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Project Overivew

Empowering female athletes to work with their menstrual cycles to maximize their training.

Athlah is a wearable health tracker and mobile application combo that automatically senses where you are in your menstrual cycle and tracks your fitness data. It helps you learn your body's cycles of ups and downs in fitness, so you can plan ahead based on predictive machine learning over time.


UX Technologist

UX Researcher

Product Designer


8 Weeks

Jan to Mar 2021

Team of One

Joan Williams (Me)


MHCI+D Course

HCID 520: User Interface Software and Technology


The Digital Interface

The digital interface is automatically updated with the phase and day in the menstrual cycle with the cycle tracker algorithm in the wearable device.

When the user opens the app, they immediately see their cycle day and what phase of the cycle they are in. By looking at the circle, they can instantly see how far they are in their cycles and what is coming up next The dots on the sections represent period days.

The red demarcation between the two colors represents ovulation day. The more purple side is the follicular phase and the redder side is the luteal phase. The color choice is intentional because females in their follicular phase are generally more laid back and positive, whereas in the luteal phase the threshold for anger and frustration is lower, hence the red.

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Basic activity information is displayed next, which will show a detailed view on click. The heart rate zones bar shows your average percentages of the heart rate zones you are hitting on any particular day during your active minutes. Under that is weight (since it fluctuates with your cycle), heart rate (from the PPG sensor), days until predicted period (from PPG sensor), and hours of sleep (from accelerometer).


The next area shows your current predicted physiology from your cycle date. The user can edit the data to improve the accuracy of the AI. Finally, there is a map of where the user is in the cycle and some basic information on how the hormones are affecting the body at that time.

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Additional Screens

In addition to the above views, I imagined an educational section to educate people in more than one medium for different learners. A trends section would help people understand when they improve the most and how they are progressing month to month vs day to day. The fitness forecast and your calendar are similar in that it gives you an area to visually plan out your next month. 

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The Wearable Prototype

The Athlah Tracker uses the PPG sensor to pick up precise physiological data about the user's heart rate. The heart rate data will be tracked during sleep to get accurate resting heart rate which an algorithm will use to pinpoint where in the menstrual cycle a person is in. Which will inform the application and what data it would produce.

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I created the physical prototype in Cinema 4D.



Spent a lot of time researching PPG sensors and understanding what its strengths and weaknesses were and by knowing it, I was able to marry my knowledge of PPG sensors and the menstrual cycle and its effects to create a product proposal. Note that the research took four weeks, one week of ideation, and the final design and branding was created in two weeks with a full course load.

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The Problems with Female Fitness

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The problem with female fitness is that it's not widely known how big of an effect the menstrual cycle has on physical fitness.
The fitness world still treats women as smaller men and we try to train as though our menstrual cycle doesn't exist, and push through our pain when we are weakest and should be taking care of ourselves. We think our progression should be linear, like men, and then let ourselves down.
Problem Space


Understanding the Cycle

For people with unaltered menstrual cycles, you go through a cycle of hormonal changes every month, each affecting your motivation and your physicality. Progression is cyclical and you may be able to see it month to month, but not week to week. Look at the chart below for a very basic overview of what kinds of changes can occur during each phase.

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Why Care About This?

Not knowing this makes us feel like we're out of control, inconsistent, not having enough willpower to get up and do that workout or not able to resist that treat. Pushing ourselves too hard when we are full of energy just to get an injury. It hurts our confidence in ourselves and makes us think maybe we can't.

This matters because female athletes can plan, take advantage of their strengths in each phase, and plan to override the hormonal effects. Knowledge is power and understanding our own bodies is the key to our success and reaching our full potential. And also knowing that we're not crazy or lazy, and that we're normal.

And the biggest takeaway is:

Every consecutive day may be different, but every month is the same (for the most part) once you figure it out. And an app can make that way easier by automating.


What's Out There Now?

