The science
Built on peer-reviewed research,
not wellness folklore
Every metric Trana computes is derived from published studies in top-tier medical journals. Here's the science behind the score.
The cosinor model
At the heart of Trana is the cosinor model — a mathematical technique that fits a cosine curve to your 24-hour heart rate and activity data. This curve captures three key properties of your rhythm:
Amplitude
How tall the wave is — the strength of your rhythm
Acrophase
When the peak occurs — the timing of your biological day
MESOR
The midline — your rhythm's average level
By fitting this model to each day's data, Trana tracks how your rhythm shifts over time — and surfaces when those shifts match patterns research links to health risks.
The circadian metrics Trana computes
Tap each metric to understand what it measures and why. Beyond the cosinor metrics below, Trana also surfaces your Sleep Regularity Index, social jet lag, and chronotype classification — each grounded in the published research listed at the bottom of this page.
Every claim, traced
What the app tells you, and why we can say it
Trana makes population-level, correlation-framed claims. Every line of copy that cites or implies research traces back to a peer-reviewed paper below.
Claim 1
Rhythm regularity matters more than sleep duration for daytime alertness
“In the research on sleep regularity, people with more consistent wake-sleep timing reported sharper daytime alertness than people who slept the same total hours on irregular schedules. Regularity is the underrated variable.”
Shown in: Insights → Science of Rhythm (Consistency beats duration); Home → Steady band copy
Supporting research
Phillips, A. J. K., Clerx, W. M., O'Brien, C. S., Sano, A., Barger, L. K., Picard, R. W., Lockley, S. W., Klerman, E. B., & Czeisler, C. A. (2017). Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing. Scientific Reports, 7, 3216.
Harvard / Brigham & Women's / MIT Media Lab. The Sleep Regularity Index predicted academic performance and circadian phase better than total sleep duration.
DOI: 10.1038/s41598-017-03171-4Lunsford-Avery, J. R., Engelhard, M. M., Navar, A. M., & Kollins, S. H. (2018). Validation of the Sleep Regularity Index in older adults and associations with cardiometabolic risk. Scientific Reports, 8, 14158.
DOI: 10.1038/s41598-018-32402-5Windred, D. P., et al. (2024). Sleep regularity is a stronger predictor of mortality risk than sleep duration. Sleep, 47(1), zsad253.
DOI: 10.1093/sleep/zsad253Claim 2
Circadian alignment affects glucose handling and metabolic markers
“People with irregular sleep-wake timing show weaker glucose handling and higher metabolic stress than people who stay consistent. Your schedule isn't just about sleep — it's about how your body handles fuel.”
Shown in: Insights → Science of Rhythm (Your clock runs your digestion); Home → Aligned band copy
Supporting research
Panda, S. (2016). Circadian physiology of metabolism. Science, 354(6315), 1008–1015.
Salk Institute. Authoritative review of circadian control of metabolism, including peripheral clocks in liver / pancreas / gut.
DOI: 10.1126/science.aah4967Scheer, F. A. J. L., Hilton, M. F., Mantzoros, C. S., & Shea, S. A. (2009). Adverse metabolic and cardiovascular consequences of circadian misalignment. PNAS, 106(11), 4453–4458.
Harvard. Experimentally induced misalignment → decreased leptin, increased glucose / insulin, reversed cortisol rhythm.
DOI: 10.1073/pnas.0808180106Chaput, J. P., et al. (2023). Sleep timing, sleep consistency, and health in adults: a systematic review. Applied Physiology, Nutrition, and Metabolism, 48(6), 620–637.
DOI: 10.1139/apnm-2022-0505Claim 3
Deep sleep, hormone release, and core body temperature run on the same 24-hour clock
“Deep sleep, hormone release, body temperature — they all run on the same 24-hour clock your score tracks. When sleep timing holds, they line up. When it drifts, they fall out of sync.”
Shown in: Insights → Science of Rhythm (Recovery happens on a schedule); Home → Aligned band copy
Supporting research
Czeisler, C. A., & Gooley, J. J. (2007). Sleep and circadian rhythms in humans. Cold Spring Harbor Symposia on Quantitative Biology, 72, 579–597.
Foundational review of sleep architecture and circadian phase coupling.
DOI: 10.1101/sqb.2007.72.064Van Cauter, E., Leproult, R., & Plat, L. (2000). Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA, 284(7), 861–868.
Growth hormone pulse coupling to slow-wave sleep stages.
DOI: 10.1001/jama.284.7.861Kräuchi, K., & Wirz-Justice, A. (1994). Circadian rhythm of heat production, heart rate, and skin and core temperature under unmasking conditions in men. American Journal of Physiology, 267(3 Pt 2), R819–R829.
Core body temperature coupling to sleep onset and circadian phase.
DOI: 10.1152/ajpregu.1994.267.3.R819Claim 4
Rhythm disruptions (jet lag, shift work) typically resolve within a week of consistent wake timing
“Travel, a hard week, a late night that rippled — your clock lost its anchor. The way back: one wake time tomorrow, outside within thirty minutes. Most people reset within a week.”
