The story behind Apple's wheelchair Activity app

Development was pretty challenging

Apple, Apple Watch, WWDC, iOS, Wheelchair, Activity App, accessiblity, interview
Credit: Apple

WWDC 2016 and Apple made many moves to improve accessibility across its products, but the introduction of a version of the Apple Watch Activity app for wheelchair users was a particularly big deal. You see, there’s never been an accurate fitness tracker like this before, and Apple has been working on it for at least a year.

'We wanted to do something'

“Apple has always led on the accessibility features. Even when we were finishing watchOS 1.0, we knew we wanted to do something for wheelchair users,” Ron Huang, Director of Software Engineering for Location and Motion Technologies explains.

Set to ship with watchOS 3 this Fall Apple’s new solution consists of two wheelchair workout apps, a setting to switch "Time to Stand" notifications to "Time to Roll," and Activity ring optimization. It's not a standalone app,  but a function that will be made available through the next version Activity app Apple Watch users already use.

I spoke with Dawna Callahan, Challenged Athletes Foundation Director of Programs, and a wheelchair user herself, who told me wheelchair users tend to be, "more sedentary compared to able-bodied people. Therefore, they are more prone to suffering from health diseases like obesity that lead to secondary diseases like heart attacks and diabetes."

The developer's story

Development, which took a year, was challenging.

Despite that over 2.2 million people depend on wheelchairs in the US alone, Apple's team found a lack of available information to help inform development of the product:

“There were a few studies, but most had really small number of subjects and done inside labs in wheelchairs provided by those conducting the study,” Huang explains.

The team initially thought measuring activity for wheelchair users would be similar to counting steps with Activity tracker, but it turned out they had to think different. The first iteration of the app overcounted by at least 50 percent..

Consider how people in wheelchairs use their chairs you’ll see lots of different criteria the sensors on the watch would have to measure and understand:

  • Wheel spin, and how far an arc the arms travel when doing this work
  • Types of push
  • Terrain – uphill, downhill, smooth and rocky ground all impact activity
  • Inactive gestures that appear to be a push
  • Distance
  • Calorific value of activity
  • Even things like wheel width and seat height had to be understood.

Apple’s engineers realized they had to develop brand new algorithms custom designed for wheelchair patients, from scratch.

roll Apple

Starting from scratch

“We found that some of the basic principles used to calculate calories don’t convert well for wheelchair users. We had to pretty much start from scratch,” Huang said.

Apple explored all the available literature, including the mobility guides patients are given when discharged from hospital.

The company then worked with the Challenge Athletes Foundation (which offers Access for Athletes grants) and the Lakeshore Foundation to conduct its own study into wheelchair use.

Unlike some previous studies, Apple wanted to gather data about how people used the kind of wheelchairs most users have. It fitted these with sensors, accelerometers and other measuring devices.

Wheelchair users taking part in the study  wore masks to measure oxygen intake and calories burned.

Rather than only conducting studies in artificial laboratory situations Apple also collected data in everyday situations, including following study participants as they went about their normal daily routine.

Apple finally accumulated 3,500 hours of data across 300 different users over 700 sessions.

The next step

The company then had to use this data to help it figure out how to measure "pushes",  the equivalent to steps for wheelchair users. This posed a new set of challenges.

“We found so many different push styles,” said Huang. "Starting off we thought counting pushes would be very similar to counting steps.”

It wasn’t. Initial software builds overcounted pushes by 50 percent.

Huang’s team began a series of iterative software improvements until the results became consistently accurate.

"The more you look into it, the harder and more challenging you realize it was,” Huang said.

The team focused on three different push styles: "The first is in a semicircle, pushing from 10 O'clock to 3 O'clock,” Huang said.

“The second is called an arc push, and it's what you do when you have to push yourself up an incline: shorter, more powerful pushes with a quick jerk to the return position to prevent yourself from rolling back. Finally, there's the semi-loop-over: a pushing style that tends only to be done in competitive situations, like wheelchair racing, where you're really leaning into the push."

applestoreunionsquare Jonny Evans

If you've visited Apple's new retail store in Union Square, San Francisco, you may have missed the access ramp that means every customer can access the store's chilled out tree-lined patio.

Why it matters

“CAF sees the Apple Watch Activity App optimized for wheelchair users as a game-changing opportunity to encourage wheelchair users to be more active,” said Callahan.

So why did Apple do this?

Apple has consistently focused on delivering best in class accessibility – Macs have long offered out of the box access to accessibility solutions you must pay for on other platforms. This is part of the company’s oft-stated mission to make a positive contribution to wider society.

In this case it has achieved something unique. “There has never been a fitness tracker that accurately captures such information,” said Huang.

This could make a significant difference to real people.

"With not being able to utilize lower extremities, it’s more challenging for wheelchair users to find activities that increase their heart rate and activity level on a regular basis,” Callahan explains.

“We are looking forward to the positive impact it will have on the users,” she said. “We are very excited to start using [the app when it ships in Fall] and share the opportunity within the wheelchair user’s community.”

Finally it is surely interesting to reflect that having developed a solution to measure the activity levels of wheelchair users, Apple has now gathered knowledge that could help inform development of activity measurement tools for other situations.

The new and updated Activity app, now with these new features, ships with watchOS 3 in Fall.

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