1) A few startups correlating the menstrual cycle and training, but neither have gained traction yet and both have manual inputs for menstruation that may not be accurate. 

2) Menstrual Trackers used for fertility, also tracks moods.

3) More articles being published about fitness and the cycle.

Clue and FitrWoman - both educate women on their cycles and the effects they have on the body.

Key Takeaways

This is all a daily, manual and labor intensive process that takes a lot of time and effort from the user. Unfortunately, self-reporting is not completely accurate which could affect results.

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Athlah Product Specification


Full Product Specification Paper

What Athlah does is automate the manual input with the algorithm that accurately tracks your menstrual cycle through the PPG sensor and visualizes physiological and psychological data side by side with the corresponding menstrual cycle data with additional educational elements.

Athlah Title
Intro to Athlah
Athlah Moodboard
Branding for Athlah
Physical Design for the Athlah Tracker Experience
Athlah Mobile Application Experience
Mobile Application Experience
Tracker Technical Specifications
Athlah Data Specifications
Athlah Tracker Data Specifications
Athlah App Data Specifications
Potential Use Cases for Athlah
Athlah Next Steps


The Research


Lit Review on Fitness Apps

I love fitness apps, so this is the space I started with in my exploration to find technologies to build off of in my academic literature review.

With fitness apps, scientists were thinking about how to get people to live healthier lives. They were looking into behavior change with dynamic goal setting and self-monitoring (Zhou, 2018), (Herrmann, Kim, 2017), accountability (Vickey, Williams, 2013), and effects of social media sharing of the data (Stragier, Merchant, 2013).


One really interesting paper was that users significantly enhanced physical activities using their exercise app vs alone, and it further increased with cooperation vs competition (Chen, Pu, 2014). Another paper looked at replacing personal fitness trainers with mobile virtual fitness apps, and the answer was that it could only assist (Chi-Wai, 2011).

These articles were great in getting a handle on the subject area, but one stood out that mentioned these apps being used in conjunction with health sensor devices (Vickey, Williams, 2013), so I researched PPG Sensors.


Lit Review on Photoplethymography (PPG) Sensors

I got the Fitbit One soon after it came out in 2010, and I've been tracking my physical activity ever since. I checked my step count and mileage multiple times a day. But, it wasn't until I switched over to the Apple Watch that I started incorporating heart rate data with the integrated PPG Sensor, and I never realized how many applications it has until this lit review.

Most of the researchers for PPG sensors focuses on the integrity of the heart rate and respiratory data captured by different types of PPG sensors and placed on different parts of the body. A few articles that were particularly interesting were about using Fitbit and Apple Watch to measure physiological parameters like heart rate variability (HRV), glucose measure, blood pressure readings, heart rate (HR), and electrocardiogram (ECG) and using them for health care and daily activity to furnish health-care providers that allow early detection and diagnosis of cardiovascular diseases and insights into patient's health (Castaneda, 2018). Another article used the PPG sensor to sense drowsy driving to prevent drunk driving (Park, 2009).

The key article that correlates PPG sensors to the menstrual cycle was the most interesting. This article noted that during certain phases of the menstrual cycle, women had significant increases in pulse rate (PR) while sleeping which results in a consistent predictor of where in the cycle a woman is. Of course, the heart rate data would need 3 months to calibrate, in which time, women would just input the first day of their last period to start the initial process.



How PPG Sensors Work

The photoplesthymosgraphy (PPG) sensors are the green, red, or blue LEDs in fitness trackers that can track heart rate and/or measure other physiological parameters like glucose measure, blood pressure readings, heart rate variability, and electrocardiogram. PPG works by using a digital CMOS camera and three wavelength LEDs photographing the same patch of skin over and over in order to detect blood perfusion in tissue by measuring the variations in the images. 

