Research

I practice human circadian engineering, turning the science of biological timing into tools that protect health and enhance performance for individuals, teams, and societies.

The body has a temporal organization system with clocks coordinating activity across the body down to the cellular level. Light, travel, work schedules, and time policy changes (e.g., daylight saving time) reset those clocks, often against biology, yet their timing is hidden (and surprisingly hard to measure). I build the tools to see it, model it, and change it.

How my research grew

01

Movement & physiology

Measuring the body outside the lab, turning noisy wearable signals into gait, heat strain and recovery

02

Behavior & rhythms

Finding patterns in sleep and activity over days and weeks, and estimating the hidden body clock behind them

03

Decision-making

Choosing actions that change that hidden state, from beliefs that update with each new observation

What I’ve done

Bioengineering moves in a loop, where new tools answer new questions and the answers show where better tools are needed. These projects show that loop in my work, from wearable sensing and state estimation to circadian modeling and decision-making.

First author

Circadian health impacts of US time policy

Why it matters

Many countries, including the United States, switch between standard time and daylight saving time each year. The switch has known short-term health effects, but the long-term health impact of each time policy had not been well evaluated.

What we did

We simulated light exposure and circadian timing across US counties under each policy and paired the results with CDC health data, estimating long-term effects from physiology rather than self-reported sleep.

Outcome

A first-author paper in PNAS with open code and an interactive county map, covered by the Washington Post, TODAY, Scientific American and Newsweek.

PaperCodeMapPress

First author

Measuring the body clock with wearables

Why it matters

Until recently, the body's central clock could only be measured in expensive, laborious protocols in a controlled lab. Measuring it in daily life opens up shift work, jet lag and other unusual light schedules.

What we did

We built a particle filter that fuses wearable light and activity data with a mechanistic circadian model to estimate circadian phase with its uncertainty, and showed when it works and where it fails, in shift workers.

Outcome

A first-author paper in the Journal of Biological Rhythms, with open code.

PaperCodePost

Led the study

Time of day, sleep and performance across the menstrual cycle

Why it matters

Women are underrepresented in sports science, and across the menstrual cycle, hormones, sleep and body-clock timing all change together, so it's hard to tell which one is shaping performance.

What we did

With nine student researchers, we ran a 10-month study in which 56 women wore sensors for 28 days, tracked hormones at home and were tested for strength and balance at 3 p.m. and 3 a.m., to separate hormonal effects from circadian and sleep effects.

Outcome

Presented at ASB, ACSM and FARM and featured in Stanford Magazine, with papers in preparation.

TalkAbstractsPress

First author and collaborator

Activity patterns and sleep as health signals

Why it matters

Changes in daily activity patterns and sleep are early signs in many mental health, age-related and neurodegenerative diseases, and wearables can track them continuously and cheaply.

What we did

I built wearable methods for sleep, breathing and activity in daily life and showed how missing data bias 24-hour rhythm measures. With collaborators, I linked the timing and regularity of daily rhythms to health in more than 90,000 UK Biobank participants.

Outcome

A first-author paper in Clocks & Sleep and collaborative papers in Psychiatry Research, the European Journal of Internal Medicine and Alzheimer's Research & Therapy, covered by Fox News, AARP and TODAY.

Data qualityMental healthPhysical healthNeurodegeneration

Supported by an NIH NRSA F31 fellowship, a Wu Tsai Human Performance Alliance postdoctoral fellowship, a $200,000 Alliance Agility grant and a Stanford Chen IPL Design Grant.

Earlier work

Predicting exertional heat stroke

Fusing gait instability with core temperature estimated from heart rate flagged all six heat-stroke cases at least 3.5 minutes ahead in field data from 1,806 service members. The method is used in military training.

PaperPatent application

Tracking gait outside the lab

Adaptive zero-velocity updates at the shank let Kalman-filter tracking follow gait during sprinting, obstacles and stairs, applied to multiple sclerosis and military load carriage.

Paper

Monitoring rehabilitation progress

A step detector built for the slow, irregular gait of stroke patients, now used in an inpatient stroke rehabilitation clinic.

Abstracts

Where my lab is going

Next, my lab will keep that loop turning toward a future where we can leverage our biological timing to optimize health and human performance.

SENSE

What time is it inside your body?

Sense the hidden timing of body clocks, and how it varies across people, from real-world wearable data.

Builds on wearable phase estimation and the menstrual-cycle study

MAP

What does living out of sync cost?

Map desynchrony among body clocks, misalignment with the outer world, and what each costs in health and performance.

Builds on the time-policy and population-rhythm work

ALIGN

What should change, for whom and when?

Align biology and society by choosing which cues, schedules and policies to change, for whom and when.

Builds on CircadianSim, releasing with its paper, and jet-lag work with athletes

Open questions

Are your body's clocks in sync?

Measuring how well the body's many clocks stay in step, and what happens when they drift.

Who feels the clock change most?

Why some people barely notice a daylight saving transition while others take weeks to recover.

Body-clock plans that adapt as you go

Light and sleep plans that update from wearable data instead of following a fixed protocol.

Circadian and menstrual rhythms together

How two of the body's rhythms interact, and how to train with both in mind.

Want to work on one of these? Prospective graduate students and postdocs, see working with me.