle movement stiffness based on user preferences.

I took the lead on investigating the stiffnesses of these elastomers under varying loading rates and temperature conditions to mimic on-ice performance, and discovered that the elastomer stiffnesses were highly dependent on temperature conditions, meaning that we needed to account for added stiffness properties during the typical product use in near-freezing ice arenas.

The above graphs depict varying force-displacement curves depicting the changes resulting from differences in elastomer geometry. Our team discovered that varying elastomer geometries enables significant customization for user preferences of ankle motion stiffnesses. However, geometries like the "vertical diamonds" introduced stress concentrations that led to failure, leading us to focus on circular hole designs for the final product.

Final Design

By combining the lessons we learned from stakeholder feedback, CAD modeling, stress testing, and on-ice testing, our team eventually created a prototype that we successfully tested on the ice.

This design didn't quite reach our desired goal of 35 degrees of ankle dorsiflexion, but this compromise was necessary to provide the user with more stability under bodyweight loads during skating.

Our primary testing stakeholder was Jeff, another athlete with a transtibial amputation. We partnered with Jeff and a local former Olympic speed skater, KC Boutiette, to provide feedback on the device's on-ice performance. It was rewarding to watch Jeff skate lap after lap with the new design under his feet and a grin on his face. Jeff has ice skated before with his regular prosthetic foot in a traditional ice skate, but he reported that our design enabled him to get into a much more athletic stance, which is key for stability during speed skating motions.

The below video shows Jeff in action!

What I learned

Designing in an unfamiliar space requires extensive research coupled with as much real-world experience with the design application context as possible! Don't design from afar—step into the shoes (or skates) of the end users!
Don't wait for the "perfect" mockup before developing physical prototypes. Our team spent several months gathering data, but we ended up learning much more with products in our hands than merely viewing them on screens.
Don't reinvent the wheel. It was tempting to build a wild new concept from the ground up, but utilizing previously validated concepts from other HCDS teams helped us more quickly and accurately develop an effective design for our end users.

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