The sensors are not as accurate during high activity while being jostled because it is relying on photographing the same spot on the skin and measuring the differences to get readings. The activity causes motion artifacts which contaminate the PPG signals. There is also a lot of programming and math involved in order to read the measurements captured by the PPG sensors. There are equations to smooth out and calculate the curves that read the heart rate, blood pressure, etc. There are also corrective equations for the motion artifacts from activity that use additional data from the accelerometer in the device. Different LED sensors have different wavelengths and are better or worse at different things. Red LEDs penetrate to deep tissue, but since the wavelengths are longer, the motion artifacts are a lot worse. Green LEDs are a good balance and seem to get the best signals. Blue was in between.

10 Limitations and Uncertainties of PPG Sensors
  1. An uncertainty I have that I haven't yet researched is that since they use cameras and LEDs in order to detect blood perfusion, maybe differences in skin pigmentation could make it easier or more difficult to produce accurate physiological readings.

  2. A limitation that I have read about is the fact that the sensors are not as accurate during high activity or when the PPG sensor is being jostled because it is relying on photographing the same spot on the skin and measuring the differences in that spot to get readings. These are called motion artifacts and they contaminate PPG signals on the wrist during exercise.

  3. Since the PPG sensor system is based on LEDs and photography, perspiration could also contaminate the PPG signals.

  4. Water and being submerged could be an issue too for activities such as swimming.

  5. With activity causing motion artifacts to the data that PPG sensors produce, and having the data be corrected by equations to get "averaging" and "predictive" data - I would argue that the data from a PPG sensor may not be good enough for a clinical setting or any circumstance that needed very precise results.

  6. Motion artifacts are a problem, because the data we do want to track on our fitness trackers usually comes from when we are working hard exercising. Will the error rate, predictive data, or averaging make enough of a difference that fitness trackers are not accurate enough for consumer needs? People do notice that different trackers produce different numbers.

  7. Different LED lights could serve different purposes. Red would not be good while in motion, but when not in motion, you could get a deeper tissue reading. Green is better in motion, but doesn't get a deeper tissue reading. There are limitations for each color LED.

  8. Since a lot of the data comes from the equations, a limitation might be the accuracy in which the math can transform the data, especially with motion artifacts and the myriad of circumstances in which these could happen.

  9. Could these equations be less accurate for different skin tones and other variations in the data such as sweat or water? How can the system account for these?

  10. How would this work with different combinations of sweat, water, skin tone variations, and heavy motion such as running in the rain? 

  11. Arm hair could also be an issue.

Assessing Maturity in PPG Sensors

In this exercise, we want to figure out where PPG sensors would be best suited to work within and be marketed towards, and in what situations this tracker might have limitations.

  1. Sweaty Runner with Light Skin has been running at a fast pace for a while and is starting to sweat profusely causing their wrist to bead up with sweat underneath the health tracker's PPG sensor and there is quite a bit of jostling.

  2. Person with Dark Skin wears the health tracker's PPG sensor normally around the house, exercising, and doing everyday things to get tracking information for their health.

  3. Person with Heart Issues with Light Skin wants to stay up to date and informed on their latest heart data through the heart rate trackers on their health tracker's PPG sensor.

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I believe with all the possible artifacts in the sensor, we should market this as a consumer level technology that is not as accurate as a clinical measurement device. We need to figure out how much dark skin pigmentation, motion, and sweat affect the sensor, and how we can use data triangulation from other measurements in the device in order to compensate for those artifacts and if we can compensate for those artifacts. Before we bring this to market, we really need to make sure this device works with all skin tones to make sure we are equitable to our entire user base.

PPG Sensor Initial Ideation
  1. Consumer fitness tracker to track heart rate during everyday workouts to understand base heart rate throughout the day and better understand overall health.

  2. Fitness tracker to measure high, medium, and low exertion during workouts to figure out how much you can push yourself.

  3. Heart rate tracker during meetings to see when people are feeling threatened or nervous.

  4. Heart rate tracker for couples to hear each other's heartbeats throughout the day.

  5. Tracker for people at bars, to access how drunk people are or to better predict what people are about to do to maybe prevent bar fights.

