Njenga KariukiWorkAmazon Health AI

2021–2023Amazon Health AI

Amazon Health AI

An organization that turned phone-camera images into health measures: body fat, waist‑to‑hip ratio, and mobility, stability and posture.

A phone screen listing shoulder, trunk, hip and lower-body scores, with next steps below.
Halo Movement’s detailed results, 2021: mobility and stability by body region.1 / 3
Role
First product lead of Amazon’s Health Computer Vision and AI organization
Scale
100+ scientists and engineers; a $100M+ a year investment portfolio I directed
Validated
Three studies in npj Digital Medicine: Body and Movement in 2022, waist-to-hip in 2023

I was the first product lead of Amazon’s Health Computer Vision and AI organization: 100+ scientists and engineers and a $100M+ a year portfolio. I set the rule that more money waited for two proofs; three of its products were validated in npj Digital Medicine.

What I decided

  1. Brought the leaders together on one direction

    I brought the organization’s leaders together for three days to agree on one direction: using the camera in everyone’s phone to help people live healthier lives.

  2. Required two proofs before more money

    Each new capability needed two proofs before more money: a customer problem stated without the technology, and experiments showing the capability worked. If either was missing, we paused further investment.

  3. Chose each measure’s clinical reference first

    For each product, I chose the clinical reference by starting from the claim we needed to publish. All three studies appeared in npj Digital Medicine, a Nature Portfolio journal.

How it worked

Before

Every measure needed a clinic and an instrument

Body fat came from a clinical dual-energy X-ray absorptiometry (DXA) scan, a movement assessment from a motion-capture suit and a physical therapist, and a waist-to-hip ratio from trained staff with a tape. Each needed a clinic and trained staff.

MeasureIn a clinicWith the phoneBody fatA clinical DXA scanPhone photosMobility,stability andpostureA motion-capturesuit and aphysical therapistFive exercisesfilmed by a phoneon the floorWaist-to-hipratioTrained staffwith a tapeThree photostaken tovoice prompts
Each measure in a clinic, and with the phone.
01 Direction

One organization, from research to products

In 2021 I became the first product lead of Amazon’s Health Computer Vision and AI organization, which ran from research and development to commercial products.

02 Measure

What the camera asked, and what came back

Halo Body estimated body fat from phone photos, and from August 2021 its scan worked from the knees up, for members in smaller rooms. Halo Movement scored mobility, stability and posture from 0 to 100, from five exercises filmed by a phone on the floor. A third model estimated waist-to-hip ratio, a body-shape measure linked to disease risk, from three photos taken to voice prompts.

An outstretched arm wearing a Halo band holds a phone showing a gray 3D body model and a body fat reading.
Halo Body’s result, in Amazon Science’s June 2021 article on how it worked: a 3D model and body fat.
03 Reference

Each measure against its own reference

Body was tested against clinical DXA scans at two clinical sites, Movement against a motion-capture suit and 13 clinical tests. The waist-to-hip model was tested on 1,200 people, 550 measured with tape by trained staff and 541 by laser body scan.

Three products, three clinical references

Each product was checked against its own clinical reference.

The data as a table
Three products, three clinical references
ProductThe phone sawChecked againstThe resultPublished
BodyFront and back photosDXA, a clinical X-ray scan, 134 adultsAbout 2.2 points, average error in body fat; the limit was 3npj Digital Medicine, June 2022
MovementVideo of five exercisesA motion-capture suit and 13 clinical tests, 150 adultsModerate to strong agreement with the suit and the 13 testsnpj Digital Medicine, September 2022
Waist-to-hipFront, side and back photosTape measures by trained staff, 1,200 peopleAbout half the error of people measuring themselvesnpj Digital Medicine, September 2023
04 Gate

Friday builds with a 1% chance of working

Some ideas started as Friday builds: each Friday a product manager, a designer and a group of engineers took on one charter, “build something that won’t work.” We chose builds with about a 1% chance of working and a tenfold gain on a business metric if they did.

Average error in waist-to-hip ratio, against trained staff with a tape

0%1232.8%1.4%The appPeople measuring themselves

Launch

On 28 September 2022, at Amazon’s devices event, I introduced Halo Rise, a bedside sleep tracker built by Amazon’s Halo Rise team.

What came next

The waist-to-hip study was published in September 2023. In June 2024 I published the method we ran, in an essay for product managers building consumer AI products.

Scatter plots and agreement plots for men and women, the points close to the line.
Waist-to-hip ratio from the app, against tape measurements by trained staff.

Sources