EZ Stretch

Developers: Richard Chen & Maria Vachaparambil

Supervising Professor:  Kevin Caves


Our client is a social butterfly that loves to be involved in as much as she can. She used to participate in a plethora of activities ranging from swimming to zumba and could walk with the help of her walker up to a few years ago. However, Cerebral Palsy caused her muscles to weaken and tighten which led her to be dependent on a wheelchair. The muscle tightness can be countered by stretching out her muscles. We created a wirelessly controlled, stretching platform which will allow her to consistently stretch her hamstrings. Frequent use of our device will hopefully enable our client to use her walker again.

Introduction and Background:

Our client is a 26 year old woman with Cerebral Palsy (CP). CP is a largely congenital disease that affects the motor area of the brain, the cerebral cortex. Characteristics of CP involve frequent contraction of muscles, spasticity, and lack of muscle coordination [1]. As CP progresses, muscles in the leg can get tighter. Tight muscles affect the dynamic movement of bones and can limit mobility. Our client once used a walker, but overtime has transitioned to a wheelchair due to excessive tightening of the hip flexor, hamstring, and calf muscles. Our client is unable to stretch by herself, so to help combat the progressive tightening, a physical therapist has weekly, hour long stretching sessions with our client at her home. The stretches are effective but the frequency of stretching is not enough to reverse the progressive tightness caused by spasticity. Although the physical therapist meetings are effective, the problem is that there is not a way for our client to consistently stretch. Weakened leg muscles prevent her from standing and stretching, and frequent muscle spasms in her hands prevents her from operating complex devices.

There are lower body stretching machines on the market that can be used independently, but all of them are either too bulky or impractical to use for a person with CP who uses a wheelchair. An example of one is the leg stretching machine shown in the figure on the right. This machine takes up significant space, and requires noticeable setup before it can be used [2]. Essentially all the devices on the market are similar to this in that they are big and bulky and cannot be operated from a wheelchair. Stretching the hamstring while seated can still be as effective as stretching the muscle in other positions [3]. An independent stretching solution suited to our client needs to be made to try and prevent further spasticity. Ideally, the stretching solution would be a device that has a simple user interface, and can be consistently used in our client’s home.

Project Goals

The device created will be one that allows our client to stretch her hamstrings frequently. First, the device must be easily set up. Furthermore, the device will be operable while seated in a wheelchair. It will be electronically powered and wirelessly controlled. These three features serve to make the device easier to use on a frequent basis. The device will also incorporate a timer and feedback system that work together to guarantee an effective stretch. These aforementioned goals will ideally result in an intuitive device.

Design and Development

We created an electro-mechanical device that uses a linear actuator to drive a platform that supports one leg. The movement causes the hamstrings to stretch. See Fig 2. for a snapshot of the device.

The device is made so that is can be used while seated on a wheelchair. It is placed directly in front of the wheelchair and the calf muscle is strapped onto it. The knees are also locked in with a belt that goes around the thighs and the wheelchair. Locking the knees during this stretch is important to achieve an effective stretch. This is achieved using a buckle belt that is looped around the wheelchair. Once strapped in, the device can be controlled with a remote that provides linear movement in an upwards and downwards direction.

Our design has two main components: the mechanical system where our client places her calf muscles and the electronic system that provides movement and feedback for the stretch as well as ensures an effective stretch.

Mechanical System: This is the main framework of the device. See Fig.1 for the components of this system marked out.

Top Plate and Base: The top plate provides the platform for our client to place her calf. The calf is placed on a surface with foam that enhances comfort and has straps to keep it in place. The top plate houses the electronics. The base of the device provides for stability.

Mounting mechanism for the actuator: We machined mounts using the A Trump milling machine to attach the actuator to the top plates and base.

Electronic System: The electronic system is remote controlled and has three main functions. The first is to provide the movement for the stretch. This is achieved using a linear actuator. A linear actuator is a device that converts the rotational motion of a motor into linear motion- upwards and downwards. The second function is to provide feedback to the client on the quality of the stretch. This is achieved using load cells and LEDs. The load cells are placed on the top plate that support the calf muscle. It is calibrated to measure the force applied on the plate by the calf muscle on the plate throughout operation. See Fig 3. for the load cells assembly.