  6. Heart rate tracker for people at concert venues to measure how much people are enjoying the event by their heart rate or if they are starting to not feel well.

  7. Anxiety tracker for people of all ages that are anxious by measuring heart rate throughout the day. Could use it in conjunction with therapy.

  8. Heart rate tracker to pinpoint menstrual cycle for fertility.

  9. Use menstrual cycle (from heart rate data) to optimize fitness.

  10. Everyday heart rate tracker for people who have mild heart issues and want a lightweight, consumer level product to help them monitor their heart rate.

  11. Heart rate tracker for helping test roller coaster rides. Have all the testers wear heart rate trackers during the roller coaster ride to see how much adrenaline is pumping during each. 

  12. Prevent SIDS in infants by having a heart rate tracker on your baby at all times.

  13. Use with people with PTSD or past trauma to help with diagnostics and figuring out what times they have the highest heart rate not from physical exertion.

  14. Use for people with high blood pressure and risk of heart attacks to keep them motivated to live a healthy lifestyle to lower their blood pressure.

  15. Use for people in prison to pinpoint aggression or anxiety and be notified immediately. "Bob, I see your heart rate has gone up. How are you feeling?"

  16. Early warning signal for getting sick and being able to proactively take vitamin C or get extra rest when you see your heart rate has been up higher than normal that day.

  17. Understand your child better by having a heart rate tracker on them at all times. Have the software notify you when your child's heart rate has gone up, and if you see that they are not doing any physical exertion, you can ask them what is going on.

Co-Design Concept Selection




Potential Impact

The potential impact of a product like Athlah could be huge. It help people with menstrual cycles by providing knowledge of themselves and normalize the changes they feel throughout the month. It also gives them a leg up in the fitness world allowing them to consciously take advantage of their strengths during different parts of the cycle and avoiding injuries.

It could help people that have been having a hard time getting into fitness finally overcome barriers they didn't know existed before.

Also, optimizing the input of the menstrual cycle data with a wearable is key, so someone can just put the Athlah on and forget it instead of taking the time to input their data every day or guess where they are in their cycle. This could easily also be accomplished with the Apple Watch, any Fitbit with the PPG sensor, and other heart rate wearables.


Next Steps

This first version of the Athlah product was to feel out what photoplethysmography could do for female health with its capability to sense where a user was in their menstrual cycle and how that could benefit female athletes and other female users passionate about fitness. An extensive lit review was done about photoplethysmography to conceptualize this product and also a quick competitive analysis, but much more work is needed to hone in on what might make this concept special to people.

Research / Testing

Since we haven’t done testing or user research yet, in the next phase of product design, we’d want to do user testing and qualitative interviews with our target audience to understand what they would want in this product, if it would be viable in the marketplace today, and if there are any gaps in the product that we could fill or add to the queue for version 2.0. With the research and testing we can really narrow down our focus to find out what is key for our users, and build out those features while cutting some other features that may not make as much sense in this particular female fitness space. But we won’t know for sure what to cut, keep, or add until we do this user research to know for sure.
Talking to female fitness experts such as Stacy T. Sims PhD, female hormone cycle expert Gabrielle Lichterman, and other experts in the field would also be key to figuring out this experience, what to offer/educate on, and fine tuning the AI and algorithms of the Athlah product.



This project has been a dream of mine for a while. I have been studying the menstrual cycle and it's effects on the body, and finally the knowledge is becoming more widespread and starting to penetrate the fitness world. When I found that PPG sensors could pinpoint where a person was in their cycle, the answer was clear to do this project. Very fulfilling.

I also really enjoyed having complete agency to think about ideas and work on something on my own. I always enjoy diving into the research and reading academic papers, and to do that to create a new product was very rewarding. I love visual design and being able to have a product where I could visualize data was a lot of fun.

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