Shown in: Home → Disrupted band copy
Supporting research
Eastman, C. I., & Burgess, H. J. (2009). How to travel the world without jet lag. Sleep Medicine Clinics, 4(2), 241–255.
Rush Medical. Phase re-entrainment rates across time-zone crossings. Typical eastward re-entrainment: ~1 hour/day; a 7-hour shift resolves in ~7 days with light-exposure anchoring.
DOI: 10.1016/j.jsmc.2009.02.006Burgess, H. J., & Eastman, C. I. (2004). Short nights attenuate light-induced circadian phase advances in humans. Journal of Clinical Endocrinology & Metabolism, 89(10), 4954–4956.
DOI: 10.1210/jc.2004-0672Khalsa, S. B. S., Jewett, M. E., Cajochen, C., & Czeisler, C. A. (2003). A phase response curve to single bright light pulses in human subjects. The Journal of Physiology, 549(Pt 3), 945–952.
Morning light = phase advance. The quantitative basis for 'get outside within 30 minutes of waking'.
DOI: 10.1113/jphysiol.2003.040477Claim 5
Morning light is the strongest entrainment signal for pulling an acrophase earlier
“Get morning light within 30 minutes of waking. Morning light is the most effective way to stop the drift.”
Shown in: Home → TONIGHT'S LEVERS; drift-later insights
Supporting research
Khalsa, S. B. S., Jewett, M. E., Cajochen, C., & Czeisler, C. A. (2003). A phase response curve to single bright light pulses in human subjects. The Journal of Physiology, 549, 945–952.
DOI: 10.1113/jphysiol.2003.040477Zeitzer, J. M., Dijk, D. J., Kronauer, R. E., Brown, E. N., & Czeisler, C. A. (2000). Sensitivity of the human circadian pacemaker to nocturnal light: melanopic response function and dose–response. The Journal of Physiology, 526(Pt 3), 695–702.
DOI: 10.1111/j.1469-7793.2000.00695.xSource papers
Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing
Phillips et al. · Scientific Reports · 2017
Introduces the Sleep Regularity Index (SRI) — a 0–100 measure of how consistent sleep timing is from night to night. Source for Trana's SRI calculation and threshold bands.
Munich Chronotype Questionnaire (MCTQ)
Roenneberg et al. · Journal of Biological Rhythms · 2003
Establishes the validated chronotype framework Trana uses to place users on the early bird → intermediate → night owl spectrum. Demonstrates that chronotype is a real, heritable trait.
Social jetlag: misalignment of biological and social time
Wittmann et al. · Chronobiology International · 2006
Defines social jet lag — the gap between weekday and weekend sleep midpoints — and links it to metabolic and cardiovascular outcomes. Source for Trana's social jet lag calculation.
Circadian Complexity Entropy and relative amplitude of heart rate predict metabolic syndrome
Kim, Mun & Lee · JMIR Medical Informatics · 2025
CCE and RA from wearable heart rate outperform traditional sleep markers for metabolic syndrome prediction.
M10/L5 onset relationships with HR-derived circadian acrophase
Wu et al. · npj Digital Medicine · 2024
Validates the relationship between activity-derived M10/L5 onset times and the heart-rate cosinor acrophase, supporting the use of activity as a backup signal when continuous HR is unavailable.
Single-harmonic cosinor fits to wearable heart rate data
Forger group (large wearable HR cosinor study) · npj Digital Medicine · 2024
Large-scale validation of the single-harmonic 24-hour cosinor model on real-world wearable HR data. Supports Trana's choice of cosinor as the primary fit method over more complex alternatives.
CosinorAge — biological age from 7-day wearable circadian data
Shim, Fleisch & Barata · npj Digital Medicine · 2024
+1 year of CosinorAge = 8–12% higher all-cause mortality risk in a study of 80,000 participants.
Wearable sleep-wake features predict next-day mood episodes
Lim et al. · npj Digital Medicine · 2024
AUC 0.80–0.98 prediction accuracy. Circadian phase delays are associated with depression; advances with mania.
Rest-activity rhythm disruption and cardiovascular disease
Makarem et al. · J Am Heart Assoc · 2024
Rhythm disruption associated with CVD, hypertension, and obesity in a nationally representative US sample.
Irregular circadian patterns and type 2 diabetes
Windred et al. · Lancet Regional Health · 2024
13 million hours of sensor data: irregular circadian patterns associated with T2D incidence.
Circadian disruption and depression in physicians
Real-world MD data · npj Digital Medicine · 2024
50,000+ days of wearable data from 800 physicians: bidirectional link between circadian disruption and depression.
What Trana does not do
Transparency is trust. Here's what we are — and what we are not.
- Trana is not a medical device and does not diagnose any condition
- Trana is not a sleep tracker — sleep is one input, not the output
- Trana does not replace clinical care — alerts are informational, not medical recommendations
- Trana does not store health data in the cloud — all processing is on-device
- Trana does not use HealthKit data for advertising or share it with third parties
- Trana does not claim to predict specific disease — it surfaces patterns that research associates with risk