Evidence
The guidelines and peer-reviewed studies behind every reference range, score and questionnaire in Sam - resting heart rate, HRV, VO2 max, sleep and stress. Sam puts your own data in context. It does not diagnose, and it does not interpret clinical findings.
Every range and threshold Sam displays, with the institution or peer-reviewed source that defines it. These are population norms used for orientation, not personal targets, and Sam does not judge your individual values against them.
60–100 bpm = normal adult range; >100 bpm (tachycardia) or <50 bpm with symptoms should prompt medical review because such extremes can signal arrhythmia, infection, or endocrine/metabolic stress.
Source: American Heart Association (AHA)
https://www.heart.org/en/healthy-living/exercise-and-physical-activity/fitness-basics/target-heart-ratesKeep within the same 60–100 bpm band; persistent values outside it carry the same tachy-/bradycardia risks noted above.
Source: American Heart Association (AHA)
https://www.heart.org/en/healthy-living/exercise-and-physical-activity/fitness-basics/target-heart-rates≥50 ms is considered low cardiac risk; <50 ms is associated with higher post-MI and all-cause mortality. Threshold defined by the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (ESC/NASPE, 1996).
Source: ESC / NASPE HRV Task Force (1996)
https://www.escardio.org/static-file/Escardio/Guidelines/Scientific-Statements/guidelines-Heart-Rate-Variability-FT-1996.pdfGood fitness ≥50 ml·kg⁻¹·min⁻¹ (men) or ≥40 ml·kg⁻¹·min⁻¹ (women); lower values fall into average / below-average categories and are linked to higher cardiometabolic risk. Normative table compiled from American College of Sports Medicine data.
Source: American College of Sports Medicine (ACSM)
https://www.scienceforsport.com/vo2-max/Sedentary <5,000 steps/day; Active ≥10,000 steps/day. Cut-points come from the Tudor-Locke step-defined activity index, widely used in epidemiological studies linking <5,000 steps with adverse metabolic profiles.
Source: Medicine & Science in Sports & Exercise
https://pubmed.ncbi.nlm.nih.gov/22208412/Accumulate ≥500–1,000 MET-min per week (≈450–900 kcal for a 70 kg adult) to meet the 2018 Physical Activity Guidelines for Americans minimum dose for substantial health benefit.
Source: U.S. DHHS / CDC
https://www.cdc.gov/physical-activity/media/pdfs/Physical_Activity_Guidelines_2nd_edition.pdfAt least 150 min/wk moderate-intensity or 75 min/wk vigorous-intensity aerobic activity, as prescribed by the WHO 2020 Global Physical Activity Guidelines, to reduce non-communicable disease risk.
Source: World Health Organization (WHO)
https://www.who.int/initiatives/behealthy/physical-activityClimbing >5 flights (≈50 steps) per day was associated with a ~20% lower risk of atherosclerotic cardiovascular disease in a 458,000-participant UK Biobank cohort.
Source: Atherosclerosis (2023) — Tulane Univ. / Harvard collaborators
https://doi.org/10.1016/j.atherosclerosis.2023.117300Normal 95–100%; urgent clinical review if ≤94%, or if a reading is ≥3 percentage points lower than the user's usual level. Threshold adopted in the NHS England COVID-19 Oximetry @ Home programme.
Source: NHS England — Oximetry @ Home
https://www.england.nhs.uk/coronavirus/wp-content/uploads/sites/52/2020/06/C1541-Self-monitoring-COVID-19-diary-version-2-January-2022.pdf12–20 breaths/min is normal; ≥22 breaths/min meets the SIRS/sepsis screening criterion for tachypnea.
Source: U.S. National Library of Medicine / NIH MedlinePlus
https://medlineplus.gov/ency/article/007198.htm36.4–37.6 °C is normal; fever ≥38 °C indicates possible infection; <35 °C signals hypothermia.
Source: Cleveland Clinic — evidence-based patient education
https://my.clevelandclinic.org/health/symptoms/10880-feverThe peer-reviewed evidence linking each tracked metric to everyday health - why step count, heart rate variability or VO2 max are worth watching as a trend over months rather than as a single reading.
High step counts are associated with reduced all-cause mortality and chronic disease risk.
Source: JAMA Network Open, 2021
Increased walking and running distance is linked to improved metabolic health and reduced obesity risk.
Source: British Journal of Sports Medicine, 2019
Caloric expenditure through activity correlates with lower risk of cardiovascular disease and diabetes.
Source: Circulation, 2016
Climbing stairs has been shown to improve musculoskeletal and metabolic health.
Source: Journal of Physical Activity & Health, 2017
Faster walking speeds are associated with lower mortality and better functional mobility.
Source: JAMA, 2011
Gold standard for assessing cardiovascular fitness. Higher VO₂ max correlates with lower cardiovascular disease risk and mortality.
Source: Circulation, 2016
Lower RHR is a marker of better cardiovascular health and aerobic fitness.
Source: American Heart Association, 2020
Higher HRV indicates better autonomic regulation and recovery, correlating with reduced cardiovascular risk.
Source: European Heart Journal, 2017
Healthy SpO₂ levels are necessary for optimal aerobic function and cardiovascular efficiency.
Source: Respiratory Medicine, 2020
Time spent in intentional physical activity is a key factor in improving cardiovascular health; regular, sustained activity increases stroke volume and oxygen uptake efficiency.
Source: Mayo Clinic Proceedings, 2018; Circulation, 2016
Activities like running and cycling improve cardiovascular fitness when performed at moderate to high intensity.