There is a cut-off force reading of 36 lbs which was determined based on empirical measurement. These measurements were taken while the client used our device in the presence of her physiotherapist and were verified by him. This is extremely important because it is an inbuilt safety feature that prevents her from overstretching. The cutoff point also informs our client that she has achieved a good stretch. This feedback is achieved through LEDs that light up on the top plate (Fig4- will insert relevant pictures). The third function is to ensure that the stretch is effective. This is done by programming the actuator to remain at its highest point for 30 seconds before coming back down. This value is consistent with current clinical practice and was referenced to us by our client’s physiotherapist [4].


Preliminary Testing:  We conducted a number of tests to ensure that our device would work during the evaluation. We knew that the load cells would have to at least withstand the weight of our client’s leg. The load cells were rated at 50 kg each, so technically they were adequate. To ensure the load cells could display a range of weights, Richard stood on a platform on top of the cells, and it accurately gave his weight. Another example of testing was to figure out how quickly the actuator moved. This is important because the actuator’s rate is necessary to set appropriate delays in the arduino code. Iterative testing also had to be conducted to ensure the code worked properly. The code is broken down into three sections: load cell, LEDs, and actuator. Each section was first tested independently on a separate breadboard before final integration. This proved useful because it enabled us to more efficiently figure out which component was at fault. While building separate subsystems on other breadboards, voltage values were checked at each important input or output. With the multimeter we noticed that some voltage regulators were not working as they should. The testing showed us that the device was in workable condition for the testing.

Client Evaluation:  The device was evaluated to assess for function, safety, feasibility, stability, and portability. The device was evaluated under the supervision of our client’s physical therapist, to ensure optimal function was achieved and safety requirements were met. In addition, the device was evaluated against the design specification and performance criteria. This involved verification testing on the designer end followed with validation testing on the client’s end. Estimated loads were calculated and components were used that could easily withstand operation loads. During the test, the device held up well, as both our client and her PT said instability was not an issue with the device. Furthermore, our client was able to easily control the device with the remote. Her leg was also able to be placed on the foam pads and strapped in snugly. Our client affirmed that the foam cushion was comfortable. The visual feedback utilized by the device was also easily understood by our client. She recognized that the green LEDs meant it was ok to go up and that the red LEDs meant to stop. Our client and her physical therapist completed a user defined scale questionnaire that aided our evaluation process. During the testing with our client we confirmed that the device met our functional goals.


The subsystems of our device culminated in a durable platform that can be easily stored in our client’s home. Each aspect of the device was shown to our client’s PT, and he gave his approval for each aspect with regards to functionality and safety. Each load bearing component was selected to be much sturdier than what is needed to withstand the loads of a single leg. Each electrical component is used safely within its operating conditions. The design provides for intuitive usage which enables our client to consistently stretch her hamstrings, which also allows for her physical therapist to focus on other muscle groups during his weekly visits. In combination, this provides a key step towards returning to walker usage. The final price of the device is about $220. No other stretching device on the market can do what ours does, in terms of wireless control, and load based feedback.


1. Cerebral Palsy Information Page. (n.d.). Retrieved September 18, 2018, from https://www.ninds.nih.gov/Disorders/All-Disorders/Cerebral-Palsy-Information-Page
2. NATIONAL SCIENCE FOUNDATION 2012 ENGINEERING SENIOR DESIGN PROJECTS TO AID PERSONS WITH DISABILITIES. (n.d.). Retrieved September 25, 2018, from http://nsf-pad.bme.uconn.edu/2012/NSF2012.pdf
3. Decoster, L. C., Scanlon, R. L., Horn, K. D., & Cleland, J. (2004). Standing and Supine Hamstring Stretching Are Equally Effective. Journal of athletic training, 39(4), 330-334.
4. Lim, K. I., Nam, H. C., & Jung, K. S. (2014). Effects on hamstring muscle extensibility, muscle activity, and balance of different stretching techniques. Journal of physical therapy science, 26(2), 209-13.


We would like to acknowledge Duke’s BME department for their ample resources, and a number of people for their help with this project: Kevin Caves, Matt Brown, Leighanne Davis, and our classmates.

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