Source: Mayo Clinic Proceedings, 2018
Adults need 7–9 hours of sleep per night for optimal health. Insufficient sleep is linked to increased risk of cardiovascular disease, obesity, and diabetes.
Source: Sleep Medicine Reviews, 2010
Ratio of time asleep to time spent in bed. Higher efficiency is associated with better recovery and reduced fatigue; inefficiency often correlates with insomnia or stress.
Source: Journal of Clinical Sleep Medicine, 2006
Deep (slow-wave) sleep is essential for physical recovery, immune function, and memory consolidation.
Source: Nature Reviews Neuroscience, 2017
Time it takes to fall asleep. Longer latency (>30 minutes) is associated with insomnia and increased stress.
Source: Journal of Psychiatric Research, 2015
Consistency of sleep and wake times. Irregular sleep patterns are linked to circadian rhythm disorders and increased cardiometabolic risk.
Source: PLOS Biology, 2017
Frequency of awakenings during the night. Frequent interruptions disrupt sleep cycles, impairing recovery and increasing fatigue.
Source: Sleep, 2014
BMI is correlated with obesity-related risks like diabetes, cardiovascular disease, and certain cancers.
Source: The Lancet, 2016
Elevated body fat is linked to increased risk of diabetes and hypertension. Lower percentages within healthy ranges correlate with better metabolic health.
Source: Obesity Reviews, 2010
Higher lean (muscle) mass correlates with improved metabolic health and reduced risk of sarcopenia with age.
Source: Journal of Cachexia, Sarcopenia and Muscle, 2019
The clinical sleep research and wearable-validation studies behind how Sam scores a night: where the thresholds for duration and sleep stages come from, and where measurement at the wrist has known limits.
The HRV-based stress literature behind Sam's stress score: how heart rate variability responds to mental and physical load, and why the score is read as a trend rather than a verdict on a single day.
Sam administers short self-report questionnaires inside its programs: the MOS Sleep Scale in the sleep program, the K10 for stress, the PAVS for exercise and the IPAQ-SF for movement. Condition programs add MEDAS-14 (high blood pressure), MIDAS (migraine), NDDI-E (epilepsy), OASIS (panic disorder), GERD-HRQL (reflux) and a PROMIS-framework check-in (gout). The references below are the primary validation sources for each instrument. Two check-ins - asthma control and hay fever symptoms - are written by us following guideline-endorsed methods (GINA and ARIA) and are not independently validated named instruments. Every answer stays self-reported: no questionnaire in Sam produces a diagnosis.
MOS-SS
Sleep program
A 12-item self-report scale on sleep over the past four weeks, covering sleep disturbance, snoring, shortness of breath or headache on awakening, sleep adequacy, daytime somnolence and average hours slept. Five subscales and the Sleep Problems Index are transformed to a 0-100 range; sleep quantity is reported as raw hours slept. Sam repeats it periodically so changes in self-reported sleep become visible over time.
K10
Stress program
A 10-item questionnaire on how often symptoms such as nervousness, restlessness, hopelessness and fatigue occurred over the past 30 days. Each item is rated on a five-point frequency scale, giving a total between 10 and 50. Sam repeats it so shifts in your own answers become visible; it does not screen you or assign a category.
PAVS
Exercise program
A two-question activity check asking on how many days per week and for how many minutes per day moderate to vigorous activity is performed. The two answers multiply into minutes per week. The same two-question format is validated in the literature under the name Exercise Vital Sign. Sam repeats it as a quick measure of self-reported activity volume.
IPAQ-SF
Movement program
A 7-item questionnaire on physical activity in the last seven days, split into vigorous activity, moderate activity, walking and time spent sitting. Days and minutes are converted into MET minutes per week, which gives a comparable volume figure across activity types. Sam uses it to track self-reported everyday movement over the course of the program.
MEDAS-14
Condition program: high blood pressure
A 14-item screener on how closely eating habits follow a Mediterranean dietary pattern, covering olive oil, vegetables, fruit, legumes, fish, nuts, red meat, sugary drinks and similar items. Each item scores 0 or 1, giving a total between 0 and 14. Sam uses it to make changes in self-reported eating habits visible over the course of the program.
MEDAS-14 measures diet, not blood pressure. It is used in this program because eating pattern is one of the things people are asked about and can change; the blood pressure readings themselves stay in your own meter.
MIDAS
Condition program: migraine
Seven questions on the past three months, of which five are scored: how many days work, household tasks, family life or leisure were missed or clearly limited by headache. The two remaining questions record headache days and pain intensity and do not count towards the total. Sam charts the total over time. The published grades exist in the literature; Sam does not assign you one.
NDDI-E
Condition program: epilepsy
A 6-item questionnaire on mood, developed specifically for people with epilepsy: its items were chosen not to overlap with cognitive difficulties or with the side effects of antiepileptic medication, which otherwise confound general mood questionnaires in this group. Sam repeats it and shows the answers over time; it does not screen for or identify depression.
OASIS
Condition program: panic disorder
A 5-item scale on anxiety over the past week, covering frequency, intensity, avoidance and interference with daily activities and with work, school or home life. Each item is rated from 0 to 4, giving a total between 0 and 20. Sam uses it as a short recurring check-in so changes in self-reported anxiety are visible over time.
GERD-HRQL
Condition program: reflux
Ten scored questions on how much reflux affected the past weeks: heartburn in general and when lying down, standing, after meals and at night, plus dietary change, difficulty and pain on swallowing, bloating and the effect of medication. Sam charts the total over time.